modern sedimentary processes in the wilmington canyon area u s east coast abstract sedimentary processes active in the wilmington canyon area during the past century are documented from geochronologic sedimentologic and radiographic analysis of sediment cores collected using primarily d s r v alvin site selection for the alvin dives and for collection of box and kasten cores was achieved using sea marc and seabeam data allowing accurate sampling of numerous subenvironments from this extensively dissected area of the continental margin 210 pb sediment accumulation rates from intercanyon areas are highest on the upper slope 1 7 mm yr 140 mg cm 2 yr and decrease with water depth to about 0 4 mm yr 36 mg cm 2 yr on the upper rise within submarine canyons accumulation rates vary dramatically from a maximum of 6 mm yr 500 mg cm 2 yr to less than 0 3 mm yr 22 mg cm 2 yr higher accumulation rates in canyons occur as a result of additional supply of older sediment probably from bioerosion of the canyon walls this is supported by observations from d s r v alvin reduced 210 pb activities and indurated mud clasts observed in several canyon cores extremely low accumulation rates in wilmington and south wilmington canyons are probably the result of strong episodic boundary currents non steady state 210 pb profiles and sedimentologic data indicate small scale mass wasting in south heyes canyon and on the lower slope and rise just north of wilmington canyon

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

observations of the internal tide in monterey canyon abstract data from two shipboard experiments in 1994 designed to observe the semidiurnal internal tide in monterey canyon reveal semidiurnal currents of about 20 cm s 1 which is an order of magnitude larger than the estimated barotropic tidal currents the kinetic and potential energy evidenced by isopycnal displacements of about 50 m was greatest along paths following the characteristics calculated from linear theory these energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of monterey bay energy propagated shoreward during the april experiment itex1 whereas a standing wave that is an internal seiche was observed in october itex2 the difference is attributed to changes in stratification between the two experiments higher energy levels were present during itex1 which took place near the spring phase of the fortnightly 14 8 days cycle in sea level while itex2 occurred close to the neap phase further evide

the characteristic time scale for basin hydrological response using radar data abstract the transformation of rainfall into runoff at a basin outlet is the combined effect of many hydrological processes which occur at a wide range of spatial and temporal scales however determining the scale of the combined hydrological response of the basin is still problematic and concepts for its definition are yet to be identified in this paper high resolution meteorological radar data are used for the determination of a characteristic temporal scale for the hydrological response of the basin the response time scale t s t s is defined as the time scale at which the pattern of the time averaged radar rainfall hietograph is most similar to the pattern of the measured outlet runoff hydrograph the existence of such similarity at a relatively stable time scale for a specific basin indicates that it is an intrinsic property of the basin and is related to its hydrological response the identification of the response time scale is carried out by analysis of observations only without assuming a specific rainfall runoff model t s is examined in four small basins 10 100 km 2 in israel the spatial scale is assumed as the entire basin for all analyzed basins a stable response time scale is identified relatively short time scales are found for the urban and arid basins 15 30 min while for the rural basins longer time scale are identified 90 180 min the issues of relationship between the response time scale and basin properties and modeling at the response time scale have yet to be determined

p and s wave velocity models of shallow dry sand formations from surface wave multimodal inversion abstractsurficial formations composed of loose dry granular materials constitute a challenging target for seismic characterization they exhibit a peculiar seismic behavior characterized by a nonlinear seismic velocity gradient with depth that follows a power law relationship which is a function of the effective stress the p and s wave velocity profiles are then characterized by a power law trend and they can be defined by two power law exponents p s and two power law coefficients p s in case of depth independent poisson s ratio the p wave velocity profile can be defined using the vs power law parameters and poisson s ratio because body wave investigation techniques e g p wave tomography may perform ineffectively on such materials because of high attenuation we addressed the potential of surface wave method for a reliable seismic characterization of shallow formations of dry uncompacted granular materials we took into account the dependence of seismic wave velocity on effective pressure

effect of basal friction on surface and volumetric strain in models of convergent settings measured by laser scanner abstract this paper uses measurements by a high accuracy laser scanner to investigate the role of basal friction on surface and volumetric strains in sandbox models simulating fold thrust belts and accretionary wedges we monitor progressive deformation wedge growth and strain distribution in three models with similar initial boundary conditions but with different basal frictions our analyses show that in addition to influencing the kinematics and geometry of model wedges basal friction also governs both the surface and volumetric strains of the wedge after 16 3 bulk shortening the volume decreased 5 0 5 9 5 0 5 and 12 5 0 5 in the models shortened above low intermediate and high friction decollements respectively applied to nature our model results suggest that more compaction and penetrative strain is expected in convergent settings with a high friction decollement than those shortened above a low friction decollement or a weak basal bed like the salt formation under parts of the zagros fold thrust belt this volume decrease probably reduces the porosity in the deformed lithologies

a preliminary experimental study of turbidite fan deposits discussion parsons et al 2002 have discussed an experimental study of turbidite fan deposits for understanding lobe switching because of the perceived importance of turbidite lobes in hydrocarbon reservoirs shanmugam and moiola 1991 this experimental study could be of value to the oil industry also experimental studies are the primary means of unraveling the complexities of the process dynamics of turbidity currents and their deposits this is because the other two options namely 1 direct observations of turbidity currents in the deep sea e g shepard et al 1979 and 2 attempts to understand turbidity currents and their fan deposits on the basis of outcrop study on land e g mutti and ricci lucchi 1972 have proven to be unsuccessful e g mutti 1992 shanmugam 2002 therefore the experimental study by parsons et al 2002 requires close scrutiny i would like to debate the following issues discussed in the paper 1 reynolds number 2 grain size variation 3 depositional bedforms and 4 importance of mud proper scaling of experimental flows to natural turbidity currents is vital according to parsons et al 2002 p 626 the reynolds number of bottom boundary layer in natural turbidity currents is often greater than 100 whereas the reynolds number of experimental turbidity currents was always much less than unity parsons et al 2002 p 626 also acknowledged that the particle reynolds number in these experiments is not compatible with values of natural flows the authors attributed these scaling difficulties to the density of the particles and the viscosity of the fluid used in their

