identification et distribution des grandes masses d eau dans les mers du labrador et d irminger the main deep water masses present at the time of the css hudson cruises in labrador and irminger seas in june 1990 and october november 1991 have been identified using characteristic temperatures t and salinities s the purpose of this study was to establish the transfer functions between micropaleontological assemblages of top sediments and thermohaline characteristics of water masses the water mass at the top of the labrador sea labrador sea water lsw is formed after intense movements of winter convection in the first 900 m depth of the water column below that depth the lsw parameters reach a double minimum s 34 80 and t 2 9 c only the sediments located on the continental slopes of greenland and labrador between depths of 500 and 1500 m are in contact with the lsw below the lsw the superior fraction of the north east atlantic deep water neadw1 is characterized by a temperature maximum 3 3 c and as such is distinguishable from the inferior fraction neadw2 the latter is ch

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

reconstruction of palaeoenvironmental conditions of the vaca muerta formation in the southern part of the neuquen basin tithonian valanginian evidences of initial short lived development of anoxia abstract the vaca muerta formation is a famous source rock being largely present in argentina the formation was examined in the southern part of the neuquen basin through clay mineral assemblage composition as well as organic and inorganic geochemical characteristics in total 259 samples were analyzed on both sides of the huincul arch major e w structure that divided the southern part of the basin into two depocentres south to this structure picun leufu area the total organic carbon content toc can reach 20 but is generally ranging from 0 1 to 6 to the north covunco area average toc does not exceed 0 5 clay mineral assemblages indicate an evolution of the sources of clastic supply through time in response to evolving weathering erosion at the regional scale redox sensitive trace element distribution shows that the particulate iron shuttle process operated with an initially euxinic depositional environment that evolved rapidly to oxygenated seawater and suboxic sediments our results suggest an episodically restricted circulation pattern that occurred at the beginning of the deposition of the vaca muerta formation highest toc content

clay mineral signature of the nw atlantic boundary undercurrent abstract surface sediments were sampled along 2 transects across the iceland and irminger basins and in the labrador sea clay mineral assemblages deduced from x ray analyses of the carbonate free

storm induced concentration of sulfurized marine origin organic matter as a possible mechanism in the formation of petroleum source rock abstract black shales though laminated are not systematically synonymous with quiet conditions of deposition a number of papers report about black shales yielding sedimentary structures echoing relatively high hydrodynamic conditions here we examine two sedimentary sequences pertaining to the late jurassic argiles de ch tillon formation of the boulonnais area northernmost france each of them including a meter thick black shale horizon the two laminated black shales contain sulfurized i e organic s rich organic matter reaching a maximum of 9 however some differences set the two black shales apart the lower one was deposited under calm suboxic to anoxic bottom water conditions the classic way the upper black shale was deposited under oxic agitated bottom water conditions not compatible with stable sulfidic conditions required for organic matter sulfurization the upper black shale experienced hydrodynamically induced concentration of sulfurized recalcitrant organic matter of marine origin the sulfurized organic matter could be preserved and quantitatively accumulated owing to its non putrescible nature leading to the formation of a potential hydrocarbon source rock the association of pyrite inclusions with sulfurized organic matter probably modified the hydrodynamic behavior of organic particles the storm induced remobilization and concentration of sulfurized organic matter implies that the sulfurization factory operated in proximal shallow environments such as estuaries mud flats or mangrove environments such a model is in agreement with findings from modern coastal shelf environments notably mangroves and fully transposable to many other sedimentary situations of any geological time period

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

morphology and structure of a landslide complex in an active margin setting the waitawhiti complex north island new zealand article i nfo multi scale gravitational instabilities are widespread in the coastal ranges of the north island of new zealand we document here a detailed analysis of the waitawhiti landslide complex located in the core of the tawhero syncline and investigate the potential landslides triggering factors in the area four contiguous large slides form the waitawhiti complex these slides involve fine grained miocene sandstones and massive fractured siltstones sliding occurs mostly along nearly horizontal strata all slides are bounded laterally and or distally by deep incised valleys three gas seeps evidencing thermogenic gas release have been discovered in the vicinity of the slides we propose that river incision continuously removing distal buttresses is the main destabilizing factor in the area however additional factors such as tectonic activity and intense rainfall cannot be excluded we also propose that fluid overpressure reducing the effective shear strength at the base of low permeability layers may have influenced the triggering of landslides in the waitawhiti area

