on applications of micro photogrammetry and geometric morphometrics to studies of tooth mark morphology the modern olduvai carnivore site tanzania abstract recent application of photogrammetric and geometric morphometric approaches to the study of cut marks on bones has yielded positive results in discriminating different types of tools and even some raw materials here we apply this analytical technique to the study of carnivore tooth scores the goal is twofold on the one hand we intend to differentiate carnivore types and on the other one we show the application of this approach to a sample of tooth scores from long bones documented at the modern assemblage of the olduvai carnivore site ocs previous taphonomic work at ocs suggested that this bone assemblage constituted a good evidence of a carcass accumulation behavior by lions followed by hyena ravaging the application of these 3d techniques to the selected sample of tooth marks shows that lions as well as spotted hyenas did indeed impart marks on the ocs assemblage this reinforces the dual nature of the assemblage and the implication of lions in its formation

biostratigraphic strontium isotopic and geologic constraints on the landward movement and fragmentation of terranes within the tofino basin british columbia significant advancements in understanding the complex evolution of the tofino basin at a convergent accretionary margin are enabled by combining contextual geologic information with new isotopic and paleontological data a high resolution cenozoic chronostratigraphy of the basin is constrained by strontium isotope ages 36 9 1 3 ma of late eocene to pleistocene foraminifers together with a revised biostratigraphy foraminifers and ichthyoliths from six offshore wells and outcrop samples new specimen thermal alteration values and existing well log data these data are integrated with archival multichannel seismic and magnetic data to interpret offshore well positions with relation to sub basins and structural highs of the pacific rim and crescent terranes and other accreted strata six regions of the tofino basin are defined based on structure and depositional differences during the eocene to holocene history of accretion and fragmentation of the crescent terrane and it underthrusting the pacific rim

approaching raw material functionality in the upper magdalenian of coimbre cave asturias spain through geometric morphometrics abstract coimbre cave penamellera alta asturias is an upper palaeolithic site in northern spain spanning an occupation sequence from the gravettian to the magdalenian periods the upper layers layer i and ii corresponding to the upper magdalenian register the highest intensity of human activity in this paper we analyse raw material functionality at the site through the study of cut marks found on bone remains at coimbre we have documented mainly quartzite followed by flint other raw materials are found in very low frequencies there are several types of local quartzite that appear mainly as flaking debitage and stone tools such as burins and scrappers on the other hand flint is mainly knapped to elaborate blades and bladelets as well as specialised implements such as different types of side scrappers retouched flakes on flint are relatively more abundant than those made on quartzite in this paper we employ the use of photogrammetry geometric morphometrics and statistics to analyse the cut marks from the upper magdalenian assemblage of coimbre cave our aim is to determine the lithic raw material preferentially used for carcass processing at the site

application of geometric morphometrics to the analysis of cut mark morphology on different bones of differently sized animals does size really matter abstract recent techniques applied to taphonomy have made advances in our understanding of bone surface modifications for many years differences in bone density according to element and variations in animal size have been considered conditioning factors for many taphonomic processes while several studies highlight how animal size and density affect fracture patterns and bone preservation rates variations in cut mark morphology are yet to be confronted against these variables here we assess the effect of these variables and their potential effect on cut mark morphology by comparing a considerable amount of cut marks on different anatomical elements of both suids and bovids experimentally produced cut mark samples were then digitally reconstructed using a david laser scanner that allowed the statistical analysis of each cut mark s shape and form geometric morphometric analysis using 2d and 3d landmark models were unable to find substantial differences in cut mark morphologies caused by either element type of carcass size

are the pacific and indo atlantic hotspots fixed testing the plate circuit through antarctica it is often assumed that hotspots are fixed relative to one another and thus constitute a global reference frame for measuring absolute plate motions and true polar wander but it has long been known that the best documented hotspot track the hawaiian emperor chain is inconsistent with the internally coherent tracks left by the indo atlantic hotspots this inconsistency is due either to unquantified motions within the plate circuit linking the pacific with other plates for example between east and west antarctica or relative motion between the hawaiian emperor and indo atlantic hotspots analysis of recent paleomagnetic results from marie byrd land in west antarctica confirms that there has been post 100 ma motion between west antarctica marie byrd land and east antarctica however incorporation of this motion into the plate circuit does not account for the cenozoic hotspot discrepancy comparison of an updated inventory of pacific and non pacific paleomagnetic data does not show a significant systematic discrepancy which along with other observations indicates that missing plate boundaries and other errors in the plate circuit play a relatively small role in the hotspot inconsistency we conclude that most of the apparent motion between the hawaiian emperor and indo atlantic hotspots is real the best estimate average drift rate between these sets of hotspots is approximately 25 mm yr since 65 ma ignoring errors in the plate circuit and a small contribution from cenozoic motions between east and west antarctica 1999 elsevier science b v all rights reserved

stability of the earth with respect to the spin axis for the last 130 million years abstract recently continental paleomagnetic data rotated into a hotspot reference frame have been used to suggest the earth rotated 18 with respect to the spin axis at 110 ma we test this true polar wander tpw hypothesis using paleomagnetic data from widespread granitic rocks of cratonal north america these data conflict with tpw predictions leading to rejection of the hypothesis the calculated polar displacement is instead consistent with motion of the atlantic hotspots during the mid cretaceous this analysis suggests that the time averaged position of the spin axis has deviated by no more than 5 over the last 130 million yr indicating that mantle mass heterogeneities have not changed rapidly enough to drive tpw

