investigation of the variability of floc sizes on the louisiana shelf using acoustic estimates of cohesive sediment properties abstract vertical profiles of suspended sediment concentration and floc size estimated from acoustic backscatter are used together with turbulent shear estimates to investigate cohesive sediment flocculation under different flow conditions concentration measurements by optical backscatter sensors at two levels are used to calibrate the acoustic backscatter intensity a strong correlation is observed between suspended sediment concentration and turbulence intensity mean size of flocs increases toward the bottom except within the bottom few centimeters where floc breakage is observed due to strong turbulence simultaneous shear rate and floc size profiles show that low shear promotes flocculation at low concentrations increasing turbulence intensity increases the amount of sediment in the water column but decreases the floc size indicating floc breakage thus these effects are seen at cm scale vertical resolution in the field for the first time the results support previously published numerical experimental and lower resolution field studies

spectral analysis of unevenly spaced climatic time series using clean signal recovery and derivation of significance levels using a monte carlo simulation abstract we present a monte carlo based method for the determination of errors associated with frequency spectra produced by the clean transformation of roberts et al 1987 the monte carlo procedure utilises three different types of simulation involving a data stripping operation and the addition of white and red noise to the analysed time series the simulations are tested on both synthetic and real data sets demonstrating the ability of the procedures to extract coherent information from time series characterised by the low signal to noise ratio that is typical of many palaeoclimatic records significance levels derived for the monte carlo spectra of four time series from the vostok ice core are utilised in the study of eccentricity components contained within the palaeoclimatic archive since 420 ka inversion of the vostok frequency spectra into the time domain reveals the differing influence of orbital parameters in the palaeoclimatic proxy records as well as the relative magnitudes of the eccentricity components contained in the time series of greenhouse gas concentration ice volume and local temperature

looking for clues to paleoceanographic imprints a diagnosis of the gulf of cadiz contourite depositional systems a new morphosedimentary map of the gulf of cadiz is presented showing the contourite depositional system on the gulf s middle slope this map is constructed from a broad da tabase provided by the spanish research council and the u s naval research laboratory our map shows that this contourite depositional system comprises five morphosedimentary sectors 1 proximal scour and sand ribbons 2 overflow sedimentary lobe 3 channels and ridges 4 contourite deposition and 5 submarine canyons the gulf of cadiz con tourite depositional system stems directly from the interaction between mediterranean out flow water and the seafloor its morphosedimentary sectors are clearly related to the sys tematic deceleration of the mediterranean outflow waters westward branches bathymetric stress on the margin and the coriolis force the slope s depositional system can be consid ered as a mixed contourite and turbidite system i e a detached combined drift and fan

wave mud interactions over the muddy atchafalaya subaqueous clinoform louisiana united states wave supported sediment transport 1 near bottom fluid mud layers were observed during two experiments conducted on the muddy atchafalaya inner shelf subaqueous clinoform louisiana united states on the face of the subaqueous delta 4 7 m water depth first experiment fluid mud layers are produced by seafloor liquefaction and resuspension forced by swells associated with cold front passages and supported by near bed wave induced turbulence the layers are episodic lifetime of 9 12 h form prior to significant postfrontal settling of sediment in the overlying water column and flow seaward downslope at about 5 cm s farther westward on the delta front finer grain size with negligible sand or coarse silt content second experiment similar wave supported fluid mud layers are observed to last longer 2 days show weaker alongshore westward flow of about 1 3 cm s the results suggest a sequence of near bed sediment transport processes triggered by frontal swell activity bed liquefaction resuspension and advection modulated by the bathymetric characteristics of the clinoform that contribute to the formation of clinoform stratigraphy of muddy subaqueous deltas

winter storm induced hydrodynamics and morphological response of a shallow transgressive shoal complex northern gulf of mexico abstract using extended deployments during seasons of low and high discharge from the atchafalaya river meteorological hydrodynamic and bottom boundary layer parameters were monitored from tiger and trinity shoal complex off louisiana coast usa during winter storms the surface current speed measured at both shoals exceeded 0 5 m s and the entire water column followed the prevailing wind direction the current speed close to the bottom exceeded 0 3 m s during high energy northerly winds the mean water level in the shoal complex increased during southerly winds and decreased during northerly winds such that the difference between wind set up and set down exceeded 0 7 m in tiger shoal and 0 6 m in trinity shoal during high energy frontal passages the swell height was inversely correlated with mean water level and increased during pre frontal phase and decreased during post frontal phase of winter storms the sea short waves height responded quickly to wind direction and speed and within a few hours after the wind shifted and blowing from the north the sea height increased during both deployments bimodal wave frequency spectrum was observed during wind veering from southerly to northerly when both sea and swell intensities were significant the tiger shoal bed sediment texture transformed drastically from mud to shell and shell hash assemblage within a period of two weeks during the december 2008 deployment backscatter signal intensity from a pulse coherent acoustic doppler profiler pcadp and its velocity estimates were used to determine the vertical extend and timing of mud resuspension and their eventual flushing out from the shoal environment when exposed to high energy winter storm passages the computed time frame for a total transformation of bottom sediment texture from muddy bottom to shell and shell hash assemblage was supported by the combined wave and bottom current induced shear stress at shoal bed the bed samples collected from tiger shoal before and after the deployment in spring 2009 consisted of more than 80 shell and shell hash which again confirmed a stable bottom as predicted from the pcadp data however the fine sand and mud dominated bed at trinity shoal was highly dynamic and experienced a few cm of ephemeral sediment deposition during the passage of each cold front as revealed from the analysis of acoustic backscatter data from the pcadp suspended sediment concentration estimated from optical backscatterance sensors obs and pcadp were in good agreement during low river discharge events in december 2008 but significantly diverged during the spring 2009 deployment when a high suspended sediment load was discharged into the shelf from the atchafalaya river and subsequently pushed farther offshore into the deployment sites by wind induced strong currents during the passage of cold fronts

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

stratigraphic significance and resolution of spectral reflectance logs in lower devonian carbonates of the barrandian area czech republic a correlation with magnetic susceptibility and gamma ray logs abstract spectral reflectance sr is a relatively novel technique which is used as a proxy for organic carbon and siliciclastic input in carbonate sediments in particular in core research this study summarizes results from high resolution outcrop sr logging of a lower devonian distal ramp carbonate section of the barrandian area czech republic the sr data were correlated with parallel petrophysical and geochemical data with an aim to improving their cyclostratigraphic and event stratigraphic interpretation potential and the gaps sr data can fill transgressive regressive trends indicated by facies stacking patterns caco 3 data and spectral gamma ray grs logs are well correlated in the regional context and point to third order eustatic sea level fluctuations peak regressions of the tr cycles are sensitively marked by cie l a b parameters and percent reflectance in colour bands the sr and magnetic susceptibility ms data are markedly cyclic on a more detailed scale their inferred periods vary between 49 2 and 205 kyr indicating that they may have been forced by orbital cycles in the milankovitch band the sr and ms cycles are either in phase or out of phase the latter cycles point to a strong diagenetic forcing of the colour cyclicity hematite concentration cycles inferred from sr signal in the pragian red hemipelagic carbonates are interpreted as reflecting changing bottom oxygenation and subsurface redox gradients during early diagenesis the cie l parameter was found to be related to the presence of diagenetic hematite which indicates that cyclostratigraphic analysis of simple greyscale data can be affected by considerable error due to chromacity although the cie l parameter is partly correlated with caco 3 concentrations the ms data are not which suggests that the ms signal can be significantly influenced by diagenetic minerals and its cyclostratigraphic interpretation can be potentially misleading the sr data backed up by grs ms and caco 3 data indicate that the red colour in the pragian hemipelagic limestones originated from early diagenetic hematite precipitation under the conditions of an oxygenated ocean floor this suggests that deep sea bottom oxygentation may have been in operation during the early devonian which is traditionally perceived as a typical greenhouse period the sr data can be obscured in several m thick zones of elevated cie l and other colour changes leaching zones related to postdepositional alteration along subvertical faults however this fault related telogenic alteration has little influence on the ms signal the combined use of sr and ms has a synergic effect and can significantly improve the interpretation of their respective cyclic signals particularly in relation to the diagenetic overprint and possible carriers of the ms

kinematic models of basement cover interaction insights from the malargue fold and thrust belt mendoza argentina abstract we investigate through natural examples from the malargue fold and thrust belt the manner in which the basement structures interact with the cover in a thick skinned fold and thrust belt our work suggests that there is a broad spectrum of basement cover interaction mechanisms with two end members coupled and uncoupled interactions the kind of bonding between basement and cover is related to the propagation to slip ratio p s because high values of this ratio indicate rapid forward propagation of shortening into the cover while low values favour welding between basement and cover structures we analyse the factors controlling the kinematics of basement cover deformation and find that not only the strength of the cover its thickness and its mechanical anisotropy control the p s and basement cover bonding but also the strain rate the thickness of synorogenic strata and the presence of pre existing faults

the unusual 3d interplay of basement fault reactivation and fault propagation fold development a case study of the laramide age stillwell anticline west texas usa abstract subsurface fault geometries have a systematic influence on folds formed above those faults we use the extraordinarily well exposed fold geometries of the laramide age stillwell anticline in west texas usa to develop a strain predictive model of fault propagation fold formation the anticline is a 10 km long nw trending ne vergent asymmetric fold system with an axis that displays a map view left stepping en echelon pattern we integrated field observations geologic and structural data cross sections and 2d kinematic modeling to establish an unusual 3d two stage model of contractional fold formation including 1 reverse reactivation of a pre existing nw striking sw dipping left stepping en echelon normal fault system in paleozoic basement rocks to generate monoclinal flexures in overlying layered cretaceous carbonate rocks and 2 the formation of a subsequent flat ramp fault system that propagated horizontally along a mechanically weak clay rich cretaceous unit before ramping up at the hinge of the pre existing monocline system strain is focused within the forelimb of the system in front of the propagating fault tip and is accommodated by a combination of interlayer slip flat ramp faulting and fracturing proximal to planes of slip this strain predictive model can be applied to similar less well exposed contractional systems worldwide and provides a new unusual example of laramide age contractional deformation

