climatic implications of the quaternary fluvial tufa record in the ne iberian peninsula over the last 500 ka the drainage area of the iberian ranges ne spain houses one of the most extensive quaternary fluvial tufaceous records in europe in this study tufa deposits in the anamaza mesa piedra and ebron river valleys were mapped stratigraphically described and chronologically referenced from u th disequilibrium series amino acid racemization and radiocarbon methods tufa deposits accumulated in cascades barrage cascades and related damming areas developed in stepped fluvial systems the maximum frequency of tufa deposition was identified at 120 ka marine oxygen isotope stage mis 5e 102 ka mis 5c 85 ka mis 5a and 7 ka mis 1 probably under warmer and wetter conditions than today additional phases of tufa deposition appear at 353 ka end of mis 11 258 180 ka mis 7 and 171 154 ka mis 6 although most tufa deposition episodes are clearly correlated with interstadial periods the occurrence of tufa deposits during the penultimate glaciation mis 6 is remarkable indicating that the onset of this stage was climatically favourable in the iberian peninsula biostatic conditions and the dynamics of karstic systems regulating tufa deposition seem to be sensitive to the precipitation regime controlled by shifts in the position of north atlantic atmospheric belts and summer insolation regulated by orbital forcing

paleoclimate and location of the border between mediterranean climate region and the saharo arabian desert as revealed by speleothems from the northern negev desert israel speleothem bearing karstic caves of the northern negev desert southern israel provides an ideal site for reconstructing the paleoclimate and paleo location of the border between mediterranean climate region and the saharo arabian desert major periods of speleothem deposition representing humid periods were determined by high resolution 230 th u dating and corresponding studies of stableisotopecompositionwereusedtoidentifythesourceofrainfallduringhumidperiodsandthevegetationtype majorhumidintervals

late quaternary environmental and human events at en gedi reflected by the geology and archaeology of the moringa cave dead sea area israel abstract the moringa cave within pleistocene sediments in the en gedi area of the dead sea fault escarpment contains a sequence of various pleistocene lacustrine deposits associated with higher than today lake levels at the dead sea basin in addition it contains chalcolithic remains and 5th century bc burials attributed to the persian period cemented and covered by late holocene travertine flowstone these deposits represent a chain of late pleistocene and holocene interconnected environmental and human events echoing broader scale regional and global climate events a major shift between depositional environments is associated with the rapid fall of lake lisan level during the latest pleistocene this exposed the sediments providing for cave formation processes sometime between the latest pleistocene ca 15 ka and the middle holocene ca 4500 bc eventually leading to human use of the cave the chalcolithic use of the cave can be related to a relatively moist desert environment probably related to a shift in the location of the northern boundary of the saharo arabian desert belt the travertine layer was u th dated 2 46 0 10 to 2 10 0 04 ka in agreement with the archaeological finds from the persian period together with the inner consistency of the dating results this strongly supports the reliability of the radiometric ages the 2 46 2 10 ka travertine deposition within the presently dry cave suggests a higher recharge of the judean desert aquifer correlative to a rising dead sea towards the end of the 1st millennium bc this suggests a relatively moist local and regional climate facilitating human habitation of the desert

230th 234u dating of holocene tufas possibilities and problems high resolution chronologies in continental carbonate deposits such as tufas are required for detailed palaeoclimatic and environmental studies this work set out to establish if high resolution u series dating of detritus rich holocene tufas is routinely possible the study centres on a paludal holocene tufa from southern england that already has an existing holocene chronology based on 14c and supported by biostratigraphy against which to compare u series dates the results show that significant detrital contamination combined with low initial u concentrations and short time for ingrowth of radiogenic 230th make high resolution u series dating of holocene tufa very difficult moreover a single 230th 232th initial value to correct for the presence of detrital 230th is not appropriate at the study site a finding that may apply to most holocene tufas total sample dissolution of coeval samples demonstrates considerable variability in the isotopic composition of the detritus the total sample dissolution data are too scattered to constrain chronologies at the required resolution and may indicate the incorporation of a 230th rich component in the detritus

hydro climate research of the late quaternary of the eastern mediterranean levant region based on speleothems research a review abstract the eastern mediterranean em levant region is the eastern borderland of the eastern mediterranean sea ems the ems brings mediterranean climate zones to the immediate coastal region and hinterland but away from the influence of the ems the region rapidly becomes a desert paleoclimate evidence derived from a large number of studies on speleothems from caves located along sharp climatic gradients enables deep insight into the climate in the em levant region growth periods and isotopic composition of speleothems from the various climate regimes capture the regional signals of temperature rainfall amount and vegetation speleothems from northern and central israel grew continuously in areas where present day annual rainfall is 400 500 mm and show that water was always available during glacials and interglacials these speleothems display a well defined 18o orbital modulation of glacial and interglacial marine isotope stages mis and show good correlations with the ems marine records pointing to strong direct sea land links the climatic record indicates relatively drier and cooler glacials but extreme wet peaks during interglacials mainly mis 5e between 128 120 ka bp pluvial conditions penetrated to the northern central and southern negev desert the present day climatic gradient between the different climatic regions existed through interglacials however growth periods of speleothems from the northern negev desert from the rain shadow desert and the dead sea basin suggest that during last glacial the desert boundary moved from its interglacial and present day position 30 km farther south and 60 km farther east due to positive water balance

effects of local geologic structure on yucca flats nevada test site explosion waveforms two dimensional linear finite difference simulations abstract two dimensional linear elastic finite difference calculations were performed for a two dimensional geologic model of yucca flats nevada test site nevada the calculations were used to produce synthetic teleseismic p wave seismograms for explosive line sources in yucca flats p wave coda in the first 5 sec is observed to be highly dependent on take off angle for the teleseismic synthetics p wave coda also varies with the position of the source in the valley structure and may produce variations in the individual station teleseismic p wave m b magnitude of up to 0 3 magnitude units however these magnitude variations should be substantially reduced by averaging over stations at multiple azimuths the reverberant coda appears to rise from scattered modal waves that are initially excited in the low velocity near surface structures of the yucca flats deposits of alluvium and tuff scattering of the waves occurs at offsets in the basement structure and at the sides of the valley the combined effects of scattering source function intrinsic attenuation and instrument response serve to obscure the p pp spectral scalloping that is expected from a linear model this loss of spectral resolution is the product of p coda filling in the p pp interference notches and the lengthening of the initial p wave source time function by a convolution of the source time function intrinsic attenuation operator and instrument response therefore short time windows 1 to 2 sec that do not include p coda energy do not have sufficient resolution to reliably detect the p pp interference notches

elastic reverse time migration elastic prestack reverse time finite difference migration of two component seismic surface data requires data extrapolation and application of an imaging condition data extrapolation involves synchronous driving of the vertical component and horizontal component finite difference meshes with the time reverse of the recorded vertical and horizontal traces respectively extrapolation uses the coupled elastic wave equation for variable velocity solved with a second order explicit finite difference scheme the imaging condition at any point in the grid is the one way traveltime from the source to that point elastic migrations of both synthetic test data and real two component common source gathers produce simpler images than acoustic migrations because of the coalescing of double reflections compressional waves and shear waves into single loci

the african humid period and the record of marine upwelling from excess 230th in ocean drilling program hole 658c using a high resolution 230 th normalized record of sediment flux we document the deglacial and holocene history of north african aridity and coastal upwelling at ocean drilling program hole 658c at both the end of the younger dryas and after the 8 2 ka event there are significant drops in terrigenous accumulation at our site indicating an increase in the monsoon moisture flux over africa at this time at 5 5 ka there is an abrupt end to the african humid period and a return to stronger upwelling conditions for carbonate and opal fluxes the 230 th normalization completely changes the shape of each record based on percentage variations alone this site is a clear example of how variations in one sediment component can obscure changes in the others and it demonstrates the need for radionuclide measurements more generally in paleoceanography by taking our new records and a large amount of previous data from this site we conclude that increases in african moisture are tightly coupled to decreases in coastal upwelling intensity

palynological approach in upper quaternary terrestrial carbonates of central italy anything but a mission impossible a palynological survey has been carried out on two late quaternary travertine s l deposits of central italy at serre di rapolano and bagnoli tuscany region the principal aim was to improve the understanding of factors that affect the accumulation and preservation of pollen grains in thermal i e travertine and ambient temperature i e calcareous tufa terrestrial carbonates for this purpose 52 526 pollen grains belonging to 118 pollen taxa from local to extra regional sources were analysed in 200 samples from different travertine and calcareous tufa lithofacies of these 97 samples generally from thermal travertines were barren in palynomorphs by contrast pollen grains in the remaining samples were well preserved and did not show differential preservation features these observations suggest that the ph of the solutions from which travertine or tufa precipitate is not a limiting factor in causing corrosion and or destruction of pollen grains rather the barrenness recorded in many samples appears to reflect a paucity of pollen rather than post depositional destruction results suggest that the depositional energy of the environment during the deposition of travertine plays an important role in controlling pollen concentration as verified in both depressions lower energy to higher pollen concentration and slopes higher energy to lower pollen concentration respectively analysis of pollen data suggests that relatively high depositional temperatures and rates of carbonate deposition are also major limiting factors for efficient accumulation of pollen grains results of this study reveal that understanding pollen taphonomy processes in travertine and calcareous tufa is critical to developing accurate palaeoenvironmental and palaeoclimatic reconstructions