bioavailable compounds in sinking particulate organic matter blanes canyon nw mediterranean sea effects of a large storm and sea surface biological processes abstract to ascertain whether the blanes submarine canyon functions as a conduit of labile organic compounds to the deep margin we analyzed phytopigment protein carbohydrate and lipid contents of sinking particles during a 6 months period comprised between a large storm event and the spring phytoplankton bloom four sediment traps were deployed at 300 900 1200 and 1500 m depth along the axis of the canyon from november 2008 to april 2009 fluxes of all study variables organic carbon proteins carbohydrates and lipids peaked from mid to late december afterwards organic matter fluxes in the upper canyon decreased to values comparable bc1200 or much lower bc900 than those observed at the beginning of the monitoring period the algal fraction of biopolymeric c i e the percentage contribution of phytopigments to biopolymeric c utilized here as an indicator of particles freshness ranging from 14 to about 100 was generally low median value about 32 and showed the highest values from november to early december 2008 at all stations except for the station at 1200 m which peaks in april 2009 a severe storm that occurred the 26th of december 2008 determined a strong increase in the downward transport of organic matter along the blanes canyon though associated with a decrease in its nutritional quality values of the protein to carbohydrate ratio utilized here as an indicator of particles nutritional quality ranged from 0 4 to 2 0 increasing from late winter to early spring at 900 and 1200 m depth in association with the spring phytoplankton bloom in superficial waters the material collected by sediment traps in spring had a higher nutritional value than in autumn winter at both stations according to the optimal foraging theory the results of this study suggest that following winter episodic events deep sea detritus feeders would need to ingest more detritus to fulfill their requirements for labile food than in spring when fresher material is derived from sinking particles associated with phytoplankton blooms we conclude that whilst submarine canyons like the blanes canyon act as major conduits for material exported from the continental shelf after high energy episodic events the supply of labile food to the deep sea benthic ecosystem is connected to biological processes occurring at the sea surface

description of new dry granular materials of variable cohesion and friction coefficient implications for laboratory modeling of the brittle crust abstract cohesion and friction coefficient are fundamental parameters for scaling brittle deformation in laboratory models of geological processes however they are commonly not experimental variable whereas 1 rocks range from cohesion less to strongly cohesive and from low friction to high friction and 2 strata exhibit substantial cohesion and friction contrasts this brittle paradox implies that the effects of brittle properties on processes involving brittle deformation cannot be tested in laboratory models solving this paradox requires the use of dry granular materials of tunable and controllable brittle properties in this paper we describe dry mixtures of fine grained cohesive high friction silica powder sp and low cohesion low friction glass microspheres gm that fulfill this requirement we systematically estimated the cohesions and friction coefficients of mixtures of variable proportions using two independent methods 1 a classic hubbert type shear box to determine the extrapolated cohesion c and friction coefficient and 2 direct measurements of the tensile strength t 0 and the height h of open fractures to calculate the true cohesion c 0 the measured values of cohesion increase from 100 pa for pure gm to 600 pa for pure sp with a sub linear trend of the cohesion with the mixture gm content the two independent cohesion measurement methods from shear tests and tension extensional tests yield very similar results of extrapolated cohesion c and show that both are robust and can be used independently the measured values of friction coefficients increase from 0 5 for pure gm to 1 05 for pure sp the use of these granular material mixtures now allows testing 1 the effects of cohesion and friction coefficient in homogeneous laboratory models and 2 testing the effect of brittle layering on brittle deformation as demonstrated by preliminary experiments therefore the brittle properties become at last experimental variables

computerized x ray tomography analysis of sandbox models examples of thin skinned thrust systems computerized x ray tomography applied to analog sandbox experiments performed in a normal gravity field makes possible the analysis of the kinematic evolution as well as the three dimensional geometry of models that simulate tectonic deformations most of the plastic or viscous analog materials generally used in a normal gravity field for such models have x ray attenuations compatible with medical scanner images models using soft cohesionless granular materials were studied faults in granular materials corresponding to dilatant zones with lower by 30 50 x ray attenuation are thus clearly visible in the tomography images kinematic analysis was done on imbricate thrust propagation in materials with an internal friction angle of 30 thrust propagation is controlled mainly by a triangular pop up structure resulting from the nucleation of two conjugate thrusts at the basal decollement the pop up structure is created immediately in front of the previous thrust three dimensional geometry analysis was tested on lateral ramps parallel to the transport direction lateral ramps were induced by changing the frictional boundary conditions at the bottom of the model though the lateral ramps strike almost parallel to the transport direction their dip angle is comparable to the dip angle of frontal ramps

high resolution shallow seismic experiments in sand part ii velocities in shallow unconsolidated sand we conducted a shallow high resolution seismic reflection and refraction experiment on a sandy beach the depth of investigation was about 2 m we interpret the data using the hertz mindlin contact theory combined with gassmann s equation these were used to obtain the vertical velocity profile then the profile was computed from seismic data using the turning rays approximation the normal moveout nmo velocity at the depth of 2 m matches the velocity profile as a result we developed a method to invert measured velocity from first arrivals i e velocity versus distance into velocity versus depth using only one adjustable parameter this parameter contains all the information about the internal structure and elasticity of the sand the lowest velocity observed was about 40 m s it is noteworthy that the theoretical lower bound for velocity in dry sand with air is as low as 13 m s we find that modeling sand as a quartz sphere pack does not quantitatively agree with the measured data however the the