implications of a connection between clay mineral variations and coarse grained debris and lithology in the central norwegian greenland sea abstract a sediment core from the central norwegian greenland sea has been studied for sedimentary features and clay mineral composition during numerous events within isotope stage 6 relatively high contents of kaolinite as well as a distinctive dropstone association originating from the barents shelf were rafted to the southwest by rapidly melting ice causing the formation of dark diamictons the strong variations in the smectite content in glacial periods were controlled mainly by ice transport rather than by current transport the main source area is the shelf of the faeroe islands

latitudinal control of astronomical forcing parameters on the high resolution clay mineral distribution in the 45 60 n range in the north atlantic ocean during the past 300 000 years the clay mineralogy of four 5 5 to 13 5 m long cores sampled between 45 and 60 n in the north atlantic ocean has been investigated at high latitudes within a well constrained chronostratigraphic scale cross correlation spectral analyses have been performed on both clay mineral and 18o planktonic records detrital clay minerals display strong signals which are coherent with the 18o record within the three main milankovitch frequency bands eccentricity obliquity and precession the climatic control on clay mineral sedimentation largely depends on the latitudinal location of the sediment cores the 100 000 year signal occurs as a uniformly acting factor whereas the 41 000 year signal dominates clay sedimentation at high latitudes and the 23 000 year signal dominates at midlatitudes we suggest that the latitudinal variations of the orbital forcing on the detrital clay mineral distribution in the north atlantic ocean not only result from climatic control of the intensity of physical and chemical weathering but also from latitudinal control on the detrital clay supply linked to influences of the high latitude wind driven and midlatitude ocean driven transportation processes respectively

multiproxy approach for holocene paleoenvironmental reconstructions from microorganisms testate amoebae and foraminifera and sediment analyses the infilling of the loire valley in nantes france foraminifera and testate amoebae are jointly used with sediment characteristics sediment size calcium carbonate c h n and s proportions and clay mineralogy to reconstruct the holocene sediment infilling of the loire estuary nantes france the results reveal the infilling of the loire valley during the holocene deposited on the hercynian substratum the first deposits are made of gravels with rare associated fauna this corresponds to the gravel lag usually present as basal deposits in the river course the clay mineralogy indicates an erosion of the substratum then from 8850 to 5850 cal yr bp estuarine fauna settled in a laminated sediment that alternates between clay and sand the smectite associated with kaolinite and illite suggests increased input from the sevre nantaise river the fauna progressively shifts from estuarine to marine indicating a rise in the sea level from 5850 cal yr bp the pace of the sea level rise slowed and channels migrated implying intense erosion after 2100 cal yr bp the fauna was dominated by testate amoebae indicating a continentalization of the environment the top samples reflect recent human activity and urbanization

an ice shelf mechanism for heinrich layer production the effect of an ice shelf in the labrador sea on ice rafted sediment delivery to the glacial north atlantic is investigated using a finite element numerical model of ice shelf flow discharge into the shelf from hudson strait creates a thick central core extending downstream into the shelf that is flanked by relatively thin ice melting at the base of the deep keel would produce cool fresh water which would rise to refreeze along the keel s flanks debris deposited by melting deep central ice could create the heinrich layers observed in the labrador sea while the debris rich ice protected by basal freezing on the flanks of the thick ice plume could transport sediment over large distances heinrich layers would be produced solely by external climate forcing without changes in ice sheet flow the mechanism is plausible if the lifetime of the ice shelf is about 1000 years

smectite composition as a tracer of deep circulation the case of the northern north atlantic abstract the link between smectite composition in sediments from the northern north atlantic and labrador sea and deep circulation is being further investigated through detailed studies of the x ray pattern of smectites and cation saturations this allows clear distinction of dominant terrigenous sources associated to the main components of the modern western boundary undercurrent time variations of smectite characteristics in two piston cores from the inlet and outlet of the western boundary undercurrent gyre in the labrador sea indicate 1 a more southern circulation of north east atlantic deep water during the late glacial 2 a step by step transition to the modern pattern of deep circulation during the late glacial holocene transition with intensification of north east atlantic deep water and davis strait overflow 3 an expansion of davis strait overflow and labrador sea water circulation in relation to ice surges and deposition of detrital layers 4 an intensified circulation of north east atlantic deep water during the younger dryas and 5 a very recent increased influence of denmark strait overflow water beginning between 4 4 and

