a diffusion adsorption model of uranium uptake by archaeological bone abstract an argument for the possibility of uranium uptake by buried bone taking place through the adsorption of uranyl species on bone mineral is advanced in the light of this a diffusion adsorption model for uranium uptake by buried bone is developed the necessary constants are evaluated from the literature and from laboratory measurements of the partition coefficient between solution and bone mineral the geochemical and hydrological parameters which control uptake are discussed the predictions of the model are shown to be in general accordance with the timescale magnitude and distribution of uranium uptake in archaeological bone using the model specific predictions of the variation of apparent uranium series ages in bone can be made and bone is shown clearly not to conform to the closed system assumption when the model is extended to tooth enamel it is found to be incompatible with the early uptake model used for esr dating but to fall between the early uptake and linear uptake models similarly it suggests that uranium series dates on enamel assuming a closed system are liable to underestimate the true age by at least one third

evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

the new hominid skeleton from sterkfontein south africa age and preliminary assessment a new hominid skeleton from sterkfontein member 2 attaches to foot bones recovered from loose blocks during the 1980s and first described in 1995 several flowstone horizons are present above and below the skeleton and have given clear palaeomagnetic signatures five changes in magnetic polarity have been identified when constrained by the available biostratigraphy this sequence can be placed confidently between 3 22 and 3 58 ma interpolation of sedimentation rates over the small intervals between reversals allows this range to be reduced to 3 30 3 33 ma the skeleton is thus the oldest yet discovered and is considered to belong to a species of australopithecus other than africanus copyright 1999 john wiley sons ltd

laminated bioturbated cycles in maastrichtian chalk of the north sea oxygenation fluctuations within the milankovitch frequency band the maastrichtian chalk of the southern central graben danish north sea is a homogeneous pure white coccolithic chalk mudstone deposited in a deep epeiric shelf sea which covered large parts of northern europe the sediment displays a pronounced cyclicity marked by decimetre thick bioturbated beds alternating with slightly thinner non bioturbated mainly laminated beds the laminated half cycles consist of alternating millimetre thick graded high porosity laminae and non graded low porosity laminae the cyclicity has been interpreted previously as caused by periods of slow background sedimentation and bioturbation interrupted by periods of rapid deposition of laminated beds with the latter reflecting random and local resedimentation processes based on textural and structural analysis the millimetre scale non graded laminae are interpreted as having been deposited directly from pelagic rain of pelleted coccoliths representing the primary production the graded laminae were deposited from small volume low density turbidity currents and suspension clouds the sedimentation rates of the cyclical chalk are similar to those known elsewhere and the lamination is interpreted as having been preserved from destruction through bioturbation by anoxic conditions at the seafloor bioturbated laminated cycles are thus formed by slow sedimentation during alternating seafloor redox conditions probably on a milankovitch scale a direct implication of this interpretation is that the cycles are areally widespread probably extending throughout the southern central graben area and may be useful for correlation and high resolution cyclostratigraphy in the chalk fields of the danish north sea if the laminated half cycles represent a few rapid resedimentation events with a high sedimentation rate as suggested by most workers then the sediment would not be truly cyclic but would represent event sedimentation within a pelagic background represented by the bioturbated beds in this case the cycles would have very limited potential for correlation

benthic palaeoecology of danian deep shelf bryozoan mounds in the danish basin abstract early danian cool water bryozoan mounds exposed in the coastal cliff stevns klint in denmark were formed shortly after the cretaceous tertiary mass extinction they represent a relatively deep water highly diverse benthic ecosystem within the epeiric seaway that covered the danish basin the mounds are 50 110 m long and reached a height of about 5 10 m above the seafloor they are asymmetrical with a steep southern and a gentle northern flank and were dominated by small suspension feeders the benthic elements generally occur as fragments set in a carbonate mud matrix the main skeletal contributors are delicate branching bryozoans with minor contributions of bryozoan sheets and nodular arborescent bryozoans locally abundant octocorals occur on the mound crests and upper parts of the steep flanks echinoids are present in minor amounts but are locally abundant serpulids crinoids asteroids brachiopods bivalves massive calcareous sponges and benthic foraminifers are generally minor contributors to the benthic mound fauna influx of planktonic foraminifers coccoliths and other planktonic organisms was high and was probably a major source of nutrient supply to the mainly suspension feeding benthic fauna the faunal association reflects a relatively low energy environment with a high possibly seasonal influx of particulate nutrients the best growth conditions with respect to nutrient influx were on the mound crest and upper steep flank reflected by the diverse and relatively largest benthic faunal elements periodic reworking and winnowing occurred across the entire mound structure but most prominent on the gentle northern flanks limiting the benthic growth and notably the colony density and size of delicate branching bryozoans vagile benthic faunas were also adapted to different areas on the mound irregular echinoids preferred the intermound areas within fine grained wackestone packstone facies where they ploughed through the sediment whereas regular echinoids were epifaunal and preferred the upper parts of the mounds possibly feeding mainly on bryozoans skeletons of both groups became concentrated at the toe of the steep flanks and in the intermound areas by physical reworking during major storms changes in faunal composition on the mound crests occurred rhythmically on both small and large scale during mound growth rhythmically recurring faunal assemblages reflect alternating hydrodynamic conditions on the seafloor with respect to nutrient influx and energy which probably were linked to short term seasonal and long term climatic variations the long term alternation may be within the milankovitch frequency band blooming events of bryozoan sheets resulted from relatively short periods with large amounts of available food and suitable substrate successful colonisation by octocorals on the other hand reflected longer term favourable conditions on the mounds possibly associated with overall higher energy levels a possible pleistocene analogue to the bryozoan dominated danian mounds occurs at the shelf slope break of the great australian bight both of these cool water mound systems deviate from most other biogenic mounds known from the fossil record in their non cemented nature regular geometry and a lack of core and flank facies

the tectonic evolution of the fennoscandian border zone in denmark abstract the fennoscandian border zone is a complex tectonic zone defining the border between the stable fennoscandian baltic shield and the metastable danish basin and polish trough it forms the northwestern part of the tornquist teisseyre lineament one of the major european tectonic sutures intricate tectonic movements took place within the fennoscandian border zone from early paleozoic to recent time it is postulated that its evolution was dominated during the early palaeozoic by tensional tectonics and during the late paleozoic by dextral wrench movements the latter led to the development of curvilinear faults and the subsidence of pull apart basins transtensional stresses governing the triassic to early cretaceous evolution of the fennoscandian border zone induced the differential subsidence of rift basins during the late cretaceous and early cenozoic dextral transpressional stresses induced the partial inversion of mesozoic basins associated with the fennoscandian border zone this is reflected by the uplift of a major anticlinorium over which cretaceous strata became progressively truncated whilst adjacent areas developed into late cretaceous early tertiary depocentres basin inversion diminishes to the northwest along the fennoscandian border zone and disappears in the skagerrak area

u pb isotopic age of the stw 573 hominid from sterkfontein south africa sterkfontein cave south africa has yielded an australopith skeleton stw 573 whose completeness has excited great interest in paleoanthropology stw 573 or little foot was found 25 meters below the surface in the silberberg grotto 238u 206pb measurements on speleothems immediately above and below the fossil remains corrected for initial 234u disequilibrium yield ages of 2 17 0 17 million years ago ma and 2 24 0 07 0 09 ma respectively indicating an age for stw 573 of close to 2 2 ma this age is in contrast to an age of approximately 3 3 ma suggested by magnetochronology and ages of approximately 4 ma based on 10be and 26al but it is compatible with a faunal age range of 4 to 2 ma

u series dating of bone using the diffusion adsorption model abstract u series dating of bone has suffered problems of reliability since its inception because bone remains an open system with respect to uranium commonly applied a priori assumptions of u uptake such as early uptake or linear uptake are inadequate because they have no physical or chemical bases no means of demonstrating which model is suitable for a particular bone and no intrinsic tests of reliability despite this and numerous examples of anomalous u series dates such assumptions are still routinely applied we address this problem using the diffusion adsorption d a model of u uptake millard and hedges 1996 which incorporates a physicochemical description of u uptake using this model we show how the u uptake of a bone responds to geochemical changes in the burial environment which can lead to phenomena such as the removal of u from bones leaching or u uptake late in their burial history recent uptake and we show how the overall uptake history is reflected in distributions profiles of u and u series isotopes across a bone section we present measurements of u concentration profiles and 230 th 234 u profiles on archeological bone from a number of different sites and burial environments and compare the results to profiles predicted by the d a model bones that have undergone complex uptake histories which include u leaching or recent uptake are identified on the basis of these profiles and rejected as unsuitable for dating for bones that appear to have undergone uptake under constant geochemical conditions the d a model is applied to calculate u series dates with much improved reliability