surface deformation and shallow dike intrusion processes at inyo craters long valley california the inyo craters are the two largest of four phreatic craters that lie within a 2 5 km long 500 to 700 m wide n s trend of faults and fissures at the south end of the inyo volcanic chain in eastern california the alignment of these features with dike fed silicic volcanic centers of the same age a few kilometers to the north suggests that they were produced during intrusion of a dike at about 650 550 yr b p e w extension south of south inyo crater is ten to several tens of meters suggesting that the dike is at least that thick to understand how the faults and fissures developed we mapped and studied the fault and fissure pattern used a theoretical boundary element model to determine the surface strain profile above a shallow dike in a purely elastic medium and conducted physical model experiments of fault and fissure growth results of the field studies and experiments indicate that deformation develops according to the following sequence 1 extension fractures and perhaps other inelastic deformation develop immediately above the dike top and on the limbs of a shallow syncline which forms above the dike 2 fissures form along two parallel trends at the surface on opposite sides of the dike plane leaving a relatively unfractured region in between 3 dip slip movement on subsurface fractures and linkage of these fractures with surface fissures produces inward facing normal fault scarps that bound a nested graben above the dike experimental graben widths are up to several times narrower than predicted from the locations of theoretical strain maxima above a dilating crack in a linearly elastic medium this fact is apparently due to the growth of a zone of inelastic deformation above the experimental dike top in the subsurface if the ratio between the depth to the dike top and the distance between the outermost surface fissures at inyo craters is within the range of ratios measured experimentally then the depth to the dike top is between 250 m and several times that a slant hole drilled in the summer of 1987 by the department of energy office of basic energy sciences intersected three breccia bodies of possibly intrusive origin directly below the center of south inyo crater between 550 m and 610 m below the crater rim no intact juvenile igneous rock was intersected suggesting that the hole passed above the magma filled dike top perhaps passing through the zone of inelastic deformation which is inferred to exist from our model results

composition export and faunal utilization of drift vegetation in the salt river submarine canyon abstract submarine canyons may be particularly important in the transport process of drift seagrasses and seaweeds from highly productive shallow lagoon areas to deeper water we studied the composition export and faunal utilization of shallow nearshore benthic vegetation as it was transported to offshore areas via the salt river submarine canyon on the island of st croix u s virgin islands the study was conducted using a saturation diving system nuls 1 hydrolab during two missions in april and august 1980 using bottom drifters deployed in salt river bay and the submarine canyon we recorded net benthic current flow up to 2 cm s 1 moving out of the lagoon and down the canyon to deeper water using bottom nets set up at the canyon head and at the 29 m isobar and from transect surveys and drift clump samples we determined drift plant export rates and drift clump biomass and species composition the dominant drift plants were thalassia testudinum and syringodium filiforme and algae in the genera dictyota dictyopterus and diloplus during the second mission the seagrass halophila decipiens became more abundant both in the drift and in large patches along the canyon floor in both missions more drift was collected in the nets during high wind conditions than during calmer days calculated turnover times ranged from 0 01 to 4 4 days for algae in the order dictyotales and 4 4 to 18 days for thalassia blades total exported biomass of drift vegetation varied between 1 4 to 65 1 kg wet wt day 1 samples of drift vegetation contained mostly juvenile forms of both invertebrates and fishes but in relatively low numbers faunal numbers were most strongly related to rate of drift movement

the statistical characteristics of convective cells in a monsoon regime darwin northern australia abstract a season of operational cell and track data from darwin australia has been analyzed to explore the statistical characteristics of the convective cell heights the statistics for the monsoon and break regimes are significantly different with the break season cells being higher for a given reflectivity threshold the monsoon cells produce more rain but there are fewer intense cells and there is a much larger contribution from stratiform rain the monsoon cells are also slightly larger but shorter lived than the breaks the shorter lifetime may reflect a more rapid transition to a longer lived stratiform character the monsoon regime is shown to be associated with large scale ascent and higher humidity that may lead to more frequent but weaker cells within regimes the subset of intense cells generally reach near the tropopause or overshoot however there is little evidence in the data for a multimodal distribution of cell heights except perhaps for the intense monsoon cases instead the pi

critical taper model of fold and thrust belts and accretionary wedges the fold and thrust belts and submarine accretionary wedges that lie along compressive plate boundaries are one of the best understood deformational features of the earth s upper crust although there is considerable natural variation among the many fold and thrust belts and accretionary wedges that have been recognized and explored several features appear to be universal in cross section fold and thrust belts and accretionary wedges occupy a wedge shaped deformed region overlying a basal detachment or decollement fault the rocks or sediments beneath this fault show very little deformation the decollement fault characteristically dips toward the interior of the mountain belt or in the case of a submarine wedge toward the island arc the topography in contrast slopes toward the toe or deformation front of the wedge deformation within the wedge is generally dominated by imbricate thrust faults verging toward the toe and related fault bend folding two north american fold and thrust belts that exhibit these features are shown in figure 1 neither of these two examples is tectonically active today the southern canadian fold and thrust belt was active during the late jurassic and cretaceous 150 100 ma whereas the southern appa lachians were deformed during the late carboniferous to permian alle ghenian orogeny 300 250 ma figure 2 shows two examples that are currently active the taiwan fold and thrust belt produced by the sub duction of the eurasian plate beneath the philippine sea plate suppe 1981 1987 and the barbados accretionary wedge produced by the sub