the holocene sedimentary regime in the northern mid atlantic ridge region the holocene 10 000 yr b p mid atlantic ridge sedimentary regime between 45 n and 65 n has been investigated by examination of sediments from 70 cores smectite chlorite and quartz 87sr 86sr isotopes and ree have been used as conservative tracers to provide source identification and to calculate accumulation rates the entire holocene sedimentary regime in this part of the atlantic can be attributed to particle fluxes from two sources the icelandic and north american systems two main transport mechanisms are identified 1 particles derived from the icelandic system have been transported southwards as far as 45 n by bottom currents 2 material coming from north america is mainly transported by the aeolian regime at 45 n the windborn accumulation rate is estimated to be 0 5 g cm 2 kyr 1 which is identical to the accumulation rate of bottom advected material from iceland finally a diagnostic model for the north atlantic sedimentary regime is proposed

wisconsin holocene paleoenvironment of the bering sea evidence from diatoms pollen oxygen isotopes and clay minerals abstract a core from the southeastern bering sea contains a depositional record of the wisconsin glacial interval and the holocene four lithologic units show distinctive changes in diatom species palynomorphs oxygen isotopes in diatom silica and clay minerals unit 4 the oldest probably represents the glacial advance of the early wisconsin and records extensive sea ice cover and a soggy herbaceous tundra on the exposed continental shelf unit 3 represents the stades and interstades of the middle wisconsin including an early period of high seasonal variability and a later period with expansion of winter sea ice in the basin and of tundra onshore unit 2 represents the late wisconsin glacial maximum and subsequent deglaciation with a tundra covered shelf sea ice cover increased to a maximum during which the surface waters were probably covered by sea ice throughout the year subsequent to the sea ice maximum the isotope ratios record a major meltwater event unit 1 represents the holocene with expansion of shrub tundra or scrub forest in the coastal upland and waters of increased temperature and salinity in the bering sea

barium in sediments off northwest africa a tracer for paleoproductivity or meltwater events 1 high resolution down core analyses of the solid phase content of total barium batot and total organic carbon toc back to 25 kyr b p were performed on a gravity core from the upper continental slope off cape yubi morocco the observed discrepancy between the two potential paleoproductivity proxies batot and toc initiated supplementary examinations of the pore water the geochemistry of the clay fraction x ray diffraction analyses and the application of a sequential ba extraction method of selected samples additionally we analyzed down core samples of the planktonic foraminifera turborotalita quinqueloba and globorotalia inflata for their ba ca ratios these analyses which were performed for the first time on these species were used to reconstruct past oceanic ba concentrations we suggest that in the study area which is characterized by high accumulation rates the preserved toc content is a valuable proxy for past primary productivity whereas the solid phase batot contents appear to be affected by other mechanisms and factors peaks of total barium content in the clay fraction and of ba ca ratios in the planktonic foraminifera shells found during the younger dryas and the heinrich 1 event are likely to result from increased meltwater influx into the northern north atlantic we suggest that ba enriched meltwater was transmitted by the eastern boundary current system from higher latitudes to the region of the canary islands total barium contents of the clay fraction batot clay and ba ca in planktonic foraminifera shells seem to be reliable proxies for this discharge of meltwater

downcore variations of sedimentary detrital 238 u 232 th ratio implications on the use of 230 th xs and 231 pa xs to reconstruct sediment flux and ocean circulation excess 231 pa and 230 th 231 pa xs and 230 th xs can be used to reconstruct past oceanic sedimenta tion 230 th normalized flux and circulation changes 231 pa 230 th xs 0 hereafter pa th these quantities are determined by computing the detrital and authigenic contributions from bulk sediment measurement the method relies on the use of a chosen constant value of the detrital 238 u 232 th activity ratio hereafter u th det in this study we have extracted the detrital fraction of the sediments from north atlantic deep sea core su90 08 43803 0 1n 30802 0 5w 3 080 m and determined its u th det value over the last 40 ky we find that u th det varied significantly through time with a minimum value of 0 4 during the holocene and a maximum value of 0 7 during the last glacial maximum lgm the sensitivity of sedimentary 230 th normalized flux and pa th is tested for our study site and for other north atlantic sites we show that the sensitivity is highly dependent on the core location and its terrigenous material supply the 230 th normalized flux and pa th signals are very robust in cores with low detrital contributions whereas they are very sensitive to u th det changes in cores with higher detrital contribution in the latter case changes in 230 th normalized flux and pa th due to the choice of a constant u th det can largely exceed the uncertainty on the 230 th normalized flux and pa th inducing potential biases in the amplitude and temporal variability of reconstructed sedimentation and ocean circulation changes