a new explanation for extreme 234u238u disequilibria in a dolomitic aquifer high 234u238u activity ratios are found in the shallow groundwater of the phreatic transvaal dolomite aquifer the aquifer is uranium poor while the waters are oxygen rich and young tritium and 14c are used to show that the disequilibrium increases the longer the water resides in contact with the dolomite host the 228ra and 222rn isotopes were used as supporting evidence that ion exchange between the 238u series nuclides in the water and the carbonate wall rock is necessary in assisting in the fractionation process the wolkberg cave speleothems preserve a record of the uranium isotopic fractionations that evolved as water flowed through the aquifer extremely variable and elevated 234u238u ratios of 2 12 are characteristic individual caverns may exhibit very large 234u238u variability in their drip water and in derivative carbonate precipitates speleothems deeper chambers where water has spent a longer time in contact with the aquifer tend to exhibit a greater degree of uranium isotopic fractionation in their speleothems the recorded fractionation process has been an ongoing one from at least the middle late pleistocene to the present the speleothem study supports the contention that ion exchange processes that produce sufficient enrichment of uranium on carbonate can provide ideal conditions for generating uranium isotopic fractionation in the water of carbonate aquifers in the absence of redox changes and within a uranium poor environment

geochemistry of campanian maastrichtian brachiopods from the rordal 1 core denmark differential responses to environmental change and diagenesis abstract past marine environmental conditions can be reconstructed from geochemical signatures of both benthic and planktic organisms and particularly brachiopods have been extensively used for this purpose however it is seldom possible to investigate the links between environmental conditions and shell geochemistry in monospecific records over extended periods of time here we present geochemical data from the 100 m thick brachiopod rich upper campanian upper maastrichtian chalk 73 8 68 6 ma of the rordal 1 drill core northern denmark two species that lived attached to small substrate argyrotheca bronnii roemer and gisilina jasmundi steinich and one secondarily free living species magas chitoniformis schlotheim have been studied for element concentrations as well as c and o isotope signatures each species has a unique chemical signature with m chitoniformis showing lowest mg and mn concentrations a bronnii the highest mn concentrations and g jasmundi the highest sr concentrations all three species display decreasing mg ca ratios throughout the studied interval and distinct mn enrichments in the campanian maastrichtian boundary cmb interval in the campanian part of the succession the three species are slightly enriched in 13 c median 13 c values of 0 0 to 0 5 and 18 o median 18 o values of 0 3 to 0 6 with respect to coeval chalk in the course of the maastrichtian the two attached species acquire progressively lighter isotopic compositions with a bronnii reaching 13 c and 18 o values 1 0 lower than coeval chalk the secondarily free living species m chitoniformis on the other hand becomes isotopically heavier and reaches 13 c and 18 o enrichments of 1 0 at the top of the core the observed differences between the species illustrate species specific signatures of biomineralisation diagenesis and response to environmental change this geochemical complexity illustrates that a comprehensive geochemistry based picture of the late cretaceous chalk sea can only be painted using detailed multi species and multi proxy datasets

beyond 500ka progress and prospects in the upb chronology of speleothems and their application to studies in palaeoclimate human evolution biodiversity and tectonics abstract this review summarises current research aimed at extending the chronology and thus scientific utility of speleothems beyond the 500 ka limit previously imposed by conventional u th dating methods the u pb decay scheme is familiar to all geoscientists but its application to speleothems is a relatively recent development and one set to revolutionise their use in studies of climate change human evolution and migration biodiversity tectonics and landscape evolution technological advances such as the introduction of multi collector icpms instruments have played a key role in this breakthrough and multiple inter laboratory and inter method comparisons provide evidence that the methodology is now mature and that the ages obtained are robust some impediments remain in particular with respect to corrections for initial isotopic disequilibrium younger samples and the construction of internal chronologies older samples but these are areas of intense research activity and are likely to see significant advances in the near future the coupling of speleothem u pb dating with other nascent technologies offering the prospect of precise palaeotemperature estimation is an exciting development in palaeoclimate science while u pb chronologies of archaeological sites are producing important new insights into human evolution although less well developed at this point the methodology appears equally well suited and significant for future studies of past faunal change and landscape evolution

late cretaceous to recent tectonic evolution of the north german basin and the transition zone to the baltic shield southwest baltic sea abstract in this study we investigate the late cretaceous to recent tectonic evolution of the southwestern baltic sea based on a dense grid of seismic reflection profiles this area covers the baltic sea sector of the salt influenced north german basin and its transition to the salt free baltic shield across the tornquist zone the upper cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high resolution time structure maps of the main horizons i e the upper cretaceous tertiary and pleistocene the upper cretaceous and tertiary layers reveal numerous significant faults throughout the study area several of these faults propagate upwards across the unconsolidated pleistocene sediments and occasionally penetrate the surface the salt influenced north german basin reveals three major fault trends nw se n s and nne ssw several of these faults are located directly above basement sub salt faults and salt pillows the majority of these faults are trending n s to nne ssw and parallel the direction of the gluckstadt graben faults in the salt free tornquist zone we identify two major shallow fault trends which are nw se and ne sw the majority of these faults are located above basement faults following the direction of the tornquist zone we conclude that generally basement tectonics controls activation and trends of shallow faults if salt is present the ductile salt layer causes a lateral shift between the sub and supra salt faults major plate reorganisation related to the africa iberia europe convergence and the subsequent alpine orogeny caused reactivation of pre existing faults and vertical salt movement in the late cretaceous the change of stress orientation from ne sw to a nw se during neogene caused another phase of fault and salt tectonic reactivation we explain that the ice sheet loading and or present day stress field may have acted in combination causing the recent tectonics and upward extension of the faults

channelling versus inversion origin of condensed upper cretaceous chalks eastern isle of wight uk evidence from regional stratigraphical patterns in santonian campanian chalk is used to infer the presence of a very broad channel system 5 km across with a depth of at least 50 m running nnw sse across the eastern isle of wight only the western part of the channel wall and fill is exposed within this channel were smaller erosional structures

an open system model for u series age determinations of fossil corals the source of excess 234u in fossil corals and its relationship to u series age determinations has been an outstanding problem in geochronology for more than 20 years with increasing numbers of u series isotope measurements in corals and significant improvements in analytical precision through mass spectrometry it is increasingly apparent that a substantial fraction of observed isotope ratios cannot be reasonably explained by closed system decay moreover observations of a positive correlation between 234u 238u and 230th 238u ratios in corals from the same terrace are difficult to explain however the decay of dissolved uranium and recoil mobilization of uranium daughters produce particle reactive 234th and 230th and the coupled addition of these th isotopes could simultaneously increase coral 234u 238u and 230th 238u here we present a quantitative model based on decay dependent redistribution of 234th and 230th permitting calculation of open system coral ages these equations provide a general solution to the recoil redistribution problem applicable to any alpha decay series while measured isotope ratios of corals from the three youngest stratigraphically defined barbados terraces are inconsistent with closed system decay they fall in broadly linear arrays agreeing with model predictions isotopic arrays of older barbados corals and corals from terraces around the world are also consistent with model predictions suggesting the open system model is generally applicable corals with extreme isotopic compositions that are impossible to produce by closed system decay are consistent with the limited range of isotopic compositions predicted by the model at ages older than 600 ka for corals from a single terrace 234th and 230th redistribution appears to be a source of systematic conventional age error even for corals with slightly elevated 234u however open system ages are consistent even for corals with extremely elevated 234u for the youngest three barbados terraces mean open system terrace ages are consistent with mean conventional terrace ages calculated from pristine samples if the most accurate conventional ages are from corals with an initial 234u 238u identical to modern seawater then the open system model will improve the accuracy of coral u series age determinations and dramatically increase the number of reliable ages