evidence for a 20 tilting of the earth s rotation axis 110 million years ago true polar wander tpw the shift of the earth s rotation axis with respect to the entire globe is most probably due to mass redistribution in the earth s mantle as a result of convection using a new rigorously selected palaeomagnetic database gathering only directions obtained from magmatic rocks we find that tpw has been clearly intermittent over the last 200 ma with two long periods of strict standstill from the present to 80 ma and from approximately 150 to 200 ma a single period of shifting is observed between 80 and about 150 ma ago this period culminates around 110 ma ago in an 20 abrupt tilting during which an angular speed exceeding 5 ma 0 5m yr may have been reached assuming that the time averaged geomagnetic field is axial our results indicate that the changes in the position of the rotation axis and therefore in the inertia tensor of the earth are intermittent we suggest that a major reorganization of the mass distribution in the earth s mantle occurred in the lower cretaceous this event concomitant with plume hyperactivity at the earth s surface and probable drastic changes at the core mantle boundary attested by the inhibition of geomagnetic reversals suggests unmixing of upper and lower mantle by avalanching of upper mantle material down to the core mantle boundary the astonishingly strict stability of the time averaged position of the rotation axis before and after this episode of shifting implies the existence of some steady convection which does not modify the large scale distribution of mass within the mantle given the intermittence of mantle avalanching we suggest that these long periods of stability correspond to the temporary reestablishment of a basically two layered convection system within the mantle

paleomagnetic poles and paleosecular variation of basalts from parana magmatic province brazil geomagnetic and geodynamic implications a paleomagnetic study was carried out along two sections altogether 35 lava flows 300 samples in the central parana magmatic province pmp brazil the two sections distanced ca 200 km apart yield statistically indistinguishable paleomagnetic poles the combined paleomagnetic pole with coordinates 85 7 n 197 9 e a95 2 6 n 35 is statistically different from previously published paleomagnetic poles for other sections of pmp we suggest that this angular difference as well as differences between previously published poles is caused by undetected local tectonic rotations not easily identified in the often poorly exposed lavas of the pmp a joint analysis of all published pmp paleomagnetic data indicate that paleosecular variation estimated as the angular standard deviation sf of the virtual geomagnetic pole distribution does not support the suggestion of anomalously high secular variation at low latitudes in the 110 195 ma period j geophys res 96 1991 3923 all sf estimates are in fact in better accordance with latitudinal dependence estimates derived from the curve for the 0 5 ma period moreover we find that all pmp paleomagnetic poles lie 10 away from the pole predicted by an assumed fixed hotspot reconstruction of south america the pmp paleomagnetic poles therefore call for either true polar wander or motion of indo atlantic hotspots 2003 elsevier b v all rights reserved

micro photogrammetric characterization of cut marks on bones in the last few years the study of cut marks on bone surfaces has become fundamental for the interpretation of archaeological sites and prehistoric butchery practices due to the difficulties in the correct identification of cut marks many criteria for their description and classifications were suggested this article presents an innovative methodology which supplements the microscopic study of cut marks despite the benefits of using scanning electron microscopy sem for the two dimensional identification of these marks it has a number of drawbacks such as the high costs and consequently the limited sample studied in this article a low cost technique for the analysis of cut mark micromorphology from a tri dimensional perspective is introduced it provides a high resolution approach to cut mark characterisation such as morphology depth width and angle estimation as well as section determination measured directly on the marks on bones macro photogrammetry records quantitative and qualitative information which can be statistically processed with standard multivariate and geometric morphometric tools

molluscan death assemblages on the amazon shelf implication for physical and biological controls on benthic populations the amazon continental shelf is an example of an environment impacted by frequent and intense physical disturbance with regions of high sedimentation rates cycles of extensive sediment erosion and deposition result in periods of sediment remobilization and instability in the seabed and cause marked seasonal and spatial variations in the transport of water column organisms and benthic infauna in this study the molluscan death assemblages on the amazon shelf are examined in an effort to understand how this physical regime is reflected in death assemblages as well as to provide insight into biological controls on mortality inner shelf regions of 20 m water depth comprise 50 of the total shelf area that extends to 100 m and have no relict shell beds or randomly dispersed shells although a few living shell bearing species are occasionally present extensive death assemblages are found deeper than 40 m bivalves were most numerous on the shelf although gastropods dominate at the stations with the most extensive shell assemblages the incidence of boring varied between 3 general groups of stations from 5 12 and 30 and tended to be similar for gastropods and bivalves evidence for significant exposure time on the sediment surface alternating with periods of burial was found fewer than one third of all specimens reached adult size suggesting settlement in a marginal habitat in general the most abundant taxa in the living community were also dominant in death assemblages the most abundant relict bivalve crassinella lunulata however which reached densities of 5578 m 2 were never found alive on the shelf this species along with old reworked fragments of coral and bryozoans indicate onshore transport from south of the shelf or from the outer shelf where relict coraline deposits are exposed followed by deposition and downward mixing of shells into the deposit in spite of the overwhelming influence of the physical regime the incidence of boring is comparable to other environments suggesting significant biological control of benthic populations