provenance of freshwater pulses in the gulf of mexico during the last deglaciation during the last deglaciation the decaying laurentide ice sheet lis delivered huge volumes of meltwater toward the gulf of mexico the present investigation of clay mineralogy and grain size characteristics of terrigenous sediments deposited in the orca basin gulf of mexico offers a unique opportunity to link the marine record of these meltwater floods with the reconstructed continental glacial history and the modeled drainage patterns five peculiar sedimentary levels characterized by high smectite content and low caco3 content were identified and occurred simultaneously with major meltwater floods according to recently published clay mineral distribution maps for north america these results help to pinpoint the southwestern margin of the lis as a main contributor to most of the meltwater discharges in addition the peculiar mineralogical composition illite and chlorite rich of the sediments characterizing the meltwater episode associated with heinrich event 1 suggests a provenance from the great lakes area supporting the interpretation of destabilization of the lis southeastern margin during this event decreased terrigenous contribution associated with changing provenance of sediments after 12 9 cal ka bp suggests strong modifications of the continental hydrography in relation to lake agassiz history and changes in the morphology of mississippi delta due to rising sea level

the impact of african aridity on the isotopic signature of atlantic deep waters across the middle pleistocene transition abstract a high resolution analysis of benthic foraminifera as well as of aeolian terrigenous proxies extracted from a 37 m long marine core located off the mauritanian margin spanning the last 1 2 ma documents the possible link between major continental environmental changes with a shift in the isotopic signature of deep waters around 1 0 0 9 ma within the so called mid pleistocene transition mpt time period the increase in the oxygen isotopic composition of deep waters as seen through the benthic foraminifera 18o values is consistent with the growth of larger ice sheets known to have occurred during this transition deep water mass 13c changes also estimated from benthic foraminifera show a strong depletion for the same time interval this drastic change in 13c values is concomitant with a worldwide 0 3 decrease observed in the major deep oceanic waters for the mpt time period the phase relationship between aeolian terrigeneous signal increase and this 13c decrease in our record as well as in other paleorecords supports the hypothesis of a global aridification amongst others processes to explain the deep water masses isotopic signature changes during the mpt in any case the isotopic shifts imply major changes in the end member 18o and 13c values of deep waters

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

biometry of emiliania huxleyi and its biostratigraphic significance in the eastern north atlantic ocean and western mediterranean sea in the last 20 000 years abstract a detailed biometric study of coccoliths of emiliania huxleyi has been performed on 34 samples from three sediment cores of the north atlantic ocean and the western mediterranean sea su90 08 m39029 7 and md95 2043 all three cores contain the last glacial interglacial transition marine isotopic stages 1 2 enabling us to study in detail the morphology of this taxon during this period of change one hundred coccoliths of e huxleyi were randomly chosen in each sample distal shield length and width measurements were performed on each of the individuals selected the data show that e huxleyi specimens larger than 4 m are frequent in glacial samples and that these larger forms decreased sharply in abundance during the deglaciation and holocene smaller forms are more abundant in this latter group of samples the decrease in larger forms seems to be time transgressive since it is recorded between 12 and 11 kyr cal bp in southern locations alboran sea and gulf of cadiz and around 8 4 kyr cal bp in the central north atlantic scanning electron microscope analyses indicated that the two forms have the same degree of calcification and hence this parameter should not be used in taxonomic classifications we suggest that the larger coccoliths belong to a cold water variety of e huxleyi which can be distinguished from the small coccolith variety in light microscope analyses by its distal shield length the decrease in the abundance of this larger variety during the deglaciation period could be used as a biostratigraphic event in the north atlantic and mediterranean areas

iron availability as a dominant control on the primary composition and diagenetic overprint of organic matter rich rocks iron is known to stimulate surface ocean productivity as well as intervene with bacterially mediated processes of organic matter remineralization during early diagenesis in this paper we examine the influence of iron supply on the geochemistry trace metals 34s organic matter of sedimentary rocks deposited in a clastic dominated marine ramp environment to this end we studied two late jurassic formations of the boulonnais area north france both formations were deposited under quite similar conditions but they differ in the reactive iron supply they received only one of the two formations was affected by the particulate iron shuttle process our results indicate that 1 the iron shuttle may be recorded through concomitant enrichments in p mo as and sb 2 a limited reactive iron supply will allow the sulfurization of organic matter even in a context of moderate productivity thus sulfurization can be a factor favoring a noticeable accumulation of organic matter iron may thus be an important agent in the c cycle