trace elements and their isotopes in bones and teeth diet environments diagenesis and dating of archeological and paleontological samples fossil biogenic apatites display trace element te compositions that can record environmental and biological signals give insights into past water compositions or be used for dating paleontological and archeological bones and teeth processes of te incorporation into apatites of skeletal phosphatic tissues are described ranging from those active in living organisms to those active during diagenesis abiotic incorporation mechanisms have been modeled theoretically and experimentally and include crystallographic controls on te partitioning coefficients inorganic surface adsorption and adsorption mediated through chelation and diffusion adsorption processes each leading to specific fractionation patterns predictions from models and experiments have been tested against te concentration and isotopic composition data on remains of contemporary wild or raised animals and on fossils of various ages and environments in living organisms tes incorporated in apatite are separated in two categories non essential elements whose concentration is compared to that of an essential element with similar behavior e g sr ca to reconstruct trophic chains and essential elements whose isotopic ratios are used to trace metabolic activity diet etc in fossils elements are incorporated during diagenesis such as rare earth elements rees and trace diagenetic processes ranging from very early quantitative adsorption likely mediated by chelators protracted diagenesis through inorganic adsorption and fractionation through diffusion adsorption to low grade metamorphism associated with intense redistribution under crystal chemical control these different steps are also identified as steps of radionuclide incorporation only samples where the earliest steps can be deciphered are useful for determining stratigraphic and archeological ages other samples will date late diagenetic events that have obliterated the paleoenvironmental signals but may be of geological significance e g tectonic events

problems associated with reworked teeth in electron spin resonance esr dating a single radiation sensitive esr signal at g 2 0018 occurs in well crystallized fossil tooth enamel but not in modern teeth in dating fossil teeth the equivalent radiation dose a needed to produce the observed esr signal is the integral with respect to time of the natural environmental dose rate experienced by the tooth after its deposition regardless of the uranium u uptake history assumed a reliable age estimate requires a good estimate for the external dose rate during the tooth s history if teeth in a stratigraphic unit have been reworked from older units or are post depositional intrusions external dose rates measured in situ do not accurately reflect those experienced by the tooth for teeth from a single unit significant variations in the calculated ages a s enamel or dentine u concentrations all indicate mixed sample collections where enough subsamples can be collected from single teeth isochron analyses negate the need for a separate external dose measurement while calculating the sample age and the external dose rate experienced by the tooth failing that modelling the sedimentary dose rates using time averaged total external dose calculations becomes necessary these principles are illustrated using teeth from the australopithecine sites sterkfontein and swartkrans south africa

ground penetrating radar imaging of carbonate mound structures and implications for interpretation of marine seismic data images of carbonate mound structures in denmark and sweden are obtained from ground penetrating radar gpr reflections and outcrop analysis the gpr data are collected in limestone quarries and provide a depth penetration of about 10 m 33 ft and a vertical resolution of about 0 5 m 1 6 ft the mounds are part of the northwest european upper cretaceous danian lower paleocene chalk group and they are similar to each other in terms of architecture spatial distribution and size with widths and lengths of 30 60 m 100 200 ft and heights of 5 10 m 16 33 ft seismic reflection images from the sea of kattegat between sweden and denmark and the north sea show large 500 1000 m 1640 3280 ft wide and 50 100 m 160 330 ft high moundlike carbonate structures interpretations of such large mounds conflict with the gpr and outcrop observations we address these conflicting observations we construct realistic reference models of carbonate mound complex geometries based on the results of the gpr measurements and outcrop analysis and calculate synthetic seismic sections for the models the modeling results show that the size of individual mounds is below the seismic resolution of 10 25 m 33 82 ft and that interference effects caused by stacks of mounds may explain the observed large moundlike structures our findings are important for the interpretation of seismic images of carbonate mound structures carbonate mound buildups may form traps and correct seismic interpretation of mound complex geometry may be essential for evaluation of the nature and reservoir potential of such structures

diagenesis of flint and porcellanite in the maastrichtian chalk at stevns klint denmark abstract flint is common in many successions but since the nodules can be the result of a series of replacement and void filling processes their origin and broader paleo oceanographic significance can remain enigmatic this study addresses the origin of flint in the campanian maastrichtian chalk of denmark using the 450 m long stevns 1 core as a natural laboratory four types of siliceous nodules occur in the core porcellanite white flint white flint with a core of dark flint and dark flint all nodules consist mainly of microquartz with subordinate lutecite spherulitic chalcedony megaquartz and dolomite the lutecite replaces macrofossil fragments mainly bryozoans and shells microquartz replaces coccoliths and the chalcedony and megaquartz are pore filling the preservation of the external shape of bryozoans shells and coccoliths suggest that siliceous nodules were formed early by a one by one volume replacement of chalk values of 18osmow of microquartz and lutecite around 33 indicate temperatures of 15 17 c at the time of precipitation in contrast the 18osmow values of megaquartz indicate precipitation at temperatures up to 48 c the occurrence of chalcedony together with more stable and ordered megaquartz in irregular voids indicates that silica gel and or opal ct transformed to the quartz phases microquartz lutecite chalcedony and megaquartz through the dissolution precipitation process ostwald ripening these results motivate a conceptual model in which the replacement process was initiated by microbial decomposition of organic matter and took place during periods of low rate of or even stopped sedimentation which fixed the redox boundary and the microbial metabolic zones at a specific depth below the sea floor biogenic opal a incorporated in the sediment column below the sea floor was dissolved and precipitated at the redox boundary as silica gel and or opal ct possibly aided by sulfide oxidizing bacteria during burial the dissolution precipitation process transformed the silica gel and opal ct to the quartz phases the results of this study indicate that precipitation of the flint precursor can be controlled by a combination of an abundant biosiliceous source and high microbial activity in the sediments immediately below the seafloor flint is therefore likely to reflect deposition in a narrow interval at relatively shallow depths and therefore might be useful in studies of shallow water carbonates

recent advances and future prospects of the u th and u pb chronometers applicable to archaeology abstract the u th chronometer has revolutionized quaternary science in the last few decades and can now be considered a well established mature technique with growing application in archaeology as an alternative to 14 c dating and osl reaching well beyond the cutoff for both these methods applying the u pb technique to material within a time frame of interest to archaeology is a challenge only recently overcome with enormous potential for future development and use in terms of range u th can generally date material of between a few years and as much as 600 ka while u pb is best suited to material of 1 million years and older u th dating is typically precise with error margins of better than 1 routinely achievable for material of the last interglacial age or younger such precision is possible with u pb dating in the mid quaternary but most ages have uncertainties in the 5 10 range carbonates are the most desirable u series target material with closed system behaviour being particularly important for u th dating making inorganic deposits such as speleothems secondary cave carbonates tufa and calcrete ideal some biogenic carbonates such as coral and eggshell are often amenable to u series dating but less ideal material such as fossil teeth bone and mollusc shell usually continue to gain uranium after deposition meaning accurate ages cannot be calculated in all cases the importance of a thorough understanding of the context of dated material cannot be overstated in this contribution we review u th and u pb dating through an archaeological lens focussing on the methods themselves how to best interpret published data and how best to avoid common pitfalls we highlight the major successes through a number of case studies and provide an overview of what we believe to be the future directions of this field

introducing a geochemical screen to identify geologically meaningful u pb dates in fossil teeth abstract previous studies have shown that radiometric dating of fossils can be complicated by post fossilisation alteration a key challenge to obtaining geologically meaningful fossilisation dates in bioapatite is identifying regions that have remained relatively undisturbed since the time of fossilisation in order to determine whether a geochemical indicator can be used to identify least disturbed regions we combine in situ trace element analysis and u pb geochronology of fossil teeth from the arroyo chijuillita member new mexico and the dinosaur park formation alberta the reliability of these u pb dates is supported by good agreement between the isotope dilution thermal ionization mass spectrometry 61 5 1 6 ma and laser ablation icp ms 64 2 2 4 ma dates for a targeted tooth region of fourteen teeth analyzed from these units two record dates within uncertainty of the depositional age one has a diffusion concave upward cross sectional yttrium profile the other a concave downward profile reflective of trace element loss it was found for teeth from both units that smaller yttrium concentration ranges are correlated with younger u pb dates likely the result of post fossilisation alteration a yttrium screen based on this relationship is proposed and is found to be a better indicator of post fossilisation open system behaviour in the samples analyzed than other geochemical features thought to be produced during fossilisation this screen provides a new tool for identifying fossil material least disturbed since fossilisation facilitating the use of bioapatite to date the time of diagenesis