new paleomagnetic results from basaltic drill cores of the nauru basin western pacific tectonic and magnetostratigraphic implications abstract the voluminous volcanic eruptions in the nauru basin western pacific have long been regarded as important research targets for tectonic history of the pacific plate and for the widespread cretaceous volcanic activity in the western pacific the nauru basin volcanic rocks were recovered at site 462 by deep sea drilling project dsdp legs 61 and 89 where more than 600 m of lavas and sills were drilled thereby making it the deepest penetration into crust of cretaceous age in the pacific ocean for paleomagnetism this section represents a unique possibility for averaging out secular variation to obtain a reliable paleolatitude estimate however previous paleomagnetic studies have only been subjected to alternating field af demagnetization on several core samples thus unable to provide comprehensive understanding on the paleolatitude of the basin the work reported here aims to determine the cretaceous paleomagnetic paleolatitude for the pacific plate and define the magnetostratigraphy for the basaltic sections drilled in the nauru basin a total of 391 basaltic rock samples were carefully re sampled from dsdp sites 462 and 462a stepwise thermal and af demagnetizations have isolated characteristic components in the majority of the samples the most important findings from this study include 1 two normal and one reversed polarity intervals are identified in site 462 and six normal and six reversed polarity intervals are found in site 462a although possible erroneous markings of the opposite azimuth for some reversed polarity cores during the dsdp coring cannot be completely ruled out 2 based on previous radiometric ages the magnetostratigraphic correlations with the geomagnetic polarity time scale gpts indicate that the lower basaltic flow unit in site 462a began to erupt at least before 130 ma no correlation is available for the upper sill unit 3 paleosecular variation for the lower flow unit has been sufficiently averaged out whereas bias may exist for that of the upper sill unit 4 the calculated mean inclination of 50 for the lower flow unit yields a paleolatitude of 30 8 s for the nauru basin at the time of emplacement this value is well to the north of suggested location in plate reconstruction models suggesting that there has been a significant amount of apparent polar wander of the nauru basin and pacific plate since 130 ma in addition the paleolatitude for the nauru basin is 7 further south and the basin s age is more than 10 my older than those of the ontong java plateau ojp which suggest that the volcanic eruptions of the lower flows in the nauru basin are unlikely related to the emplacement of the ontong java plateau

lithoprobe southern vancouver island cenozoic subduction complex imaged by deep seismic reflections reply the lithoprobe seismic reflection project on vancouver island was designed to study the large scale structure of several accreted terranes exposed on the island and to determine the geometry and structural characteristics of the subducting juan de fuca plate in this paper we interpret two lithoprobe profiles from southernmost vancouver island that were shot across three important terrane bounding faults leech river san juan and survey mountain to determine their subsurface geometry and relationship to deeper structures associated with modem subduction the structure beneath the island can be divided into an upper crustal region consisting of several accreted terranes and a deeper region that represents a landward extension of the modern offshore subduction complex in the upper region the survey mountain and leech river faults are imaged as northeast dipping thrusts that separate wrangellia a large mesozoic paleozoic terrane from two smaller accreted terranes the leech river schist mesozoic rock

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

large scale motion between pacific and atlantic hotspots studies of true polar wander tpw the rotation of the solid earth with respect to the spin axis1 have suggested that there has been 10 15 of relative motion over the past 130 myr refs 2 4 in such studies the orientation of the spin axis is recovered from continental palaeomagnetic poles corrected for relative plate motions and compared with a deep mantle reference frame defined by hotspot locations but deducing relative plate motions becomes increasingly difficult for older mesozoic time periods hindering tests of tpw on timescales comparable to those of large scale mantle convection moreover the assumption of hotspot fixity is controversial5 6 we examine here a more direct approach7 8 using palaeolatitudes derived from pacific guyots contrary to predictions from tpw models these data suggest only minor latitudinal shifts of pacific hotspots during the cretaceous period instead of tpw relative motion between the atlantic and pacific hotspot groups9 is required at a velocity of approximately 30 mm yr 1 more than 50 larger than previously proposed5

analysis of long term variations in the geomagnetic poloidal field intensity and evaluation of their relationship with global geodynamics summary the 1167 published cooling unit cu palaeointensity estimates contained in the 400 10 ma portion of the pint global database were rigorously filtered according to accurate age determinations palaeodirectional reliability recognition of polarity and the method of palaeointensity acquisition the remaining 865 estimates group 1 were further filtered to ensure self consistency reducing the data set to 425 estimates group 2 group 1 and 2 data were clustered into temporally and or spatially distinct rock suites rs enabling each part of the record to be assessed for potential biasing by overrepresentation of palaeosecular variation psv the record was segmented according to the distribution of the data rather than using arbitrary time windows to ensure quasi consistent behaviour within each segment differences between these segments clearly indicate that a significant long timescale 10 7 and 10 8 yr variation of the mean geomagnetic poloidal field intensity gpfi occurred during the 400 10 ma period and hence that changing lowermost mantle conditions affect the capacity of the geodynamo to generate a poloidal field both the mean dipole moment and its standard deviation appear to be a function of the range of values each cu may adopt at one particular time this range is itself controlled by the variation of the maximum limit of dipole moment while the value of the minimum limit remains relatively constant tentative support is provided for the recent suggestion that psv may have been reduced during the cretaceous normal superchron cns though more data are needed in the range 120 60 ma to confirm this no conclusive evidence was found to support the suggestion that the gpfi record may be biased towards low or high values by palaeointensity determinations obtained using methods that do not adopt ptrm checks indeed offsets caused by unreliable data in well represented parts of the record are likely to be random and cancel one another out when gpfi variation is analysed at a sufficiently high resolution to allow comparisons with the geomagnetic polarity reversal frequency rf it is not possible to confirm whether the two parameters are anticorrelated decoupled or related in some more complex way however it is clear that gpfi and rf are definitely not positively correlated as has been previously suggested the present database documents sharp increases in gpfi around the onset times of the two recognized superchrons itself implying an anticorrelation the implications for geodynamo and mantle modelling of both an anticorrelation and a decoupling of the geomagnetic parameters are discussed briefly a generic geodynamic model is proposed to explain the relationship between observed longterm changes in gpfi and global geodynamic processes the model predicts that changes in gpfi result from a chain of geodynamic processes extending from crust to core beginning with plate reorganizations at the surface and culminating in increases in the vigour of outer core convection supercontinents are transient surface expressions of such geodynamic processes and provide the potential to test the generic model four time stages are proposed to describe the major long term changes in gpfi since the early devonian 400 350 350 250 250 175

