u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

the abrasion of modern and archaeological bones by mobile sediments the importance of transport modes abstract fresh weathered archaeological and fossilized bones were subjected to a series of abrasion experiments using fine sand in an annular flume in order to link bone surface abrasion to flow regimes and sediment transport modes compare these effects on bones of different states and quantify the extent and types of wear occurring flow velocities were chosen to replicate the predominant transport modes of bedload saltation and suspension comparative scanning electron microscopic image analysis was performed to assess the degree and type of wear occurring on each bone type for the different transport modes over a range of exposure periods from 24 to 72 h these preliminary investigations have shown that both the amount and type of wear experienced was related to the bone type duration of exposure and the mode of sediment transport with wear being the result of deformation rather than cutting wear the formation of scour pits in the sand bed on the upstream side of the bone samples significantly reduced wear and appears to be an important control mechanism for impact related wear that has been overlooked until now

imaging capability of cross hole seismic reflection surveys1 in seismic migration it is important to sample a range of dips around the local structural dip at each image point meaningful images are obtained only where this condition holds for cross hole seismic reflection surveys the distribution of dips sampled at each image point is controlled principally by the survey geometry including source and receiver array lengths and their element spacings using a real data set as an example the authors show how survey geometry can limit imaging capability close to the boreholes and even in the middle of the section between the boreholes at the processing stage effective removal of direct waves and accurate estimation of the velocity field are essential for optimizing image quality for migration they propose a generalized berryhill gb scheme which is based on the kirchhoff integral and takes into account both the near field and far field terms this should improve the ability to image close to source and receiver arrays provided that the element spacing in the nearby array is small enough

234u 238u mass spectrometry of corals how accurate is the uth age of the last interglacial period direct measurement of u and th by mass spectrometry recently provided a spectacular improvement in the precision of coral dating by the uth disequilibrium method 1 mass spectrometric data also provide a much better resolution for the examination of subtle diagenetic effects revealed by small variations of the 234u 238u ratio such perturbations may strongly affect the accuracy of the uth chronometer a compilation of all the corals analyzed to date by mass spectrometry shows that most of the corals from terraces of the last interglacial have initial 234u 238u ratios higher than present day seawater in contrast to modern holocene and last glacial corals some samples that have very high 234u 238u initial ratios up to 1 2 and high u concentrations up to 4 ppm were probably contaminated by continental groundwaters however even apparently pristine samples have 234u 238u initial ratios which are still slightly higher than present day seawater mean value 1 160 compared to 1 140 1 150 2 with little overlap between the two distributions this difference in the u initial ratio raises some uncertainty about the accuracy of the uth age determinations of these corals in spite of the fact that the 234u230th ages cluster in a narrow range between 122 and 133 kyr the data could also be interpreted as resulting from slight contamination of corals that are significantly older than 125 kyr two possible explanations may explain these data 1 all these samples may have been diagenetically altered since they all come from surface outcrops which have been directly exposed to precipitations or soil waters for 125 kyr in this case the true age of these corals remains uncertain depending on the timing of the alteration process i e initial late or continuous 2 the second possibility is that some of the differences in 234u 238u ratios measured in 125 kyr cold corals compared to modern seawater may be due to a higher 234u 238u ratio in seawater 125 kyr ago this could result from temporal variations in the weathering regimes of continental land masses

glacial cycles jive talking switches in the glacial interglacial cycle are linked to climatic change which is one reason for wanting to know more about them the history of such switches can in part be traced by estimating sea level which reflects the amount of water locked up in ice sheets a study that uses the red sea as a gauge now takes estimates of lows in sea level back 500 000 years well beyond the last glacial period

investigating human and megafauna co occurrence in australian prehistory mode and causality in fossil accumulations at cuddie springs abstract human arrival in sahul pleistocene australia and new guinea has long been argued as the catalyst in the decline and disappearance of a suite of extinct animals referred to as megafauna the debate concerning causality in sahul is highly polarised with climate change often cited as the alternative explanatory model on continental australia there are few datasets available with which to explore the likely processes leading to the extinction events at the present time there is one site in new guinea nombe rockshelter and one on continental australia cuddie springs where the coexistence and temporal overlap of humans and megafauna has been identified the cuddie springs pleistocene archaeological site in southeastern australia contains an association of fossil extinct and extant fauna with an archaeological record through two sequential stratigraphic units dating from c 36 to c 30 ka ago a taphonomic study of the fossil fauna has revealed an accumulation of bone in a primary depositional context consistent with a waterhole death assemblage overall the faunal assemblage studied here n 8146 nisp 1355 has yielded little direct evidence of carnivore damage or human activities post depositional factors such as physical destruction incurred by trampling compaction of sediments and or the hydrological status of the lake at that time have played important roles as the only known site on continental australia where megafauna and humans co occur the cuddie springs faunal assemblage yields equivocal evidence for a significant human role in the accumulation of the fauna here at the present time there is no evidential basis to the argument that humans had a primary role in the extinction of the australian megafauna the first colonisers are likely to have preyed upon those few species known to have persisted to this time but their impact may have been restricted to the tail end of a process that had been underway for millennia prior to human arrival