climatic fluctuations and sea surface water circulation patterns at the end of the cretaceous era calcareous nannofossil evidence abstract new paleoecological data are presented for late maastrichtian calcareous nannofossil assemblages of the indian ocean and the boreal epicontinental chalk sea these data are compiled with recent results in the tropical atlantic pacific and tethys oceans in order to characterize environmental changes by the end of the cretaceous era the paleobiogeographic distribution of the warm water species micula murus is updated and indicates the existence of major sea surface currents in the late maastrichtian atlantic ocean similar to the present day the end maastrichtian greenhouse warming is characterized at tropical and subtropical latitudes by an increase in abundance of m murus and the temporary disappearance of the high fertility marker biscutum constans in the boreal realm the greenhouse episode is marked by a contemporaneous acme of watznaueria barnesiae coincident with very rare occurrences of m murus and other tropical nannofossil species which have never been reported before at boreal latitudes a review of cyclostratigraphic and calcareous nannofossil data in the atlantic pacific indian and tethys oceans points to the following evolution of sea surface paleotemperatures for the last ca 350 380 kyr of the cretaceous the end maastrichtian greenhouse warming lasted on average a little more than 200 kyr and was followed by a ca 100 120 kyr cooling in the tethys a 30 40 kyr additional pulse of warming is highlighted immediately below the cretaceous paleogene boundary these findings indicate an important instability of the climate system at the end of the maastrichtian most likely caused by deccan volcanism the calcareous nannofossil species richness dropped during the end maastrichtian greenhouse warming which may indicate environmental stress and or ocean acidification however nannoplankton diversity returned rapidly to higher values after this climatic episode and remained high up to the cretaceous paleogene boundary no significant extinction is recorded in this biotic group prior to the boundary clay

directly dating geologic events u pb dating of carbonates 1 carbonates are ubiquitous forming in a variety of settings including caves soils the oceans during burial from hydrothermal fluids and along faults u pb dating of carbonates is applicable to almost the entire geologic time scale with results from pleistocene speleothems showing great promise for dating records 1 ma old here we review studies of u pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphic associations and the behavior of u and pb in various fluids we detail the steps required to select suitable samples summarize current laboratory techniques and provide directions for improvement of analytical protocols the u pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped

stratal geometries facies and sea floor erosion in upper cretaceous chalk normandy france unusual lenticular stratal geometries and facies of the upper cretaceous chalk of coastal haute normandie france are described and interpreted thirteen facies within these chalks are described and illustrated on the basis of field thin section and sem investigations nannofossil mudstones nannofossil hardgrounds echinoderm wackestones and packstones echinoderm hardgrounds bryozoan mudstones and wackestones bryozoan hardgrounds bryozoan packstones and wackestones inoceramid wackestones inoceramid hardgrounds sponge hardgrounds marly chalks conglomeratic chalks and debris flow chalks these facies occur within lenticular bedded structures with both concave up and concave down geometries which have been previously interpreted as megaripples mud mounds or tectonic structures detailed examination of the structures and the associated facies indicates that the concave up geometries were formed from submarine erosion and redeposition in nw se longitudinal channels the concave down geometries developed between adjacent channels assessment of the regional and temporal setting indicates that the erosion occurred in the armorican cornubian straits of the anglo paris basin during sea level lowstands within these straits channelling is preferentially developed on the positive south western block to the lillebonne fecamp cotentin fault

seismic stratigraphy and geological evolution of the cenozoic cool water eucla platform great australian bight seismic images of the continental margin in the western great australian bight reveal the internal anatomy of a long lived cenozoic cool water carbonate shelf the cenozoic succession is divisible into seven seismic sequences that reflect four depositional phases phase a paleocene middle eocene is a progradational siliciclastic wedge deposited in a depositional sag and represents lowstand and transgressive sedimentation phase b middle eocene earliest middle miocene contains cool water ramp carbonates with biogenic mounds eocene oligocene overlain by a warm water flat topped platform rimmed by the early middle miocene little barrier reef coeval deep water carbonate deposition formed a multi lobed sediment apron this phase was terminated by gentle uplift and tilting throughout southern australia in the late middle miocene phase c late miocene early pliocene represents cool water lowstand wedge and ramp deposition and contains numerous biogenic mounds in the youngest sequence this phase is terminated by an unconformity attributed to marine erosion phase d pliocene quaternary is a thick succession of cool water carbonates with spectacular clinoform ramp geometry that forms most of the modern outer shelf and contains large deep water biogenic mounds this platform the first large cool water carbonate shelf imaged by high quality seismic reflection data demonstrates the interaction between regional tectonic and local and global paleo oceanographic processes as australia drifted northward during the cenozoic the great australian bight moved from high to middle latitudes and the regional oceanographic regime remained cool water largely because of coeval development of the antarctic circumpolar current in the evolving southern ocean short episodes of warm water deposition probably reflect incursions of a proto leeuwin current from the indian ocean whereas growth of the miocene coral algal little barrier reef resulted from a short term global increase in sea surface temperatures this platform dominated by stacked carbonate ramps is most similar to the west florida shelf but contains many more biogenic mounds the western great australian bight carbonate platform is an excellent modern analog for the mesoscale structure of cool water platforms in the older geologic record

geological evolution of the chalk group in the northern dutch north sea inversion sedimentation and redeposition in contrast to the norwegian and danish sectors where significant hydrocarbon reserves were found in chalk reservoirs limited studies exist analysing the chalk evolution in the dutch part of the north sea to provide a better understanding of this evolution a tectono sedimentary study of the late cretaceous to early palaeogene chalk group in the northern dutch north sea was performed facilitated by a relatively new 3d seismic survey integrating seismic and biostratigraphic well data seven chronostratigraphic units were mapped allowing a reconstruction of intra chalk geological events the southwestward thickening of the turonian sequence is interpreted to result from tilting and the absence of coniacian and santonian sediments in the western part of the study area is probably the result of non deposition seismic truncations show evidence of a widespread inversion phase the timing of which differs between the structural elements it started at the end of the campanian followed by a second pulse during the maastrichtian a new finding not reported before after subsidence during the maastrichtian and danian renewed inversion and erosion occurred at the end of the danian halokinesis processes resulted in thickness variations of chalk units of different ages in summary variations in sedimentation patterns in the northern dutch north sea relate to the sub hercynian inversion phase during the campanian and maastrichtian the laramide inversion phase at the end of the danian and halokinesis processes additionally the late cretaceous sea floor was characterized by erosion through contour bottom currents at different scales and resedimentation by slope failures

stable isotope records across the cretaceous paleogene transition stevns klint denmark new insights from the chromium isotope system abstract late cretaceous to early paleogene time represents a critical transitional period in earth history global events include short term instability in climate and ocean circulation large igneous province emplacement and catastrophic extinction of marine and terrestrial fauna due at least in part to a bolide impact event the response of the ocean system to cretaceous paleogene k pg global events has been the subject of much research yet fundamental questions remain regarding carbon cycling climate ocean mixing and redox conditions to help elucidate paleoceanographic changes across the k pg transition we revisit the classic maastrichtian to danian chalk limestone succession at stevns klint denmark with a suite of new geochemical data including insights from the redox sensitive chromium isotope system we use carbon and oxygen isotope trends to form a well constrained framework for the succession before presenting strontium isotope chromium isotope and rare earth element data for the units deposited both before and after the k pg event carbon isotopes show only minor perturbation across the k pg boundary and oxygen isotopes record a prominent positive excursion with both of these trends standing in contrast to many k pg boundary sections worldwide strontium isotopes record a spike towards more radiogenic values which is consistent with a globally observed short term weathering pulse the chromium isotope profile of maastrichtian chalk begins with strongly positive values followed by a sharp negative excursion associated with a facies shift and initiation of bottom currents in the chalk sea 53 cr values then recover before falling steadily across the k pg boundary and into the danian limestone chromium isotope trends do not correspond to changes in hydrothermal input or basin redox conditions instead we propose that mixing of water masses with distinct chromium isotope signatures controlled temporal chromium isotope variability the local mixing event inferred from our maastrichtian chromium isotope data could be related to a temporary inflow of tethyan bottom waters or the shift from end maastrichtian greenhouse warming associated with deccan volcanism to the worldwide cooling phase that immediately preceded the k pg boundary no immediate change in chromium isotopes is recorded across the k pg boundary indicating that the bolide impactor did not substantially perturb the marine chromium cycle at least at the scale resolvable by our data instead chromium isotope trends continued to be controlled by local oceanographic processes highlighting the potential of the chromium isotope system to record isotopic heterogeneity and mixing events in ancient oceans