geophysics of the pitman fracture zone and pacific antarctic plate motions during the cenozoic multibeam bathymetry and magnetometer data from the pitman fracture zone fz permit construction of a plate motion history for the south pacific over the past 65 million years reconstructions show that motion between the antarctic and bellingshausen plates was smaller than previously hypothesized and ended earlier at chron c27 61 million years ago the fixed hot spot hypothesis and published paleomagnetic data require additional motion elsewhere during the early tertiary either between east antarctica and west antarctica or between the north and south pacific a plate reorganization at chron c27 initiated the pitman fz and may have been responsible for the other right stepping fracture zones along the ridge an abrupt 8 clockwise rotation in the abyssal hill fabric along the pitman flowline near the young end of chron c3a 5 9 million years ago dates the major change in pacific antarctic relative motion in the late neogene

response to comment on stability of the earth with respect to the spin axis for the last 130 million years by p camps m prevot m daignieres and p machetel

reorganization of miocene deep water circulation in response to the shoaling of the central american seaway 1 the response of ocean circulation to the shoaling of the central american seaway cas is investigated using the massachusetts institute of technology mit ocean general circulation model ogcm in contrast to earlier model studies it is found that significant amounts of deep water are formed in the north atlantic prior to the closure of the cas however the circulation pattern is fundamentally different from the modern ocean in the upper layers of the cas there is a relatively strong geostrophic flow from the pacific to the atlantic controlled by the pressure difference across the seaway however when the cas is deeper than the level of north atlantic deep water nadw outflow a significant amount of nadw passes through the cas to the pacific ocean in the pacific the deep water traverses the basin from east to west in a relatively narrow zonal jet and becomes a southward flowing western boundary current before it joins with the antarctic circumpolar current acc to the south this implies that deep sea sediment records from the miocene pacific ocean could have been influenced by relatively young nadw and provides a new framework for the interpretation of geochemical tracer data diversification of benthic foraminifer fauna suggests that the cas shoaled to a depth of about 1000 m toward the end of the middle miocene this would have prevented the passage of nadw to the pacific and established the modern deep water circulation pattern at that time

accretion and recent deformation of sediments along the northern cascadia subduction zone new multichannel seismic reflection profiles acoustic imagery and swath bathymetric data from the vancouver island continental margin reveal the surface morphology cross sectional geometry and deformation style of this part of the cascadia accretionary prism the incoming 3 to 5 km thick sediment section fails most commonly along landward dipping thrusts that penetrate to or very close to the top of the underlying oceanic crust the faults are listric with approximately circular cross sections and hanging wall sediments are back tilted in a planar manner high near lithostatic pore pressures in the deeper part of the section are inferred from the flattening of the faults near the decollement and from the long distances over which the decollement has propagated seaward the faults dip more steeply at 40 45 near the surface where pleistocene turbidites are displaced similar folds have developed where the turbidites are particularly thick 4 km and near hydrostatic pore pressures are inferred to occur in the turbidite part of the section an increase in pore pressure with depth is expected as a consequence of sedimentation and tectonic loading particularly because the deeper hemipelagic sediments are probably far less permeable than are the overlying turbidites the top of the downgoing juan de fuca plate which defines the base of the accreted sedimentary wedge beneath the margin is well imaged in the new seismic reflection profiles and is further defined by land reflection data seismic refraction and earthquake hypocenters the landward dipping continental backstop to the prism is also well located if these constraints are used for the geometry of the accretionary prism a general balance is found between the present prism volume and the estimated total sediment supply over the approximately 42 m y accretion history this result along with the observation that deformation front faults penetrate most or all of the sediment section suggests that little or no sediment has been subducted since initiation of the present phase of subduction in the eocene application of the critically tapered wedge model of davis and others to the observed prism geometry suggests that high average pore pressures occur in the prism particularly the seawardmost part beneath the lower slope beneath the continental shelf the dip of the subducting slab increases to greater than 11 a dip that according to the critically tapered wedge model is too steep to allow upward growth of an accretionary prism this provides a simple explanation for ongoing subsidence of the tofino sedimentary basin over the older part of the accretionary complex to the southeast the juan de fuca plate dips much more gently beneath the olympic peninsula of northern washington allowing the accretionary prism to grow upward well above sea level to form the olympic mountains

the effect of diagenesis and fluid migration on rare earth element distribution in pore fluids of the northern cascadia accretionary margin analytical challenges in obtaining high quality measurements of rare earth elements rees from small pore fluid volumes have limited the application of rees as deep fluid geochemical tracers using a recently developed analytical technique we analyzed rees from pore fluids collected from sites u1325 and u1329 drilled on the northern cascadia margin during the integrated ocean drilling program iodp expedition 311 to investigate the ree behavior during diagenesis and their utility as tracers of deep fluid migration these sites were selected because they represent contrasting settings on an accretionary margin a ponded basin at the toe of the margin and the landward tofino basin near the shelf s edge ree concentrations of pore fluid in the methanogenic zone at sites u1325 and u1329 correlate positively with concentrations of dissolved organic carbon doc and alkalinity fractionations across the ree series are driven by preferential complexation of the heavy rees simultaneous enrichment of diagenetic indicators doc and alkalinity and of rees in particular the heavy elements ho to lu suggests that the heavy rees are released during particulate organic carbon poc degradation and are subsequently chelated by doc ree concentrations are greater at site u1325 a site where shorter residence times of poc in sulfate bearing redox zones may enhance ree burial efficiency within sulfidic and methanogenic sediment zones where ree release ensues cross plots of la concentrations versus cl li and sr delineate a distinct field for the deep fluids z 75 mbsf at site u1329 and indicate the presence of a fluid not observed at the other sites drilled on the cascadia margin changes in ree patterns the presence of a positive eu anomaly and other available geochemical data for this site suggest a complex hydrology and possible interaction with the igneous crescent terrane located east of the drilled transect