mid to late holocene paleoclimatic changes and paleoenvironmental shifts inferred from pollen and diatom assemblages at lake hamra wadi el natrun western nile delta north western desert egypt abstract four palynological and three diatom zones of mid to late holocene are identified along a 370 cm long radiocarbon dated sediment core collected in lake hamra at wadi el natrun western nile delta egypt the mid late holocene between the predynastic to old kingdom was terrestrial wetland habitat with high seasonal rainfall and or nile flood as revealed by the dominance of cyperaceae pollen therefore people gathered in and around the nile valley and the agricultural activities increased during the early stage of late holocene coincident with the old kingdom to middle kingdom the paleoclimate became more arid with low seasonal precipitation and or nile flood as reflected by the increasing abundance of poaceae pollen and the absence of diatoms in addition to low values of toc tn ts c s and high values of c n these drought conditions possibly played a role in the old kingdom collapsing the late stage of the late holocene showed terrestrial wetland habitat with brackish conditions coupled with aquatic contribution under oxic conditions as inferred by the dominance of typha sp and amaranthaceae pollens as well as the diatom assemblages the relatively high values of toc c n c s coupled with low values of ts and tn reveal terrestrial origin of organic matter the late holocene recent has turned into a terrestrial wetland habitat with more brackish conditions and increasing in the seasonal rainfall as supported by the marked increasing of cyperaceae pollen the overall increase of the diatom inferred salinity dis as well as the marked increasing of c s tn and decreasing of toc c n and ts values towards the recent point to higher saline brackish wetland paleoenvironment and a terrestrial origin of the organic matter with more aquatic contribution under oxic conditions

synoptic conditions of fine particle transport to the last interglacial red sea dead sea from nd sr compositions of sediment cores abstract the sediments deposited at the depocenter of the dead sea comprise high resolution archive of hydrological changes in the lake s watershed and record the desert dust transport to the region this paper reconstructs the dust transport to the region during the termination of glacial marine isotope stage 6 mis 6 135 129 ka and the last interglacial peak period mis5e 129 116 ka we use chemical and nd and sr isotope compositions of fine detritus material recovered from sediment core drilled at the deepest floor of the dead sea the data is integrated with data achieved from cores drilled at the floor of the red sea thus forming a red sea dead sea transect extending from the desert belt to the mediterranean climate zone the dead sea accumulated flood sediments derived from three regional surface cover types settled desert dust mountain loess soils and loess soils filling valleys in the dead sea watershed termed here valley loess the valley loess shows a distinct 87sr 86sr ratio of 0 7081 1 inherited from dissolved detrital calcites that originate from dried waterbodies in the sahara and are transported with the dust to the entire transect our hydro climate and synoptic conditions reconstruction illustrates the following history during glacial period mis6 mediterranean cyclones governed the transport of saharan dust and rains to the dead sea watershed driving the development of both mountain soils and valley loess then at heinrich event 11 dry western winds blew saharan dust over the entire red sea dead sea transect marking latitudinal expansion of the desert belt later when global sea level rose the dead sea watershed went through extreme aridity the lake retreated depositing salt and accumulating fine detritus of the valley loess during peak interglacial mis 5e enhanced flooding activity flushed the mountain soils and fine detritus from all around the dead sea and red sea marking a significant contraction of the desert belt at the end of mis 5e the effect of the regional precipitation diminished and the dead sea and red sea areas re entered sever arid conditions with extensive salt deposition at the dead sea

northward intrusions of low and mid latitude storms across the saharo arabian belt during past interglacials the rain regime of the levant during the late quaternary was controlled primarily by mediterranean cyclonic systems associated with north atlantic climate shifts lake levels in the dead sea basin have been robust recorders of the regional hydrology and generally indicate highstand wet conditions throughout glacial intervals and lowstands dry during interglacials however sporadic deposition of travertines and speleothems occurred in the negev desert and arava valley during past interglacials suggesting intrusions of humidity from southern sources probably in association with enhanced activity of mid latitude red sea synoptic troughs and or low latitude tropical plumes the southerly incursions of wetness were superimposed on the long term interglacial levantine arid conditions as refl ected by the current prevailing hyperaridity and could have had an important impact on human migration through the red sea dead sea corridor

finite difference simulations of seismic scattering implications for the propagation of short period seismic waves in the crust and models of crustal heterogeneity synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two dimensional media with random spatial variations in seismic velocity the results of this study provide important insights about the propagation of short period 5 the self similar medium is characterized by a scattering q that is constant with frequency whereas theory predicts that the apparent q in an exponential medium is proportional to frequency these alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal q at frequencies greater than about 1 hz assuming that scattering is responsible for most of the attenuation at these frequencies measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation scattering q 200 in these cases q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission q of the medium the cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium the self similar random medium proposed here for the crust produces waveform variations at high frequencies 15 30 hz similar to those reported for actual small scale seismic arrays with apertures of hundreds of meters

seasonal rainfall in the sinai desert during the late quaternary inferred from fluorescent bands in fossil corals skeletal bands of alternating high and low density in massive coral species have been used to record their growth history1 2 in the red sea living colonies of the genus porites deposit low density skeletal bands during summer and high density bands during winter3 additionally yellow green fluorescence can sometimes be seen in these massive corals imparted to them by the incorporation of humic material carried by coastal runoff4 annual banding of fluorescent sequences in living scleractinian corals has proved to be useful in the study of terrestrial runoff in the near shore environment5 6 here we report the finding of similar yellow green fluorescent bands in fossil porites from late quaternary reef terraces in southern sinai which are absent from living porites in the nearby fringing reefs the periodic sequences of the fluorescing humics were found to be superimposed on the low density sub bands of the fossil corals we interpret our observations as evidence that during the late quaternary reef forming peaks the climate was wetter than the extreme desert conditions now prevailing with a possible summer rainfall regime

timing and intensity of groundwater movement during egyptian sahara pluvial periods by u series analysis of secondary u in ores and carbonates abstract wet climatic episodes are known to have prevailed in the egyptian sahara several times during the late quaternary most recently during the holocene 8000 yr ago earlier wet episodes have been recognized as having occurred during the past 300 000 yr and have been dated by u series methods in speleothems and in lake travertines we show here that the times of enhanced groundwater movement can also be determined by 230 th 234 u dating of secondary u in ores of uranium iron and phosphate we also present evidence that such acceleration of groundwater movements is indicated by relatively low 234 u 238 u activity ratios in the secondary uranium our new data show that pluvial periods in egypt occurred during marine oxygen isotope stages 4 5 6 and 7 and therefore are consistent with the view that the wet episodes are the results of migration of the tropical monsoonal belt driven primarily by the 23 000 yr precession cycle of the milankovich curve modulated by the 100 000 yr eccentricity cycle

travertines in the northern hula valley israel this study describes the field and petrographic relationships of a widespread deposit of pleistocene travertines in the northern hula valley northern israel the travertines interfinger with conglomerate deposits and basaltic lava flows field relationships and radiometric dating indicate that the travertines accumulated intermittently over the past million years and their formation virtually stopped 25 000 years ago the travertines are characteristically highly porous some of the pores as well as some spar filled voids preserve the shapes of stalks and leaves the abundance of plant material suggests that photosynthesis rather than bacterial or abiogenic processes was the main mechanism which induced carbonate precipitation the reasons for travertine accumulation in the past and for the cessation of its formation today are ascribed to differences in the palaeogeographic setting in the past water flow is viewed as having been mostly sluggish and a widespread and shallow sheet of water was formed the lush vegetation combined with the relatively long residence time of the water in the area led to increased efficiency of the calcium carbonate precipitation today by contrast water flows rapidly in gorges precipitating only a small fraction of its load of dissolved calcium carbonate the conjectured change in hydrological conditions is ascribed to rejuvenation of faulting activity in the late quaternary