a large mammal site in a meandering fluvial context fonelas p 1 late pliocene guadix basin spain sedimentological keys for its paleoenvironmental reconstruction abstract the fonelas p 1 large mammal site is located stratigraphically in the youngest unit late pliocene pleistocene of the endorheic fill of the guadix basin betic cordillera at the site location this unit is represented by fluvial sediments of the basin s axial drainage system the general succession of the site consists of stacked fining upward cycles basically beginning with gravel and or sand filling a meandering channel and concluding with floodplain mud and carbonate each of the cycles is made up of four facies associations determined by sedimentological analysis of the sections measured in the paleontological excavation of the site these associations correspond to sedimentation in definite areas of the fluvial system a filling of a sinuous channel at maximum activity b levee deposits c abandoned channel and d floodplain in the cycle in which the site is located there is a fifth association e where the main fossil concentration is found fonelas p 1 this is a facies bioturbated by mammals moving over sediments of the abandoned channel association c by space time reconstruction of the fluvial environments we can infer that the morphological depression caused by a meander abandonment due to chute cut off was used as a hyena den the animal settlement ended when overflow from the laterally migrating active channel began to bury the abandoned meander with floodplain sediments

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

taphonomic and paleoecologic investigations of the late cretaceous santonian iharkut vertebrate assemblage bakony mts northwestern hungary abstract the iharkut vertebrate locality an open pit mine in the bakony mountains western hungary has provided a rich and diverse assemblage of late cretaceous santonian continental vertebrates the isolated and associated remains represent 31 different taxa including fish amphibians turtles lizards pterosaurs crocodilians non avian dinosaurs and birds sedimentologic investigations suggest that the iharkut depositional environment was represented by the floodplain of a very low gradient river the 10 50 cm thick bonebed of site sz 6 is the most important fossiliferous layer in the open pit mine and analysis of this site indicates alternating energy conditions during the bone accumulation which resulted in fossils of different states of preservation being deposited together the vertebrate assemblage of site sz 6 includes three main different subsets with widely different taphonomic history the characteristics and the preservation mode high rate of abrasion and the spherical shape of the bone pebbles suggest that this type of the isolated bones was more exposed to abrasion and probably the remains were transported from farther away than the other isolated bones the second group includes 88 of the iharkut collection containing most of the identified isolated bones and teeth and represents polytypic attritional remains transported and deposited by high density flow during ephemeral flood events meanwhile the monospecific ankylosaur skeletal material from iharkut site sz 6 may represent a mass death assemblage because seven skeletons of hungarosaurus were discovered from an area of approximately 400 m 2 and in many cases close to each other in the same layer the iharkut vertebrate assemblage is dominated by bones of aquatic semi aquatic animals while the number of terrestrial animal remains is subordinate the taphonomic analysis of the ankylosaur material from iharkut locality further strengthens the previously suggested hypothesis that some of the ankylosaurs preferred wetland habitats e g areas along fluvial systems while the other two herbivorous dinosaur groups from iharkut ornithopods and ceratopsians were probably living in distal habitats

taphonomy of vertebrate assemblages from the paleogene of northwestern wyoming and the neogene of northern pakistan abstract we compare the taphonomy of vertebrate assemblages from two long continental records the early paleogene of the bighorn basin wyoming and the neogene siwalik sequence of northern pakistan both sequences contain a similar array of fluvial facies and the abundance of these facies differs among formations we document environments of preservation of vertebrate localities over time to determine comparability of fossil assemblages within and between sequences changes in sample size and species richness are noted to reveal potential sampling effects on patterns of faunal turnover preservational history determined the environment sample size quality of specimens taxonomic composition and spatial and temporal resolution of fossil assemblages and thereby the quality of the fossil record and its suitability for further analyses in both sequences changes in prevailing taphonomic processes reflect changes in lithofacies and habitat distribution correlated changes are found in fossil productivity species richness and faunal composition both sequences contain some episodes of apparent faunal change in which appearances and disappearances of rare taxa can be attributed principally to changes in sample size the paleogene record has high taxonomic resolution i e to genus or species for most mammalian fossil remains temporal and spatial averaging of paleogene fossil assemblages changes with lithofacies the neogene record has higher taxonomic resolution for remains of small mammals different preservational circumstances impose different constraints on paleocological and evolutionary analyses the best opportunities for paleocommunity reconstruction are provided by high taxonomic resolution large samples nd varied environments of preservation these circumstances are found in limited portions of each record the best opportunities for documenting evolution within lineages and species replacement patterns are provided by high taxonomic resolution high temporal resolution and consistent preservational context these taphonomic attributes pertain to the more common paleogene mammals particularly from the rich paleosol localities of the willwood formation and to the more common neogene small mammals from abandoned channel fills of the siwalik record