compressive marks from gravel substrate on vertebrate remains a preliminary experimental study abstract lakeshore sites such as cerro de la garita miocene of teruel spain and seneze pliocene of haute loire france yielded fossils with distinct puncture marks these marks were described as punctures surrounded by plastically deformed bone and were proposed to have been caused by compression or trampling on bones against coarse sediment grain when deposited in damp environments a series of experiments was performed to test this hypothesis cow red deer and fallow deer metapodials were compressed by applying a mechanical load on them against a gravel substrate under dry damp environments results confirm that these characteristic puncture marks are associated with compression efforts on bones in wet environments

orbitally paced climate oscillations across the oligocene miocene boundary the late oligocene and early miocene periods some 21 to 27 million years ago have generally been viewed as times of moderate global warmth and ice free conditions yet several lines of evidence suggest that this interval was punctuated by at least one and possibly several episodes of high latitude cooling and continental glaciation1 2 3 here we present stable isotope and per cent coarse fraction data from an equatorial western atlantic deep sea sediment core that provide high resolution records of the climate variability across the oligocene miocene transition 22 5 25 7 million years ago a strong 40 kyr periodicity in the oxygen isotope record is consistent with a high latitude orbital obliquity control on ice volume and temperature orbital influences are also apparent at precession and eccentricity frequencies including a series of 400 kyr oscillations that culminate in distinct maxima at the oligocene miocene boundary about 23 7 million years ago covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the 400 kyr cycles particularly at the oligocene miocene boundary

taphonomic identification of cut marks made with lithic handaxes an experimental study abstract recent experimental studies have developed new diagnostic criteria to differentiate between trampling and cut marks within cut marks these diagnostic criteria have been useful to differentiate between marks made with simple and retouched flakes the present study expands the application of these criteria using a multivariate analysis to discriminate marks created with handaxes from those made with stone tool flakes a discriminant analysis resulted in a selection of specific variables which can successfully differentiate cut marks made with handaxes from those created with retouched flakes in more than 80 of occasions the utility of this analogical taphonomic signature created by handaxes is discussed in the light of their potential value as butchering tools

origin of igneous rocks associated with melanges of the pacific rim complex western vancouver island canada the pacific rim complex prc has previously been interpreted as a late mesozoic subduction complex that formed along the western margin of vancouver island this paper examines a specific aspect of this interpretation that igneous rocks within the prc are fault slices derived from the footwall or hanging wall of a subduction thrust the footwall would have been an oceanic plate and the hanging wall wrangellia a large coherent terrane that underlies most of vancouver island new mapping has shown that the prc comprises a lower mesozoic volcanic unit herein named the ucluth formation and a superjacent sequence more than 2 km thick of lower cretaceous sediment rich melanges within the melanges are large blocks of volcanic and plutonic rocks most of which were derived from the underlying ucluth formation a minor fraction of these blocks cannot be assigned to ucluth they consist of upper jurassic pillow basalt and rare ultramafite fossil ages and chemical data indicate that the bulk of the igneous rocks in the prc as represented by the ucluth formation and blocks derived from the ucluth could not have come from wrangellia nor from a subducting oceanic plate the blocks of upper jurassic pillow basalt do represent fragments of oceanic crust but field relations indicate that they are not fault slices the mudstone matrix surrounding the blocks contains interbeds of green tuff which are shown to be scree deposits derived from the ucluth and the upper jurassic pillow basalts my interpretation is that the prc melanges formed by surficial mass wasting and not by faulting along a subduction thrust furthermore regional geologic relations indicate that the present location of the prc outboard of wrangellia is a result of strike slip faulting during the latest cretaceous or early tertiary this event postdates the formational age of the melanges by at least 45 m y an appendix of chemical analyses locality descriptions sample petrography analytical methods and estimated accuracy is available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document t89 004 2 50 payment must accompany order

true polar wander an analysis of cenozoic and mesozoic paleomagnetic poles a true polar wander path is presented for the past 180 ma tracing the relative motion between the hotspot framework and the geomagnetic poles deduced from worldwide paleomagnetic data a relative displacement of 22 10 is observed the motion between the two reference frames has not been smooth episodes of rapid motion on the order of 80 100 mm yr include the present 65 50 ma 115 85 ma and 180 160 ma periods of slow or little polar motion less than 20 mm yr are observed at 50 5 ma and 160 115 ma the effect of plate motions is removed using morgan s plate motion model a19 this model is tied to a hotspot reference frame assumed to be fixed in the mantle the rotated paleopoles are grouped by ages and then averaged they are found to cluster about points distinct from the north pole as defined by the hotspots these points trace out a path of motion between the rotation axis and the hotspots or mantle this is interpreted as a shifting of the entire earth in response to a change in the principal axes of the moment of inertia of the mantle paleomagnetic poles of the past 7 m y are examined independently this eliminates a dependence on the fixed hotspot hypothesis since plate motions are essentially negligible for this time span there is a deviation of 5 2 between the present geographic north pole and the average of the paleopoles at 5 ma this is too great to attribute to plate motion interpreted as true polar wander the rate of this polar motion is about 1 m y astronomical measurements for the past 80 years have recorded actual motion of the earth s rotational axis up to 1 m y in the direction of eastern canada this agrees in rate with paleomagnetic polar motion of the past 7 m y and in both rate and direction for the past 2 m y

neogene strontium isotope stratigraphy foraminifer biostratigraphy and lithostratigraphy from offshore wells queen charlotte basin british columbia canada strontium isotope ages of foraminifers from early miocene to late pliocene neogene sequences 21 2 3 4 ma are reported for the first time from the queen charlotte basin qcb in queen charlotte