late quaternary stage 2 and 3 meltwater and heinrich events northwest labrador sea two major meltwater events are documented in cores from the nw labrador sea one occurred ca 20 000 14c yr b p in association with deposition of a major detrital carbonate unit both prior to and after this event 18o values of near surface planktonic foraminifera were 4 5 indicating fully enriched glacial values a younger event ca 14 000 14 c yr b p is characterized by a dramatic change in 18o from 4 5 to 2 0 and coincided with the retreat of ice from the outer se baffin shelf possibly into hudson strait these meltwater events coincide with heinrich h layers 1 and 2 from north atlantic sediments the 14 000 14c yr b p meltwater event indicates that the eastern margin of the laurentide ice sheet also underwent rapid retreat at approximately the same time as other ice sheet margins around the ne north atlantic a third major detrital carbonate event at the base of hu87 033 009 possibly correlative with heinrich layer 3 occurred ca 33 960 675 14 c yr b p however this is older than the accepted date for h 3 of 27 000 14c yr b p and may be h 4

shelf erosion and glacial ice proximity in the labrador sea during and after heinrich events h 3 or 4 to h 0 as shown by foraminifera

dredging and canal gate technologies in portus the ancient harbour of rome reconstructed from event stratigraphy and multi proxy sediment analysis ancient harbours are rich archives of human environment interaction however dating harbour deposits and correlating their stratigraphy is a major challenge because of typically high sedimentation rates over short periods and possible curative dredging events portus the maritime harbour of rome at the height of the roman empire was a port complex composed of basins and canals connecting the commercial harbour to rome via the tiber river sediment core cps1 in the narrowest of these canals canale traverso is located centrally in what was the capital city s commercial hub and contains a continuous harbour depositional record with average sedimentation rates greater than 1 cm per year here we use piston coring high resolution core scanning and a multi proxy sediment analysis including for the first time paleo and rock magnetism and bulk and clay mineralogy in order to overcome the problems of dating harbour deposits and correlating their stratigraphy the method allowed precise identification of major reworked events including a dredged deposit and a hyperpycnal deposit which improve the chronostratigraphy and water depth reconstruction and sheds light on harbour technologies at the height of the roman empire a debris layer with abundant ceramic fragments and rocks marks the decommissioning of canale traverso and provides a new chronostratigraphic marker at portus multi proxy riverine input signatures point to the possible use of canal gate technology for water flow management

mineralogical kar and 87sr 86sr isotope studies of holocene and late glacial sediments in a deep sea core from the northeast atlantic ocean abstract fine grained silicate fractions m and 2 16 m of holocene and late glacial sediments in a deep sea core from the northeast atlantic ocean 47 30 n 19 30 w have been analysed by x ray diffraction k ar and sr isotopic methods during the holocene the k ar apparent ages and the 87 sr 86 sr ratios of the clay size minerals averaged 436 22 13 ma and 0 72638 0 00051 respectively the k ar values essentially reflect the high 40 ar contribution from the detrital mica in binary smectite mica mixtures where smectite is a low potassium and tertiary quaternary component higher k ar age value up to 569 124 112 ma are determined for the coarser 2 16 m fractions which contain in addition to mica other detrital k bearing phases amphibole k feldspar and plagioclase an important change in the mineralogical composition and the k ar ages is displayed by the silicate fractions of a thin layer of ice rafted detritus located at the termination of the last glaciation their k ar apparent ages increase to 773 933 ma and correspond to an increase of the detrital supply amphibole mica and feldspar from the precambrian terrains of north america or greenland and a dilution or a decrease of the input of basaltic material smectite oligoclase from the region of iceland

abrupt changes in marine conditions sunneshine fiord eastern baffin island nwt during the last deglacial transition younger dryas and h 0 events