styles of folding within thrust sheets examples from the appalachian and rocky mountains of the u s a and canada abstract folds in a single thrust sheet can be classified as trailing edge formed over footwall ramps intraplate due to shortening within the body of the sheet and leading edge leading edge folds are usually removed by erosion at the front of a thrust sheet but their unfaulted equivalents can be examined at the lateral termination of the thrusts most folds of these various classes possess a kink band geometry with sharp hinges and long planar limbs the orderly nature of kink band folds breaks down when thin incompetent units separate thicker competent members the resulting fold geometry ranging from simple disharmonic to hinge collapse is controlled by the thickness of interbedded incompetent materials the appalachian and rocky mountain thrust belts provide examples of these various classes and styles of folds

how do horizontal frictional discontinuities affect reverse fault propagation folding abstract the development of new reverse faults and related folds is strongly controlled by the mechanical characteristics of the host rocks in this study we analyze the impact of a specific kind of anisotropy i e thin mechanical and frictional discontinuities in affecting the development of reverse faults and of the associated folds using physical scaled models we perform analog modeling introducing one or two initially horizontal thin discontinuities above an initially blind fault dipping at 30 in one case and 45 in another and then compare the results with those obtained from a fully isotropic model the experimental results show that the occurrence of thin discontinuities affects both the development and the propagation of new faults and the shape of the associated folds new faults 1 accelerate or decelerate their propagation depending on the location of the tips with respect to the discontinuities 2 cross the discontinuities at a characteristic angle 90 and 3 produce folds with different shapes resulting not only from the dip of the new faults but also from their non linear propagation history our results may have direct impact on future kinematic models especially those aimed to reconstruct the tectonic history of faults that developed in layered rocks or in regions affected by pre existing faults

qualitative and quantitative approaches in palaeohydrography a case study from core top parameters in the gulf of cadiz palaeoceanography relies on the assumption that parameters measureable in sediment cores correlate reliably to hydrographic parameters areas of dynamic watermass mixing which generally have steep hydrographic gradients therefore provide both a tempting target large spatial and temporal differences in temperature and salinity and a significant challenge high flow velocities and high noise for palaeoceanographers here we investigate the ability of parameters measured on core tops to be used as the basis for simulating regional hydrography within one globally important area of watermass mixing the gulf of cadiz using grainsize sediment composition benthic foraminiferal assemblage and benthic foraminiferal stable isotope analysis it is possible to build an effective framework for qualitative constraint of the position of the modern mediterranean outflow water mw plume we propose that the gulf of cadiz slope can be sub divided into 8 hydrographic zones reflecting these parameters proximal mw core mw1 steep slopes core mw1 gentle slopes distal mw1 distal mw2 lower limit of mw plume north atlantic deep water and ambient atlantic water we anticipate that compilation of time slice data will reveal hydrographic sub divisions of the slope for the past in a similar manner improving our understanding of past changes in the size and position of the mw plume but more work needs to be done before a secure protocol for quantitative reconstruction can be created stable isotope analysis alone is insufficient for the task with 13c behaving in a non conservative manner and 18ocalcite acting in an ambiguous way due to the competing influences of 18owater and temperature it is likely that if a single parameter that unambiguously determines the difference between mediterranean water and atlantic water can be identified combination with 18ocalcite will allow extension of our qualitative analysis into a quantitative means of palaeohydrographic reconstruction for this region similar complexity to that found in this study would be expected in any mixing region and in particular on the majority of sediment drifts we recommend that core top surveys similar to this study are performed on these sediment drift systems before any form of quantitative palaeohydrology is attempted

productivity and paleoceanographic implications on the tore seamount iberian margin during the last 225 kyr foraminiferal evidence foraminifera counts and climatic assemblages from the tore seamount are used to approach the glacial and interglacial changes in temperature and productivity on the iberian margin over the last 225 kyr chronostratigraphy is based on globigerinoides ruber and globigerina bulloides oxygen isotopes and supported by foraminifera and carbonate stadial fluctuations foraminifera indicate cooling from late interglacial stage 5 to the beginning of termination i ti neogloboquadnna pachyderma s reflects cold conditions during glacial stages 4 2 in contrast glacial stage 6 is dominated by warmer n pachyderma d and dutertrei and a restricted arctic assemblage past sea surface temperatures confirm the general cooling reaching 4 3 c simmax 28 during stage 2 multiple productivity proxies such as organic carbon productivity related foraminifera and 13c constrain the changes observed a productivity increase occurs after interglacial stage 5 enhanced from late glacial stage 3 to ti present day satellite detected phytoplankton plumes off portugal would have accounted in the past glacial stages for the general productivity increase over the tore on top of this welldefined peaks of organic carbon and productivity related foraminifera correspond with heinrich events 1 4

fold generated imbricates examples from the caledonides of southern norway abstract the cambro silurian sequence of the oslo region contains fold trains and closely spaced imbricate thrust faults the imbricates could be interpreted as having ramped off the sole detachment and generated fault propagation folds several imbricate thrusts however appear to die out both downwards and upwards into folds this suggests that the thrusts were generated within the cambro silurian sequence and propagated down to the sole thrust rather than propagating upwards from the sole thrust the mechanical stratigraphy is apparently responsible for this style where during folding relatively brittle limestone members faulted in the highly strained fold forelimbs prior to through going faulting developing in the shales understanding the origin of such imbricates is important when choosing a method of section restoration

bedding plane slip in initial stages of fault related folding abstract frictional slip along bedding planes contributes to fault related folding of layered rocks we use numerical experiments to investigate the deformation of frictional bedding planes near dipping faults under layerparallel contraction and extension within the numerical experiments contraction boundary conditions produce asymmetric anticlines and extension produces asymmetric synclines the fold shape may be used to infer dip of the underlying fault in situations where the fault may not be observable additionally sense of slip along bedding planes may indicate proximity to the fault tip under uniform remote tectonic strain fault slip induces deformation in both the hangingwall and the footwall at depths as shallow as 1 km there is no significant difference between fold amplitudes in the hangingwall and the footwall this result is contrary to many kinematic models currently in use kinematic models of fault related folds commonly include the development of flat ramp and flat ramp flat fault geometries which may be attributed to initial ramp thrusting and later flat development our mechanical models show that fault flats may be produced from fault ramps due to slip along frictional bedding planes near the thrust fault tips our numerical experiments also evaluate joint initiation joints perpendicular to bedding are promoted in extensional environments we compare the results of the mechanical model to kinematic models of fault propagation folds and conclude that mechanical models offer important insights to better understand the folding process

the role of fractures in the structural interpretation of sheep mountain anticline wyoming the development of fractures in the sedimentary layers of sheep mountain anticline a laramide asymmetric fault cored fold of the bighorn basin is documented and interpreted to constrain the kinematic evolution of the fold the fracture pattern is interpreted to identify five main fracture sets a fracture set striking 110 set i oblique to the future fold trend is interpreted as a regional fracture set that predates laramide compression a joint set set ii striking 045 and present in the hinge and backlimb is related to the ne oriented laramide compression just prior to and during initial anticline growth joints striking 135 set iii parallel to the fold trend are found within the hinge and are interpreted to have developed in response to the bending of layers the two youngest fracture sets are attributed to a late stage of fold growth a joint set set iv in the backlimb striking parallel to the set i fractures but vertical and a fracture set in the forelimb consisting of set i fractures reactivated as reverse faults the relative chronology mode of formation opening vs shearing and structural locations of these fractures suggest the following kinematics of folding at sheep mountain anticline little or no lateral fold propagation no hinge migration and limb rotation with only minor limb flexure and stretching

winds in the strait of gibraltar summary automated meteorological observations were made from october 1985 to september 1986 in the narrows of the strait of gibraltar additional surface and upper air measurements were made in the strait from may to july 1986 the main wind events in summer were mostly mesoscale levanters winds from the east through the strait and a lesser number of synoptic scale levanters and westerlies during mesoscale levanters the wind speed increased and the pressure decreased from gibraltar downstream through the narrows as far as tangier a mesoscale low and the highest winds were found over the axis of the strait north of tangier high velocity 20 m s winds occurred only under 1 km height the air temperature profile became progressively warmer moving from gibraltar towards tangier a weak air temperature inversion decreased in height to the west of the narrows venturi flow as an explanation for the downstream increase of the low level winds during a levanter is inconsistent with observations a new model is proposed to explain the wind field associated with levanter winds in the strait that includes some orographic blocking and low level convergence into the narrows some west side divergence due to drag over water and leeside heating that generates a leeside mesoscale low pressure the surface low accelerates the surface winds to their maximum strength well downstream of the narrows a similar flow regime has been observed recently in the sea level channel between hawaii and maui