crystal chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenvironmental reconstructions abstract fossil biogenic apatites display rare earth element ree patterns which have been proposed to reflect environmental and biological controls on past seawater composition these patterns can be separated in two groups 1 patterns that are similar to those of open ocean and epicontinental waters and 2 patterns that exhibit a strong enrichment in intermediate ree bell shaped patterns because ree trapping in biogenic apatites occurs mostly post mortem it is essential to understand the crystal chemical inorganic factors that can influence the fractionation of ree between apatite and water a model is proposed by which partition coefficients of ree between apatite and water for a substitution mechanism can be extrapolated from mineral melt partition data to seawater or sedimentary basin conditions these are compared with available experimental partition coefficients for ree adsorption mechanism and used to discuss ree patterns in fossil biogenic apatites calculations of ree patterns for apatites at equilibrium with water show that the bell shaped patterns in fossil apatites can be explained by fractionation with seawater or continental fluids at low temperature under crystal chemical control involving a substitution mechanism and in the context of extensive or late diagenesis in that case the equilibrium composition of the fluid cannot be unequivocally determined from observed ree concentrations in fossil apatites this type of sample is inappropriate to discuss the past environmental or biological controls on ree concentrations in the ocean other sample compositions suggest little to moderate alteration of the original oceanic to freshwater pattern through the adsorption mechanism in the context of weak or early diagenesis and may be used with caution for that purpose

an extensive erosion surface of a strongly deformed limestone bed in the gushan and chaomidian formations late middle cambrian to furongian shandong province china sequence stratigraphic implications abstract in order to understand sequence development and sea level fluctuations during the late middle cambrian to early furongian on the north china epeiric platform the present study focuses on a unique subtle erosion surface of an extensive approx 100 km strongly deformed limestone bed in the uppermost part of the gushan formation shandong province china the gushan formation and the overlying chaomidian formation consist mainly of shales and a variety of carbonates that were deposited in subtidal environments e g deep subtidal shallow subtidal shoreface shoal subtidal microbial flat and restricted platform interior three third order depositional sequences s1 3 are identified each of which comprises a thin transgressive systems tract tst and a relatively thick highstand systems tract hst each sequence is bounded by a drowning unconformity sb1 a subaerial unconformity sb2 or a surface of submarine erosion sb3 the upper sequence boundary sb2 of sequence 1 s1 is represented by a subtle erosion surface of an extensive deformed limestone bed with a wide variety of soft sediment deformation structures e g lime mudstone breccias chaotic wacke packstone laminae and fragments homogenized oolites and clastic dykes and is overlain by small sporadic microbial buildups and an extensive bioclastic grainstone bed the deformed limestone was formed during early diagenesis by differential deformation processes brecciation liquefaction fluidization and injection which were most likely induced by pore water overpressure during the period of rapid sea level fall despite the lack of subaerial exposure features e g paleokarst paleosol etc the characteristics of the erosion surface cutting well lithified sediment below the missing of a significant geological record the prochuangia biozone and the worldwide correlatable positive carbon isotope excursion collectively indicate that the erosion surface developed under conditions of subaerial exposure after contemporaneous marine cementation of the deformed sediment the missing of the prochuangia biozone is most likely due to non deposition at a subaerial hiatal surface the erosion surface was submerged as a result of subsequent rise in sea level where sporadic microbial buildups formed under suitable conditions freshly deposited winnowed shell dominated transgressive lag deposits containing chuangia trilobite fragments brachiopod shells and abundant glauconite grains formed with continued rise in sea level which became in turn overlain by shale dominated facies the unique combination of the subtle erosion surface sensu stricto a subaerial unconformity and the underlying deformed limestone bed provides an important criterion for recognizing the subtle changes in relative sea level on shallow epeiric platforms

a multi disciplinary seriation of early homo and paranthropus bearing palaeocaves in southern africa abstract fossils of early homo and paranthropus have been recovered from several sites in southern africa unfortunately their precise age has historically been difficult to assess hampering the reconstruction of their relationships to each other and to fossils from eastern africa multi dating strategies combining biochronological archaeological palaeomagnetic electron spin resonance esr and uranium series techniques are now clarifying their age the following sequencing of sites is suggested swartkrans member 1 2 0 ma gondolin 1 8 ma kromdraai 1 8 1 7 ma sterkfontein m5a 1 8 1 4 ma swartkrans m2 1 7 1 1 ma sterkfontein m5b 1 4 1 1 ma sterkfontein m5c 1 3 0 8 ma swartkrans m3 1 0 0 6 ma the position of coopers d and drimolen is difficult to access because they only have faunal age ranges 1 9 1 6 ma esr suggests mixing is a potential major problem in multi generational sites the oldest southern african representatives of early homo and paranthropus occur around 2 1 1 9 ma in swartkrans member 1 and are recorded almost continuously in the palaeocave deposits until around 1 0 0 6 ma in swartkrans member 3 currently these data suggest that paranthropus and homo first occur significantly later in the southern african record than the eastern african record moreover paranthropus persists much later in southern africa than in eastern africa

lower pliocene hominid remains from sterkfontein cosmogenic aluminum 26 and beryllium 10 burial dates of low lying fossiliferous breccia in the caves at sterkfontein south africa show that associated hominid fossils accumulated in the lower pliocene these dates indicate that the skeleton stw 573 and newly discovered specimens from jacovec cavern have much the same age approximately 4 million years these specimens are thus of an age similar to australopithecus anamensis from east africa

contemporary flowstone development links early hominin bearing cave deposits in south africa abstract the cradle of humankind cave sites in south africa preserve fossil evidence of four early hominin taxa australopithecus africanus australopithecus sediba paranthropus robustus and early homo in order to integrate this record into a pan african scenario of human evolutionary history it is critical to have reliable dates and temporal ranges for the southern african hominins in the past a lack of precise and accurate chronological data has prevented the evaluation of the temporal relationships between the various sites here we report new uranium lead u pb radiometric ages obtained from sheets of calcium carbonate flowstone inter bedded between clastic cave sediments at the site of swartkrans providing bracketing ages for the fossiliferous deposits the fossil bearing units of swartkrans specifically the hanging remnant and lower bank of member 1 are underlain by flowstone layers dated to 2 25 0 05 ma and 2 25 0 08 ma and capped by layers of 1 8 0 01 ma and 1 7 0 07 ma the age bracket of the member 1 deposits is therefore between 2 31 and 1 64 ma however by combining the u pb with biostratigraphic data we suggest that this can be narrowed down to between 1 9 and 1 8 ma these data can be compared with other recently dated sites and a radiometrically dated u pb age sequence formed sterkfontein member 4 swartkrans member 1 malapa and cooper s d from this new u pb dataset a pattern of contemporary flowstone development emerges with different caves recording the same flowstone forming event specifically overlapping flowstone formation takes place at swartkrans and sterkfontein at 2 29 ma and 1 77 ma and at sterkfontein and malapa at 2 02 ma this suggests a regional control over the nature and timing of speleothem development in cave deposits and these flowstone layers could assist in future correlation both internal to specific deposits and regionally between sites