u series and oxygen isotope chronology of the mid pleistocene lake amora dead sea basin abstract this study establishes for the first time the chronology and limnological history of lake amora dead sea basin israel whose deposits the amora formation comprise one of the longest exposed lacustrine records of the pleistocene time the amora formation consists of sequences of laminated primary aragonite and silty detritus ca sulfate minerals halite and clastic units this sedimentary sequence was uplifted and tilted by the rising sedom salt diapir exposing 320 m of sediments on the eastern flanks of mt sedom the arubotaim cave ac section the chronology of the ac section is based on u disequilibrium dating 230th 234u and 234u 238u ages combined with floating 18 o stratigraphy and paleomagnetic constraints the determination of the 230th 234u ages required significant corrections to account for detrital th and u these corrections were performed on individual samples and on suites of samples from several stratigraphic horizons the most reliable corrected ages were used to construct an age elevation model that was further tuned to the oxygen isotope record of east mediterranean foraminifers based on the long term similarity between the sea and lake oxygen isotope archives the combined u series 18 o age elevation model indicates that the exposed amora sequence was deposited between 740 and 70 ka covering seven glacial interglacial cycles marine isotope stages mis 18 to 5 taking the last glacial lake lisan and the holocene dead sea lacustrine systems as analogs of the depositional limnological environment of lake amora the latter oscillated between wet glacial and more arid interglacial conditions represented by sequences of primary evaporites aragonite and gypsum that require enhanced supply of freshwater to the lakes and clastic sediments respectively the lake evolved from a stage of rapid shifts between high and low stand conditions during 740 to 550 ka to a sabkha like environment that existed at the ac site between 550 and 420 ka this stage was terminated by a dry spell represented by massive halite deposition at 420 ka mis12 11 during mis10 6 the lake fluctuated between lower and higher stands reaching its highest stand conditions at the late glacial mis6 after which a significant lake level decline corresponds to the transition to the last interglacial mis5 low stand lake represented by the uppermost part of the formation 18 o values in the primary aragonite range between 6 0 and 1 3 shifting cyclically between glacial and interglacial intervals the lowest 18 o values are observed during interglacial stages and may reflect short and intense humid episodes that intermittently interrupted the overall arid conditions these humid episodes expressed also by enhanced deposition of travertines and speleothems seem to characterize the negev desert and in contrast to the overall dominance of the atlantic mediterranean system of rain patterns in the dead sea basin some humid episodes during interglacials may be traced to southern sources

seismic energy partitioning and scattering in laterally heterogeneous ocean crust we present finite difference forward models of elastic wave propagation through laterally heterogeneous upper oceanic crust the finite difference formulation is a 2 d solution to the elastic wave equation for heterogeneous media and implicitly calculates p and sv propagation compressional to shear conversion interference effects and interface phenomena random velocity perturbations with gaussian and self similar autocorrelation functions and different correlation lengths a are presented which show different characteristics of secondary scattering heterogeneities scatter primary energy into secondary body waves and secondary stoneley waves along the water solid interface the presence of a water solid interface in the model allows for the existence of secondary stoneley waves which account for much of the seafloor noise seen in the synthetic seismograms for the laterally heterogeneous models

characteristics evolution and distribution of quaternary channel calcretes southern jordan cemented and calcretized conglomerates of quaternary age are found within ancient river channels exposed at various heights between 1 and 125 m above the current bed of the wadi dana in southern jordan in cross section the calcrete deposits are typically lensoid in shape and are found in lling palaeochannels cut into the bedrock the fossilized channel sediments preserve evidence of past river conditions sediment loads source areas phases of river down cutting and sediment accretion as well as post depositional alteration processes samples have been analysed in thin section and under the scanning electron microscope in order to determine the calcrete micromorphology cement types and crystal sizes the results show that the river deposits have undergone signi cant displacement and replacement of the detrital grains by caco3 and this has resulted in the cementation in places of over 4 m of river material the cements display an alpha type fabric with no evidence of biogenic activity the nature of the cement fabric within and between deposits differs as a function of two key variables i the speci c location within the channel and ii height above the modern wadi oor firstly in many of the deposits cement crystal size varies with sparite dominating at depth within impermeable palaeowadi channels whereas on the anks of the channels and near the top of the channels micrite is the main type of cement these variations are thought to be a result of differences in the length of residence time of calcium carbonate rich uids in different parts of the channel and the spatially varying in uence of evaporation secondly distinct changes in cement fabric can be seen in channels of different ages with a reduction in the amount of micrite and an increase in the amount of secondary recrystallized pore lling spar over time copyright 2004 john wiley sons ltd

geoacoustic scattering from seafloor features in the rose area a strong refraction branch diffraction has been observed on ocean bottom hydrophone data from the rivera ocean seismic experiment rose modeling of the interaction between seismic acoustic energy and the ocean bottom has shown that this arrival could be caused by scattering from common seafloor features seismic acoustic wave propagation was computed for models of marine seismic refraction lines using a 2d heterogeneous formulation of the elastic wave equation these models demonstrate that a significant amount of energy is diffracted from seafloor structures such as hills and valleys when both the direct water wave and the refracted compressional wave traveling through the upper crust are incident upon a structure since much of the diffracted energy travels through the crust the diffracted arrivals appear on the refraction branch of the seismograms at large ranges energy partitioning at the seafloor of the two incident wave types produce both compressional p and shear s diffracted phases in

sand sheet dynamics and quaternary landscape evolution of the selima sand sheet southern egypt abstract the selima sand sheet occupies more than 120 000 km 2 of the hyperarid uninhabited darb el arba in desert centered at the border of egypt and sudan at latitude 22 n and is characterized by a featureless surface of lag granules and fine sand broken only by widely separated dune fields and giant ripples of varying height and wavelength monitoring of the largest of these chevron shaped ripples using repeat orbital images and field surveys indicates migration rates of 500 1000 m yr accompanied by 0 2 0 cm erosion or deposition of the youngest sand sheet stratigraphic units beneath this active surface several developmental stages of sand sheet sediments have undulatory upper contacts and varying degrees of pedogenic alteration the younger stages retain their horizontal lamination and have cracking patterns indicative of past wetter conditions while older stages have lost their laminar structure through pedogenesis historical remains in the desert as well as 14 c and uranium series dating indicate that the younger strata of the sand sheet have a very low accumulation rate despite the active movement of the surface the lower strata were extensively modified during mid and late pleistocene pluvials resulting in an initial undulatory surface that set the stage for later accumulation of sand sheet below these quaternary sediments lies irregular topography dissected by channels of mid tertiary drainage the selima sand sheet is neither the result of net aggradation nor degradation but results from inheritance of an initial fluvial landscape increasingly modified during climatic cycles wet periods led to local drainage and deposition while the increasingly severe arid periods of the late pleistocene and holocene resulted in deposition of the blanketing bimodal sediments of the sand sheet

freshwater on the route of hominids out of africa revealed by u th in red sea corals a fundamental issue in the evolution of human culture concerns the route and conditions of anatomically modern hominids during the migration out of africa a particular question is how could anatomically modern hominids cross the hyperarid arabian deserts here we outline the evidence for significant presence of freshwater along the red sea shores during the last interglacial period freshwater caused an extensive recrystallization of coral reefs from aragonite to calcite indicating uplift of the reefs through well developed phreatic freshwater coastal aquifers applying novel open system u th dating methodology to the calcitic corals we dated the freshwater recrystallization to ca 140 ka consistent with other geological lines of evidence placing the migration of anatomically modern hominids out of africa at the onset of the last interglacial

constraining initial 230th activity in incrementally deposited biogenic aragonite from the bahamas the 230th content of subsurface bahamas seawater has been estimated from incrementally deposited aragonite skeletons of sclerosponges using u series age models which imply syndepositional incorporation of 230th first order age models assuming constant growth rate and zero initial 230th activity display an average surface age of 63 18 y despite the fact that the surfaces of the organisms were known to be alive at the time collection in the 1990s a knowledge of the initial 230th activity is necessary to incorporate the surface age constraint into an age model in the bahamas this approach estimates an initial 230th 232th activity ratio of 4 3 1 1 when applied to several individuals of the caribbean sclerosponge ceratoporella nicholsoni these results differ from the same approach applied to previous work on jamaican sclerosponges accreting aragonite in an environment closer to crustal sources and with less carbonate substrate we report new measurements of jamaican sclerosponge suggesting initial activity ratios of 230th 232th of 1 albeit with a high amount of uncertainty indicating a regional difference in initial thorium activities the estimates of initial 230th 232th activity ratios in the bahamas are similar to the dissolved ratio rather than the particulate ratio and can be explained by mixing of open ocean water and bank top surface water however no information regarding temporal changes in the amount of initial 230th 232th activity available for incorporation into biogenic aragonite can be constrained using this approach growth rates do not change after correction for initial thorium and they display an inverse relationship with depth although this paper deals uniquely with sclerosponge aragonite it is likely that the approach can be used on any incrementally deposited biogenic aragonite provided information is known a priori about the first order growth model and there is evidence that initial thorium incorporation is representative of ambient environment rather than individual physiology

late quaternary sediments minerals and inferred geochemical history of didwana lake thar desert india abstract variations in clastic sediment texture mineralogy of both evaporites formed at the surface and precipitates formed below the lake floor and the relative chemical activities of the major dissolved components of the chemical precipitates have allowed reconstruction of the history of salinity and water level changes in didwana lake thar desert india hypersaline conditions prevailed at about the last glacial maximum with little evidence of clastic sediments entering the lake between ca 13 000 and 6000 b p the lake level fluctuated widely the lake alternately hypersaline and fresh and clastic sediments were delivered to the lake at a low rate deep water conditions occurred ca 6000 b p and clastic influx increased abruptly the water level dropped towards 4000 b p when the lake dried briefly since 4000 b p the lake has been ephemeral with a lowered rate of sedimentation and mildly saline conditions rather like those of today this sequence of changes documented in the lake parallels changes in vegetation recorded in published pollen diagrams from both the thar and the arabian sea correlation of the various lines of evidence suggests that the climate of the last glacial maximum at didwana was dry and windy with a weak monsson circulation the monsson was re established between ca 13 000 and a little before 6000 b p and when winter rainfall increased ca 6000 b p the lake filled to its maximum depth