surface facies and sediment dispersal patterns southeastern gulf of cadiz spanish continental margin abstract grain size of 294 samples and mineralogical analysis of 364 surface samples from the spanish continental shelf and upper slope of the gulf of cadiz delineate four sediment facies that derive mainly from siliciclastic sources the northern area is formed by the mud rich prodelta of the guadalquivir river parallel to the coast and progradational towards the southeast it exhibits a typical bulk mineral association of illite smectite kaolinite chlorite in the north central area there is a smaller coarser grained prodelta in the bay of cadiz linked to the guadalete river which offshore becomes connected to the guadalquivir prodelta its mineral association is quartz illite kaolinite chlorite in the southern area where fluvial input is negligible the characteristic coarse grained facies generally corresponds to relict late pleistocene reworked deposits the typical mineral association is quartz calcite aragonite smectite mixed layer clay minerals the fourth area corresponds to the shelf break and upper slope offshore cadiz bay where a westward grain size coarsening differentiates the deposits of the last low sea level stand and no typical mineral association exists the mineralogy of the terrigenous deposits indicates a source area from paleozoic sequences of the sierra morena to the north and the subbetic units and gibraltar flysch to the east the neogene deposits of the guadalquivir depression are an additional source of shelf sediments the surface sediment distribution on the inner continental shelf is largely determined by the southeastern atlantic water flow the terrigenous input from rivers and the shelf physiography sediment dispersal on the outer continental shelf and upper slope in contrast largely reflects the location of low sea level stand the development of palimpset deposits and the location of the mediterranean undercurrent over the margin

constraints on the depth geometry and kinematics of blind detachment faults provided by fault propagation folds an example from the mesozoic fold belt of south china abstract the mesozoic multi layered thin skinned fault related fold belt in south china is characterized by propagation chevron folding and thrust faulting we examine the geometry and depth of blind detachment faults in this belt using faults and folds that crop out along a well defined cross section a combination of parameters such as backlimb dip angle 2 interlimb angle height of anticline h thickness of the referenced layer h0 width of the anticline ab and thickness change ratio of layering within the forelimb tf t are used to develop new equations to estimate the geometry and depth of the detachment faults in the cross section the huangdushan chevron anticline has parameters revealing a blind fault with a ramp angle of 42 and a flattened segment at a depth of 4 9 km based on existing seismic data we interpret this blind fault as a backthrust developed over an in sequence imbricated duplex of cambrian to ordovician strata a chevron anticline at qiyueshan also reveals a backthrust fault however a broad anticline in lengzhuba and a small cylindrical sinusoidal anticline in yupize reveal a flat ramp flat detachment fault with flat segments at depths of 7 4 and 3 4 km respectively suggesting that the sinian strata were thickened probably by an out of sequence imbricated duplex our results indicate that the flat ramp flat detachment fault along the bottom of the sinian strata produced the out of sequence imbricated duplex and cylindrical sinusoidal folds the in sequence imbricated duplex produced backthrusts and related chevron anticlines we consider that this fault related fold belt was produced by collision between the yangtze block and north china blocks

deformation within foreland thrust sheets by populations of minor faults the dominant deformation mechanism within foreland thrust sheets is the displacement of blocks of weakly deformed rock on discrete mineral coated minor faults in highly deformed layers at the bases of three southern appalachian foreland sheets such minor faults are members of families or populations of consistently oriented structures the deformation style is similar in all three sheets rock nearest each thrust was shortened in the direction of sheet transport and thickened by a family of faults oriented at low angles to the thrusts rock further above each thrust experienced only the first of these two deformation stages statistical analyses of fault populations from these three sheets demonstrate that their deformation is quantitatively as well as qualitatively similar deformation due to movement on minor faults is statistically homogeneous at the scale of an outcrop in one of these sheets strain due to minor faults can be measured in that sheet a strain profile across this sheet is similar to strain profiles across continuously deformed sheets from internal portions of mountain belts suggesting that their responses to emplacement are similar

alternative model of thrust fault propagation a widely accepted explanation for the geometry of thrust faults is that initial failures occur on deeply buried planes of weak rock and that thrust faults propagate toward the surface along a staircase trajectory we propose an alternative model that applies gretener s beam failure mechanism to a multilayered sequence invoking compatibility conditions which demand that a thrust propagate both upsection and downsection we suggest that ramps form first at shallow levels and are subsequently connected by flat faults this hypothesis also explains the formation of many minor structures associated with thrusts such as backthrusts wedge structures pop ups and duplexes and provides a unified conceptual framework in which to evaluate field observations

fault propagation folds above thrusts with constant dip abstract previous models of fault propagation folds have been extended to include the case where folding initiates above a thrust ramp of constant dip the model may be useful in analyses of fold thrust structures in thin and thick skinned compressional terrains it may be most applicable to fault propagation folds that develop as a fault propagates from a thick massive brittle unit into a thinly layered anisotropic unit

measurements of wave attenuation due to a soft bottom the swamp experiment the sea wave attenuation measurement program swamp was designed to provide measurements of the attenuation of waves as they travel from deep water to relatively shallow water off the mississippi delta the soft bottom was suspected of causing strong attenuation in the area this effect has now been measured a wave staff and electromagnetic current meter were used to estimate directional wave spectra at the cognac platform in 312 m 1025 feet of water and at platform vv in south pass block 27 in 19 m 63 feet of water in addition measurements of vertical bottom motion were made at platform vv seven storm periods from sepember 1979 to february 1981 were studied the directional spectral comparisons showed that the theoretically calculated refraction and shoaling can explain the changes in the spectra when the wave height is low however as the wave height increases a nonlinear attenuation mechanism becomes increasingly strong the attenuation is a strong function of deep water wave height and a weak function of wave frequency the bottom motion measurements showed that the bottom moved downward with small amplitude under wave crests

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

water waves over a muddy bed a two layer stokes boundary layer model this study aims to develop an asymptotic theory for the flow kinematics of a thin layer of viscous mud under water surface waves the mud depth the mud stokes boundary layer thickness and the wave amplitude are assumed to be comparable with one another and much smaller than the wavelength by virtue of this sharp contrast in length scales boundary layer equations are used to describe motion of both the mud and the immediately overlying water analytical solutions are sought and explicit expressions are obtained under progressive waves for the fluid velocity fields interface wave characteristics and wave damping rate at the first order and the steady mean discharge rate and mass transport velocity of mud at the second order effects of the mud layer thickness density and viscosity ratios on these kinematic quantities are examined in detail

paleoceanographic reconstructions from planktonic foraminifera off the iberian margin temperature salinity and heinrich events a quantitative analysis of planktonic foraminifera in a core from the iberian margin allows a reconstruction of the evolution of oceanographic parameters during the last glacial cycle with a resolution of 1000 years a principal component analysis performed on 19 species allows the identification of 11 intervals characterized by increased abundances of the subpolar species the youngest six of these intervals are correlated with the last 6 heinrich events hes the five cold events older than stage 4 are dated at 81 90 110 129 and 140 ka respectively paleotemperatures reconstructed using the modern analog technique indicate 4 c decreases during all even numbered isotopic stages and stage 3 during the hes temperature decreases reach 10 c and seawater 18o anomalies reach 1 temperature and salinity reconstructions indicate that the environment of the iberian margin has been under the combined influence of global factors such as the migration of the polar front and iceberg discharge and of regional factors such as the precipitation evaporation regime on both oceanic and continental area

observations of nearshore wave dissipation over muddy sea beds 1 wave propagation on the louisiana inner shelf is studied using concurrent measurements at two shallow water ocean observatory sites in sedimentary environments dominated by mud at one site and sand at the other contrary to the widely accepted hypothesis that mud induced wave dissipation is important only for long waves observations show significant damping of high frequency short waves which interact weakly with the bottom the mechanism of short wave dissipation is not understood numerical simulations show that other dissipative processes such as refraction or depth limited breaking do not account for the magnitude of the observed effects independent observations of strong sediment re working during storms suggest that these effects are related to sediment resuspension processes

kinematics of large scale tip line folds from the high atlas thrust belt morocco abstract the kinematics of several tip line folds situated along the south atlas front near goulmima morocco is established using both forward modelling and analysis of syn folding deformation from the sahara foreland to the atlas the two successive major structures forming the mountain front in this area fit geometrically with a generalised fault propagation fold model and a model of fault propagation fold altered by late transport on the upper flat respectively field evidence shows that the two folds are developed more or less synchronously the analysis of minor structures helps address the question of migrating hinges vs fixed hinges during the fold s growth

high resolution digital image treatment to color analysis on cores from iodp expedition 339 approaching lithologic features and bioturbational influence abstract color analysis was conducted on selected cores from sites u1385 and u1389 from iodp expedition 339 based on a recently developed high resolution digital image treatment to explore its relationship with lithologic features e g percentage of sand this first step can be of potential usefulness in characterizing discriminating between different types of registered sediments in the iodp expedition 339 turbidites contourites and associated sediments and then for more general studies involving different lithologies sedimentary parameters and ichnological variations differentiation between types of deposits holds particular interest in the context of the mediterranean outflow water mow evolution and related depositional processes whose study was one of the main aims of iodp expedition 339 color characterization was executed on high resolution digital images by applying a method based on adjustment modification including levels brightness and vibrance followed by pixel measurement the applied methodology allows for a precise characterization of colors improving upon previous color descriptions by means of munsell color conducted on board during expedition 339 itself the studied interval is subdivided into four parts based on grain size analysis and color according to pixel values these parts are identified as a 120 b 90 c 140 and d 160 being well correlated with the corresponding lithology parts a and c with similar pixel values correspond to calcareous silty mud mudstone part b would correlate with calcareous silty sand sandstones and part d corresponds to calcareous mud sand content distribution throughout the studied interval bears a close relationship with the differentiated parts a to d intervals having a higher percentage of sand present a lower mean pixel value and darker color whereas the finer grained intervals contain sediments lighter in color represented by higher pixel values however as proved the proposed relationship between color sedimentological features type of sediment must be considered with some caution ichnological analysis reveals the influence of trace fossils on color variations in the sediment regardless of the size of traces and amount of bioturbation the infilling material of trace fossils being the most determinant factor thus lower bioturbated surfaces 6 by small trace fossils chondrites show higher influence on color variations 102 vs 107 than higher bioturbated surfaces 25 by large trace fossils thalassinoides 110 vs 112 due to the color of the infilling material 56 in the case of chondrites and 90 in the case of thalassinoides thus a detailed ichnological analysis should accompany the sedimentological study of deep sea modern cores in order to avoid misinterpretations of the sedimentological parameters involved