creation and destruction of weddell sea floor in the jurassic new paleomagnetic data invite reassessment of the breakup history of parts of the pacific margin of gondwana due to the mesozoic opening of the southern ocean basins these data indicate clockwise rotation of the antarctic peninsula relative to east antarctica between 175 and 155 ma that would have created as much as 1000 km of pre anomaly m25 ocean floor in the weddell sea basin the paleomagnetic data also suggest that between 155 and 130 ma the antarctic peninsula rotated counterclockwise relative to east antarctica rotation that along with the southward motion of east antarctica would have caused subduction of the newly created weddell sea ocean floor beneath the southern antarctic peninsula east vergent folding and thrusting of jurassic back arc basin rocks along the southeastern antarctic peninsula known as the palmer land event probably resulted from deformation along this newly created convergent margin the presence of jurassic weddell sea floor would have isolated eastern gondwana east antarctica australia and india from the antarctic peninsula and western gondwana africa and south america encouraging increased marine faunal connections between the pacific and weddell sea mozambique somali ocean basins during the 175 to 130 ma interval after 130 ma the antarctic peninsula would have been connected to east antarctica via the other west antarctic terranes thereby facilitating land migrations between eastern and western gondwana

regional velocity depth anomalies north sea chalk a record of overpressure and neogene uplift and erosion a normal velocity depth trend for the upper cretaceous danian chalk group is determined by identifying interval velocity data that represent maximum burial in areas unaffected by overpressuring these data are derived from 845 wells throughout the north sea basin data from pelagic carbonate deposits on a stable plateau constrain the trend for shallow depths positive velocity anomalies relative to the trend are mapped along the western and eastern margins of the north sea basin and reflect regional neogene uplift and erosion of up to 1 km along the present day limit of the chalk a hiatus at the base of the quaternary increases in magnitude away from the basin center where a complete cenozoic succession is found this hiatus is consistent in size with the missing section estimated from chalk velocities when allowance is made for the quaternary reburial of the chalk negative velocity anomalies in the central and southern parts of the basin outline an area within which overpressures in the chalk exceed 10 mpa equivalent to a burial anomaly greater than 1 km relative to the normal trend the chalk pressure system is primarily dependent on overburden properties because retention of overpressure generated by the load of the upper overburden depends on the thickness and sealing quality of the lower overburden therefore the chalk is considered to represent a regional aquitard and the hydrodynamic model of long distance migration within the chalk is rejected the neogene uplift and erosion of the margins of the north sea basin and the rapid late cenozoic subsidence of its center fit into a pattern of late cenozoic vertical movements around the north atlantic

buried pockmarks on the top chalk surface of the danish north sea and their potential significance for interpreting palaeocirculation patterns three dimensional 3d seismic data from the southern danish north sea were used to analyse the morphology and spatial distribution of depressions in the danian chalk deposit previously these depressions were either interpreted as karst structures or pockmarks the observed depressions occur in an interval from 25 ms below to 12 ms above the top chalk surface three types of depressions were differentiated based on their plan view geometry and their degree of symmetry type 1 comprising sub circular and symmetrical depressions is the dominant group ca 70 type 2 elongated and symmetrical depressions represents only a small fraction ca 5 the elongated and asymmetrical depressions of type 3 compose ca 25 in cross section each depression type can be either characterised by a v or a u shape the maximum size of the depressions ranges from 50 to 580 m with an average internal depth of 10 m we interpret the depressions as pockmarks formed by the expulsion of biogenic or thermogenic fluids at the danian seafloor likely the initial form of the pockmarks has been circular type 1 and was subsequently modified for types 2 and 3 to an elongated form by currents the long axis of the pockmarks is interpreted to represent the effective current direction the inferred direction is sub parallel to the palaeobathymetric contours the 3d seismic interpretation of pockmarks presented in this paper contributes to the understanding of fluid migration and palaeocirculation patterns during the sedimentation of the terminal chalk group in the southern danish north sea

contourite drift types and their distribution in the north and south atlantic ocean basins abstract patterns of sediment accumulation under the control of deep bottom currents depend on interacting factors intensity of the regional deep circulation morphology of the sea floor coriolis effects abundance of terrigenous and biogenic supplies subsequent turbidity of deep nepheloid layers and depth of the ccd based on many examples of bottom current deposits from the atlantic and from other oceans we recognise three major types of contourite accumulation 1 giant elongate drifts 2 contourite sheets and 3 channel related drifts they generally occur in distinct topographic settings and show different geometries facies and rates of deposition in the north atlantic strong bottom circulation an open basin system and high sediment supply have led to the construction of large elongate contourite drifts which have striking relief 200 1000 m above the surrounding sea floor and are composed of muddy contourites rich in calcareous pelagic material in the south atlantic strong bottom currents are often trapped in gyre like circulation patterns around topographically closed basins or are accelerated through deep narrow connecting passages the resulting deposits are mainly extensive contourite sheets covered by fields of large sediment waves and channel related drifts including contourite fans constructed at the downstream exit of deep passages

the cretaceous palaeogene boundary at stevns klint denmark inversion tectonics or sea floor topography the cretaceous palaeogene boundary interval is exposed over 12 km in the coastal cliff stevns klint denmark an important lowermost danian hardground has been interpreted as an originally horizontal marine abrasion surface its present elevation varies from a few metres below to about 35 m above sea level this relief has traditionally been considered as resulting from late or post danian laramide folding new seismic profiles offshore stevns klint show however that the base chalk reflector is not folded is remarkably planar and has a gentle northward dip thus the folding hypothesis cannot be upheld seismic stratigraphic analysis of the chalk group necessitates a fundamental revision of general ideas of chalk deposition a highly irregular sea floor topography was formed at many levels and includes broad valleys ridges channels drifts and mounds a system of major wnw ese oriented valleys and ridges can be traced into the succession exposed in stevns klint and further inland where it corresponds to the relief of the cretaceous palaeogene boundary the marked topographic elements of the chalk sea floor are elongate with a wnw orientation roughly parallel to the axis of the danish basin and to the sorgenfrei tornquist zone forming the ne border of the basin the sea floor relief undoubtedly reflects the influence of strong contour parallel bottom currents the cretaceous palaeogene boundary succession at stevns klint was thus developed on an underlying sea floor topographic relief of about 40 m recognition of the highly irregular current influenced topography of the late cretaceous sea floor stands in marked contrast to the conventional picture of quiet pelagic deposition of the chalk

conodont u th he thermochronology a case study from the illinois basin abstract acquisition of thermochronologic data in carbonates and shales has traditionally been elusive owing to the paucity of dateable minerals in these lithologies conodont apatite u th he cahe thermochronology has the potential to fill this need we acquired 50 u th he dates for conodonts with cai values 1 5 from seven pennsylvanian shale and limestone samples from two drillcores in the illinois basin we also obtained x ray microcomputed tomography microct results for 8 conodonts to evaluate the accuracy of alpha ejection corrections the simplified geometric corrections yield corrected dates within 5 of those derived from 3d characterization using microct nearly all of the conodont cahe dates are substantially younger than their depositional age indicating that maximum post depositional temperatures of 90 c caused he loss over geologic timescales the youngest and most reproducible dates consist of whole platform elements from shales and may record a regional late cretaceous early tertiary cooling and erosion event the remainder of the data exhibit strong negative date u and date th correlations characterized by higher and more variable th u than the conodonts with reproducible dates these patterns are best explained by u loss with more limited th loss the results suggest that whole platform elements and higher u th conodont materials are the most promising targets for cahe analysis

dating open systems by the 238 u 234 u 230 th method application to quaternary reef terraces abstract the sedimentation conditions and diagenetic processes of biogenic and inorganic carbonates are such that the assumptions of a closed system evolution and the absence of initial th invoked in classical 238 u 234 u 230 th dating methods are very often not fulfilled for such material this problem is of interest for all studies requiring accurate dating of corals or aragonite rich sediments as in palaeoclimatology or neotectonics extending the approach of henderson and slowey nature 404 2000 61 66 we propose a consistent model that takes into account possible initial 230 th excess and where continuous selective redistribution gain or loss of 234 u 234 th and 230 th is controlled by recoil processes this model applied to quaternary marine terraces in barbados marie galante lesser antilles arc and pacific islands is able to explain the large scatter in isotopic compositions observed in the series of cogenetic corals or sediments we show that recoil processes generally tend to increase the 234 u 238 u and 230 th 234 u ratios with time leading to an overestimation of the apparent ages calculated using classical methods on the basis of simple assumptions identical marine initial 234 u 238 u 0 and 230 th 232 th 0 ratios we propose a method for calculating a best estimate of the age of cogenetic series our model offers an alternative way to date old reef terraces where corals are almost systematically altered and where classical dating methods do not apply it may also explain the apparent variations of the 234 u 238 u seawater initial ratio estimated from corals formed in the last 300 ka and the apparent uncoupling between sea level highstands and high latitude northern hemisphere summer insolation our set of equations can be applied to all weathering processes where the mobility of u series isotopes is controlled by recoil