the melting history of the late pleistocene antarctic ice sheet spatial and temporal variations in the sea levels of the past 20 000 years around the globe place constraints on the melting history of the major late pleistocene ice sheets the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9 000 6 000 years ago when it may have lagged behind minor melting of the antarctic ice sheet continued throughout the holocene

late pleistocene and holocene sea level change along the australian coast abstract tectonically the australian continent is relatively stable and as such it provides a good platform for studying late pleistocene and holocene sea level change the observations indicate that present sea level was reached at about 6000 years ago and that since then level has remained constant to within a few metres considerable spatial variability in the amplitude of the emergence and in the time at which sea levels first reached their present values have been observed spatial variability has also been observed in the sea level during the last glacial maximum and during the late phase of the holocene transgression much of this variaiblity is the result of the earth s adjustment to the glacial melting in the late pleistocene early holocene time and the concomitant distribution of this meltwater into the oceans conclusions that are drawn from matching observations with this glacio hydro isostatic model include the following 1 the mantle viscosity increases with depth the average upper mantle viscosity is about 2 3 10 20 pa s and the average lower mantle defined as below 670 km depth viscosity is about 10 22 pa s the average lithospheric thickness for the coastal and offshore region is about 70 80 km lateral variations in these mantle parameters are indicated 2 the addition of melwater into the oceans did not cease 6000 years ago but continued at a reduced rate up to more recent times adding an amount of water equivalent to a 3 m sea level rise in this interval 3 the amplitude of the holocene emergence is a function inter alia of coastal geometry and significant variations occur over distances of a few hundred kilometres and more holocene highstands of 1 2 m are generally well developed at the continental margins but are less well developed or do not developed at all at offshore islands and reefs 4 variations in the time of maximum emergence also occur being earlier at upstream tidal river sites than at coastal sites at offshore reefs or islands the sea level curve lags the coastal curves by 1000 years or more 5 considerable spatial variability occurs in the sea levels at the time of the last glacial maximum with variations of up to 30 m occurring across the continental shelves 6 there is generally no need to invoke tectonic movements to explain the sea level data along the australian coast but possible exceptions occur for the perth region and for tasmania

late holocene aggradation in the lower humber river valley toronto ontario alluvial fills are common in the lower reaches of rivers along the western shore of lake ontario the humber river floodplain at toronto is underlain by a 2 5 km long wedge of alluvium that thins upstream from lake ontario floodplain sediments were studied for their lithology 14c age and fossil pollen on the levees grey clay is overlain by oxidized silt and sand sediment cores from two flood ponds grade upward from gravel sand and silt to silty marl mineral peat and clay to heterogeneous silt and sand base level lake ontario rise directly controlled aggradation between 6500 and 1800 years ago after which time base level no longer directly controlled aggradation because levees had emerged alongside the channel and reduced the supply of sediment to the floodplain for the past 150 years upstream forest clearance and urbanization increased sediment input to the floodplain broadened the levees and filled the flood ponds average flood pond aggradation rates were estimated from seven 14c date

heat flow observations on the bermuda rise and thermal models of midplate swells the bermuda rise is a broad topographic swell which is apparent in both residual depth and geoid anomaly maps of the western north atlantic the magnitudes of the depth and geoid anomalies associated with the bermuda rise are similar to the anomalies associated with other swells surrounding recent volcanic islands e g hawaii suggesting that despite the lack of recent volcanism on bermuda the rise has a similar origin to other midplate swells results are reported from 171 new heat flow measurements at seven carefully selected sites on the bermuda rise and the surrounding seafloor off the bermuda rise the basement depths are generally shallower and the heat flow higher than either the plate or boundary layer models predict with the measured heat flow apparently reaching a uniform value of about 50 mw m 2 on 120 m y old crust on the bermuda rise the heat flow is significantly higher 57 4 2 6 mw m 2 than off the swell 49 5 1 7 mw m 2 the magnitude of the anomalous heat flux 8 10 mw m 2 is comparable to that previously found along the older portion of the hawaiian swell near midway the existence of higher heat flow on both the hawaiian swell and bermuda rise indicates that these features fundamentally have a thermal origin the differences in the shape uplift and subsidence histories of the hawaiian swell and bermuda rise can be quantitatively explained by the different absolute velocities of the pacific and north american plates moving across a distributed heat source in the underlying mantle two dimensional numerical convection models indicate that the observed depth geoid and heat flow anomalies are consistent with simple convection models in which the lower part of the thermally defined plate acts as the upper thermal boundary layer of the convection

uranium series ages of corals and coexisting phosphate deposits on pelsaert reef complex houtman abrolhos islands western australia abstract an unusually well defined association between guano derived phosphate rock apatite and coral carbonates on pelsaert island has provided an opportunity to test uranium series dating methods as applied to insular phosphorites the phosphate deposit which is bracketed by late pleistocene and holocene corals with 230 th 234 u ages of 120 000 and 4700 yr b p respectively has 230 th 234 u ages ranging from 85 000 to 112 000 yr b p the mutually consistent results suggest that phosphate deposition commenced soon after the peak of the last interglaciation and has been largely controlled by sea level fluctuations and probably other factors associated with late quaternary climate in this area