origin of red pelagic carbonates as an interplay of global climate and local basin factors insight from the lower devonian of the prague basin czech republic abstract red pelagic sediments are relatively common in the phanerozoic they are often interpreted as products of sea bottom oxidation during greenhouse climate showing a conspicuous alternation with black shales and thus carrying important palaeoceanographic information the lower devonian pragian carbonate strata of the prague basin czech republic praha formation contain a marked band of red pelagic carbonate up to 15 m thick which can be correlated for several tens of km we investigated seven sections 17 to 255 m thick of the prague basin using the methods of facies analysis outcrop gamma ray logging diffuse reflectance spectroscopy optical microscopy element geochemistry magneto mineralogy and electron microprobe analysis the aim was to find the mineral carriers of the red colour investigate the stratigraphic context of the red carbonates and evaluate the local and global prerequisites for their formation the red pigmentation represents enrichment by hematite with respect to goethite approximately 31 of the total reflectance falling in the red colour band represents a threshold for red coloration the red pigmentation is carried by submicronic hematite dispersed in argillaceous pelagic calcilutite and or inside skeletal allochems gamma ray log correlation indicates that the red carbonate band developed in stratigraphic levels with low sedimentation rates typically from 1 to 7 1 mm kyr which are comparable to the mesozoic rosso ammonitico facies the red beds and the whole praha formation pragian to early emsian are characterized by low toc values

fault displacement distance relationships as indicators of contractional fault related folding style we present a method of using fault displacement distance profiles to distinguish fault bend shear fault bend and fault propagation folds and use these insights to guide balanced and retrodeformable interpretations of these structures we first describe the displacement profiles associated with different end member fault related folding models then provide examples of structures that are consistent with these model based predictions natural examples are imaged in high resolution two and three dimensional seismic reflection data sets from the niger delta sichuan basin sierras pampeanas and cascadia to record variations in displacement with distance updip along faults termed displacement distance profiles fault bend folds exhibit constant displacement along fault segments and changes in displacement associated with bends in faults shear fault bend folds demonstrate an increase in displacement through the shearing interval and fault propagation folds exhibit decreasing displacement toward the fault tip more complex structures are then investigated using this method demonstrating that displacement distance profiles can be used to provide insight into structures that involve multiple fault related folding processes or have changed kinematic behavior over time these interpretations are supported by comparison with the kinematics inferred from the geometry of growth strata overlying these structures collectively these analyses illustrate that the displacement distance approach can provide valuable insights into the styles of fault related folding

climatic and oceanographic changes in the northeast atlantic reflected by magnetic properties of sediments deposited on the portuguese margin during the last 340 ka abstract rock magnetic parameters measured along two giant piston cores md95 2040 40 34 n 9 51 w and md95 2042 37 47 n 10 09 w collected off the portuguese margin related to other proxy climatic data have been used to reconstruct magnetic mineralogical changes of in relation to environmental and climatic conditions over the north atlantic western europe and northwest africa during the last three climatic cycles since isotope stage 10 thin discrete layers containing coarse grains of titano magnetite are associated with events of iceberg discharge during heinrich events 1 6 heinrich quat res 29 1988 142 that have equivalent events in isotope stages 5 8 concentrations of fine grained ti magnetite and hematite goethite varying in phase opposition are directly linked with alternations of cold and warm climatic periods spectral analyses of the rock magnetic signals reveal milankovitch periods at 100 and 41 ka confirming the relationship with long term climatic changes at high latitudes the nature ti magnetite and size range of the finest ferrimagnetic fraction as well as its variation suggest a control by deep currents carrying a colloidal clayey fraction from remote sources iceland faeroes mid atlantic ridge variation of hematite goethite contents is linked with transport by rivers and winds from the neighbouring continent a tight correlation with the d o cycles in greenland ice records confirms that north atlantic oceanic regimes and continental wind regimes were strongly influenced by millennial scale climatic changes throughout the last 350 ka

chemical weathering and provenance evolution of holocene recent sediments from the western indus shelf northern arabian sea inferred from physical and mineralogical properties abstract we present a multi proxy mineral record based on x ray diffraction and diffuse reflectance spectrophotometry analysis for two cores from the western indus shelf in order to reconstruct changing weathering intensities sediment transport and provenance variations since 13 ka core indus 10 is located northwest of the indus canyon and exhibits fluctuations in smectite illite chlorite ratios that correlate with monsoon intensity higher smectite illite chlorite and lower illite crystallinity normally associated with stronger weathering peaked during the early mid holocene the period of maximum summer monsoon hematite goethite and magnetic susceptibility do not show clear co variation although they both increase at indus 10 after 10 ka as the monsoon weakened at indus 23 located on a clinoform just west of the canyon hematite goethite increased during a period of monsoon strengthening from 10 to 8 ka consistent with increased seasonality and or reworking of sediment deposited prior to or during the glacial maximum after 2 ka terrigenous sediment accumulation rates in both cores increased together with redness and hematite goethite which we attribute to widespread cultivation of the floodplain triggering reworking especially after 200 years ago over holocene timescales sediment composition and mineralogy in two localities on the high energy shelf were controlled by varying degrees of reworking as well as climatically modulated chemical weathering

structural models of faulted detachment folds faulted detachment folds represent a common structural style in several hydrocarbon producing fold and thrust belts including the zagros idaho wyoming utah carpathian and albanide belts and several deep water fold belts including the mississippi fan and per dido belts these structures form in units with high competency contrasts and display a transition in deformational behavior from detachment folding to progressive fault propagation with increasing shortening the structures first form by symmetric or asymmetric detachment folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require the movement of material from the synclines to the anticlines contin ued shortening results in tighter folds with limb rotation by hinge migration limb segment rotation and internal shear rotation of limb segments between locked hinges results in thrust faults which propagate through deformation zones on the frontlimb and possibly the backlimb the faults may terminate both up and down section within brittle or ductile deformation zones eventually a through going fault connects one of the major faults with the basal detach ment variations in the structural geometry are related to the rela tive thickness and competency of the units and the mechanisms of deformation because faulted detachment folds superficially resem ble fault propagation folds their geometry can be misinterpreted in areas of poor data quality characteristic features for distinguish ing these structures include 1 smaller variations in anticlinal length during fold evolution 2 a more open and rounded fold geometry 3 complex and nonuniform variations in fault slip 4 a significant variation in deformational behavior among different units and 5 fold fault relationships indicating transition from folding to faulting such as footwall synclines and decapitated fold geometries

paleoceanographic significance of sediment color on western north atlantic drifts i origin of color reflectance spectra collected during odp leg 172 were used in concert with solid phase iron chemistry carbonate content and organic carbon content measurements to evaluate the agents responsible for setting the color in sediments factor analysis has proved a valuable and rapid technique to detect the local and regional primary factors that influence sediment color on the western north atlantic drifts sediment color is the result of primary mineralogy as well as diagenetic changes sediment lightness is controlled by the carbonate content while the hue is primarily due to the presence of hematite and fe 2 fe 3 changes in clay minerals hematite most likely derived from the permo carboniferous red beds of the canadian maritimes is differentially preserved at various sites due to differences in reductive diagenesis and dilution by other sedimentary components various intensities for diagenesis result from changes in organic carbon content sedimentation rates and h2s production via anaerobic methane oxidation iron monosulfides occur extensively at all high sedimentation sites especially in glacial periods suggesting increased high terrigenous flux and or increased reactive iron flux in glacials 7 2002 elsevier science b v all rights reserved

stratification effects by cohesive and noncohesive sediment this study focuses on stratification effects induced by the interaction between suspensions of fine grained cohesive and noncohesive sediment and the turbulent flow in estuarine and coastal environments a concise literature review reveals that this interaction may cause an appreciable modification of the vertical profiles of velocity vertical eddy viscosity diffusivity and reynolds stresses this interaction is further studied with a one dimensional vertical 1dv numerical model which includes the standard k turbulence model with buoyancy destruction terms application of this model to the experimental results by coleman 1981 shows that the measured changes in the velocity profile can be explained entirely by sediment induced buoyancy effects it is argued that capacity for cohesive sediment is cc e a fluid mud layer is formed upon the deposition of the cohesive sediment flocs contrary to the case with noncohesive sediment where the depositing grains immediately form a rigid bed thus a two layer fluid system develops causing significant damping of the vertical mixing processes decreasing the carrying capacity further this positive feed back results in a catastrophic collapse of the turbulence field and the concentration profile a scaling law for this saturation behavior is derived from classical stratified flow theory this law is sustained with a series of numerical experiments with the 1dv model it also predicts the suspended sediment concentrations observed in the yellow river to the right order of magnitude it is concluded that sediment induced buoyancy yields appreciable stratification effects at already moderate suspended sediment concentrations in the case of cohesive sediment these stratification effects can result in a catastrophic collapse of the turbulent flow field and the vertical profile of suspended sediment concentration