simulation of field injection experiments in heterogeneous unsaturated media using cokriging and artificial neural network 1 simulations of moisture flow in heterogeneous soils are often hampered by lack of measurements of soil hydraulic parameters making it necessary to rely on other sources of information in this paper we develop a methodology to integrate data that can be easily obtained for example initial moisture content i bulk density and soil texture with data on soil hydraulic properties via cokriging and artificial neural network ann based pedotransfer functions the method is applied to generate heterogeneous soil hydraulic parameters at a field injection site in southeastern washington state stratigraphy at the site consists of imperfectly stratified layers with irregular layer boundaries cokriging is first used to generate three dimensional heterogeneous fields of bulk density and soil texture using an extensive data set of field measured i which carry signature about site heterogeneity and stratigraphy soil texture and bulk density are subsequently input into an ann based site specific pedotransfer function to generate three dimensional heterogeneous soil hydraulic parameter fields the stratigraphy at the site is well represented by the estimated pedotransfer variables and soil hydraulic parameters the parameter estimates are then used to simulate a field injection experiment at the site a relatively good agreement is obtained between the simulated and observed moisture contents the spatial distribution pattern of observed moisture content as well as the southeastward moisture movement is captured well in the simulations in contrast to earlier work using an effective parameter approach yeh et al 2005 we are able to reproduce the observed splitting of the moisture plume in a coarse sand unit that is sandwiched between two fine textured units the simple method of combining cokriging and ann for site characterization provides unbiased prediction of the observed moisture plume and is flexible so that additional measurements of various types can be included as they become available

environmental control on a land sea transitional setting integrated sedimentological geochemical and faunal approaches because of their location at the interface between sea and emerged lands so called transitional environments are characterized by strong spatial and temporal variability in terms of sedimentological physicochemical and geochemical parameters an increasing number of studies put forward the use of bioindicators as a tool for environmental monitoring however the sensitivity to these environmental parameters is commonly tested separately even though it is known that interactions are numerous within this complex ecosystem an integrated methodological study was conducted in lake varano italy on the basis of 45 spatially distributed samples throughout the area and selected environmental parameters trace elements organic matter clay mineral assemblages grain size of sediment and water characteristics four factors are identified the lake varano ecosystem is predominantly influenced by terrigenous inputs first order factor the clastic fractions of the sediments supply a large range of trace elements occasionally in relatively high concentrations under such circumstances despite occasionally exceeding of threshold limits the trace element pollution can generally be ruled out the organic content combined with depth is the second key factor in lake varano the organic content is high and may lead to seasonal eutrophication as a third order factor although only analyzed once oxygen orp salinity and ph gradients show that foraminiferal diversity is positively influenced by more saline conditions the fourth order factor is the sediment size to conclude this paper illustrates the interest in and need to conduct a detailed integrated sedimentological study of a site prior to any examination of its ecological status possible occurrences of sources of pollution

clay mineral evidence of nepheloid layer contributions to the heinrich layers in the northwest atlantic abstract the clay fraction of four cores drilled in the north atlantic ocean was studied at a very high resolution over the last 150 ka in order to record the mineralogical signature of heinrich events factor analysis of clay mineralogy establishes that three independent factors represent the main variations a detrital factor illite chlorite kaolinite a smectite factor and a mixed layer factor ivml illite vermiculite mixed layered clay the clay mineral fraction of core su90 38 drilled in the northeastern atlantic basin did not record any heinrich event whereas large changes in the clay mineral fraction occurred during heinrich events h1 h2 h4 and h5 in the three cores from the northwestern atlantic basin cores su90 08 su90 11 and su90 12 heinrich layers are characterized by increases in the detrital factor in cores su90 08 and su90 11 and sharp increases in the mixed layer factor in cores su90 11 and su90 12 the geographical setting of the cores the pattern of surface intermediate and deep water circulation and the main sources of clay minerals allow recognition of two major mechanisms involved in the deposition of the heinrich layers 1 an increased supply of detrital clay minerals by the icebergs and 2 a specific input of illite vermiculite mixed layer clay minerals by a nepheloid layer

contrasting rainfall patterns over north america during the holocene and last interglacial as recorded by sediments of the northern gulf of mexico 1 the comparison of geochemical and mineralogical characteristics of terrigenous sediments deposited in the northern gulf of mexico gom during the holocene and last interglacial lig is used to document the impact of slight differences in insolation and ice sheet retreat rates on moisture transfer and precipitation patterns over central north america the records indicate distinct sedimentological signatures over the two time periods which likely reflect a modification of the main detrital provenance during the lig compared to the holocene here we postulate that the observed differences in the terrigenous supply during the lig relative to the holocene reflect a northeast migration of the main precipitation belt over the mississippi river watershed likely in response to deglaciation of the laurentide ice sheet prior to the peak in boreal summer insolation and the overall greater increase in boreal summer insolation relative to the holocene these combined effects allowed more northward migration of the jet stream atlantic warm pool and intertropical convergence zone than during the holocene which may have also forced the bermuda high farther to the northeast of its present position thereby pumping more moisture from the gom and the caribbean region into both the upper mississippi river and northeast great lakes area