multigrid migration reducing the migration aperture but not the migrated dips given a frequency f cdp interval x and upper surface velocity v 0 the spatial nyquist criterion defines a range of unaliased emergence angles for seismic reflection events for migration events outside that range should be discarded beforehand by dip filtering or the migration operator should be trained to ignore them in this paper we express the spatial nyquist criterion as a limitation on the cdp interval rather than on emergence angle which allows x to be adjusted as a function of emergence angle increasing with decreasing emergence angle we exploit this fact by creating two separate migration grids a fine grid with trace spacing x for migrating events with large emergence angles and a coarse grid with trace spacing 2 x for migrating events with small emergence angles combining the two migrations is straightforward the coarse grid migration involving one half the number of input traces and one half the number of output traces represents a considerable time savings over the smal

millennial scale changes in north atlantic deep water circulation during marine isotope stages 11 and 12 linkage to antarctic climate the time interval represented by marine isotope stages mis 11 and 12 ca 360 470 ka may contain the most extreme glacial and interglacial climate conditions of the late pleistocene sediments from the bermuda rise western north atlantic provide clues to the nature of climate variability during this period our geochemical records indicate that millennial scale climate instability and associated changes in north atlantic deep water nadw production occurred during both interglacial mis 11 and glacial mis 12 stage 12 is punctuated by a series of interstadial events that occurred at a 5 6 k y periodicity and the occurrence of ice rafted debris at various times during stage 12 indicates that icebergs were present at least as far south as 34 n during this glacial period within the limits of our correlation the atmospheric temperature changes recently reported for the vostok ice core for the stage 11 time period appear to be represented by coeval changes in nadw flow specifically warming in antarctica is associated with increased production of nadw

pleistocene sea levels from raised coral reefs of haiti the elevations and ages of a sequence of three uplifted pleistocene coral reefs on the northwest peninsula of haiti have been determined with the assignment of a sea level of 6 meters relative to the present day at 130 000 years before present and constant uplift of the reefs the data indicate that sea level stood 10 and 13 meters at 108 000 and 81 000 years before present respectively these results are in substantial agreement with those reported for barbados and new guinea and support the hypothesis of constant uplift for each area sea level data from raised reefs indicate that the interglacial marine oxygen isotope oscillations during oxygen isotope stage 5 are a result of 30 percent ice volume effects and 70 percent temperature effects

constraints on the age and duration of the last interglacial period and on sea level variations the relation between height and age of shorelines formed during the last interglacial period as revealed by coral reefs cannot be related directly to changes in ocean volume because of the effect of isostatic uplift in response to changes in ice sheet loading sea level changes at sites near the melting ice sheet such as bermuda and the caribbean islands differ from those along the australian margin modelling of these differences constrains the times of onset and termination of the last interglacial which are at variance with those deduced from oxygen isotope studies of deep sea cores

millennial scale variability in western subtropical north atlantic surface and deep water circulation during marine isotope stages 11 and 12 1 marine isotope stages miss 11 and 12 460 380 ka contain what may be the most extreme climate conditions of the last 500 000 years and occurred at a time when earth received a similar amount of solar insolation as the most recent glacial interglacial cycle two high deposition rate sediment cores ocean drilling program sites 1059 31 6 n 75 4 w 2985 m and 1055 32 6 n 76 2 w 1799 m from the western north atlantic were studied in order to examine the nature of millennial scale variability in north atlantic surface and thermohaline circulation during this time interval detailed records of 18o and 13c in the benthic foraminifera species cibicidoides wuellerstorfi and the planktonic species globigerinoides ruber white as well as detailed records of carbonate content were generated for both sites these records suggest rapid variability in the strength of north atlantic deep water production throughout miss 11 and 12 most of the observed changes in deep water circulation appear to be associated with or coupled to changes in sea surface hydrography the duration of interglacial conditions during mis 11 20 000 30 000 years is much longer than subsequent interglacial stages combined 18o measurements and mg ca based temperature estimates from g ruber suggest sea surface temperatures increased 2 3 c across the mis 12 mis 11 transition