turbidite record of frequency and source of large volume 100 km3 canary island landslides in the last 1 5 ma implications for landslide triggers and geohazards during the last two decades numerous studies have focused on resolving the landslide histories of the canary islands issues surrounding the preservation and dating of onshore and proximal submarine landslide deposits precludes accurate determination of event ages however submarine landslides often disaggregate and generate sediment gravity flows volcaniclastic turbidites sampled from madeira abyssal plain piston cores represent a record of eight large volume failures from the western canary islands in the last 1 5 ma during this time there is a mean recurrence rate of 200 ka while the islands of el hierro and tenerife have individual landslide recurrences of 500 ka and 330 ka respectively deposits from the 15 ka el golfo landslide from el hierro and 165 ka icod landslide from tenerife are examined this study also identifies potential deposits associated with the orotava 535 ka guimar 850 ka and rogues de garcia landslides 1 2 ma from tenerife el julan 540 ka and el tinor 1 05 ma landslides from el hierro and the cumbre nueva landslide 485 ka from la palma seven of eight landslides occurred during major deglaciations or subsequent interglacial periods which represent 55 of the time however all of the studied landslides occur during or at the end of periods of protracted island volcanism which generally represent 60 of the island histories although climate may precondition failures it is suggested that volcanism presents a more viable preconditioning and trigger mechanism for canary island landslides

physical chemical and sedimentological aspects of the mediterranean outflow off iberia a multidisciplinary study of the mediterranean outflow in the region west of the strait of gibraltar and off the southern and southwestern coasts of the iberian peninsula was developed in the frame of the canary islands azores gibraltar observations project two high resolution ctd surveys which included water sampling for chemical nutrients and dissolved oxygen and sedimentological analyses took place in september 1997 summer cruise and january 1998 winter cruise in the study region the correspondence between the high salinity mediterranean water mw layer and the low nutrient content and relatively high abundance of particles was a general result further details of the thermohaline analysis and of the geostrophic computations especially for the layer of mw are compared with the results obtained for the chemical properties and the sedimentological characteristics

comparison of statistical and artificial neural network techniques for estimating past sea surface temperatures from planktonic foraminifer census data we present the first detailed and rigorous comparison of six different computational techniques used to reconstruct sea surface temperatures sst from planktonic foraminifer census data these include the imbrie kipp transfer functions iktf the modern analog technique mat the modern analog technique with similarity index simmax the revised analog method ram and for the first time a set of back propagation artificial neural networks ann trained on a large faunal data set including a modification where geographical information was added among the input variables annd by training the techniques on an identical database we were able to explore the differences in sst reconstructions resulting solely from the use of different mathematical methods the comparison indicates that while the iktf technique consistently shows the worst performance ann and ram perform slightly better than mat and that the inclusion of the geographical information into the training database simmax and annd further improves the accuracy of modern sst estimates however when applied to an independent validation data set and an additional fossil data set the results did not conform to this ranking the largest differences in the reconstructed sst values occurred between groups of techniques with different approaches to sst reconstruction that is ann and annd produced sst reconstructions significantly different from those produced by ram simmax and mat the application of the various techniques to the validation data set which allowed comparison of sst reconstructions with instrumental records suggests that artificial neural networks might provide better paleo sst estimates than the other techniques

a bingham plastic model for a muddy seabed under long waves the dynamics of cohesive mud under wave action is important to the geological processes along some coastlines because of the complex rheological properties there have been vastly different models for predicting the effect of mud on wave attenuation this paper focuses on a non newtonian behavior of highly concentrated mud whereby shearing strain occurs only if the shear stress exceeds a certain threshold called the yield stress the wave induced motion in a thin mud layer beneath a clear water layer is studied there are circumstances in which the yield stress is dominant and acts like a coulomb friction mud motion can change from continuous to intermittent as the wave attenuates the effects of the non newtonian behavior on wave damping are compared to other more common causes of dissipation

observations of suspended sediment stratification from acoustic backscatter in muddy environments abstract vertical profiles of suspended sediment concentration estimated from acoustic backscatter are used to re examine the relation between sediment stratification and floc size in a cohesive sedimentary environment concentration measurements by optical backscatter sensors at two vertical levels are used to calibrate the acoustic backscatter intensity in spite of the complexities due to the rapidly changing flow and cohesive sediment properties the estimates of sediment concentration reproduce well the observations together with the vertical profiles of suspended sediment concentration measured current profiles are used to calibrate a one dimensional vertical 1dv boundary layer numerical model for combined wave current flow on muddy beds the numerical simulations are used to investigate the effect of the floc size on the vertical structure of the suspended sediment concentration profile for similar flow conditions smaller flocs result in more mixed profiles with higher concentration in the upper water column and lower near bed concentration this is the first time this effect is seen in direct field observations and confirms previously published numerical results

the factors controlling vertical color variations of north atlantic madeira abyssal plain sediments abstract colors of madeira abyssal plain sediments north east atlantic were determined with a simple colorimeter and described in the second cie 1976 color space l a b color space l a b values of the original sediment core and the powdered sediments vary sharply with depth and these variations were found to be due to changes in the contents of calcium carbonate organic matter iron and manganese the vertical color profiles are essentially conserved after drying and powdering these results suggest that this rapid measurement method with the colorimeter can be used in quantitative color determination of marine sediments aboardship as a result of quantitative studies among l a b values calcium carbonate organic carbon iron and manganese contents of powdered sediment samples the following conclusions were obtained 1 l value psychometric lightness is controlled by calcium carbonate for whitish color and by organic matter for blackish color the redox fronts can be easily characterized by a sharp decrease in l value 2 a value psychometric red green chromaticness is controlled by iron for pelagic sediments by manganese carbonate and iron oxide and hydroxide for calcareous turbidites and turbidite g and by pigments and iron ii bearing minerals for greenish and grayish turbidites 3 b value psychometric yellow blue chromaticness is controlled by iron contents probably in the form of hydroxides for calcareous turbidites

signatures of the mediterranean outflow from a north atlantic climatology 1 salinity and density fields using historical data from the national oceanic data center the climatology of the eastern north atlantic basin has been investigated for the purpose of detailing the mediterranean outflow water in terms of its salinity density and flow patterns part 1 of this work is a descriptive analysis of the fate of the mediterranean water once it flows out of the strait of gibraltar tracing the salinity and density signatures high resolution maps of the climatological outflow are presented with an emphasis on the continuity of the water from its source from the climatological fields a continuous signal of mediterranean water is tracked northward to 50 20 n yet its westward advection is limited to the tagus basin recirculations of mediterranean water in the gulf of cadiz and in the bay of biscay deduced from property signals are also detailed iorga and lozier this issue present absolute velocity fields from a diagnostic model constrained by geostrophic dynamics conservation of mass and no flux boundary conditions

bottom turbulence on the muddy atchafalaya shelf louisiana usa 1 wave current and sediment observations collected in approximately 5 m depth on the muddy atchafalaya clinoform la usa are used to study the interaction between near bed wave induced turbulent flows and suspended sediment characteristics in a muddy environment low wave bias estimates of near bed reynolds stresses are strongly correlated with flow accelerations and suspended sediment concentration as previously observed on sandy beaches where accelerations have been associated with bed fluidization and sediment transport a detailed numerical analysis of the observations is performed based on a uni dimensional boundary layer model that accounts for the coupling between the fluid and the cohesive sediment phases the numerical simulations suggest that sediment induced stratification effects are of the same order of magnitude as turbulent dissipation and thus play a significant role in the turbulent kinetic energy balance within the tidal boundary layer however inside the wave boundary layer the ratio of stratification to shear induced turbulence production i e gradient richardson number decreases significantly and shear induced turbulence production dominates for these observations the vertical structures of currents and reynolds stresses are relatively insensitive to the exact floc size

diffuse spectral reflectance as a proxy for percent carbonate content in north atlantic sediments diffuse reflectance records from fern drift in the north atlantic faithfully record sediment percent carbonate a high resolu tion reflectance based age model for these sediments derived from an orbitally tuned age model for western equatorial atlantic ceara rise sediments was generated by spectral frequency mapping power spectra of the fern drift record indicate statistically significant sub milankovitch cyclicity at 7 6 8 4 and 4 8 6 1 kyr we infer that these 8 and 5 kyr cycles document a linkage between north and equa torial atlantic climate given our ability to correlate these records these climate cycles influence atlantic basin carbonate prior to the intensification of northern hemisphere glaciation and thus must arise from some portion of the climate system other than the dynamics of large ice sheets the presence of these peaks which could be related to equatorial clipped precession implies a possible non linear response to milankovitch forcing abstract diffuse reflectance records from feni drift in the north atlantic faithfully record sediment percent carbonate a high resolu tion reflectance based age model for these sediments derived from an orbitally tuned age model for western equatorial atlantic ceara rise sediments was generated by spectral frequency mapping power spectra of the feni drift record indicate statistically significant sub milankovitch cyclicity at 7 6 8 4 and 4 8 6 1 kyr we infer that these 8 and 5 kyr cycles document a linkage between north and equa torial atlantic climate given our ability to correlate these records these climate cycles influence atlantic basin carbonate prior to the intensification of northern hemisphere glaciation and thus must arise from some portion of the climate system other than the dynamics of large ice sheets the presence of these peaks which could be related to equatorial clipped precession implies a possible non linear response to milankovitch forcing

wave mud interaction over the muddy atchafalaya subaqueous clinoform louisiana united states wave processes 1 observations of wave and sediment processes collected at two locations on the atchafalaya inner shelf show that wave dissipation in shallow muddy environments is strongly coupled to bed sediment reworking by waves during an energetic wave event 2 m significant wave height in 5 m water depth acoustic backscatter records suggest that sediment in the surficial bed layer evolves from consolidated mud through liquefaction fluid mud formation and hindered settling to gelled under consolidated mud net swell dissipation increases steadily during the storm from negligible prestorm values consistent with bed softening but shows no correlation with detectable fluid mud layers remarkably the maximum dissipation rate occurs poststorm when no fluid mud layers are present in the waning stage of the storm the contribution of different wave forcing processes to wave dissipation is analyzed using an inverse modeling approach based on a nonlinear three wave interaction model although wave mud interaction dominates dissipative processes nonlinear three wave interactions control the shape of the frequency distribution of the dissipation rate in the wake of the storm the viscosity values predicted by the inverse modeling converge toward measured values characteristic for gelled mud in a trend that is consistent with a fluid mud entering dewatering and consolidation stages