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

paleomagnetism of 122 ma plutons in new england and the mid cretaceous paleomagnetic field in north america true polar wander or large scale differential mantle motion a paleomagnetic study of cretaceous white mountains plutonic complexes in new hampshire and vermont yields high unblocking temperature dual polarity magnetizations in different types of igneous rocks the resulting pole position for three plutons 71 9 n 187 4 e a95 6 9 age 122 5 ma agrees with previously published mid cretaceous poles for north america which together give a mid cretaceous standstill reference pole slightly revised from globerman and irving 1988 at 71 2 n 194 1 e a95 3 7 n 5 studies we argue on the basis of the wide geographic distribution of these studies the variety in tectonic settings and rock types positive reversal tests and an overall reversal pattern consistent with geomagnetic polarity time scales that this mean pole represents the north american mid cretaceous reference field for nominally 36 m y 124 to 88 ma the standstill pole limits to within 4 the motion of the north american plate relative to the earth s spin axis during the same mid cretaceous interval the new england hotspot track 124 ma monteregian hills 122 5 ma cretaceous white mountains and 103 to 84 ma new england seamounts requires 11 4 of north poleward motion of north america in direct conflict with the paleomagnetic standstill a similar 13 discrepancy is independently demonstrated between the spin axis and the tristan da cunha hotspot track on the african plate during the mid cretaceous interval the hotspot spin axis discrepancies ended by 90 ma when it is shown that both atlantic hotspots agree with north american and african dipole paleolatitudes and present day locations nondipole fields are an unlikely explanation of the uniform motion of these two widely separated hotspots with respect to the spin axis leaving as possible interpretations true polar wander and large scale but differential mantle motion the southerly motion of the mid cretaceous louisville hotspot relative to the spin axis is ostensively at odds with what would be predicted under the true polar wander interpretation and points to differential mantle kinematics the motions of the three widely separated mid cretaceous hotspots with respect to the spin axis may be related to the recently proposed increase in global oceanic lithosphere production rates which gave rise to the mid cretaceous superplume

integrated geophysical modelling of terranes and other structural features along the western canadian margin an integrated geophysical data set has been used to develop structural models across the continental margin west of vancouver island canada a modern accretionary complex underlies the continental slope and shelf and rests against and below the allochthonous crescent and pacific rim terranes these terranes in turn abut against the pre tertiary wrangellia terrane that constitutes most of the island gravity and magnetic anomaly data constrained by seismic reflection seismic refraction and other data were interpreted to determine the offshore positions of these terranes and related features iterative 2 5 dimensional forward models of anomaly profiles were stepped laterally along the margin to extend areal coverage over a 70 km wide swath oriented normal to the tectonic features an average model was then developed to represent this part of the margin the pacific rim terrane appears to be continuous and close to the coastline along the length of vancouver island consistent with emplacement by strike

the northern cascadia subduction zone at vancouver island seismic structure and tectonic history the structure and tertiary tectonic history of the northern cascadia subduction zone have been delineated by a series of new multichannel seismic lines acquired across the continental shelf to the

structure petrology and tectonic history of the leech river complex northwest of victoria vancouver island the leech river complex 45 km northwest of victoria consists of metamorphosed pelitic rocks sandstone and minor volcanic rocks chert and conglomerate of probable late jurassic to cretaceous age the assemblage experienced two similar deformational events during which regional shortening induced macroscopic east plunging folds and related coaxial mesoscopic linear structures parasitic folds and axial plane cleavages fragmentation along the developing cleavages disrupted layering and eventually led to transposition during both events regional progressive low pressure greenschist to amphibolite facies andalusite staurolite biotite metamorphism began during the first deformation and extended into the waning stages of the second intrusion of composite felsic sills was synchronous with deformation and metamorphism which concluded about 39 41 ma according to k ar data the leech river fault which forms the southern boundary of the complex is a zone of two to four subparallel faults all are re

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

a new method for the quantitative analysis of cutmark micromorphology abstract cutmarks found on the fossilised bones of butchered animals provide direct evidence for the procurement of meat through technological means as such they hold some of the oldest available information on cognitive ability and behaviour in human evolution here we present a new method that allows a three dimensional reconstruction of cutmark morphology and the quantification of profile parameters we have tested this new technique on cutmarks that were experimentally inflicted on a pig rib using a steel knife and an un retouched flint flake at different angles the method allows for the cross sectional shape the sharpness and depths of the resulting cutmarks to be quantified the data show that knife mark sections are characterised by a v shape or shape depending on the inclination of the knife cutmarks produced with the flint flake were less clearly defined and generally less sharp than those produced by the knife we discuss the method s potential to provide new information on butchery technique and cognitive abilities developed by the human lineage from the earliest tool using hominins through to modern homo sapiens