variability in upwelling fields in the northwestern indian ocean 2 data model comparison at 9000 years b p theoretical investigations in the form of general circulation model gcm simulations and empirical studies of pollen lake levels and marine sediments suggest that the indian summer monsoon was intensified 9000 years ago at a time of increased summer radiation about 8 in the northern hemisphere the southwesterly summer monsoon winds and their pattern of wind stress curl cause coastal upwelling along the coast of arabia stronger summer winds therefore should intensify coastal upwelling incorporation of the broad scale gcm winds into a high resolution ocean model of the arabian sea produces distinct patterns of stronger upwelling at 9000 years b p to verify these patterns in the geologic record we mapped upwelling assemblages of planktonic foraminifera and estimated sea surface temperature sst to define the magnitude and spatial distribution of monsoonal upwelling at 9000 years b p we found that the upwelling assemblage increased in abundance and the august ssts were several degrees celsius cooler off arabia than present however in the central and eastern arabian sea the tropical assemblage increased and the ssts were warmer than present values the sst gradient across the arabian sea was greater 6 c at 9000 years b p than it is today 4 c these observations are consistent with the model results that show increased divergence upwelling and a thinner upper layer or shallower thermocline in the westernmost arabian sea and increased convergence downwelling and a thicker upper layer in the central and eastern arabian sea in this experiment the use of low resolution winds from a general circulation model ncar ccm in a high resolution ocean model seems to be appropriate for simulating the long term averages observed in the marine sediments

late quaternary paleoclimate in semiarid northeastern brazil from u series dating of travertine and water table speleothems abstract fossil travertine and subaqueous speleothems in presently dry caves suggest periods of enhanced ground water recharge during the quaternary period in semiarid northeastern brazil travertine deposits and water table speleothems were dated by the 230 th 234 u technique yielding new evidence for the timing of past periods of increased rainfall the travertine was deposited in two distinct phases extensive in situ deposits during marine isotope stage 2 and fragmentary indurated deposits dating to ca 400 000 yr b p possibly marine isotope stage 10 or 12 dating of water table speleothems showed that the regional water table was 13 1 m above the present level at the last glacial maximum a second site yielded ages suggesting a still higher water table during marine isotope stage 6 these new data demonstrate that northeastern brazil did not follow the general pattern of a dry last glacial maximum as suggested by other continental records in amazonia and southeastern brazil and as depicted in recent general circulation model gcm simulations our results thus indicate that significant variability in regional rainfall patterns occurred in the area during glaciations and caution against overgeneralization of paleoclimate patterns

theory of equivalent staggered grid schemes application to rotated and standard grids in anisotropic media the previous finite difference numerical schemes designed for direct application to second order elastic wave equations in terms of displacement components are strongly dependent on poisson s ratio this fact makes theses schemes useless for modelling in offshore regions or even in onshore regions where there is a high poisson s ratio material as is well known the use of staggered grid formulations solves this drawback the most common staggered grid algorithms apply central difference operators to the first order velocity stress wave equations they have been one of the most successfully applied numerical algorithms for seismic modelling although these schemes require more computational memory than those mentioned based on second order wave equations the goal of the present paper is to develop a general theory that enables one to formulate equivalent staggered grid schemes for direct application to hyperbolic second order wave equations all the theory necessary to formulate these schemes is presented in detail including issues regarding source application providing a general method to construct staggered grid formulations to a wide range of cases afterwards the equivalent staggered grid theory is applied to anisotropic elastic wave equations in terms of only velocity components or similar displacements for two important cases general anisotropic media and vertical transverse isotropy media using respectively the rotated and the standard staggered grid configurations for sake of simplicity we present the schemes in terms of velocities in the second and fourth order spatial approximations with second order approximation in time for 2d media however the theory developed is general and can be applied to any set of second order equations in terms of only displacement velocity or even stress components using any staggered grid configuration with any spatial approximation order in 2d or 3d cases some of these equivalent staggered grid schemes require less computer memory than the corresponding standard staggered grid formulation although the programming is more evolved as will be shown in theory and practice with numerical examples the equivalent staggered grid schemes produce results equivalent to corresponding standard staggered grid schemes with computational advantages finally it is important to emphasize that the equivalent staggered grid theory is general and can be applied to other modelling contexts e g in electrodynamical and poroelastic wave propagation problems in a systematic and simple way

finite difference synthetic acoustic logs the finite difference method is a powerful technique for studying the propagation of elastic waves in boreholes even for the simple case of an open borehole with vertical homogeneity the snapshot format of the method displays clearly the interaction between the borehole and the rock and the origin and evolution of phases we present an outline of the finite difference method applied to the acoustic logging problem including a boundary condition formulation for liquid solid cylindrical interfaces which is correct to second order in the space increments absorbing boundaries based on the formulations of reynolds 1978 and clayton and engquist 1977 were used to reduce reflections from the grid boundaries results for a vertically homogeneous sharp interface model are compared with the discrete wavenumber method and excellent agreement is obtained the technique is also demonstrated by considering sharp and continuous transitions damaged zones at the borehole wall and by considering the effects of wa

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

quaternary palaeogeomorphologic evolution of the wadi faynan area southern jordan abstract the faynan area comprises a complex assemblage of deposits and landforms of varying nature age and position in the landscape the dominant facies are fluvial slope and aeolian at least eight palaeochannels are present at different heights within the wadis dana and ghuwayr fewer terraces are preserved in the wadi faynan planated surfaces leaving low gradient straths rock cut channels and fluvial deposits are all evident the continuing drop in regional base level as a result of subsidence of the dead sea trough has driven incision and aided in the retention of many of the terrace deposits as they have been abandoned as the wadi systems have eroded downwards calcretisation has enhanced the preservation potential of many of the fluvial deposits a large proportion of these deposits are comparable to those found in the modern wadi systems and it is thought that they formed under arid conditions similar to those that exist today two of the terrace deposits appear to reflect slightly wetter conditions as they consist of finer grained better sorted materials and display evidence of biological activity there are at least four distinct alluvial fan and slope deposits that have formed at the edge of various mountain fronts the fans have been entrenched to varying degrees and are likely to have formed at different times in the quaternary possibly when conditions were more humid or during periods of increased tectonic activity aeolian deposits indicate a marginally drier phase in the late glacial maximum and similar sediments of mid holocene age could either reflect increasing aridity at this time as has been suggested by frumkin et al 1991 and or be a result of the increasing impact of humans on the landscape many of the deposits are beyond the age range of optically stimulated luminescence osl and radiocarbon dating techniques but a proposed stratigraphy is supported by some numerical dates on the younger deposits and associated archaeological artefacts

dead sea drawdown and monsoonal impacts in the levant during the last interglacial sediment cores recovered by the dead sea deep drilling project dsddp from the deepest basin of the hypersaline terminal dead sea lake floor at 725 m below mean sea level reveal the detailed climate history of the lake s watershed during the last interglacial period marine isotope stage 5 mis5 the results document both a more intense aridity during mis5 than during the holocene and the moderating impacts derived from the intense mis5e african monsoon early mis5e 133 128 ka was dominated by hyperarid conditions in the eastern mediterranean levant indicated by thick halite deposition triggered by a lake level drop halite deposition was interrupted however during the mis5e peak 128 122 ka by sequences of flood deposits which are coeval with the timing of the intense precession forced african monsoon that generated mediterranean sapropel s5 a subsequent weakening of this humidity source triggered extreme aridity in the dead sea watershed and resulting in the biggest known lake level drawdown in its history reflected by the deposition of thick salt layers and a capping pebble layer corresponding to a hiatus at 116 110 ka the dsddp core provides the first evidence for a direct association of the african monsoon with mid subtropical latitude climate systems effecting the dead sea watershed combined with coeval deposition of arabia and southern negev speleothems arava travertines and calcification of red sea corals the evidence points to a climatically wet corridor that could have facilitated homo sapiens migration out of africa during the mis5e peak the hyperaridity documented during mis5e may provide an important analogue for future warming of arid regions of the eastern mediterranean levant

simulation of long period 3 d elastic responses for whole earth models summary improvements in gdsn seismic data quality and advances in numerical algorithms for solution of the wave equation now make it useful and feasible to simulate long period elastic responses for 3 d whole earth models the algorithm used is eighth order finite differencing on a staggered grid this allows stable computation at boundaries with large contrasts in poisson s ratio such as the core mantle boundary as the solution automatically generates all wave types it may lead to prediction of previously unobserved or misinterpreted phases and allow more detailed analysis of all phases simulations of large e g nuclear explosions and double couple earthquake sources reveal the effects on relative amplitudes of their respective radiation patterns in both wavefield snapshots and seismogram profiles a large number of phases are affected even by a single smooth bump on the core mantle boundary a 3 d whole earth model implicitly contains the travaltimes for all source receiver positions and for any source configuration the corresponding amplitudes of all phases thus 3 d numerical modelling of whole earth responses is a potentially valuable diagnostic and interpretive tool and a basis for globalization in contrast to regionalization of traveltime tables