rounding hinges to fault bend folding geometric and kinematic implications fault bend folding is a common folding mechanism in thrust and fold belts worldwide the widely used kink band geometric model of fault bend folding necessitates complex ramp segmentations to reproduce the rounded shape of many natural thrust related anticlines curvilinear hinge sectors provide a geometric and kinematic alternative solution to kink bands for modelling curved hinge folds we developed an analytical solution for modelling fault bend folding using circular hinge sectors the velocity field of this kinematic solution is different from that associated with the classical kink style model our solution predicts the development of curvilinear anticlines above staircase fault geometries the occurrence of limb rotation and consequently the development of rotational syngrowth wedges on both the forelimb and the crest conversely to the kink style kinematics curvilinear hinge sectors imply a dependence of deformation intensity from the fold shape and stratigraphic position of the folded layer application to natural thrust related anticlines validates the effectiveness of curvilinear fault bend folding

enhanced productivity on the iberian margin during glacial interglacial transitions revealed by barium and diatoms the portuguese margin is at a critical location for studies of the ocean s behaviour during glacial interglacial climatic changes and the rapid accumulation rates of the sediments enable high resolution palaeoclimatic investigation the sedimentary record of the past 350 ka has been investigated in a 35 m long core from 3 5 km water depth on the slope at 40 n by geochemical isotopic and micropalaeontological techniques the caco3 content of this core as a function of time contains significant milankovitch orbital frequencies of 18 8 23 7 38 0 and 100 6 ka but these are driven primarily by dilution by clay flux variations rather than by caco3 productivity variations the largest signals in the productivity indicators corg ba al and diatom abundance are all observed as simultaneous peaks at the oxygen isotope stage boundaries 10 9 and 6 5 with the signal magnitude in the order 10 9 6 5 for all three indicators smaller coincident signals in corg ba al but not diatoms are also observed at the oxygen isotope stage 2 1 boundary other less prominent peaks in the corg and ba al profiles occur elsewhere including heinrich event horizons but these are not always simultaneous and none contain evidence of the dissolution prone diatom microfossils the 10 9 6 5 and 2 1 oxygen isotope stage transitions represent the three most extreme glacial interglacial sea level rises in the past 350 ky possibly in the same sequence of magnitude when sea level rose rapidly by 120 m from glacial low stands to interglacial high stands the productivity signals at these transitions are contained within 5 ka including bioturbation

geometric analysis of hybrid fault propagation detachment folds abstract fault propagation folds and many detachment folds may be analyzed using a single geometric model a modification of a previously published approach allows the interpreter to quantitatively predict thrust fault trajectory and displacement from the geometry of an associated fault propagation detachment anticline because geological and geophysical data typically constrain the mesoscopic and macroscopic forms of folds more completely and more accurately than they constrain faults this technique offers a useful way to rapidly construct balanced structural cross sections in detached fold thrust systems

implications for sedimentation changes on the iberian margin over the last two glacial interglacial transitions from 230thexcess 0 systematics abstract the portuguese margin is well suited for studies of the contrasts in north atlantic circulation during glacial and interglacial times because of its rapid sediment accumulation rate this paper reports a 230thexcess 0 based study of sediment accumulation over the past 140 ky a period which includes the last two glacial interglacial transitions in two cores at 2 4 and 3 5 km water depth on a slope transect at 40 n although the independently determined mean sediment accumulation fluxes over the past 140 ky are unequivocally high with means of 13 2 and 10 5 g cm 2 ky 1 in the two cores conventional application of the 230thexcess 0 method yields consistently lower fluxes with means of 3 5 and 3 8 g cm 2 ky 1 these 230thexcess 0 estimates are interpreted as representations of the regional depositional flux through time this 230thexcess 0 regional flux is composed of a carbonate flux of

a high resolution coupled riverine flow tide wind wind wave and storm surge model for southern louisiana and mississippi part i model development and validation abstract a coupled system of wind wind wave and coastal circulation models has been implemented for southern louisiana and mississippi to simulate riverine flows tides wind waves and hurricane storm surge in the region the system combines the noaa hurricane research division wind analysis system h wind and the interactive objective kinematic analysis ioka kinematic wind analyses the wave model wam offshore and steady state irregular wave stwave nearshore wind wave models and the advanced circulation adcirc basin to channel scale unstructured grid circulation model the system emphasizes a high resolution down to 50 m representation of the geometry bathymetry and topography nonlinear coupling of all processes including wind wave radiation stress induced set up and objective specification of frictional parameters based on land cover databases and commonly used parameters riverine flows and tides are validated for no storm conditions while winds wind waves hydrographs and high wa

variability of the western mediterranean sea surface temperature during the last 25 000 years and its connection with the northern hemisphere climatic changes sea surface temperature sst profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a w e latitudinal transect encompassing the gulf of cadiz atlantic ocean the alboran sea and the southern tyrrhenian sea western mediterranean the results document the sensitivity of the mediterranean region to the short climatic changes of the north atlantic ocean particularly those involving the latitudinal position of the polar front the amplitude of the sst oscillations increases toward the tyrrhenian sea indicating an amplification effect of the atlantic signal by the climatic regime of the mediterranean region all studied cores show a shorter cooling phase 700 years for the younger dryas yd than that observed in the north atlantic region 1200 years this time diachroneity is related to an intra yd climatic change documented in the european continent minor oscillations in the southward displacement of the north atlantic polar front may also have driven this early warming in the studied area during the holocene a regional diachroneity propagating west to east is observed for the sst maxima 11 5 10 2 kyr b p in the gulf of cadiz 10 9 kyr b p in the alboran sea and 8 9 8 4 kyr b p in the thyrrenian sea a general cooling trend from these sst maxima to present day is observed during this stage which is marked by short cooling oscillations with a periodicity of 730 40 years and its harmonics

modern and last glacial maximum eolian sedimentation patterns in the atlantic ocean interpreted from sediment iron oxide content eolian dust derived from the desert regions of north africa is blown far into the tropical atlantic ocean by persistent easterly and northeasterly winds in this paper we demonstrate that the iron oxides hematite and goethite are a worthwhile addition to proxy monitors of eolian sedimentation in the tropical atlantic iron oxides are identified by diffuse reflectance spectrophotometry a technique capable of identifying these minerals in concentrations as low as 0 01 by weight we analyze samples from both the modern and last glacial maximum lgm synoptic levels from 178 sample locations yielding a total of 356 samples distributed throughout the atlantic ocean to determine the relative contribution of the iron oxides we factor analyzed the modern and lgm levels as a single data set the iron oxide factor explains about 25 of the variance in the combined core top and lgm data set mapped factor scores for the lgm and modern ocean indicate high iron oxide values are present in just two regions one off eastern north america and the other off northwest africa in the region off eastern north america iron oxide occurs primarily during the lgm as the previously noted brick red lutite a unique sediment type derived from the erosion of permo carboniferous red beds in atlantic canada a larger lobe shaped area of iron oxide rich sediment is present off northwest africa in both the modern and lgm levels the modern iron oxide lobe is coincident with the distribution of eolian dust as determined by observations from ships satellites and analysis of air samples during the lgm iron oxides exhibit a similar distribution except the southern margin of the region shifts equatorward and iron oxide concentration increases

nonlinear wave dynamics in the presence of mud induced dissipation on atchafalaya shelf louisiana usa abstract the interplay between wave nonlinearity and mud induced dissipation is studied here using wave and sediment transport measurements collected in winter 2008 on the atchafalaya shelf louisiana between the 8 m and the 4 m isobaths this study focuses on the relatively energetic storm that occurred on march 4th 2 m wave height in 8 m water depth which caused significant bed reworking and left in its wake a 20 cm layer of hindered settling fluid mud while the net wave dissipation rate was maximal during the hindered settling phase after the storm consistent with previous observations significant dissipation was observed throughout the storm duration with a secondary maximum associated with the peak of the storm and the maximum bed reworking effects the effects of mud induced dissipation on the nonlinear shoaling process are investigated here using triads a newly developed spectral model for nonlinear shoaling of waves with mud parameter values estimated using a crude inverse modeling approach the model was used to separate the effects of mud induced dissipation from nonlinear transfers during both the erosion and deposition phases of bed reworking numerical simulations show that nonlinear transfers are always active even under strong dissipation regimes remarkably they also suggest that heavy mud induced dissipation causes the nonlinear energy cascade to revert direction with bulk transfers occurring from high frequency to low frequency spectral bands this supports the hypothesis that the interplay between mud induced dissipation which is much more significant than the bottom dissipation over sandy beds and wave nonlinearity can drain energy from the entire spectrum and not just from the frequency bands that interact directly with the seafloor the decay of high frequency variance induced by the reversal of spectral flux in effect reduces the nonlinearity of the wave field