uranium isotopes in surface waters from southern africa abstract the 234 u 238 u activity ratio in river water in southern africa is generally higher than that reported for rivers in other regions of the world this is interpreted as due to the prevailing environmental conditions in this warm dry region mechanical weathering predominates over chemical weathering causing the isotope activity ratio of leached uranium to be on average 2 03 0 42 as compared to a ratio of 1 20 for river water in the more humid tropical and temperate regions the isotopic composition of leachable uranium from river sediment is similar to that in the water rivers draining the witwatersrand gold and uranium mining area clearly show pollution inputs characterised by high uranium content and low activity ratios

the development and seismic expression of synsedimentary features within the chalk of southern england seismic reflection data acquired onshore to the north of bournemouth southern england image clearly a series of prominent concave up troughs or depressions and concave down mounded structures within the white chalk subgroup the chalk lithostratigraphy in the area of study is established from borehole geophysical log correlations these correlations then provide calibration of the seismic reflection data indicating that the structures are concentrated at levels between the lewes nodular chalk formation and tarrant chalk member and towards the base of the portsdown chalk formation onlap downlap and truncation of reflectors are observed with the most dramatic features forming a stacked series directly overlying faulting of jurassic strata similar stratal geometries have been described from comparable levels in the chalk of the north sea and in outcrop in britain and france to many they represent channels formed by submarine erosion and redeposition of the chalk during relative sea level falls linked to tectonics we also interpret a number of apparently incisive structures and slumped infill sequences described here as being of primary syndepositional origin the slumping and the close association of these features with underlying faults and proximity to nearby major crustal faults may be indicative of submarine erosion of the chalk caused by sea level changes linked to syndepositional fault movements however evidence of toplap downlap pairs is also suggestive of more aggradational mounding or laterally migrating surfaces or facies belts the presence of any such structures implies rapid lateral variations in the chalk that would have implications not only for aquifer management and future storage schemes but also during the processing of seismic reflection data and general studies and correlations of the chalk across southern britain

cyclostratigraphy of the reference section for the cretaceous white chalk of northern germany lagerdorf kronsmoor a late campanian early maastrichtian orbital time scale new carbonate records of the upper campanian lower maastrichtian white chalk of northern germany at lagerdorf kronsmoor represent a continuous succession suitable for time series analysis the boreal chalk succession is characterized by several intervals of reduced carbonate content in the basiplana spiniger polyplocum upper langei and upper grimmensis granulosus to pseudoobtusa boreal macrofossil zones which are mainly related to periods of increased detrital supply results of spectral analysis on the carbonate time series allow the detection of the periodicities of long and short eccentricity the long eccentricity signal can be extended to the entire upper campanian comprising a total of 15 25 long eccentricity cycles a minimum time span of 6 2 ma and an age of 77 5 0 4 ma for the lower upper campanian boundary the long eccentricity cycles detected from chalk carbonate contents correlate with long eccentricity cycles detected in self potential logs of boreholes proving their significance within different depositional settings and rates of subsidence in the north german basin the biostratigraphic consistent occurrence of long eccentricity cycles provides evidence for the completeness of the sedimentary record the long term intervals of increased detrital supply are the expression of increased progradation of clay minerals related to a long term sea level fall with superimposed short sea level falls within a 2 5 million year interval spanning the campanian maastrichtian boundary it cannot be decided from the present state of knowledge if this signal is controlled by increased erosion due to uplift of inverted structures by eustatic sea level fall or a combination of both the detection of the long eccentricity suggests an orbital forcing superimposed on a long term regressive trend

integrated seismic interpretation of the carlsberg fault zone copenhagen denmark summary we locate the concealed carlsberg fault zone along a 12 km long trace in the copenhagen city centre by seismic refraction reflection and fan profiling the carlsberg fault is located in a nnw sse striking fault system in the border zone between the danish basin and the baltic shield recent earthquakes indicate that this area is tectonically active a seismic refraction study across the carlsberg fault shows that the fault zone is a low velocity zone and marks a change in seismic velocity structure a normal incidence reflection seismic section shows a coincident flower like structure we have recorded seismic signals in a fan geometry from shots detonated both inside the low velocity fault zone and up to 500 m away from the fault zone the seismic energy was recorded on three receiver arrays 1 5 to 2 4 km long arcs across the expected location of the 400 to 700 m wide fault zone at distances of up to 7 km from the shots shots detonated inside the fault zone result in 1 weak and delayed first arrivals on the receivers located inside the fault zone compared to earlier and stronger first arrivals outside the fault zone 2 strong guided p and s waves as well as surface waves inside the fault zone the fault zone is a shadow zone to shots detonated outside the fault zone finite difference wavefield modelling supports the interpretations of the fan recordings our fan recording approach facilitates cost efficient mapping of fault zones in densely urbanized areas where seismic normal incidence and refraction profiling are not feasible

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

lu hf isotope systematics of fossil biogenic apatite and their effects on geochronology abstract reliable methods for direct dating of biogenic apatite from pre pleistocene fossils are currently not available and recent attempts using the lu hf decay system yielded highly inaccurate ages for both bones and teeth the geological processes accounting for this poor accuracy of lu hf chronometry are not yet understood here we explore lu hf systematics in fossil bones and teeth in detail by applying five different sample digestion techniques that are tested on bones and composites of bone and sediment our current dataset implies that dissolution methods only slightly affect the resulting lu hf ages while clear differences between the individual digestion techniques became apparent for element concentrations by analysing the insoluble leftovers from incomplete sample dissolution four main reservoirs of hf in fossil bones were identified 1 a radiogenic end member associated with apatite 2 an unradiogenic end member represented by the authigenic minerals or the embedding sediment 3 a highly unradiogenic end member that can be attributed to detrital zircon and 4 a moderately soluble phase probably a zr hf phosphate that yielded very low lu hf but a highly radiogenic hf isotope composition at the same time this zr hf phase must have been precipitated within the fossil bone sample at a late stage of burial history thereby incorporating radiogenic 176 hf released from apatite surfaces over geological timescales a second focus of our study is the effect of different sediment matrices and of crystal size on the preservation of pristine lu hf isotope compositions in bioapatite because near depositional lu hf ages of phosphate fossils have previously been reported for the london clay england and a calcareous marl from tendaguru tanzania we herein investigate specimens fossilised in carbonate matrices calcareous marl from oker germany carbonate concretions from the santana formation brazil carbonate from the eifel germany and argillaceous matrices with low permeability oil shale of messel germany posidonienschiefer of holzmaden germany materials analysed from these localities include bones teeth conodonts as well as coproliths and diagenetic minerals siderite montgomeryite and messelite near depositional lu hf ages were obtained for a bony fish sample notelops brama encapsulated in an early diagenetic carbonate concretion from the early cretaceous santana formation brazil and for conodonts from a middle devonian carbonate from the eifel germany low 176 lu 177 hf ratios in all materials from the middle eocene messel oil shale e g bones fish scales sediment siderite result in poor age precision and an age that is near depositional due to this large analytical error in agreement with previous results all other ages determined here for both bones and teeth are by far younger than respective chronostratigraphic ages a model illustrating the behaviour of lu and hf over time with respect to the fossilisation process is presented which accounts both for the formation of a late diagenetic radiogenic zr hf phase and long term open system behaviour the continuous lu hf element exchange between the fossils and the embedding sediment is probably related to the nm scale crystal size of fossil bones dentine and also of enamel that generate large surface areas facilitating sorption desorption processes and open system behaviour