palynology of pleistocene travertines from the arava valley israel abstract pollen samples from the arava travertines dated to oxygen isotope stages 5 and 7 show relatively high arboreal pollen levels these spectra are probably a result of an expansion of the mediterranean maquis in transjordan which indicates periods of wetter climatic conditions these periods probably represent humid fluctuations within stages 5 and 7

dead sea pollen provides new insights into the paleoenvironment of the southern levant during mis 6 5 abstract the paleoclimate of the southern levant especially during the last interglacial lig is still under debate reliable paleovegetation information for this period as independent evidence to the paleoenvironment was still missing in this study we present a high resolution pollen record encompassing 147 89 ka from the dead sea deep drilling core 5017 1a the sediment profile is marked by alternations of laminated marl deposits and thick massive halite indicating lake level fluctuations the pollen record suggests that steppe and desert components predominated in the dead sea surroundings during the whole investigated interval the late penultimate glacial 147 3 130 9 ka and early last glacial 115 5 89 1 ka were cool and relatively dry with sub humid conditions confined to the mountains that sustained moderate amounts of deciduous oaks prior to the lig optimum a prevalence of desert components and a concomitant increase in frost sensitive pistachio trees demonstrate the occurrence of an arid initial warming phase 130 9 124 2 ka the lig optimum 124 2 ka 115 5 ka was initiated by an abrupt grass expansion that was followed by a rapid spread of woodlands in the mountains due to increased moisture availability the remarkable sclerophyllous expansion points to a strong seasonal moisture deficit these results contradict previous dead sea lake level investigations that suggested pluvial glacials and a warm dry lig in the southern levant prominent discrepancies between vegetation and dead sea lake stands are also registered at 128 115 ka and the potential causes are discussed in particular while the pollen spectra mirror increased effective moisture during the lig optimum the massive halite deposition is indicative of an extremely low lake level given that the climate amelioration triggered the migration of early modern humans to the southern levant we speculate that the diverse ecosystems in the region provided great potential for their residence across the eastern mediterranean region an analogous vegetation succession pattern is observed

contrasting diagenesis of two carboniferous oolites from south wales a tale of climatic influence two oolites in the dinantian mississippian lower carboniferous of glamorgan sw britain were deposited in similar depositional environments but have contrasting diagenetic histories the brofiscin and gully oolites occur in the upper parts of shallowing upward sequences formed through strandplain progradation and sand shoal and barrier growth upon a southward dipping carbonate ramp the brofiscin oolite is characterized by a first generation cement of equant calcite spar preferentially located at grain contacts and forming non isopachous fringes around grains interpreted as meteoric vadose and phreatic in origin isopachous fibrous calcite fringes of marine origin are rather rare and occur only at a few horizons burial compaction was not important and porosity was occluded by poikilotopic calcite spar fitted grain grain contacts locally occur and could be the result of near surface vadose dissolution compaction syntaxial overgrowths on echinoderm debris are common pre compaction overgrowths are cloudy inclusion rich and probably of meteoric origin and post compaction overgrowths are inclusion free by contrast the gully oolite has little first generation cement however marine fibrous calcite is common in oolitic intraclasts as isopachous fringes of acicular calcite crystals closely associated with peloidal internal sediment and early equant drusy calcite spar occurs in the uppermost part of the gully beneath a prominent palaeokarst where pedogenic cements also occur the major feature of gully diagenesis is burial compaction resulting in extensive grain grain dissolution and microstylolitic grain contacts and post compaction poikilotopic spar occluded remaining porosity the brofiscin oolite is pervasively dolomitized up dip but the gully oolite for the most part only contains scattered pre compaction dolomite rhombs and late veins of baroque dolomite with less pervasive dolomitization the difference in diagenetic style of the two dinantian oolites is attributed to prevailing climate the paucity of early meteoric cements in the gully is a result of an arid climate and this is supported by the nature of the capping palaeokarst the abundant meteoric cements in the brofiscin reflect a more humid climate and effective meteoric recharge also resulted in up dip pervasive mixing zone dolomitization the style of early diagenesis in these two oolites exerted a major control on the later burial diagenesis in the brofiscin the early cements inhibited grain grain dissolution and pressure solution while these processes operated extensively in the gully oolite thus prevailing climate can influence a limestone s diagenetic history from near surface through into deep burial

a multi methodological approach to reconstruct the configuration of a travertine fissure ridge system the case of the cukor quarry suttő gerecse hills hungary abstract travertines are continental carbonates that precipitate from spring waters mainly due to co2 degassing they are widely quarried as building stone which has led to numerous often abandoned travertine quarry outcrops these and other outcrops however merely represent the surface expressions of the complex architecture of travertine bodies and their deep rooted feeding systems integration of field observations and geochemical analyses with crucial subsurface geophysical data is required in order to fully understand travertine systems and their relationship to the local geological framework such a multi methodological approach is illustrated here for the case of the abandoned cukor quarry radio magnetotelluric rmt and electrical resistivity tomography ert surveys provide unique insights into local tectonics geobody architecture and the topography preceding travertine deposition altogether the lens shaped isolated domal geobody with spring proximal lithofacies and subvertical bedding in addition to the contrasting geochemistry and age with surrounding travertine enabled the unequivocal reconstruction of the dismantled cukor fissure ridge this study illustrates the high potential of this multi methodological approach on poorly exposed strongly weathered quarried and tectonically deformed travertine bodies and provides information on the complex feeding system beneath travertine deposits their reconstruction can be interpreted in light of the neo tectonic expression of regional uplift helps to complete the regional tectonic history and provides insights into older landscapes that lack preservation or would no longer be immediately recognized at the surface

finite difference seismograms for sh waves the accuracy of the finite difference method for generating synthetic seismograms of sh wave propagation in cylindrically symmetric media is discussed the finite difference method has the advantage that arbitrary density and velocity fields in the medium may be specified a point source is generated by a simple transformation of a line source the accuracy of the finite difference seismograms in flat and dipping layered media is confirmed by comparison with the generalized ray method a source radiation pattern is inserted by introducing a near field which has permanent displacement near the source strong motion synthetics are constructed with this new method for the 1968 borrego mountain earthquake as recorded at el centro good fits to the data are achieved using the laterally varying model determined by a detailed refraction survey and the source parameters determined by teleseismic waveform modeling shallow faulting is no longer necessary to explain the long period surface wave development

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

ages of travertine deposits in eastern grand canyon national park arizona abstract travertine deposits in eastern grand canyon national park arizona are inferred to have formed under conditions of effective wetness that were greater than present uranium series dating of 17 samples indicates that the deposits formed at about 15 000 71 000 111 000 171 000 and 338 000 yr b p intervals of travertine deposition are essentially contemporaneous with dated high paleolake levels montane glacial maxima and high paleowater table levels from several great basin localities

early and middle holocene wood exploitation in the fayum basin egypt the early and middle holocene of north africa was a time of dramatic climatic and social change including rapid shifts in vegetation communities and the introduction of domesticated plants and animals recent research from the fayum basin of egypt which holds archaeological evidence for early use of domesticates aims to place inhabitants of that region within their contemporary environmental setting we present here results of wood charcoal analysis from three early and middle holocene deposits on the north shore of the fayum and reconstruct both contemporary woodland ecology and patterns of anthropogenic wood use in total three woodland communities likely existed in the area but inhabitants of this region made heavy use of only the local lakeshore woodland emphasizing tamarisk tamarix sp for fuel while seasonally watered wadi woodlands were not harvested for fuel more arid locations on the landscape were evidencing regional mobility between ecological zones results indicate that wood was locally abundant and that inhabitants were able to select only preferred species for fuel this study provides further evidence for low level food production in the fayum that preserved critical ecosystem services rather than dramatic niche construction to promote agriculture as seen elsewhere in middle holocene southwest asia

influence of near source volcano topography on the acoustic wavefield and implication for source modeling in near source conditions 5 km the atmosphere is often assumed to be fully transparent to acoustic waves and to have a small effect on the acoustic wavefield as a consequence the propagation of the acoustic waves in the atmosphere near the source is often neglected and waveform is compensated only in amplitude by the inverse of the distance from the source however the amplitude distribution at five infrasonic stations deployed around the active craters of the stromboli volcano reveals anomalous decay up to 11 db larger than expected which cannot be explained in terms of energy loss for geometrical spreading the distribution of amplitude decay changes for different source positions suggesting a strong relationship with the source to receiver path geometry by using 2d fdtd modeling we show that the anomalous amplitude distribution of the acoustic waves at stromboli is not necessarily due to the source radiation pattern but it is strongly influenced by the topography of the ground atmosphere interface diffraction and reflection of topography contaminate the acoustic wavefield and have a strong effect in reducing the amplitude and altering the waveform our work demonstrates that line of sight conditions are quite difficult to be achieved in acoustic experiments and that a detailed knowledge of the topography along the crater receiver path is necessary whenever infrasound waveforms are used to invert for the source process