the development of seismic reflection sandbox modeling analog sandbox models provide cheap concise data and allow the evolution of geological structures to be observed under controlled laboratory conditions seismic physical modeling is used to study the effects of seismic wave propagation in isotropic and anisotropic media and to improve methods of data acquisition processing and interpretation by combining these two independent modeling techniques the potential exists to expand the benefits of each method for seismic physical modeling the main advantages are that the seismic data collected from these models contain natural variations that cannot be built into conventional solid models which are machined with predetermined structures in addition the cost and construction time to build these models is significantly reduced for sandbox modeling the ability to record three dimensional 3 d seismic images before the model is manually sectioned for conventional two dimensional 2 d structural interpretation allows far more detailed study of subtle 3 d structures than previously possible in the past other workers have attempted to use unconsolidated sands for seismic physical models but these attempts have been unsuccessful because of the lack of control or understanding of the natural variations that occur throughout the models the aim of our research has been to overcome such problems and to develop techniques to alter the acoustic impedance of sand layers thereby allowing the subsequent ultrasonic seismic recording of 3 d fault systems in sand analog geological models

impact of mesoscale meteorological processes on anomalous radar propagation conditions over the northern adriatic area the impact of mesoscale structures on the occurrence of anomalous propagation ap conditions for radio waves including ducts super refractive and subrefractive conditions were studied the chosen meteorological situations are the bora wind and the sporadic sea land breeze sb lb during three selected cases over a large portion of the northern adriatic for this purpose we used available radiosoundings and numerical mesoscale model simulations of real cases and their sensitivity tests at a horizontal resolution of 1 5 km and 81 vertical levels the model simulated the occurrences of ap conditions satisfactorily although their intensities and frequency were underestimated at times certain difficulties appeared in reproducing the vertical profile of the modified refractive index which is mainly dependent on the accuracy of the modeled humidity the spatial distributions of summer ap conditions reveal that the surface layer above the sea roughly between 30 and 100 m asl is often covered by super refractive conditions and ducts the sb is highly associated with the formations of ap conditions i in the first 100 m asl where trapping and super refractive conditions form because of the advection of cold and moist air and ii inside the transition layer between the sb body and the elevated return flow in the form of subrefractive conditions when deep convection occurs all three types of ap conditions are caused by the downdraft beneath the cumulonimbus cloud base in its mature phase that creates smaller but marked pools of cold and dry air the bora wind usually creates a pattern of ap conditions associated with the hydraulic jump and influences distribution of ap conditions over the sea surface

tidal rhythmites in a deep sea environment an example from mio pliocene misaki formation miura peninsula japan abstract the mio pliocene misaki formation miura peninsula japan is characterized by alternation of mafic scoriaceous pebbly sandstone pumiceous sandstone and siltstone and mudstone formed in a fore arc basin in an arc arc collisional zone the qualitative as well as quantitative evidences of tide during the misaki sedimentation in the jogashima area miura peninsula are presented here the lunar synodic period of 28 days lunar month extracted from the misaki tidal rhythmite agrees well with the published miocene tidal rhythmite data the couplet series of the misaki tidal rhythmite however is often interrupted by downslope resedimentation via turbidity currents intense penecontemporaneous deformation and bioturbation association of deep sea turbidites mass flow deposits and tidal rhythmite suggest misaki sedimentation in the miura peninsula took place in a submarine canyon setting

three dimensional geometry and kinematics of experimental piggyback thrusting the three dimensional geometry and kinematics of piggyback stacks of imbricate thrust sheets are illustrated and discussed using a single model shortened in a squeeze box strike parallel geometric elements simulated include lateral ramps eyed sheath folds splays and thrust thrust interference fine details of these structures were exposed by eroding a shortened wedge of sand using a newly developed vacuum eroding technique a kinematic analysis of the model shows a stepwise increase in imbricate thrust spacing and or a decrease in rate of nucleation of imbricate thrusts in the direction of thrust transport despite the steady forward advance of a rear wall the piggyback wedge accreted episodically recording different strain domains in longitudinal cross sections strain partitioning in single layers by bed length balancing showed an increase in layer shortening with volume loss and a corresponding decrease in imbricate thrusting and ramp folding with depth

geology of great abaco submarine canyon blake plateau observations from the research submersible alvin abstract nine dives in the research submersible alvin were made into great abaco submarine canyon to depths ranging from 1850 to 3666 m our observations indicate that the walls of this canyon are distinctly terraced consisting of nearly vertical to overhanging rock cliffs and intervening less steep sediment covered slopes the wall rock consists mostly of massive shallow water limestones and dolostones of cretaceous age coated on exposed surfaces with manganese oxides these rocks are heavily jointed fractured and thus very blocky to angular in appearance with sponges and other sessile organisms commonly attached talus slopes and sedimentary breccia deposits containing angular boulders are present at the base of these steep escarpments short term bottom current measurements in the axis of the eastern part of the canyon indicate that currents are relatively weak reaching velocities of only 10 cm sec this relatively placid setting is further corroborated by the abundance of turtle grass thalassia found along the canyon axis however abundant subdued symmetrical ripple marks and large scour depressions at the base of boulders indicate that high energy events sporadically impact the canyon axis contemporary erosional activity along the axis of the western headward part of the canyon appears to be more significant as evidenced by asymmetrical ripple marks sand waves and bioerosion great abaco canyon has evolved with time via a variety of processes including 1 faulting 2 subsidence 3 defacement and 4 erosional down cutting the location orientation and initiation of this canyon appear to be structurally controlled by the great abaco fracture zone during pre santonian time regional subsidence during the mesozoic allowed the walls of great abaco canyon to build vertically by accretion of shallow water limestones whereas joint controlled defacement has widened the canyon while maintaining steep walls erosional down cutting in the canyon axis by carbonate sediment gravity flows also appears to have been important episodically particularly during the miocene and pleistocene