the early pleistocene stone tools from vallparadis barcelona spain rethinking the european mode 1 abstract the vallparadis site contains a long and continuous archaeological sequence dating to between the late early pleistocene and the first half of the middle pleistocene levels 10 and 10c unit evt7 have yielded abundant macrofauna and mode 1 stone tools calibrated by paleomagnetism and by biostratigraphy to the upper limit of the jaramillo subchron 0 98 ma and by u series esr to 0 83 0 13 ma the industries elaborated from local raw materials are of small size the chaines operatoires used for lithic production are poorly elaborated and are based on an anvil knapping technique shaped tools include notches becs scrapers and denticulates on small pebbles clasts fragments and flakes as well as a large single chopper using a techno typological study and comparisons with other known early pleistocene sites in spain orce and atapuerca and elsewhere in eurasia we propose that these sites belong to an analogous mode 1 techno complex with a variability range the fundamental difference between them lies in the retouched tools because these are poorly represented in europe prior to around 1 ma in contrast orthogonal knapping methods were used in the exploitation of the cores during all this period the successive episodes of interbreeding and independent evolution regarding the phylogenetic reports on the hominin remains from atapuerca would have probably led to regional technological traditions in the european mode 1 lithic record

wavefront sets analysis of limited aperture migration sections although geophysical literature is quite rich in papers on migration there are only a few papers that treat lam limited aperture migration deterministic and stochastic criteria for the reconstruction of reflection interfaces in prestack migration were derived and demonstrated on synthetic and real data examples a real data set was acquired offshore the brazilian coast courtesy of petrobras the reconstruction of reflection interfaces in lam depends on the relative position of normal bundles as defined here and gradients to the reflection interfaces the derived stochastic criterion relates the variance of normal bundles to the variance of slowness in the medium these criteria will help the geophysicist to identify directly distorted regions caused by lam and those regions that are correctly migrated

extended range luminescence chronologies suggest potentially complex bone accumulation histories at the early to middle pleistocene palaeontological site of huescar 1 guadix baza basin spain abstract the palaeontological site of huescar 1 contains a diverse faunal assemblage and has played an important role in establishing local scale biozone successions in the guadix baza basin here we provide the first ages for the fossil bearing deposits at this site using a suite of extended range luminescence dating approaches including optically stimulated luminescence osl of quartz supergrains multi grain and single grain thermally transferred osl of quartz and post infrared infrared stimulated luminescence of k feldspars assessments of luminescence characteristics and laboratory quality assurance tests indicate that the huescar 1 sediments are well suited for extended range dating applications and the resultant chronologies obtained using different luminescence approaches display a high degree of consistency our combined luminescence ages reveal that the fossil bearing fluvial sediments at this marginal lacustrine site were deposited 420 460 ka or possibly 420 570 ka which is younger than some of the tentative late early to early middle pleistocene ages inferred from faunal associations comparison of the dating results with taphonomic taxonomic and geomorphic evidence suggests that the site may preserve an admixture of bones in primary depositional context and reworked fossils sourced from potentially older deposits in the surrounding valley as such the luminescence ages obtained for the host sediments may not be contemporaneous with all of the faunal remains preserved at huescar 1

glacial rebound and relative sea level variations a new appraisal summary late pleistocene and holocene changes in sea level at technically stable shorelines contain information on the melting history of the ice sheets and on the response of the earth to changes in surface loads on time scales of 104yr some separation of parameters defining the ice loads and the earth s response can be achieved by examining sea level change at different sites around the world and at different epochs this paper examines the mathematical requirements for obtaining satisfactory solutions for the sea level equation rather than emphasizing results for the earth s response to the surface loads an examination of the equation expressing the sea level variation on a viscoelastic earth indicates that careful consideration needs to be given to both the definition of the ice load and the geometry of the redistributed water load if geophysically significant earth response parameters are to be deduced from observations of relative sea level the spectrum of the 5 x 5 area mean description of the ice load widely used in glacial rebound studies contains significant power at high degrees n 30 and can result in substantial spatial variations in sea level unless a thick lithosphere is introduced in the earth s response function a smoothed 1 1 description of the ice model avoids these high degree oscillations in relative sea level and produces satisfactory sea level results without requiring a thick lithosphere at far field sites the holocene sea levels are sensitive to the earth s response to the meltwater loading in the vicinity of the site and a high degree spatial resolution of coastline geometry is required to model the mantle flow driven by the differential loading about the site at some sites convergence of the solution to the sea level equation is not obtained even when the solution is expanded to degree 180 convergent solutions at lower degrees can be achieved by introducing earth models with a moderately thick lithosphere if high resolution ice and meltwater load models are not used then the tendency will be to overestimate the effective elastic thickness of the lithosphere estimates of mantle viscosity are also of questionable value if these high resolution models are not used a preliminary examination of sea levels at sites in both the near and far field places an upper limit of about 50 80 km on the effective lithospheric thickness these sea level observations are also consistent with an upper mantle viscosity of about 1021 pas with a lower mantle viscosity in the range of 1021 1023pa s