charophyte remains from wadi howar as evidence for deep mid holocene freshwater lakes in the eastern sahara of northwest sudan abstract field research in the eastern sahara northwest sudan revealed extensive early to mid holocene lake marl deposits bearing gyrogonites of charophytes green algae stoneworts along the lower course of the wadi howar an extinct tributary to the nile the charophyte flora of a paleolake southwest of jebel rahib 17 31 n 26 52 e dated prior to 4720 110 yr b p is mainly composed of the ecologically sensitive species nitellopsis obtusa which indicates permanent relatively deep 4 12 m and cool oligotrophic freshwater the study of nitellopsis sites provides a new and promising approach to the reconstruction of quaternary paleoenvironments of deserts

continuous pollen diagrams for the last 3 5 m y from israel vegetation climate and correlation with the oxygen isotope record abstract several continuous pollen diagrams have been obtained from boreholes penetrating the entire quaternary sequences of the hula and dead sea lakes in the jordan rift valley israel the dead sea served as a terminal base level through this period thus ensuring a complete continuous deposition volcanic intercalations within the hula lake sediments permit some control of the absolute datings a paleoclimatic model for the last 150 k y based on better dated sequences serves as a basis for correlating the israeli sections with the oxygen isotope records known from the oceans and the mediterranean the glacial phases are manifested in israel by periods of somewhat lower temperatures and higher rainfall some in summertime the interglacials are hot and dry with saharan conditions prevailing the interstadials are of the present day character of a short rainy winter and a dry hot long summer the first major cooling of the quaternary in israel took place some 2 4 2 6 m y ago followed by a series of alternating wetter and drier phases corresponding quite well to changes in the global ice volume expressed by the oxygen isotope curves it seems however that some successions of the glacial phases are grouped in israel into longer wetter periods with the interglacials manifested as interstadials a similar case is seen for some of the interglacials successions with glacial phases as interstadials a possible explanation for the difference between the continental and the ocean records may lie in the distribution of the global ice volume differences in the accumulations of ice at the arctic and antarctic regions during some of the glacial phases could explain the extent of a glacial period on land while not being apparent from the oxygen isotope records and vice versa for the interglacials thus a well developed ice cap on antarctica may cause only a minor glaciation in the northern hemisphere but be recorded as a full glacial in the oceans

reflections from a randomly grooved interface ultrasonic modelling and finite diff erence calculation1 this study utilizes ultrasonic water tank modelling to examine the complexities which can result when seismic energy is diffracted by even a simple 3d interface structure ultrasonic laboratory modelling is carried out in our in house water tank using an aluminum block to simulate very simple ocean bottom topography the topography consists of parallel depressions which simulate valleys running parallel to a mid ocean spreading ridge this study shows that the phase and amplitude of primary ocean bottom reflections can vary strongly with the azimuth of propagation the trailing energy coda also varies dramatically as a function of propagation direction showing the importance of developing a seismic model which includes the full 3d azimuthal distribution of interface structure

early holocene basinal sediments of the dakhleh oasis region south central egypt abstract twenty samples of artifactual ostrich eggshell and hearth charcoal firmly to loosely associated with basinal lacustrine playa and sand sheet sediments in the dakhleh oasis region of south central egypt yield radiocarbon ages between ca 8800 and ca 4700 yr b p the sediments record variable sedimentary responses to an early holocene pluvial interval in this virtually rainless region differences of hydrogeology and morphometry among and within basin types complicate paleoclimatic interpretation

evidence of past environmental conditions during the evolution of a calcretised wadi system in southern jordan using stable isotopes abstract a stratigraphically and temporally ordered sequence of channel calcretes preserved along the wadi dana southern jordan records the quaternary evolution of the formation and infilling of rock cut channels and their subsequent incision in a tectonically subsiding basin it is currently unknown under what palaeoenvironmental conditions these non pedogenic calcretes formed stable isotope analyses have been used to investigate whether any past topographical hydrological vegetational diagenetic and or temporal signatures can be identified from the channel calcretes the results of this research indicate that channel calcrete development is influenced by altitudinal variation affecting vegetation and hydrology within the landscape as well as location within individual wadi channels which has an affect on diagenetic processes the lack of calcretisation of a terrace that is between 1 and 1 5 m above the modern wadi floor supports the idea that the environment is currently too arid for calcrete to develop thus the presence of older wadi dana channel duricrusts suggests wetter conditions when they formed the 18o data of the calcrete implies cooler conditions than today as there is little evidence of a strong evaporative effect any temporal control is limited and mainly a function of stratigraphic position with some numeric dating

towards a high resolution global deep sea chronology for the last 750 000 years abstract variations in the ratio of 18 o 16 o as measured in shells of marine calcareous microfossils are primarily dominated by changes in global ice volume hence these variations provide a set of global time lines in deep sea sediments it is likely that the timing of major changes in oxygen isotope values is strongly influenced if not controlled by variations in the geometry of the earth s orbit since the variation of orbital parameters can be accurately calculated the opportunity exists for transforming this orbital chronology into a geological chronology through careful correlation of oxygen isotope records in a set of deep sea cores from the sub antarctic south atlantic and equatorial pacific we have assembled a composite isotopic section spanning the last 750 000 years with an average sedimentation rate of 2 3 cm 1000 years a new chronology for this time period was developed by adjusting the ages of the oxygen isotope stage boundaries in this composite section so as to extend the consistent phase relationships that exist between variations in oxygen isotope ratios and changes in obliquity and precession during the last 300 000 years to the entire 750 000 year record previously identified difficulties in phase locking precession with the filtered isotopic signal between 365 000 and 465 000 years b p have been resolved with the recognition that precessional variations have an average period of 19 000 years and not 23 000 years during this interval since this new age model yields the best match between variations in obliquity and precession and their corresponding frequency components in the oxygen isotope record we believe that it presents the most accurate chronology yet developed for deep sea sediments with this new age model providing the time control power spectral analyses of south atlantic and sub antarctic chemical and biotic indices show that there is a strong tendency for variance to be concentrated at frequencies corresponding to periods of 100 000 41 000 and 23 000 years

quasi cylindrical 2 5d wave modeling for large scale seismic surveys 1 the most common form of seismic exploration remains a nearly linear survey with data acquisition lines including the source and receivers the interpretation of amplitude and waveform information for such linear acquisition requires consideration of 3d seismic wavefields in many scenarios the structure is approximately 2d but still modeling is needed for point sources in recent years 2 5d modeling methods have been developed for the simulation of 3d seismic wavefields in media varying in two dimensions although the computer memory requirements are only slightly larger than those for 2d computations the computation times are too long for ready application to actual surveys to overcome this problem we propose a new approach for modeling 2 5d seismic wavefields using a quasi cylindrical representation we show an implementation of this approach using the finite difference method and demonstrate the validity and efficiency of the technique with numerical examples including a profile across a realistic model of subduction zone structure

uranium series dating of quaternary deposits abstract this is a review of u series dating methods as applicable to terrestrial sedimentary materials alpha counting techniques allow the dating of carbonates and phosphates with a precision of 5 to 10 over the time range from 1 ka to 350 ka atom counting methods mass spectrometry and ams substantially increase precision and may increase the range problems of contamination and open system behavior are discussed correction for detrital contaminant is demonstrated in the dating of speleothem from a cave in italy

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

desert speleothems reveal climatic window for african exodus of early modern humans one of the fi rst movements of early modern humans out of africa occurred 130 100 thousand years ago ka when they migrated northward to the levant region the climatic conditions that accompanied this migration are still under debate using high precision multicollector inductively coupled plasma mass spectrometry mc icp ms u th methods we dated carbonate cave deposits speleothems from the central and southern negev desert of israel located at the northeastern margin of the saharan arabian desert speleothems grow only when rainwater enters the unsaturated zone and this study reveals that a major cluster of wet episodes the last recorded in the area occurred between 140 and 110 ka this episodic wet period coincided with increased monsoonal precipitation in the southern parts of the saharanarabian desert the disappearance at this time of the desert barrier between central africa and the levant and particularly in the sinai negev land bridge between africa and asia would have created a climatic window for early modern human dispersion to the levant