ten turbidite myths abstract during the past 50 years the turbidite paradigm has promoted many myths related to deep water turbidite deposition john e sanders 1926 1999 a pioneering process sedimentologist first uncovered many of these turbidite myths this paper provides a reality check by undoing 10 of these turbidite myths myth no 1 turbidity currents are non turbulent flows with multiple sediment support mechanisms reality turbidity currents are turbulent flows in which turbulence is the principal sediment support mechanism myth no 2 turbidites are deposits of debris flows grain flows fluidized flows and turbidity currents reality turbidites are the exclusive deposits of turbidity currents myth no 3 turbidity currents are high velocity flows and therefore they elude documentation reality turbidity currents operate under a wide range of velocity conditions myth no 4 high density turbidity currents are true turbidity currents reality ph h kuenen 1950 introduced the concept of turbidity currents of high density based on experimental debris flows not turbidity currents high density turbidity currents are sandy debris flows myth no 5 slurry flows are high density turbidity currents reality slurry flows are debris flows myth no 6 flute structures are indicative of turbidite deposition reality flute structures are indicative only of flow erosion not deposition myth no 7 normal grading is a product of multiple depositional events reality normal grading is the product of a single depositional event myth no 8 cross bedding is a product of turbidity currents reality cross bedding is a product of traction deposition from bottom currents myth no 9 turbidite facies models are useful tools for interpreting deposits of turbidity currents reality a reexamination of the annot sandstone in se france which served as the basis for developing the first turbidite facies model suggests a complex depositional origin by plastic flows and bottom currents myth no 10 turbidite facies can be interpreted using seismic facies and geometries reality individual turbidity current depositional events commonly centimeters to decimeters in thickness cannot be resolved in seismic data all turbidite myths promote falsehood and should be abandoned

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

anisotropic surface wave characterization of granular media abstractin unconsolidated granular media the state of stress has a major effect on the elastic properties and wave velocities effective media modeling of granular packs shows that a vertically oriented uniaxial state of stress induces vertical transverse isotropy vti characterized by five independent elastic parameters the rayleigh wave velocity is sensitive to four of these five vti parameters we have developed an anisotropic rayleigh wave inversion that solves for four of the five independent vti elastic parameters using anisotropic thomson haskell matrix equations that can be used to determine the degree of anisotropy and the state of stress in granular media the proposed method incorporates an initial model search guided by rock physics models and dispersion curve inversion that uses a gradient based solver we carried out the inversion on a synthetic example and a real data set in which we inverted for in situ elastic moduli of unconsolidated sands at very low effective stress the synthetic

a reconnaissance survey of the whittard sea fan southwestern approaches british isles abstract the whittard fan is a deep sea fan 148 km long by 111 km wide located in water depths between 3600 and 4400 m at the mouth of the whittard canyon southwest of the british isles a reconnaissance survey examined fan morphology sediments and bottom currents well developed diurnal tidal cycles occur with u 100 max reaching 16 cm s sufficient to erode and transport sediment at some locations at present major fan processes are apparently inactive and sedimentation is predominantly hemipelagic but other material is supplied by slope failure off the continental slope anomalous bottom topography may be interpreted as sediment waves indicating the existence of a slope parallel bottom current which may modifiy the fan surface

physical modelling of a surface wave survey over a laterally varying granular medium with property contrasts and velocity gradients laboratory experiments using laser based ultrasonic techniques can be used to simulate seismic surveys on highly controlled small scale physical models of the subsurface most of the time such models consist in assemblies of homogeneous and consolidated materials to enable the physical modelling of unconsolidated heterogeneous and porous media the use of granular materials is suggested here we describe a simple technique to build a two layer physical model characterized by lateral variations strong property contrasts and velocity gradients we use this model to address the efficiency of an innovative surface wave processing technique developed to retrieve 2 d structures from a limited number of receivers a step by step inversion procedure of the extracted dispersion curves yields accurate results so that the 2 d structure of the physical model is satisfactorily reconstructed the velocity gradients within each layer are accurately retrieved as well confirming current theoretical and experimental studies regarding guided surface acoustic modes in unconsolidated granular media

small scale physical modeling of seismic wave propagation using unconsolidated granular media laboratory physical modeling and laser based experiments are frequently proposed to tackle theoretical and methodological issues related to seismic prospecting e g when experimental validations of processing or inversion techniques are required lasers are mainly used to simulate typical field acquisition setups on homogeneous and consolidated materials assembled into laboratory scale physical models pms of various earth structures we suggested the use of granular materials to study seismic wave propagation in unconsolidated and porous media and target near surface exploration and hydrogeologic applications we designed and tested the reproducibility of an experimental procedure to build and probe pms consisting of micrometric glass beads gbs a mechanical source and a laser doppler vibrometer were used to record small scale seismic lines at the surface of three gbs models when guided surface acoustic mode theory should prevail in such unconsolidated granular packed structure under gravity we only considered elastic wave propagation in stratified media to interpret recorded data thanks to basic seismic processing and inversion methods first arrivals and dispersion analyses we were able to correctly retrieve the gradients of pressure and shear wave velocities in our models a 3d elastic finite difference simulation of the experiment offered despite significant differences in terms of amplitudes a supplementary validation of our approximation as far as elastic properties of the medium were concerned

deep flow variability in a deeply incised mediterranean submarine valley blanes canyon abstract deep flow variability in blanes canyon is analyzed by means of a unique dataset in which the canyon was instrumented at its axis and at the two canyon walls from march 2003 to july 2004 the mean intensity of deep currents range between 3 5 cm s 1 at the canyon axis 1500 m and 5 4 cm s 1 upstream canyon wall 900 m a wavelet analysis shows that the energy is concentrated in the 2 30 day band and it is mainly associated to single not periodical not wave related events uncoupled at the different canyon sites an empirical orthogonal function analysis shows two main patterns of current variability explaining 65 of the total variance the first mode represents intensifications of the typical along bathymetry pattern of currents over the canyon the second mode corresponds to near bottom upwelling events along the canyon axis with water exiting the canyon through the canyon head after discussing possible forcing mechanisms it is here suggested that such deep upwelling events are associated to offshore displacements of the northern current namely the interaction of the current with the particular shape of the canyon topography at large depths 1800 m would be responsible for the observed deep upwelling events