the last interglacial ocean the final effort of the climap project was a study of the last interglaciation a time of minimum ice volume some 122 000 yr ago coincident with the substage 5e oxygen isotopic minimum based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean last interglacial sea surface temperatures sst were compared with those today there are small sst departures in the mid latitude north atlantic warmer and the gulf of mexico cooler the eastern boundary currents of the south atlantic and pacific oceans are marked by large sst anomalies in individual cores but their interpretations are precluded by no analog problems and by discordancies among estimates from different biotic groups in general the last interglacial ocean was not significantly different from the modern ocean the relative sequencing of ice decay versus oceanic warming on the stage 6 5 oxygen isotopic transition and of ice growth versus oceanic cooling on the stage 5e 5d transition was also studied in most of the southern hemisphere the oceanic response marked by the biotic census counts preceded led the global ice volume response marked by the oxygen isotope signal by several thousand years the reverse pattern is evident in the north atlantic ocean and the gulf of mexico where the oceanic response lagged that of global ice volume by several thousand years as a result the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years these regional lead lag relationships agree with those observed on other transitions and in long term phase relationships they cannot be explained simply as artifacts of bioturbational translations of the original signals

excavation of buried late acheulean mid quaternary land surfaces at duinefontein 2 western cape province south africa abstract duinefontein 2 dft2 preserves at least two buried land surfaces within a 10 m thick dune plume on the atlantic coast of south africa about 35 km north of cape town optically stimulated luminescence dating indicates that the sands enclosing the upper surface accumulated around 270 ky ago while the sands between the two surfaces were accumulating about 290 ky ago excavation so far has focused on the upper buried surface which is now exposed over 480 m 2 historically there was no body of fresh water nearby and the surrounding vegetation was a variant of the regional fine leafed shrub or fynbos pedogenic alteration of the sands and bones of water loving mammals and amphibians indicate however that the bones and associated acheulean artifacts accumulated near the edge of a large pond or marsh in addition the principal mammal species buffalo wildebeest and kudu imply a sharply different regional vegetation in which grass and broad leafed bush were much more common the artifacts are distributed across the upper buried surface in no apparent pattern but the large mammal bones tend to occur as clusters of skulls vertebrae ribs and other axial elements often in near anatomical order limb bones are mostly missing and the clusters appear to mark carcasses from which the limb bones were selectively removed the bones rarely show marks from stone tools but marks from carnivore teeth are common together with numerous hyena coprolites the abundant tooth marks suggest that hyenas and perhaps other carnivores were largely responsible for carcass disarticulation the human role appears to have been insignificant which suggests that local acheulean people obtained few large mammals whether by hunting or scavenging among the small number of other acheulean carcass sites for which bone damage observations are available the best documented sites suggest the same limited human ability to acquire large mammals but many additional sites will be necessary to determine if this was the acheulean norm greatly expanded excavation of the lower buried surface at dft2 can provide an additional high quality data point

u series and amino acid racemization geochronology of bermuda implications for eustatic sea level fluctuation over the past 250 000 years abstract bermuda is a stable mid oceanic carbonate platform for which a particularly complete record of late pleistocene eustatic sea level fluctuation has been reconstructed from a detailed study of geological field relationships combined with an extensive programme of u series and amino acid racemization geochronology only twice in the past 250 000 yr has sea level in bermuda been above its present level once at approximately 200 k y when it stood at about 2 m and most recently at 125 4 k y when it stood at 5 1 m these times of interglacial high sea level are characterized by the development of patch reefs and marine calcarenites at elevations above present sea level episodes of lower sea stand onto the bermuda platform at elevations higher than 20 m are observed within the two interglacial periods and are characterized by the deposition of eolianites by contrast glacial periods are times of residual soil formation and deposition of speleothems in caves at elevations below present sea level excellent correlation is observed between the bermuda glacio eustatic sea level record and other marine and terrestrial paleoclimate records

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

glacial cycles toward a new paradigm the largest environmental changes in the recent geological history of the earth are undoubtedly the successions of glacial and interglacial times it has been clearly demonstrated that changes in the orbital parameters of our planet have a crucial role in these cycles nevertheless several problems in classical astro nomical theory of paleoclimate have indeed been iden tified 1 the main cyclicity in the paleoclimatic record is close to 100 000 years but there is no significant orbitally induced changes in the radiative forcing of the earth in this frequency range the 100 kyr problem 2 the most prominent glacial interglacial transition occurs at a time of minimal orbital variations the stage 11 problem and 3 at 0 8 ma a change from a 41 kyr dominant periodicity to a 100 kyr periodicity occurred without major changes in orbital forcing or in the earth s configuration the late pleistocene transition prob lem additionally the traditional view states that the climate system changes slowly and continuously together with the slow evolution of the large continental ice sheets whereas recent high resolution data from ice and marine sediment cores do not support such a gradual scenario most of the temperature rise at the last termi nation occurred over a few decades in the northern hemisphere indicating a major and abrupt reorganiza tion of the ocean atmosphere system similarly huge iceberg discharges during glacial times known as hein rich events clearly demonstrate that ice sheet changes may also be sometimes quite abrupt in light of these recent paleoclimatic data the earth climate system ap pears much more unstable and seems to jump abruptly between different quasi steady states using the concept of thresholds this new paradigm can be easily integrated into classical astronomical theory and compared with recent observational evidence if the ice sheet changes are by definition the central phenomenon of glacial interglacial cycles other components of the climate sys tem atmospheric co2 concentration southern ocean productivity or global deep ocean circulation may play an even more fundamental role in these climatic cycles