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

clay mineral dispersal patterns in the north bering and chukchi seas abstract characterization of the clay mineralogic constituents of the m e s d equivalent spherical diameter size fraction of contemporary marine and fluvial sediments from the north bering sea chukchi sea region and adjacent land areas has resulted in delineation of suites dominated by broadly defined illitic and expandable group components with lesser amounts of chlorite and kaolinite distribution patterns elucidated indicate net northward transport of sediments relatively enriched in the expandable group with predominant terrigen ous source from the yukon river system this material is distributed across the study area in a medial zone along a general north south trend with peripherally decreasing relative amounts of this expandable group component and concomitant relative increases in the illitic components these patterns are consistent with known physical oceanographic and regional geologic relationships in terms of sediment sources transport processes and depositional mechanisms the foregoing suggest further that consideration of the stratigraphic relationships of these clay mineral component types as a function of time in relevant marine sediments north and south of the present bering strait should be informative with respect to regional quaternary paleogeography as related to global sea level fluctuations during glacial and interglacial episodes

the importance of the terrigenous fraction within a cold water coral mound a case study in the nineties cold water coral mounds were discovered in the porcupine seabight ne atlantic west of ireland a decade later this discovery led to the drilling of the entire challenger cold water coral mound eastern slope porcupine seabight during iodp expedition 307 as more than 50 of the sediment within challenger mound consists of terrigenous material the terrigenous component is equally important for the build up of the mound as the framework building corals moreover the terrigenous fraction contains important information on the dynamics and the conditions of the depositional environment during mound development in this study the first in depth investigation of the terrigenous sediment fraction of a cold water coral mound is performed combining clay mineralogy sedimentology petrography and sr nd isotopic analysis on a gravity core md01 2451g collected at the top of challenger mound sr and nd isotopic fingerprinting identifies ireland as the main contributor of terrigenous material in challenger mound besides this a variable input of volcanic material from the northern volcanic provinces iceland and or the nw british isles is recognized in most of the samples this volcanic material was most likely transported to challenger mound during cold climatic stages in three samples the isotopic ratios indicate a minor contribution of sediment deriving from the old cratons on greenland scandinavia or canada the grain size distributions of glacial sediments demonstrate that ice rafted debris was deposited with little or no sorting indicating a slow bottom current regime in contrast interglacial intervals contain strongly current sorted sediments including reworked glacio marine grains the micro textures of the quartz sand grains confirm the presence of grains transported by icebergs in interglacial intervals these observations highlight the role of ice rafting as an important transport mechanism of terrigenous material towards the mound during the late quaternary furthermore elevated smectite content in the siliciclastic glaciomarine sediment intervals is linked to the deglaciation history of the british irish ice sheet biis the increase of smectite is attributed to the initial stage of chemical weathering processes which became activated following glacial retreat and the onset of warmer climatic conditions during these deglaciations a significant change in the signature of the detrital fraction and a lack of coral growth is observed therefore we postulate that the deglaciation of the biis has an important effect on mound growth it can seriously alter the hydrography nutrient supply and sedimentation processes thereby affecting both sediment input and coral growth and hence coral mound development