the vertical structure of turbidity currents and a necessary condition for self maintenance a simple numerical model predicts that properties of a turbidity current can vary significantly in the vertical direction particularly when more than one sediment size is in suspension each sediment size decreases in concentration with increasing distance from the bottom boundary at a rate which depends on its settling velocity the current velocity the entrainment coefficient and the bottom slope however it is shown that the details of the vertical distribution of sediment load do not necessarily greatly influence either the vertical structure of the hydraulic properties of the flow velocity stress or the bulk properties such as the entrainment coefficient at least when only one sediment size is in suspension the ability of a turbidity current to sustain itself is strongly dependent on the sediment load and an autosuspension criterion is obtained by taking into account the vertical structure of the currents the model turbidity currents often cannot maintain their sediment in suspension even when the bottom stress is greater than the critical stress of deposition for low concentration flows when this happens the concentration near the bottom increases without limit as the turbidity current evolves with time in real turbidity currents grain grain interactions which become important at high concentrations may at times cause the current to quickly deposit its near bottom sediment load this is suggested as a possible mechanism for the formation of the poorly sorted sediments frequently found in turbidites

depositional events in santa monica basin california borderland over the past five centuries the southern california coastal climate is characterized by decadal and generational floods that discharge one to three orders of magnitude more sediment than the average annual contribution these can produce turbidity currents directly or load the canyons and slopes with sediments that then may fail and form turbidity flows seismic activity is high on this transform margin and can trigger slope failures where slope sedimentation rates are high and sediments are unstable these events produce slope failures and slides and slumps in canyon heads which evolve into turbidity currents of sufficient volume to reach the adjacent margin basin floors such events occur at approximately century frequency this paper describes six basin floor turbidites that have been mapped in box cores sampling roughly the top 40 50 cm from the basin floor or santa monica basin in the california borderland these deposits were laid down during the past 500 years of record their depositional areas have been conservatively estimated to range from 500 to almost 1500 km2 and contain masses of sediment ranging from 10 000 000 to 100 000 000 tons this compares with a long term average annual terrigenous contribution rate of about 4 000 000 tons yr from the adjacent major streams although annual rates vary from 0 to 60 000 000 tons over the last century of record three of the six events have been related to two major floods 1884 6 1969 and to one major seismic event the mission earthquakes of 1822 1812 the older turbidites were deposited before european entry to the area and cannot be assigned to an historic event but from their size were probably seismically triggered and are the largest of the six events it is likely that other smaller events are masked by the more recent turbidites particularly in the area where box cores are dominantly composed of turbidites these features exhibit average outcrop thickness of 2 to 7 cm with maxima of the order of 10 cm thickness yet represent major events and significant volumes of sediment they also document that the two major sources for such events floods and seismic events produce deposits of very different mass and can probably be separated in the record on that basis thus the frequency of major floods and of major earthquakes in the region could be defined from study of such deposits in longer cores these deposits also provide examples of continued turbidity current activity to the basin floors at a time of high sea level this is contrary to the passive models for sequence stratigraphy depositional patterns

convective rain cells radar derived spatiotemporal characteristics and synoptic patterns over the eastern mediterranean 1 this paper examines the spatiotemporal characteristics of convective rain cells over the eastern mediterranean northern israel and their relationship to synoptic patterns information on rain cell features was extracted from high resolution weather radar data the radar gauge adjustment validation cell segmentation and tracking techniques are discussed at length at the beginning of the paper convective rain cells were clustered into three synoptic types two winter lows deep cyprus lows and shallow lows and one tropical intrusion active red sea trough using several ncep ncar parameters and empirical distributions were computed for their spatial and temporal features in the study region it was found that the active red sea trough rain cells are larger live for less time and possess lower rain intensities than the rain cells generated by the winter lows the cyprus low rain cells were found to be less intense and slightly larger on average than the shallow low rain cells it was further discovered that the preferential orientation of the rain cells is associated with the direction and velocity of the wind the effect of distance from the coastline was also examined an increase in the number and area of the rain cells near the coastline was observed presumably due to the sea breeze convection the mean rainfall intensity was found to peak near the shore and decrease with distance inland this information is of great importance for understanding rain patterns and can be further applied in exploring the hydrological responses of the basins in this region

recent sedimentation on the shelf and upper slope in the bay of anamur southern coast of turkey abstract sedimentological studies supported by uniboom profiles and sonographs of surface sediments from a part of the narrow southern shelf of anatolia indented by the head of a submarine canyon and partly covered by meadows of macrophytobenthos revealed abrupt lateral and vertical variations in the holocene sedimentary facies these variations have essentially been controlled by the migration of depocentres palaeo topography of the shelf and an overall decrease in the rate of fluviatile sediment supply in the late holocene as sea level reached approximately its present position nearly 5 ka b p the bulk of the siliciclastic input began to be trapped in the inner shelf zone most of the terrigenous mud bypasses the shelf to be trapped in the canyon head but transport of modern detrital sand and gravel does not take place across the shelf this is because of the relative weakness of the onshore offshore currents the prevailing microtidal conditions and a belt of phytobenthos between 10 and 30 m which traps the sediments the plants also create the ecological conditions favourable for biological carbonate production however some gravel and sand size relict sediments have been transported from the outer shelf into the canyon head by gravity induced or cross canyon currents the mudline occurs at about the 100 m isobath marking the deepest limit of effective bottom turbulence for the resuspension of silt and clay on the shelf