coastal morphology and late quaternary history cayman islands west indies abstract instrumental surveys of coastal profiles in the cayman islands western caribbean reveal the presence of a horizontal erosional bench at 1 9 m on grand cayman and a deep horizontal notch at 6 4 m on cayman brac but no raised erosional features on little cayman each island is surrounded by a horizontal constructional raised reef usually below 2 m here dated by u series methods as 124 000 8000 yr old and hence broadly contemporary with other western atlantic raised reefs of similar elevations the different raised erosional features indicate independent vertical tectonic movement of the three islands predating the formation of the raised reef the accordance and horizontality of the raised reef indicates stability of the islands since the last interglacial times an erosional notch at present sea level has formed since the sea reached its present level less than 2100 b p and algal benches on exposed coasts are also in equilibrium with present conditions

the early to middle pleistocene boundary in the baza basin spain abstract the continental vertebrate fauna of cullar baza 1 granada spain occur immediately above the matuyama brunhes polarity boundary and therefore represent an initial record for the middle pleistocene all polarity zones for the late pliocene through middle pleistocene are found in an 80 m section which includes this fossil quarry the existing collection of abundant remains of micro mammals macro mammals and lithic artifacts indicating human activity can now be assigned an earliest middle pleistocene age of 0 75 ma another section 25 km across the neogene baza basin also has the matuyama brunhes polarity boundary however in this case the huescar 1 fossil quarry and the puerto lobo sites are both below the polarity boundary thus representing a record of the late early pleistocene at 0 9 ma differences in micro mammal species across these matuyama brunhes boundaries are significant and justify an approximately coincident biostratigraphic boundary between the biharian and toringian stages

gulf stream and western boundary undercurrent variations during mis 10 12 at site 1056 blake bahama outer ridge abstract the stable isotopic composition of two planktonic foraminifer species globigerinoides sacculifer and neogloboquadrina dutertrei and two benthic foraminifer species cibicidoides wuellerstorfi and uvigerina peregrina was measured at sub orbital resolution through the marine isotope stages miss 10 11 and 12 345 460 ka at site 1056 on the blake bahama outer ridge planktonic foraminifers were counted for the interval 405 450 ka at 2 4 kyr resolution site 1056 32 29 n 76 20 w is located on the continental slope water depth 2167 m beneath the gulf stream the average rate of sediment accumulation through the interval is 11 4 cm kyr but sediment accumulation is much more rapid during glacial intervals 15 17 cm kyr the decline in percent carbonate during glacial intervals and its rise during interglacials indicates that the increased sediment supply is of terrigenous origin low carbonate values and low benthic 13c which are both associated with a weak western boundary undercurrent and low north atlantic deep water production persist for 6 kyr after the benthic 18o record indicates that ice volume has begun to decrease recovery of carbonate and benthic 13c values is abrupt and rapid millennial scale variation 3 4 kyr is apparent in the glacial intervals of the planktonic 18o records and is more pronounced in a 18o record which represents the temperature range in the photic zone semi precessional 10 12 kyr cycles are apparent in the planktonic 13c record the millennial scale cycles are largely caused by an increase in g sacculifer 18o and represent surface warming they are interpreted as representing periodic increases in westward intensification of the gyre the semi precessional cycles are driven by changes in the n dutertrei 13c and represent fluctuations in the gulf stream itself and therefore likely have a tropical origin planktonic foraminifer census counts did not show an expected response to one of the largest glacial interglacial transitions of the late pleistocene the most obvious change was an increase in faunal diversity during mis 12 2 the interval of maximum 18o values this suggests that cool slope water and warm subtropical gyre water penetrated a more sluggish gulf stream with greater frequency at this time the millennial scale maxima in the 18o record are accompanied by decreases in diversity which is consistent with the interpretation of surface warming during these events

vertebrate taphonomy in circum lake environments three cases in the guadix baza basin granada spain abstract this work analyses the origin and taphonomy of three plio pleistocene mammal assemblages from the guadix baza basin granada spain huelago huescar 1 and cullar de baza 1 similarities and differences in the taphonomic features are evaluated with regard to marginal lacustrine sedimentary processes involved in the accumulation of these mammal assemblages selective preservation of skeletal part and taxa in relation to facies have been explored to determine their suitability for palaeoecological analysis the mortality in cullar de baza 1 and huelago 1 corresponds to a catastrophic pattern but other taphonomic features of the bones indicate that accumulation processes were diachronic as occurred in huescar 1 this could be explained by selective predation and or seasonal accumulation of bones hydraulic sorting and transportation greatly controlled the size and shape of accumulated skeletal elements and the different preservational circumstances of each environment largely constrained the taxonomic composition of the fossil bone assemblages autochthonous fauna only occurs in huescar 1 corresponding to subaquatic environments the absence of carnivores among the identifiable remains from huelago 1 has no plausible taphonomic or sedimentological explanation nevertheless after taking into account the taphonomic factors the differences in taxonomic composition between these three mammal assemblages reflect differences in the surrounding habitats the great diversity of ruminant artiodactyls in particular browsers is indicative of wooded or bushy areas in the surroundings of huelago 1 although not in the immediate area of the lake margin this diversity coincides with that observed in other villafranchian localities and represents the greatest diversity of artiodactyls known from the neogene and quaternary record of western europe in turn the high diversity of sub aquatic forms and a smaller variety of artiodactyl species in huescar 1 reflects an open sparsely forested environment susceptible to seasonal drought a similar sparse forested environment has been deduced for cullar de baza 1 the climate and environmental conditions in huescar 1 and cullar de baza 1 are consistent with a climatic deterioration at the beginning of the middle pleistocene glacial pleistocene