distribution and geometry of facies and early diagenesis the key to accommodation space variation and sequence stratigraphy upper cretaceous congost carbonate platform spanish pyrenees abstract through only moderate structural deformation the upper cretaceous carbonates of the tremp region in the spanish pyrenees can be studied in the form of a platform to basin cross section comparable in scale to that of a seismic section this study examines the upper turonian to mid coniacian congost platform and its associated basinal succession the sedimentology facies geometries and cycle stacking patterns along with evidence of exposure of the platform are interpreted in terms of fluctuations in relative sea level and variations in accommodation space differences in the facies and early diagenesis of carbonates from different parts of the congost platform suggest two separate phases of platform development an earlier more land ward platform was dominated by clinoforms prograding on to a sloping basin floor with a thin lagoonal sand bank facies upon the platform itself supplying abundant excess sediment to the clinoforms a later more basin ward platform has a more complex internal geometry of depositional units and marginal rudist coral buildups the interpretations are used to propose a new sequence stratigraphic architecture for the congost platform involving two sequences the second produced through dynamic forced regression sequence boundaries are characterised by subaerial exposure on the platform top that can be correlated with hardgrounds and or glauconitic horizons within the more basinal locations overlain by deeper water facies the presence of a submarine onlap surface and down slope slide deposits immediately above the sequence boundary suggests that the major transgressive event that followed sequence boundary development was brought about by local extensional tectonic activity the small scale cyclicity within the sequences and the major falls in sea level that produced the sequence boundaries are interpreted to have resulted largely from eustatic processes probably with tectonic enhancement

vegetation invasions into absolute desert a 45 th000 yr rodent midden record from the calama salar de atacama basins northern chile lat 22 24 s plant macrofossils percentage abundance of grass taxa fecal pellet d13 c and plant cuticle contents from 49 fossil rodent middens dated by 14 c record changes in local vegetation and precipitation since 45 ka calibrated or measured to thousands of calendar years before present in the central atacama desert lat 228 248s of northern chile the midden sites are along the hyperarid upper margin 2400 3100 m of the absolute desert in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs conditions between 40 and 22 ka may have been at least intermittently dry and possibly cooler as implied by four middens with low species richness we infer a large increase in summer rainfall between 16 2 and 10 5 ka on the basis of the lowering of steppe grasses by as much as 1000 m prominence of c4 grasses and summer annuals high species richness and displacement of northern species at least 50 km south of their modern ranges the precipitation increase was greatest for a cluster of middens between 11 8 and 10 5 ka abrupt drying evident in a dramatic decrease in grass abundance occurred after 10 5 ka at all four midden localities increased percentages of

a review of finite difference methods for seismo acoustics problems at the seafloor understanding seismic wave propagation in realistic seafloor environments is essential for many problems in marine seismology finite difference methods are becoming increasingly popular in solving propagation problems as the limitations of other techniques which apply only at high frequency or for flat lying media become fully appreciated the seafloor problem a high contrast in poisson s ratio at a rough sharp interface is particularly challenging and many published formulations fail to solve it accurately the purpose of this paper is to summarize the published finite difference formulations for the elastic wave equation and to outline their applicability to seafloor problems

paleoclimatic implications of u series dates for lake sediments and travertines in the arava rift valley israel abstract the sayif travertines and lacustrine limestones cropping out in the northern arava valley a region of extreme aridity have been dated by the 230 th 234 u disequilibrium method the consistency between the stratigraphic position and the apparent ages at each of the sampling sites strongly supports the reliability of the ages most of the ages fall within two clusters that are coincident with ages representative of oceanic oxygen isotope stages 5 and 7 the colder intervening stage 6 was not a period of substantial travertine formation during the warmer global episodes of isotopic stages 5 and 7 the arid south of israel apparently was considerably wetter than at present

quaternary morphotectonic mapping of the wadi araba and implications for the tectonic activity of the southern dead sea fault 1 the dead sea strike slip fault accommodates the northward motion of arabia relative to sinai at a rate of 5 mm yr the southern segment of the fault the wadi araba fault runs along a valley blanketed in quaternary sediments we first focused on understanding the relative and absolute timing of emplacement of the alluvial surfaces we then determined the probable source of the sediments before assessing their lateral offset to constrain the late pleistocene fault slip rate seven successive morphostratigraphic levels were identified at two sites we recognized an alluvial sequence of five to seven successive levels with ages getting younger northward a pattern consistent with the western block moving southward relative to two fixed feeding channels located to the east surface samples were collected for10be cosmogenic radionuclide dating fans f3 and f5 were found to be synchronous from site to site at 102 26 ka and 324 22 ka respectively while f4 could be dated at 163 19 ka at one site only these are minimum ages assuming no erosion of the alluvial surfaces at least two of these periods are correlated with wet periods that are regionally well documented further analyses of tectonic offsets are affected in most cases by large uncertainties due to the configuration of the sites they indicate maximum offsets of 5 5 km for the oldest possibly 1 ma old surfaces they lead to bracketing of the fault slip rate between 5 and 12 mm yr with preferred values of 5 7 mm yr for the last 300 ka

a review of the tagus river tufa deposits central spain age and palaeoenvironmental record here we determined the aminostratigraphy and aminochronology of tufa deposits located in central spain associated w i t h the tagus river and some o f its tributaries the henares dulce cifuentes ruguilla trabaque escabas and guadiela rivers w e used aspartic acid and glutamic acid racemization ratios obtained from the ostracod herpetocypris reptans tufa accumulations were found to be of different origins those in t h e henares cifuentes and ruguilla rivers are of paludal origin w h i l e those in t h e dulce and tagus rivers are o f fluvial origin a generally g o o d correspondence was found b e t w e e n the age o f the deposits and the position of the terraces above the current thalweg however the geomorphological evolution of the henares cifuentes and ruguilla rivers infilling of pre existing valleys has produced deposits of distinct ages at the same elevation above the current river thalweg and sometimes older tufas are located b e l ow younger ones we distinguished eight main tufa deposition episodes these occurred predominantly during even marine isotopic stages mis at 4 0 6 90 mis 11 2 6 4 68 mis 7e 189 4 0 mis 7a 130 27 mis 6 5e 101 2 5 mis 5c 3 2 10 mis 3 1 4 4 mis 1 a n d 6 2 mis l k a these results are in agreement w i t h the dating of similar deposits from nearby areas and other zones of s p a i n a n d europe the tufa stable isotope compositions were similar to other examples in central and southern spain a n d their plot falls in the same field as other lowland european stream tufas o x y g e n stable isotopes were influenced mainly b y temperature a n d rainfall the 51 3c values indicated a major effect o f soil derived carbon rather t h a n carbon from the catchment area but moderated in each tributary b y evaporation flow regime and biological effects photosynthesis

sediment and pollen evidence for an early to mid holocene humid period in the eastern sahara a major problem in the study of holocene palaeoenvironments of the arid and wind deflated sahara is the low preservation potential of sediments from which a record of past climatic change can be established several indirect and imprecisely dated pieces of evidence have suggested humid episodes in the holocene that may have supported more productive ecosystems and denser human populations than today searches for reliable proxy data on past climates however have failed to yield satisfactory results we report here the discovery of buried lake muds in north west sudan in the hyperarid core of the eastern sahara which yield sedimentological and palynological data clearly interpretable as recording an early to mid holocene humid episode that supported a relatively deep stratified lake surrounded by tropical savanna woodland vegetation

surface motion over a sedimentary valley for incident plane p and sv waves abstract finite difference techniques are applied to study the response of a sedimentary basin in an isotropic elastic half space to vertically incident compressional and shear sources the sedimentary rock of the basin is modeled as a transversely isotropic material improved finite difference approximations to the boundary conditions are developed of primary interest is the formation of rayleigh waves over the flank of the basin displacement time series at points on the free surface and rayleigh orbits are plotted three dimensional spectral amplitude graphs of the entire time series up to a period of temporary quiescence are presented the rayleigh wave is the dominant scattered phase for the basin geometry considered having 20 to 30 per cent of the source displacement amplitude at the free surface in a basin with 26 flanks 0 7 km depth 6 km width over a half space whose acoustic impedance contrast with the basin was two the effect of varying the degree of compressional anisotropy in the basin on the amplitudes of refracted and scattered phases of engineering interest was minimal

brunhes epoch paleoclimates of japan and israel abstract continuous pollen diagrams for the brunhes epoch two from lake biwa japan and two from the dead sea rift israel are the basis for reconstructing paleoenvironments and paleoclimatic trends on both sides of asia east and west at approximately the same latitudes the mid 30 n the paleoclimatic curves are compared and correlated with the ocean oxygen isotope records the correlation is based on detailed and better dated climatic models obtained for both localities for the last 100 150 k y generally similar climatic trends have been observed for both sides of asia correlating to the oxygen isotope curves the glacial phases are manifested by cooler and more humid periods the interglacials by a temperate climate in japan and a warm dry climate in israel local climatic responses to global cooling or warming differ in japan and israel and peaks of the oxygen isotope curves may appear amplified or reduced in any of the regions the climatic responses to global processes differ from japan to israel in terms of amplitude but not the style of changes the causes for these differences in amplitude may lie with either the different local conditions japan being mainly controlled by the ocean while israel is strongly influenced by the sahara or differences in the global distribution of ice through the ages not recorded in the oxygen isotopes as long as the ice volume remains constant