foraminiferal response to the petm recorded in the sw tarim basin central asia abstract the paleocene eocene p e boundary interval is the most significant climatic transition during the cenozoic when the petm paleocene eocene thermal maximum caused rapid warming and severe fluctuation of the earth system especially in marine settings the sw tarim basin represents a distal branch of the ne tethys exposing paleocene to eocene successions that include the qimugen formation and provide optimal section for investigating the p e boundary transition by detail field based lithological records and the planktonic and benthic foraminiferal assemblage analysis the p e boundary was redefined within the black mudstone bed of the qimugen formation the planktonic foraminiferal assemblages recorded in the qimugen formation may be subdivided into four biozones including bioevents of globanomalina pseudomenardii globanomalina luxorensis and pseudohastigerina wilcoxensis planktonic foraminiferal turnover is marked by the cool water subbotinids disappearance give way to warm water muricate taxa co varying with the gradual disappearance of benthic foraminifera the foraminiferal assemblages together with other identified microfossils suggest a shallow marine environment in which transgressions related to the sea level fluctuation of the tethyan domain took place in the paleocene to eocene boundary interval

cenozoic ichthyolith biostratigraphy tofino basin british columbia five new late eocene pliocene ichthyolith zones are defined based on indigenous faunal occurrences in strata that outcrop along western vancouver island and samples from six offshore tofino basin wells five new interval zones are each defined based on distinct transported ichthyolith assemblages results are correlated within the framework of established cenozoic west coast and arctic foraminifer zones and ichthyolith occurrences in deep sea core samples and cretaceous queen charlotte group and nanaimo group strata of coastal british columbia the use of multiple data sets was important to interpret complex active tectonic margin sedimentation and structures the integrated ichthyolith and foraminifer biostratigraphy allowed an interpretation of well log data and lithology reports also we reassessed previous offshore seismic data evaluated fossil preservation and thermal alteration and distinguished transported from indigenous ichthyolith occurrences these data allowed a reinterpretation of tectonic segments and associated strata of the pacific rim and crescent terranes and the cascadia accretionary complex onshore and offshore vancouver island tectonically active phases during the eocene and oligocene early miocene resulted in transport of cretaceous to eocene ichthyoliths from structural highs to lows indicating proximity of the pluto i 87 and zeus d 14 wells to the tofino fault between the pacific rim and crescent terranes and suggesting derivation with coeval hesquiat peninsula strata an unconformity above the eocene crescent formation volcanics in prometheus h 68 and zeus d 14 wells is correlated with the pluto i 87 and apollo j 14 well stratigraphy an upper miocene unconformable surface coincides with accretion and uplift of the cascadia accretionary complex

eocene deep sea communities in localized limestones formed by subduction related methane seeps southwestern washington densely populated communities of soft bottom dwelling taxa similar to those found today along subduction zones off the coasts of japan and oregon have been discovered in very localized deep water limestones of late middle to late eocene age along the southwestern margin of washington subduction was prevalent in this area during this time and compressive forces squeezed subsurface methanerich waters onto the ocean floor where opportunistic bivalves especially modiolus calyptogena and thyasira vestimentiferan tube worms serpufid tube worms siliceous sponges very small limpets trochid and turbinid archaeogastropods and other macrobenthos colonized these assemblages are the earliest recorded biologic communities formed in response to methane seeps in subduction zones

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

paleomagnetism of mesozoic kimberlites in southern africa and the cretaceous apparent polar wander curve for africa including those previously published good paleomagnetic data have been obtained from 48 of 51 sites in 28 separate kimberlites radiometric dates by one or more methods are available for 17 of these bodies and range from 81 to 145 ma with maxima around 90 and 120 ma these ages correlate with geochemical contrasts distinguishing what have been designated group i younger and ii older kimberlites smith et al 1985b stable magnetization appears to be associated with magnetite developed deuterically after emplacement but in most bodies secular variation has not been completely averaged in the remanence acquired the distribution of vgps calculated is distinctly but not sequentially streaked yet correlates broadly with the older and younger petrochemical types mean north poles calculated on this basis yield kp1 n 14 81 100 ma 64 1 n 226 1 e a95 5 2 and kp2 n 10 113 145 ma 47 6 n 269 9 e a95 9 7 with the exception of one undated pipe meltonwold which was not included in the averages and the melilititic male fissure at swartruggens in group ii average all the kimberlites sampled are normally magnetized including these new data 10 of 17 published african cretaceous poles meet acceptability criteria specified and define an apparent polar wander apw curve from 130 to 75 ma the curve appears to consist of two segments trending latitudinally before 100 ma and meridionally thereafter the latter trend is evident even in the distribution of the individual kp1 poles and may be related to the true polar wander speculated by gordon and livermore 1987 to have occurred in that interval

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

arctic dinoflagellate migrations mark the strongest oligocene glaciations here we report on mid oligocene globally synchronous arctic dinoflagellate migration events calibrated against chron c9n we show that sudden appearances and marked abundance increases of the arctic taxon svalbardella at lower and middle latitudes coincide with the oi 2b benthic d 18 o glacial episode dated as ca 27 1 ma these unprecedented migrations are taken to indicate anomalously strong surface water cooling during oi 2b time in turn associated with strong concomitant antarctic ice sheet growth and sea level lowering we estimate the duration of these unique svalbardella migrations and the associated episode of profound cooling as 500 k y our records suggest a close link between this distinct oligocene glaciation episode strong sea level fall and the classic lower upper oligocene or rupelian chattian boundary dating this boundary as ca 27 1 ma