production of calcareous nannofossil ooze for sedimentological experiments the notion of fine grained pelagic carbonates as uniform monotonous sequences of sediments settled in a quiescent environment has been challenged over the past few decades fine grained pelagic carbonates can undergo substantial reworking after their first deposition as illustrated by an abundance of sedimentary structures such as drifts moats sediment waves and channels documented in the upper cretaceous chalk group of nw europe despite chalk being a major hydrocarbon reservoir rock of the north sea surprisingly little is known about the physical behavior of the pelagic carbonate sediment from which the chalk formed calcareous nannofossil ooze this poses a serious challenge to the understanding of the depositional system and the properties of facies distribution experimental tests such as those performed in laboratory flumes are necessary to provide empirical data on this subject however the use of modern calcareous nannofossil ooze as an analogue for cretaceous ooze is associated with a number of disadvantages such as generally higher noncarbonate content and smaller coccolith size of modern oozes here we document a preparation method for the production of calcareous nannofossil ooze for the purpose of physical experiments based on disaggregation of upper cretaceous chalk through repeated freezing and thawing we further document the textural characteristics of the ooze compared to the original chalk based on quantitative backscatter scanning electron image analysis laser diffraction granulometry and smear slides the upper cretaceous chalk chosen for disaggregation is highly friable due to delicate contact cement and has a low noncarbonate content 2 wt a high porosity friability and good nannofossil and microfossil preservation these characteristics allowed an effective disaggregation of the chalk matrix into its basic nannofossil and microfossil components which show good preservation through the disaggregation process textural analysis of chalk used for disaggregation and the produced ooze shows no significant differences between the two thus validating the use of the freeze thaw method for production of experimental ooze to model the basic depositional behavior of cretaceous chalk

high resolution shear wave seismics across the carlsberg fault zone south of copenhagen implications for linking mesozoic and late pleistocene structures abstract the carlsberg fault zone cfz is a nnw sse striking structure close to the transition zone between the danish basin and the baltic shield we examine the fault evolution by combining very high resolution onshore shear wave seismic data one conventional onshore seismic profile and marine reflection seismic profiles the faulting geometry indicates a strong influence of triassic subsidence and rifting in the central european basin system growth strata within the cfz surrounding hollviken graben reveal syntectonic sedimentation in the lower triassic indicating the opening to be a result of triassic rifting in the upper cretaceous growth faulting documents continued rifting these findings contrast the late cretaceous to paleogene inversion tectonics in neighboring structures such as the tornquist zone the high resolution shear wave seismic method was used to image faulting in quaternary and danian layers in the cfz the portable compact vibrator source elvis iii s8 was used to acquire a 1150 m long seismic section on the island amager south of copenhagen the shallow subsurface in the investigation area is dominated by quaternary glacial till deposits in the upper 5 11 m and danian limestone below in the shear wave profile we imaged the uppermost 30 m of the western part of cfz the complex fault zone comprises normal block faults and one reverse block fault the observed faults cut through the danian as well as the quaternary overburden hence there are strong indicators for ongoing faulting like mapped faulting in quaternary sediments and ongoing subsidence of the eastern block of the cfz as interpreted by other authors the lack of earthquakes localized in the fault zone implies that either the frequency of occurring earthquakes is too small to be recorded in the observation time span or that the movement of the shallow sub surface layers may be due to other sources than purely tectonic processes

timescales and mechanisms of ree and hf uptake in fossil bones abstract rare earth element ree patterns of fossil bones and teeth are widely used as proxies for provenance taphonomy and palaeoenvironment in order to investigate if fossil bones behave as closed systems over geologic time ree profiles were analysed by la icpms along cross sections of 54 bones from various well characterised and well dated settings these include terrestrial and marine diagenetic environments covering early triassic to holocene ages in general all fossil bones exhibit the highest ree concentrations at the outer rim gradually decreasing by up to four orders of magnitude toward the inner bone cortex intra bone ree concentration gradients decrease significantly from quaternary via tertiary to mesozoic specimens suggesting long term ree uptake and open system behaviour of fossil bone this view is further corroborated by 176lu 176hf dating of selected samples all yielding significantly younger ages than the known chronostratigraphic ages hence there is clear evidence for long term open system behaviour of fossil bones with respect to ree which is in marked contrast to currently accepted models suggesting that ree uptake is only early diagenetic although unexpected statistically significant four to seven point isochrons are observed for four fossil dinosaur bone samples and one upper triassic mastodonsaurus tooth with mswds ranging from 0 083 to 4 5 notably mobility of lu alone cannot account for the observed age patterns assuming constant lu uptake rates over time the radiometric ages should only be as low as half of the chronostratigraphic age however a six point isochron defined by subsamples of a single upper triassic mastodonsaurus tooth yields an age of 65 2 1 1 ma mswd 0 68 much younger than half of the stratigraphic age ca 234 ma hence hf must also undergo late diagenetic exchange likely mechanisms to account for the presence of statistically meaningful isochrons as well as for the late diagenetic exchange of both ree and hf are diffusion adsorption and dissolution reprecipitation processes

the late cretaceous early paleocene palaeobathymetric trends in the southwestern barents sea palaeoenvironmental implications of benthic foraminiferal assemblage analysis the late cretaceous foraminiferal assemblages from five wells drilled in the southwestern barents sea were analysed using morphogroup analysis in order to understand the palaeoenvironment and palaeobathymetry of the study area morphogroup analysis of assemblages in the upper cretaceous kveite formation suggests stable possibly middle to lower bathyal mesotrophic and relatively well oxygenated environments in the tromso basin during the late cretaceous the depositional setting of upper cretaceous kviting formation in the tectonically more stable hammerfest basin was probably shallower but still represents a deep water environment similar to that of the kveite formation a shallowing regional bathymetry in the southwestern barents sea is indicated by the general decreasing trend in the relative abundance of tubular forms and the species diversity of assemblages which reflects the regional late cretaceous paleocene uplift prior to the break up of the greenland norwegian sea changes in the relative abundance of morphogroups and in the main constituent in the cumulative length of tubular taxa from rhizammina to rhabdammina near the top of kveite formation agree with the possible existence of bottom water currents c 2011 elsevier b v all rights reserved

u pb dating of fossil enamel from the swartkrans pleistocene hominid site south africa abstract we demonstrate that young fossil enamel older than the range of the u series 300 ka can be dated by the u pb methods using new models of u and pb loss and uptake contrary to the current hypothesis of u uptake that only considers the adsorption diffusion mechanism we here develop a complete time dependent model which takes gains and losses of the most critical nuclides 238u 234u and 230th into account both during chemical dissolved u and physical th and u recoil processes lead is assumed to be a mixture between two components of common pb and a radiogenic component the proportions of these components are calculated from the pb isotope abundances and u pb ratios we apply this new u pb method to bovid enamel from the swartkrans cave gauteng province south africa this cave has yielded abundant early pleistocene hominid remains attributed to paranthropus and homo as well as various associated archaeological vestiges biochronological comparisons with east africa have provided age estimates ranging between 1 8 and 1 0 ma which however remain poorly constrained after correction for initial 234u disequilibrium and further 238u loss the u and pb isotope data yield ages of 1 83 1 38 1 36 0 29 and 0 83 0 21 ma for the three stratigraphic units members 1 2 and 3 respectively we discuss the consequences of these radiometric results for hominid evolution in south africa

bottom current controlled sedimentation a synthesis of the contourite problem abstract an overview of the main items concerning deep bottom current controlled deposits is presented these include the definition of contourites their processes of deposition and facies characteristics contourite drift types and seismic patterns the interplay of turbidity and bottom current processes and the correlation between bottom current processes and global changes in climate sea level from this discussion several of the more significant problems are highlighted which we believe should be priority targets for future research 1 identification of contourites especially in ancient series where they are interbedded with turbidites and other facies 2 refinement of the numerous parameters used as tracers of palaeocirculation patterns 3 understanding the interaction between the different types of bottom currents and also between bottom current and other deep water processes 4 distinction in the sedimentary record between the effects of short time scale bottom current variations due to regional causes like benthic storms and geological scale current fluctuations related to climatic or astronomic control 5 understanding the control of glacial interglacial climatic cycles on the nature and rate of contourite deposition