southward migration of rain tracks during the last glacial revealed by salinity gradient in lake lisan dead sea rift abstract the paleosalinity of the late pleistocene lake lisan during its highstand between 27 000 and 15 000 years b p is evaluated from biological data diatoms cyanobacteria fish and ostracods and chemical data sr ca and na ca ratios in authigenic aragonite the data indicate a zone of maximum salinity at the southern part of the lake in the vicinity of the present dead sea basin while most of the freshwater input to lake lisan originated from the jordan river in the north and runoff from the eastern and western parts of the drainage basin our analysis indicates a significant additional contribution from a southern freshwater source at present the contribution of the southern source to the dead sea is minimal hence it appears that in addition to the prevailing rain originating from the mediterranean an additional southern source of rain was more active during the last glacial than today this may be explained by migration of rain tracks whose moisture originated in the atlantic from the mediterranean southwards

great sand sea and selima sand sheet eastern sahara geochronology of desertification the relation of playa sediments and associated archeological sites with longitudinal dunes allows estimation of ages for the two uppermost strata of the great sand sea active dune formation corresponds with interpluvial periods of hyperaridity dune stability corresponds with semiarid pluvial periods archeological sites associated with truncated paleosols in the selima sand sheet suggest a similar climatic relation and indicate that the isohyets of central sudan shifted at least 400 kilometers northward during the peak of pluvials

finite difference seismic modeling of axial magma chambers we tested the feasibility of using finite difference methods to model seismic propagation at 10 hz through a two dimensional representation of an axial magma chamber with a thin liquid lid our technique produces time series of displacement or pressure at seafloor receivers to mimic a seismic refraction experiment and snapshots of p and s energy propagation the results indicate that our implementation is stable for models with sharp velocity contrasts and complex geometries we observe a high energy downward traveling shear phase observable only with borehole receivers that would be useful in studying the nature and shape of magma chambers the ability of finite difference methods to model high order wave phenomena makes this method ideal for testing velocity models of spreading axes and for planning near axis drilling of the east pacific rise in order to optimize the benefits from shear wave imaging of sub axis structure

3d eight order elastic finite difference modeling of refraction and strong motion data from the coyote lake region california abstract 3d elastic modeling of vertical component explosive source refraction data is performed to constrain the shallow part of a velocity model followed by 3d modeling of three component strong motion data from a spatially and temporally extended earthquake source in that model modeling is by eighth order finite differencing on a staggered grid which automatically generates all body and surface waves including multiples and conversions application is to the 1981 usgs refraction survey and the 6 august 1979 coyote lake event in central california 3d modeling was able to reproduce the main observed features in both the refraction and earthquake data for the refraction data the synthetics explain local variations in first arrival travel times reverberations in the near surface sediments and surface waves for the strong motion data the initial arrival times and amplitudes are determined by the position and orientation of the initial rupture the shapes of the trailing edges of the pulses are modified by the actual source distribution changes of source position of 1 to 2 km are easily resolvable through changes in the position of nodal planes discontinuities in material properties e g layering produce a coda of multiples and converted waves lateral variations in velocities especially in the upper few kilometers change the energy distribution among the trace components by 3d refraction and so shift the apparent source directivity and position as well as contributing to the coda remaining differences between the observed and synthetic data are attributed to local seismometer coupling effects very local site structures and phenomena such as anelasticity and anisotropy which are not explicitly modeled

pleistocene paleoclimate of the arid region of israel as recorded in calcite deposits along regional transverse faults and in veins abstract the 18o and 13c values of the calcites associated with e w and ne sw transverse faults in the negev israel indicate that calcite was deposited from meteoric water a regional change in the 18o and 13c values was observed the 18o content in the calcite increases from the southwestern 18 o 17 8 to the northeastern 18 o 2 9 part of the region the 13c values show the opposite trend of the 13c content decrease from 2 in the south to 10 in the northeast these trends had to reflect changes in regional paleoclimate suggesting a change in the isotopic composition of the solution from which the calcite was deposited in different periods the variations in the 18o values reflect shifts in the 18o values of precipitation and are associated with a change in the source of moist air masses which came from the equatorial atlantic in the early pleistocene and from the mediterranean during a later period variations in 13c values reflect changes from humid to arid conditions two modes of calcite deposition are suggested 1 precipitation of calcite minerals in the unsaturated zone following the dissolution in the soil or 2 calcite deposition that occurred as co2 was lost during emergence of paleogroundwater from lower cretaceous and jurassic aquifers

finite difference seismograms for laterally varying marine models summary the method of finite differences is applied to the elastic wave equation to generate synthetic seismograms for laterally varying seafloor structures the results are compared with borehole seismic data from the gulf of california deep sea drilling project site 485 in which lines were shot over flat and rough topography the significant new phenomenon observed in both the synthetic seismograms and the field data is the generation of a double head wave due to the interaction of the incident wavefront with the side of a hill and the flat seafoor adjacent to the hill in these models the hills are on the order of a seismic wavelength in height and steep velocity gradients occur over distances comparable to wavelengths ray theoretical methods would not be suitable for studying such structures true amplitude record sections are obtained by the finite difference method which show for these models that the head wave generated at the flat seafloor adjacent to the hill is lower in amplitude than if the hill were not present and is lower in amplitude than the head wave generated at the hill a second feature which is important for borehole receivers is the existence of the direct wave root in the upper basement this energy occurs below the sharp interface when the direct wave impinges on the interface from above there is no corresponding snell s law ray path for this energy and the energy is evanescent with depth in the lower medium the properties of both the double head wave and the direct wave root are clearly demonstrated in the finite difference snapshot displays

paleoclimate and vegetation of the last glacial cycles in jerusalem from a speleothem record a speleothem isotopic record taken from jerusalem is used to reconstruct regional climate over the last 170 000 years glacial periods in jerusalem were generally cooler and wetter than the present climate stage 5e in the desert margin of jerusalem was extremely unstable dry and warm and instability persisted throughout the transition to glacial conditions the climate after stage 5e became gradually cooler and wetter over a 20 000 year interval and did not recover to interglacial conditions in stages 5c and 5a the 13 c varied by up to 12 from glacial stages 6 4 3 2 values of 10 to 12 that reflect dense c 3 vegetation above the studied cave and up to 0 in early stage 5 when there was probably complete loss of vegetation the climatic instability during interglacial periods is much larger than during glacial periods and glacial interglacial transitions do not behave the same in each climatic cycle in this region

the role of diffusion during carbonate diagenesis abstract the dissolution reprecipitation process which characterizes the early mineralogical stabilization of carbonate sediments takes place in a somewhat open chemical system studies of the trace element chemistries and isotopic compositions of carbonate grains before and after stabilization have documented the exchange of ions between the diagenetic site and the aquifer solution if the pores at reaction zone and in the immediate neighborhood of the diagenetic site are of insufficient diameter to allow effective solution flow the exchange of ions between the diagenetic site and the aquifer solution the large volume of water which flows through the macropores of the carbonate sediment takes place by aqueous diffusion this paper examines diffusion applied specifically to the conditions of carbonate diagenesis the diffusion equation modified to these circumstances serves as a guide to understanding the diffusion process at a given temperature three variables determine the efficacy of diffusion the diffusion coefficient the pore path and geometry and the concentration gradient the diffusion coefficient may be considered a measure of the inherent velocity at which a given ion travels under standard conditions the double positive cations common in carbonates ca2 sr2 ba2 zn2 mg2 etc and the carbonate anion all have similar diffusion coefficients thus this term of the equation exerts little influence during normal carbo ate diagenesis the pore path and geometry refer to the distance from aquifer to reaction zone and the diameter shape and directness of the pore passage this term is difficult to quantify in diagenetic systems but is constant for different ions at a single diagenetic site the longer and the more complex the path the less effective diffusion is there is a general facies dependence to this term grainstones have short paths from reaction zone to aquifer due to their permeability whereas mudstones and wackestones are characterized by long and torturous paths through the mud grains to the aquifer solution exchange of ions in the fast situation is more effective than in the second the concentration gradient the difference between the concentration of an ion in th reaction zone and in the proximal aquifer solution is the most variable parameter in diffusion the sign of the gradient which may be positive or negative indicates the direction of diffusion transport of the ions toward the region of lower concentration one cation may diffuse from the reaction zone while simultaneously a second cation diffuses toward the reaction zone this two way traffic has been documented in diagenetic calcite corals sr2 diffuses away from and mg2 diffuses toward the diagenetic site additionally one cation may diffuse effectively whereas a second diffuses ineffectively the latter species being characterized by a weaker concentration gradient thus a given diagenetic site may be chemically open for one cation and simultaneously somewhat closed for another application of diffusion principles to the aragonite calcite transformation during early diagenesis indicates the compositions of solutions and diagenetic calcites undergo temporal changes early on with few active diagenetic sites sr2 diffuses effectively from the reaction zone to the aquifer since there is a steep concentration gradient diagenetic calcites are relatively low in sr2 because of its effective removal from the diagenetic site as the number of active diagenetic sites increases so much sr2 may be delivered to the aquifer that sr2 builds up in the aquifer solution and the concentration gradient shallows diffusion from individual sites becomes less effective sr2 concentrates in the reaction zone and diagene ic calcites enriched in sr2 are produced as more and more aragonite is consumed a final phase is reached in which less total sr2 is delivered to the aquifer and the system returns to the conditions characteristic of the early phase