oceanographic processes and morphosedimentary products along the iberian margins a new multidisciplinary approach abstract our understanding of bottom currents and associated oceanographic processes e g overflows barotropic tidal currents including intermittent processes e g vertical eddies deep sea storms horizontal vortices internal waves and tsunamis is rapidly evolving many deep water processes remain poorly understood due to limited direct observations but can generate significant depositional and erosional features on both short and long term time scales this paper represents a review work which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the iberian continental margins this review explores the implications of the studied processes given their secondary role relative to other factors such as mass transport and turbiditic processes and highlights three major results a contourite depositional and erosional features are ubiquitous along the margins indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation b the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient including the contourite terraces development and c contourites deposits exhibit greater variation than the established facies model suggests therefore a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development an integrated interpretation of these oceanographic processes requires an understanding of contourites seafloor features their spatial and temporal evolution and the near bottom flows that form them this approach will synthesize oceanographic data seafloor morphology sediments and seismic images to improve our knowledge of permanent and intermittent processes around iberia and evaluate their conceptual and regional role in the margin s sedimentary evolution given their complexes three dimensional and temporally variable nature integration of these processes into sedimentary oceanographic and climatological frameworks will require a multidisciplinary approach that includes geology physical oceanography paleoceanography and benthic biology

organic enrichment of submarine canyon and continental shelf benthic communities by macroalgal drift imported from nearshore kelp forests remotely operated vehicle rov surveys were conducted over a 3 year period to evaluate the importance of macroalgal drift exported from nearshore forests of giant kelp macrocystis pyrifera to adjacent submarine canyon and continental shelf benthic habitats abundant macroalgal drift was found in the carmel submarine canyon 153454 m depth but was rare at pt joe a continental shelf habitat 9 km away 87 357 m depth most of the drift parcels consisted of brown algae but 10 other categories were found including green and red algae and the surfgrass phyllospadix spp m pyrifera drift accounted for as much as 20 of the density of drift parcels in the carmel submarine canyon and up to 50 of the drift parcels at pt joe from previously determined turnover rates of drift m pyrifera and the standing stock estimates from the present study we estimated that the rate of carbon flux associated with drift m pyrifera to the benthos of the cannel submarine canyon was 45 2 mg c m z d i based on published estimates of carbon flux from vertically sinking particulate organic carbon at 400 m depth in the nearby monterey submarine canyon and our estimates of kelp derived carbon flux drift m pyrifera can account for 20 83 of the total particulate organic carbon reaching the sea floor in the carmel submarine canyon we conclude that drift macrophytes provide significant enrichment of organic carbon to the benthos above that provided by vertically sinking particulate organic material the extent to which this alters the structure of benthic communities compared to areas without organic enrichment by drift macrophytes remains unknown and awaits further study deep sea benthic communities are entirely dependent on imported primary production for metabolic energy except hydrothermal vent and cold seep communities whose energy is provided by chemolithoautotrophy organic carbon arrives at the sea floor as small detrital particles episodic deliveries of large organic parcels such as large animal carcasses actively swimming zooplankton turbidity currents and macrophyte detritus rowe 1981 the relative importance of these organic carbon pathways no doubt varies with habitat and distance from shore although quantification of these pathways is still in its infancy gage and tyler 1991 pilskaln et al 1996 rowe 1981 the macrophyte detritus pathway may be particularly important in deep sea environments adjacent to productive neat shore habitats such as seagrass meadows or kelp forests where macrophyte detritus removed from these habitats may be transported offshore to deep sea benthic communities via bottom currents josselyn et al 1983 menzies et al 1967 suchanek et al 1985 vetter and dayton in press forests of giant kelp

sandbox experiments on gravitational spreading and gliding in the presence of fluid overpressures whereas in previous analogue experiments on gravitational spreading and gliding detachment occurred on a ductile layer we have used a relatively new technique of injecting compressed air into sand packs so as to simulate the effects of fluid overpressures in sedimentary strata and to trigger slope instabilities in our experiments the governing equations yield scales for dimensions stresses and fluid pressure however the more transitory phenomena of production and decrease of overpressure cannot be suitably scaled by using layers of differing permeability we are able to produce sharp detachments in models made of sand alone the experiments involve gravity spreading or gravity gliding in gravity spreading propagation of the detachment and of extensional deformation depends on the fluid pressure for medium values of fluid overpressure normal faults are closely spaced numerous and bound rotated blocks they propagate progressively toward the back of the model for the highest pressures the deformation propagates very fast and faults bound non rotated blocks which slide on an efficient basal detachment fault dips are also controlled by fluid pressure and by frictional resistance at the base to model gravitational gliding required an apparatus with a more complex system of air injection we did a series of experiments using injection windows of various lengths and compared the results with predictions from a quasi 3d analytical model of sliding in contrast with predictions for an infinite slope sliding depends on 1 the fluid overpressure on the detachment 2 the fluid overpressure in the body of the sliding sheet and 3 the shape of the detachment surface in particular we show that frictional resistance at the lower edge is a primary control on the dynamics of gliding

tidal motions and tidally induced fluxes through la linea submarine canyon western alboran sea detailed observations from two mooring lines deployed in la linea submarine canyon western alboran sea are presented this is a narrow canyon in the sense that its width is always less than the internal radius of deformation tidal currents within the canyon are polarized in the along canyon direction according to its narrow nature they have considerable amplitude values of around 0 5 m s are often observed and are forced by the internal pressure gradients associated with the baroclinic tide that is generated in the surroundings subsequent amplification of onshore baroclinic currents within the canyon accounts for the large amplitude observed cross shelf exchange through the canyon due to tidal motions is different from zero despite the close to zero mean of tidal currents the explanation is based on the asymmetry of water properties flowing up canyon and down canyon some sort of tidal rectification regarding the energy flux the canyon seems to be an adequate conduit to carry energy to the shore estimations made from our observations indicate that energy input onto the shelf per unit length parallel to the shore at the canyon head is enough to maintain mixing on the shelf at intermediate depths