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

least squares migration of incomplete reflection data a least squares migration algorithm is presented that reduces the migration artifacts i e recording footprint noise arising from incomplete data instead of migrating data with the adjoint of the forward modeling operator the normal equations are inverted by using a preconditioned linear conjugate gradient scheme that employs regularization the modeling operator is constructed from an asymptotic acoustic integral equation and its adjoint is the kirchhoff migration operator we tested the performance of the least squares migration on synthetic and field data in the cases of limited recording aperture coarse sampling and acquisition gaps in the data numerical results show that the least squares migrated sections are typically more focused than are the corresponding kirchhoff migrated sections and their reflectivity frequency distributions are closer to those of the true model frequency distribution regularization helps attenuate migration artifacts and provides a sharper better frequency distribution of estimated reflectivity the least squares migrated sections can be used to predict the missing data traces and interpolate and extrapolate them according to the governing modeling equations several field data examples are presented a ground penetrating radar data example demonstrates the suppression of the recording footprint noise due to a limited aperture a large gap and an undersampled receiver line in addition better fault resolution was achieved after applying least squares migration to a poststack marine data set and a reverse vertical seismic profiling example shows that the recording footprint noise due to a coarse receiver interval can be suppressed by least squares migration

early human occupation of iberia the chronological and palaeoclimatic inferences from vallparadis barcelona spain abstract vallparadis is one of the best calibrated and most accurately dated archaeological sites from the european early pleistocene chronological analyses combined with palaeomagnetism esr u series and osl and the biochronology of macro and micromammals are fully consistent and situate the site just above the upper limit of the jaramillo subchron in this article we compare the mandibular first molar m1 of individual adult specimens of mimomys savini recovered from level 10 evt7 at vallparadis with specimens from the stratigraphic sequence at gran dolina atapuerca fuente nueva 3 and barranco leon d orce this comparison allows us to chronostratigraphically relate level 10 at vallparadis with level td5 at gran dolina and to fix the former s chronology to around 0 98 0 95 ma mis 27 and therefore prior to level td6 in which fossil remains of homo antecessor were recovered the chronology of vallparadis and the set of contemporary palaeoclimatic proxies regarding the iberian peninsula strengthen the hypothesis that hominins continuously populated europe at least in iberia throughout the late early pleistocene between the jaramillo subchron and the matuyama brunhes boundary by overcoming the climatic fluctuations and changes to the landscape that occurred during this period

u series dating of last interglacial high sea stands barbados revisited u series chronologies of the emerged coral limestone terraces on barbados west indies together with those of the terraces from new guinea have formed the basis for most late pleistocene eustatic models the so called barbados sea level model has been challenged in recent years however a major issue is whether during oxygen isotope stage 5e when rendezvous hill reef complex on barbados island formed the sea rose above the present position for one relatively brief period of 10 000 yr or for two or more periods spanning approximately from 140 000 to 115 000 yr b p evidence for the latter scenario has not come from initial studies of barbados but from elsewhere it is also inconclusive because of the dating uncertainties involved we have carried out careful redeterminations of u series ages on a suite of 29 acropora palmata samples systematically collected from four of the lowest terraces on the island diagenetic disturbance may have caused the age spreads at some sampling outcrops a model for the diagenetic exchange of uranium isotopes in coral samples with those in groundwater explains the anomalous 234u238u ratios in samples with apparently unaltered mineralogy aragonite and trace element mg and sr chemistry it shows that age dispersions of 5 10 can be engendered by a u exchange coefficient of the order of 10 6 yr 1 the lower limit terrace ages estimated from averaging the multiple measurements are 81 000 2000 yr worthing 105 000 1000 yr ventnor 120 000 2000 yr maxwell and 117 000 3000 yr rendezvous hill no evidence was found of previously inferred bipartite sea levels centering around 118 000 and 135 000 yr ago this study documents the need of dating coral with the high precision sensitivity mass spectrometric techniques for future resolution of the temporal relationships among sea level changes climate oscillations and astronomical forcing relationships originally addressed by the barbados sea level model