wave sediment interaction on a muddy inner shelf during hurricane claudette measurements of wave and suspended sediment concentration ssc were conducted near the 5 m isobath on the muddy inner shelf fronting atchafalaya bay louisiana during hurricane claudette the data show that wave and current activity resuspended large quantities of sediment with ssc r 0 5 kg m 3 throughout the water column in the waning phase of the storm settling generated a suspension layer with concentrations over 1 7 kg m 3 measured as high as 1 m above the bottom numerical simulations of post storm sediment settling showed that observations are consistent with a high density fluid mud layer ssc between 10 and 20 kg m 3 and separated from the upper water column by a lutocline located at about 1 m above the bottom the formation of the fluid mud layer is correlated with strong broad spectrum wave dissipation consistent with the hypothesis that surface interface wave interaction plays an important part in the energy transfer from the surface to the soft bottom 2004 elsevier ltd all rights reserved

a compilation of western european terrestrial records 60 8 ka bp towards an understanding of latitudinal climatic gradients terrestrial records of past climatic conditions such as lake sediments and speleothems provide data of great importance for understanding environmental changes however unlike marine and ice core records terrestrial palaeodata are often not available in databases or in a format that is easily accessible to the non specialist as a consequence many excellent terrestrial records are unknown to the broader palaeoclimate community and are not included in compilations comparisons or modelling exercises here we present a compilation of western european terrestrial palaeo records covering entirely or partially the 60 8 ka intimate time period the compilation contains 56 natural archives including lake records speleothems ice cores and terrestrial proxies in marine records the compilation is limited to include records of high temporal resolution and or records that provide climate proxies or quantitative reconstructions of environmental parameters such as temperature or precipitation and that are of relevance and interest to a broader community we briefly review the different types of terrestrial archives their respective proxies their interpretation and their application for palaeoclimatic reconstructions we also discuss the importance of independent chronologies and the issue of record synchronization the aim of this exercise is to provide the wider palaeo community with a consistent compilation of high quality terrestrial records to facilitate model data comparisons and to identify key areas of interest for future investigations we use the compilation to investigate western european latitudinal climate gradients during the deglacial period and despite of poorly constrained chronologies for the older records we summarize the main results obtained from nw and sw european terrestrial records before the lgm

new insights into deformation mechanisms in the gravitationally driven niger delta deep water fold and thrust belt we use two and three dimensional seismic reflection data from the deep water niger delta fold and thrust belt to document evidence for two discrete postfaulting deformation mechanisms an early phase of thrust propagation folding is followed by folding caused by thickness changes within the basal shale detachment unit the later phase of folding is caused by a lateral redistribution of the strata within the basal detachment unit this example of late deformation occurred over a 4 5 m y period as a result of the displacement of approximately 590 km3 370 mi3 of the underlying strata within the detachment unit in another deformation event in the basal detachment unit about 160 km3 100 mi3 moved laterally creating a synform in the overburden and parallel onlap fill indicative of the relatively rapid creation of accommodation space on the basis of seismic reflection data from the delta and a consideration of the volumes and rates of movement of sedimentary rock we conclude that the poorly imaged succession commonly referred to as mobile shale cannot deform solely by ductile mechanisms as interpretations of shale tectonic provinces have commonly suggested but instead by brittle processes that involve thickening by thrust faulting and subseismic accommodation structures processes such as liquefaction where a complete loss of shear strength is observed had a minimal function therefore the term mobile shale in this setting is widely exaggerated an awareness of postfaulting deformation mechanisms will be important for the successful exploration of gravitationally driven fold and thrust belts

new techniques in sediment core analysis an introduction marine sediment cores are the fundamental data source for information on seabed character depositional history and environmental change they provide raw data for a wide range of research including studies of global climate change palaeoceanography slope stability oil exploration pollution assessment and control and sea floor surveys for laying cables pipelines and siting of sea floor structures during the last three decades a varied suite of new technologies have been developed to analyse cores often non destructively to produce high quality closely spaced co located downcore measurements characterizing sediment physical properties geochemistry and composition in unprecedented detail distributions of a variety of palaeoenvironmentally significant proxies can now be logged at decadal and in some cases even annual or subannual scales allowing detailed insights into the history of climate and associated environmental change these advances have had a profound effect on many aspects of the earth sciences particularly palaeoceanography in this paper we review recent advances in analytical and logging technology and their application to the analysis of sediment cores developments in providing access to core data and associated datasets and data mining technology in order to integrate and interpret new and legacy datasets within the wider context of sea floor studies are also discussed despite the great advances in this field however challenges remain particularly in the development of standard measurement and calibration methodologies and in the development of data analysis methods new data visualization tools and techniques need to be developed to optimize the interpretation process and maximize scientific value amplified collaboration environments and tools are needed in order to capitalize on our analysis and interpretation capability of large multi parameter datasets sophisticated yet simple to use searchable internet databases with universal access and secure long term funding and data products resulting in user defined data mining query and display so far pioneered in the usa and australia provide robust models for efficient and effective core data stewardship

observations on cohesive bed reworking by waves atchafalaya shelf louisiana 1 wave current acoustic backscatter and suspended sediment concentration measurements both single point and vertical profiles estimated by conversion of acoustic backscatter data are used to investigate wave current cohesive sediment interaction on the muddy atchafalaya inner shelf during an energetic storm we propose that bed state follows a cycle of dilation due to fluidization erosion deposition with fluid mud formation and consolidation a one dimensional vertical cohesive sediment transport model is calibrated using current and concentration profiles to estimate the physical parameters that could not be measured directly e g bottom stresses estimated bed position and computed bottom stresses suggest that the critical erosion threshold is in the range of 0 3 pa to 0 5 pa the study site is impacted by a sediment laden fresh water plume coming from the atchafalaya river mouth bed density evolution during the storm is estimated from vertical sediment exchange between the water column and the bed excluding the duration of passage of a sediment carrying water front the values are in the range of 1 030 kg m3 to 1 200 kg m3and indicate that the bed density increases during the erosion phase and decreases during deposition at the end of the storm it shows a steady increasing trend during hindered settling and exceeds the space filling value during consolidation both the critical erosion shear stress and bed density values are consistent with the results of laboratory tests on samples from the experimental site

late holocene rupture of the northern san andreas fault and possible stress linkage to the cascadia subduction zone we relate the late holocene northern san andreas fault nsaf paleo seismic history developed using marine sediment cores along the northern california continental margin to a similar dataset of cores collected along the cascadia margin including channels from barclay canyon off vancouver island to just north of mon terey bay stratigraphic correlation and evidence of synchronous triggering imply earthquake origin and both temporal records are compatible with onshore paleoseis mic data in order to make comparisons between the temporal earthquake records from the nsaf and cascadia we refine correlations of southern cascadia great earth quakes including the land paleoseismic record along the nsaf during the last 2800 yr 15 turbidites including one likely from the great 1906 earthquake establish an average repeat time of 200 yr similar to the onshore value of 240 yr the combined land and marine paleoseismic record from the southern cascadia subduction zone includes a similar number of events during the same period while the average recurrence interval for full margin cascadia events is 520 yr the southern cascadia margin has a repeat time of 220 yr similar to that of the nsaf thirteen of the 15 nsaf events were preceded by cascadia events by 0 80 yr averaging 25 45 yr as compared to 80 400 yr by which cascadia events follow the nsaf based on the temporal association we model the coseismic and cumulative post seismic deformation from great cascadia megathrust events and compute related stress changes along the nsaf in order to test the possibility that cascadia earth quakes triggered the penultimate and perhaps other nsaf events the coulomb fail ure stress cfs resulting from viscous deformation related to a cascadia earthquake over 60 yr does not contribute significantly to the total cfs on the nsaf however the coseismic deformation increases cfs on the northern san andreas fault nsaf b y up to about 9 bars offshore of point delgada most likely enough to trigger that fault to fail in north to south propagating ruptures

lateral variations in sediment composition and bedding in middle triassic interplatform basins buchenstein formation southern alps italy hemipelagic deposits are widespread in triassic sequences of the alpine belt and provide important data for stratigraphy and the study of bedding rhythms the area of the western and central dolomites of northern italy escaped strong alpidic deformation and preserves such deposits in their original palaeogeographic setting the buchenstein formation the object of this study was deposited in up to 1000 m deep middle triassic interplatform basins which extend over an area of 500 km 2 within the dolomites excellent outcrops and volcaniclastic markers allow a detailed correlation of the formation in both laminated anoxic and bioturbated facies down to a bed scale and show its relationship to coeval carbonate platforms correlation of lithostratigraphically well constrained intervals in the bioturbated facies reveal that lateral thickening and thinning of the deposits depends on the amount of shallow water debris in the succession and is a function of the distance to coeval carbonate platform sources in the laminated background deposit thickness variations in limestones and marls parallel the thickness variations in ash layers and were caused by local redeposition of sediment on the basin floor lateral persistence of laminae indicates that bottom currents were weak in the buchenstein basin but were able to redeposit mud in a significant way in the area around seceda and geisler western dolomites a lateral transition from dark grey laminated to grey bioturbated to red bioturbated facies is observed which is probably linked to local relief with different oxygenation conditions on the sea floor a comparison shows that decimetre scale bedding is preserved in all facies types and that the bedding rhythm is partly the result of different cementation of the sediment during early diagenesis correlation of individual layers in the bioturbated facies reveals that beds are thicker and enriched in lime mud in the western part of the basin and decrease in thickness and contain less micrite towards the east further away from the main shallow water areas nearslope calciturbidites change gradually from distinct layers into lateral arrays of micrite nodules and bands further out in the basin these observations point to a platform source of lime mud in the buchenstein basin

fault displacement gradient folds and the structure at lost hills california u s a abstract geometric models of fault propagation folds require that the underlying fault tip propagate upward across layering however related folds can be generated if the tip remains stationary or even moves back along the ramp as a pre existing fault is reactivated fault propagation folds detachment folds as well as those produced when there is no propagation are generated by a displacement gradient along the underlying fault and as a general class can be called fault displacement gradient folds new geometric equations are derived which relate fold shape to displacement gradient and fault propagation folds are a special case of these more general equations growth sequences associated with these structures have been used to distinguish fault propagation folds from fault bend folds when the underlying structure is obscured a displacement gradient fold in which the fault tip retreats back down the ramp generates a growth sequence that in some cases could be confused with that of a fault bend fold the structure at lost hills in the san joaquin valley of california u s a has been interpreted as a fault bend fold but it may be a displacement gradient fold which formed as a pre existing fault was reactivated during a pliocene change in plate motion