cold water coral carbonate mounds as unique palaeo archives the plio pleistocene challenger mound record ne atlantic through the interplay of a stabilising cold water coral framework and a dynamic sedimentary environment cold water coral carbonate mounds create distinctive centres of bio geological accumulation in often complex continental margin settings the iodp expedition 307 drilling of the challenger mound eastern porcupine seabight ne atlantic not only retrieved the first complete developmental history of a coral carbonate mound it also exposed a unique early pleistocene sedimentary sequence of exceptional resolution along the mid latitudinal ne atlantic margin in this study a comprehensive assessment of the challenger mound as an archive of quaternary palaeo environmental change and long term coral carbonate mound development is presented new and existing environmental proxy records including clay mineralogy planktonic foraminifer and calcareous nannofossil biostratigraphy and assemblage counts planktonic foraminifer oxygen isotopes and siliciclastic particle size are thereby discussed within a refined chronostratigraphic and climatic context overall the development of the challenger mound shows a strong affinity to the plio pleistocene evolution of the northern hemisphere climate system albeit not being completely in phase with it the two major oceanographic and climatic transitions of the plio pleistocene the late pliocene early pleistocene intensification of continental ice sheet development and the mid pleistocene transition to the more extremely variable and more extensively glaciated late quaternary mark two major thresholds in challenger mound development its late pliocene 2 74 ma origin and its middle late pleistocene to recent decline distinct surface water perturbations i e water mass polar front migrations productivity changes melt water pulses are identified throughout the sequence which can be linked to the intensity and extent of ice development on the nearby british irish isles since the earliest pleistocene glaciation induced shifts in surface water primary productivity are thereby proposed to fundamentally control cold water coral growth which in turn influences on mound sediment accumulation and hence coral carbonate mound development throughout the pleistocene as local factors such as proximal ice sheet dynamics and on mound changes in cold water coral density significantly affected the development of the challenger mound they can potentially explain the nature of its palaeo record and its offsets with the periodicities of global climate variability on the other hand owing to this unique setting a regionally exceptional high resolution palaeo record of early pleistocene ca 2 6 to 2 1 ma environmental change including early british irish ice sheet development broadly in phase with the 41 ka paced global climate system is preserved in the lower challenger mound all in all the challenger mound record highlights the wider relevance of coral carbonate mound archives and their potential to capture unique records from dynamic continental margin environments

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

effect of a retreating subduction zone on deformation in simple regions of plate convergence plane strain two dimensional finite element models are used to calculate deformation patterns within model mountain belt systems where subduction zone retreat the process by which space is created between the subducting pro and overriding retro lithospheres either by motion of one or both is active the model uses coulomb plastic and thermally activated power law viscous rheologies overall deformation is determined by balancing the internal strength of the model layer against the sum of applied boundary stresses plus the gravitational stress induced by mass redistribution within the deforming model the effect of incorporating retreat in the subduction setting diffuses deformation as the moving retreating subduction zone deforms a larger cross sectional area of material for a shorter period of time than equivalent models without subduction zone retreat material is deformed while within the subduction zone but once the material has passed completely through the moving subduction zone it is passively appended onto the retrolithosphere and is no longer deformed thus relative to a convergent setting without subduction zone retreat the retreating convergent zone has an areally extensive zone of simple deformation a deformation factor is derived which characterizes the deformation shortening the material experienced within the subduction zone variable is the ratio of convergence rate rate at which material enters the subduction zone to subduction rate rate at which material is subducted variables and f the fraction of the layer that is subducted together determine the dominant style of deformation in the orogenic zone subduction zone retreat is shown to have significant and predictable effects on the model morphology e g basin or mountain formation and on the model geology e g its presence suggests lower topography lower metamorphic grade rocks at the surface and simpler deformational structures which agree with observations

clay mineralogy of surface sediments as a tool for deciphering river contributions to the cariaco basin venezuela 1 the mineralogical composition of 95 surface sediment samples from the cariaco basin continental shelf and orinoco delta was investigated in order to constrain the clay mineral main provenance and distribution within the cariaco basin the spatial variability of the data set was studied using a geo statistical approach that allows drawing representative clay mineral distribution maps these maps are used to identify present day dominant sources for each clay mineral species in agreement with the geological characteristics of the main river watersheds emptying into the basin this approach allows 1 identifying the most distinctive clay mineral species ratios that determine particle provenance 2 evaluating the respective contribution of local rivers and 3 confirming the minimal present day influence of the orinoco plume on the cariaco basin sedimentation the tuy unare and neveri rivers are the main sources of clay particles to the cariaco basin sedimentation at present the tuy river is the main contributor of illite to the western part of the southern cariaco basin continental shelf the unare river plume carrying smectite and kaolinite has a wide westward propagation whereas the neveri river contribution is less extended providing kaolinite and illite toward the eastern cariaco basin the manzanares araya tortuga and margarita areas are secondary sources of local influence these insights shed light on the origin of present day terrigenous sediments of the cariaco basin and help to propose alternative explanations for the temporal variability of clay mineralogy observed in previously published studies