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time

paleomagnetic evidence for motion of the hawaiian hotspot during formation of the emperor seamounts the bend in the hawaiian emperor chain is the best example of a change in plate motion recorded in a fixed hotspot frame of reference alternatively the bend might record primarily differences in motion of the hawaiian hotspot relative to the pacific lithosphere new paleomagnetic data from the emperor chain support the latter view althouth the rate of motion is difficult to constrain because of uncertainties posed by true polar wander and limited sampling of the chain the best available paleomagnetic data suggest pacific hotspots may have moved at rates comparable to those of lithospheric plates 30 mm yr 1 in late cretaceous to early tertiary times 81 43 ma if correct this requires a major change in how we view mantle dynamics and the history of plate motions in the early to mid cretaceous 128 95 ma hotspots in the atlantic moved at similar rates these episodes during which groups of hotspots appear to move rapidly are separated by times of much slower motion such as the past 5 m y

crustal structure of the cascadia subduction zone southwestern british columbia from potential field and seismic studies the northern cascadia subduction zone is a region of convergence between the oceanic explorer and northern juan de fuca plates and the continental north american plate potential field and new seismic reflection data coupled with previous seismic results and geology enable derivation of a series of density magnetic susceptibility cross sections and a block density model from the ocean basin to the volcanic arc from 2 5 and 3 dimensional interpretations the lateral extent and thickness of the accreted wedge vary significantly along the zone the narrow metasedimentary pacific rim terrane lies immediately west of wrangellia and extends the length of vancouver island consistent with its emplacement by strike slip faulting following the accretion of wrangellia the ophiolitic crescent terrane is a narrow slice lying seaward of the pacific rim terrane but not extending northward beyond the juan de fuca plate in this region the crescent terrane was emplaced in a strike slip or obliquely convergent style

mid cretaceous polar standstill of south america motion of the atlantic hotspots and the birth of the andean cordillera article i nfo a paleomagnetic study on mid cretaceous rocks from the san bernardo foldbelt patagonia yields high unblocking temperature and high coercivity magnetizations the results indicate absence of relative vertical axis rotations during development of the foldbelt with the associated pole position being highly concordant with coeval poles from brazil and patagonia taken together mid cretaceous poles derived from studies in widely distributed localities provide supportive evidence that south america was essentially motionless with respect to the paleomagnetic axis from ca 125 to at least 100 ma the paleolatitudes of south america are not consistent with the occurrence of mid cretaceous true polar wander suggesting that the previously observed discrepancy between the paleomagnetic and the fixed indo atlantic hotspot reference frames be related to motion of the atlantic hotspots in agreement with this the discrepancy is diminished by half when the cretaceous poles of the americas are observed in a moving hotpots reference frame with the residual offset being comparable to that seen for younger time intervals the south american paleopoles and the moving hotspot framework provide a kinematic scenario that allows relating the extensional tectonics in the early stages of andean evolution with episodic divergence between the trench and the continental interior likewise the beginning of contractional events correlates with model predicted westward acceleration of south america in the late cretaceous suggesting that the continent episodically overrode the andean trench by those times we argue that this change in andean tectonic regime is associated to major plate reorganization at ca 95 ma

orbitally induced climate and geochemical variability across the oligocene miocene boundary to assess the influence of orbital scale variations on late oligocene to early miocene climate and ocean chemistry high resolution 5 kyr benthic foraminiferal carbon and oxygen isotope and percent coarse fraction time series were constructed for ocean drilling program site 929 on ceara rise in the western equatorial atlantic these time series exhibit pervasive low to high frequency variability across a 5 myr interval 20 5 25 4 ma the records also reveal several large scale secular variations including two positive 1 6 oxygen isotope excursions at 22 95 and 21 1 ma suggestive of large but brief glacial maxima mi 1 and mi 1a events of miller et al 1991 and a long term cyclical increase in the carbon isotopic composition of seawater shift of 1 52 that reaches a maximum coincident with peak 18o values at 22 95 ma lower resolution 25 kyr records constructed from benthic and planktonic foraminifera as well as bulk carbonate at a shallower site on ceara rise site 926 for the period 21 7 24 9 ma covary with site 929 18o values reflecting changes in antarctic ice volume likewise covariance among carbon isotopic records of bulk sediment benthic and planktonic foraminifera suggest that the low frequency cycles 400 kyr and long term increase in 13c values represent changes in the mean carbon composition of seawater co2 the time series presented here constitute the longest most continuous and highest resolution records of pre pliocene climate and oceanography to date the site 929 carbon and oxygen isotope power spectra show significant concentrations of variance at 400 100 and 41 kyr demonstrating that orbitally induced oscillations have been a normal characteristic of the global climate system since at least the oligocene including periods of equable climate and times with no apparent northern component water production

cut marks and raw material exploitation in the lower pleistocene site of bell s korongo bk olduvai gorge tanzania a geometric morphometric analysis the lower pleistocene site of bell s korongo bk in olduvai gorge tanzania has been a key site for the study of the origin of human behaviour the lower archaeological levels of bk are characterized by anthropogenic activity related to the exploitation of megafauna elephant hippopotamus sivatherium and smaller game zebra wildebeest and antelopes these remains display a high frequency of cut marks the exceptional state of preservation of the bk fossil assemblage has allowed a wide range of different analyses that among other things detected the use of quartzite in butchering activities through the study of cut marks following up previous analyses this paper presents the study of a series of cut marks from the bk faunal assemblage using a 3d geometric morphometric methodological approach in order to determine the mineralogical properties of the quartzite used at the site bk cut marks are compared with experimentally produced cut marks using 9 mineralogically different quartzite types from olduvai gorge this comparative analysis provides valuable hints about the exact nature of the raw materials used in butchering activities the results presented here identify a preferential use of quartzite with a finer granular composition suggesting that hominin populations were already selecting the best raw materials for their use in specific activities 1 3 mya