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

constraints on deformation mechanisms during folding provided by rock physical properties a case study at sheep mountain anticline wyoming usa summary the sheep mountain anticline wyoming usa is a well exposed asymmetric basementcored anticline that formed during the laramide orogeny in the early tertiary in order to unravel the history of strain during folding we carried out combined anisotropy of magnetic susceptibility ams anisotropy of p wave velocity apwv and fry strain analyses the results are compared to previously published stress strain data from calcite twins at the microscopic scale and from fracture sets at the mesoscopic scale and are used to discuss the kinematics and mechanics of forced folding the results obtained in sandstone and carbonate lithologies demonstrate a good agreement between 1 the principal axes of the ams and apwv tensors 2 stress strain tensors derived from calcite twins 3 fry strain axes and mesoscopic fracture sets furthermore these tensors are coaxial with the main structural trends of the anticline the differences between ams and apwv fabrics on one hand and the differential stress values of the forelimb and the backlimb on the other hand emphasize how the macroscopic asymmetry of sheep mountain anticline affects the strain pattern at the microscopic scale the data set presented in this paper offers a consistent mechanical scenario for the development of sheep mountain anticline

relay zones between mesoscopic thrust faults in layered sedimentary sequences abstract we examine the geometry formation and destruction of relay zones in well bedded sedimentary sequences containing thrust fault segments with maximum observed displacements of 0 64 8 m contractional extensional and neutral relay zones are distinguished based on the stepping sense of the interacting fault segments and the orientation of the associated fault slip vectors large displacement gradients 0 17 1 0 in relay zones are mainly accommodated by folding with aggregate displacements maintained across segment boundaries and a significant component of the fault slip converted to fold related shortening folds in contractional relay zones verge in the direction of hanging wall motion with the steeper limb defining a parallelogram shaped zone between thrusts fault segment lengths are established after minimal displacement and folds in relay zones grow between segments as displacement accrues on the thrusts with increasing displacement upper and lower thrust tip lines in contractional and extensional relay zones are fixed at stratigraphic boundaries while the lateral thrust tip lines may propagate in a strike parallel direction upper and lower tip lines may eventually propagate to bypass relay zones that formed early in the fault growth history contractional relay zones remain intact at higher displacements than extensional relay zones

promotion of meridional overturning by mediterranean derived salt during the last deglaciation we demonstrate that changes in the behavior of the mediterranean outflow water mow prior to and through the last deglaciation played an important role in promoting meridional overturning circulation moc estimation of past mow salt and heat fluxes indicates that they gradually increased through the last deglaciation between 17 5 and 14 6 thousand years ago ka b p where b p references year 1950 net evaporation from the mediterranean exported sufficient fresh water from the north atlantic catchment to cause an average salinity increase of 0 5 psu throughout the upper 2000 m of the entire north atlantic to the north of 25

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

late stage evolution of fault propagation folds principles and example abstract fault propagation folding commonly occurs near the fronts of mountain belts this type of folding may even represent in some thrust systems the major mode of deformation however fault propagation folds are frequently altered by two kinds of late stage evolution breakthrough thrusting or transport on the flat we model the geometric features of these kinds of fold in particular the late stage modification and present the algorithms and equations used in an original program an application based on an example from the atlas mountains of algeria illustrates the main features of the model

response of iberian margin sediments to orbital and suborbital forcing over the past 420 ka here we report 420 kyr long records of sediment geochemical and color variations from the southwestern iberian margin we synchronized the iberian margin sediment record to antarctic ice cores and speleothem records on millennial time scales and investigated the phase responses relative to orbital forcing of multiple proxy records available from these cores iberian margin sediments contain strong precession power sediment redness a and 570 560 nm and the ratio of long chain alcohols to n alkanes c26oh c26oh c29 are highly coherent and in phase with precession redder layers and more oxidizing conditions low alcohol ratio occur near precession minima summer insolation maxima we suggest these proxies respond rapidly to low latitude insolation forcing by wind driven processes e g dust transport upwelling precipitation most iberian margin sediment parameters lag obliquity maxima by 7 8 ka indicating a consistent linear response to insolation forcing at obliquity frequencies driven mainly by high latitude processes although the lengths of the time series are short 420 ka for detecting 100 kyr eccentricity cycles the phase relationships support those obtained by shackleton antarctic temperature and the iberian margin alcohol ratios c26oh c26oh c29 lead eccentricity maxima by 6 kyr with lower ratios increased oxygenation occurring at eccentricity maxima co2 ch4 and iberian sst are nearly in phase with eccentricity and minimum ice volume as inferred from pacific 18oseawater lags eccentricity maxima by 10 kyr the phase relationships derived in this study continue to support a potential role of the earth s carbon cycle in contributing to the 100 kyr cycle

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

determining the composition of late quaternary marine sediments from nuv vis and nir diffuse reflectance spectra abstract as the length of marine cores increases and sampling intervals decrease the need for rapid and inexpensive means of determining sediment composition has become apparent in this study we examine one potentially useful technique for assessing compositional changes in marine cores diffuse reflectance spectrophotometry we examined nearultraviolet visible and near infrared reflectance spectra from five data sets each data set consists of calibration samples and test samples the calibration samples spectra were related to a sediment component using multiple linear regression the resulting regression or calibration equations were then evaluated using the test samples calibration equations were written relating spectra to several sediment components including carbonate atlantic and east pacific rise odp site 847 organic carbon content atlantic and east pacific rise and opal content east pacific rise the correlation coefficients for the regression equations ranged from a high of 0 99 for carbonate and opal at odp site 847 to a low of 0 97 for atlantic carbonate indicating that spectral variations are highly correlated to sediment composition all of the equations include a substantial number of variables from shorter visible and longer near ultraviolet wavelengths suggesting that these wavelengths are especially important for devices designed specifically to scan marine cores although equations for estimating organic and carbonate content appear independent of other sediment components the opal equation is strongly dependent on carbonate content indicating that opal concentration is correlated to carbonate content tests of the calibration equations indicated that all our equations reasonably estimate the pattern of changes either down core or in surface sediments where our spectral estimates have difficulty is with absolute values frequently over or underestimating observed values by a substantial amount within these limitations diffuse reflectance spectrophotometry can be a useful tool for characterizing marine cores and as our understanding of the relationship between spectra and mineralogy improves so will estimates of absolute values

sediment delivery and depositional patterns off adelie land east antarctica in relation to late quaternary climatic cycles article i nfo this study focuses on the understanding of depositional patterns over late quaternary glacial interglacial cycles and of the influence of diagenesis on geochemical sedimentary records from the continental margin off adelie land east antarctica we provide a complete analysis of the 30 m long sediment core md03 2603 collected on a deep sea sediment mound deposit the lr04 benthic oxygen isotope stack vs down core records of ba al and ba ti atomic ratios reflectance data and micropaleontological evidence allow to determine a detailed chronology back to 490 ka bp long lived uranium and thorium 238 u 234 u 232 th and 230 th provide an assessment of lateral vs vertical sediment advection by constraining the sediment focusing factor is high in most glacial intervals when mostly detrital material was transported down slope and focused to the core area interglacials display highs in ba al and ba ti coupled to low values related to stronger contour current flow biogenic fractions are more abundant during interglacials and more diluted by detrital fractions during glacials the diatom assemblage is dominated by the open ocean species fragilariopsis kerguelensis but glacial intervals display an increase of sea ice related and coastal species the integrated approach high resolution record of major and minor elements uauth 15 n norg 13 c and corg provides key insights into how redox conditions affect glacial interglacial sedimentation processes our evidence shows that diagenetic effects due to development of reducing conditions and consequent higher preservation of organic matter may overprint the paleoclimatic significance of some proxies involved into a sequence of diagenetic remineralization pathways comparison of the marine record to ice core data epica dome c edc allows to extend the information to the whole east antarctic margin sediment proxies of increased burial of biogenic material or increased preservation of organic matter are linked to climatic amelioration on the continent highs in edc dust flux correlate with high mn al and mo al ratios within the sediment record confirming that establishment of colder conditions on the continent triggered changes in sedimentation rates at the glacial interglacial transition which in turn affected the development of reducing redox fronts within the sediment

digital image analysis of outcropping sediments comparison to photospectrometric data from quaternary loess deposits at şanoviţa romania and achenheim france abstract the possibility to use colour data as extracted from two selected loess paleosol sequences is discussed here colour data are a fast and inexpensive method of proxy data generation we compare the outcome from analysing outcrop images taken by digital cameras in the field and spectral colour data as determined under controlled laboratory conditions by nature differences can be expected due to variations in illumination moisture and sample preparation outcrop inclination may be an issue for photographs correction for this is possible when marks can be used for rectification in both cases the data extracted from the images match the visual impression of the photos well and are useful for obtaining a more quantitative measure for field observations smoothness as measured by autocorrelation is high for an image from achenheim france where an image with a width of ca 1 1 m and a depth of 1 6 m was analysed data from a narrower image part from anovi a romania are noisier in both cases a significant correlation between data extracted by digital image analysis and laboratory measurements could be established suggesting that image analysis is a useful tool where outcrop and light conditions allow good photographs with similar illumination especially where high resolution proxy data is required