elasticity profile of an unconsolidated granular medium inferred from guided waves toward acoustic monitoring of analogue models abstract the monitoring of materials elastic parameters during geological analogue experiments would highly improve the interpretation of involved processes it would more particularly help the implementation of joint analytical or numerical analyses we propose laser doppler vibrometry as a probing tool for the systematic characterisation of analogue models we therefore develop an experimental set up to record small scale seismic lines at the surface of an unconsolidated granular medium in laboratory conditions pressure wave first arrival times and surface wave dispersion are then inverted for a one dimensional pressure and shear wave velocity structure inferred profiles appear to match previously thoroughly estimated properties of the probed medium thus validating our approach

macrofaunal communities within and adjacent to a detritus rich submarine canyon system abstract macrofaunal abundance biomass diversity and species assemblages within scripps and la jolla submarine canyons are compared with those on the nearby continental shelf and slope our primary objective was to examine the effect of detrital aggregates on infaunal communities within canyons two submarines a remotely operated vehicle rov and a soutar box corer were used to collect samples within the canyons organic enrichment by macrophyte detritus was evident from canyon heads down to 550 m and evidence of strong currents coarse sediment was found down to 700 m infaunal density and biomass were higher in the canyons than outside at all depths where comparative data were available 100 500 m infaunal assemblages in canyons were distinct from those at reference stations both the canyon and non canyons samples showed community differentiation with depth species diversity was generally high but decreased with depth outside of canyons and increased with depth within the canyons low diversity at shallow depths within the canyon is attributed to a combination of organic enrichment and physical disturbance submarine canyons are commonly found to contain distinct species assemblages or higher faunal densities and or biomass than nearby non canyon regions at similar depths canyons are regular features along most ocean margins and appear to be important as sites of enhanced secondary production provide diverse habitats and act as conduits of coastal detritus to the deep sea

control of pore fluid pressure on depth of emplacement of magmatic sills an experimental approach article in sedimentary basins the emplacement of magmatic sills tends to occur within rock of low mechanical competence and permeability such as shale this often contains pore fluids at abnormally high pressure we first theoretically show that in anisotropic media the higher the pore fluid pressure the deeper the sill emplacement then we introduce a new technique for analogue modelling of such intrusive bodies under conditions of fluid overpressure greater than hydrostatic which corroborate the theoretical analysis as an analogue of brittle sediment we use a diatomite powder this material is a dry fine grained frictional cohesive and permeable material as an analogue for magma we take a silicone putty rtv silicone which is at first newtonian but then solidifies at room temperature we use compressed air as a pore fluid under these experimental conditions we investigate the intrusion of magma into the host powder under various fluid overpressures in homogeneous diatomite powder having uniform cohesion intrusive bodies are segmented dykes these become feeders to sills if the fluid overpressure exceeds the weight of overburden where the sedimentary column has a horizontal discontinuity in strength the transition from dyke to sill occurs at a smaller overpressure hydrostaticb exb1 as a possible illustration of these results we consider sills within source rocks of the neuquen basin and of the parana basin both in south america where overpressure may have resulted from maturation of organic material

episodic accretion and strain partitioning in a model sand wedge we model led thrust wedge accretion and deformation partitioning in a passively layered sand detached and shortened above a smooth rigid decollement the thrust wedge accretes in piggyback style during forward advance of a rear wall the passively layered sand accommodates the shortening penetratively by kinking ramp folding and by imbrication in single layers the style of compression changes with time and or stratigraphic position within the sand prism initial penetrative layer shortening above a slipped zone of decollement is succeeded by formation of monoclinal or conjugate shear bands at temporary terminations of decollement the shear bands subsequently narrow down and lock as thrust ramps the model sand wedge accrets episodically rather than steadily episodicity is controlled by the stick slip mode of decollement propagation and by volume loss and compaction of the wedge material in response to convergence this results in formation of a wedge with a convex upwards cross sectional topography

contemporary sedimentary processes in the monterey canyon fan system abstract a study of the monterey canyon and fan was conducted to investigate contemporary sedimentary activity using a camera sled alvin dives and sea beam bathymetry physical characteristics and plan view morphology of the walls terraces thalweg floor and levees of the monterey canyon and fan as well as the gullied and non gullied regions of the adjacent continental slope have been studied the canyon floor and fan valley thalweg channel from 2900 to 3500 m exhibited properties indicative of moderate to low energy conditions weak currents smoothed sea bed deposits of disintegrated kelp bioturbated mud substrate fecal pellets absence of scour chemosynthetic communities consisting of clams and a pogonophoran were found in the fan valley from 3000 to 3600 m local areas of rockfalls and slumps from the canyon and fan valley walls were not fresh sedimented abundantly colonized by benthic biota terraces and levee crests were mud draped and bedrock exposures on canyon walls were encrusted by benthic organisms freshest disturbances were found in gullies on the adjacent continental slope where bedrock was scoured clean of sediment and loose debris a major submarine slide detached from escarpments on the lower slope and extends across the fan the slide surface was mud draped hummocky and contained bedforms with wavelengths up to 150 m and up to 10 m relief the survey was conducted shortly before the loma prieta earthquake october 17 1989 that caused substantial ground motion in on shore regions of monterey bay any substantial sub sea disturbances generated by the ensuing earthquake should be discernable from the pre earthquake state by comparison with the deep sea photographs and observations

contemporary channel levee systems in active borderland basin plains california continental borderland abstract long range large scale side scan gloria information other seismic reflection profiling studies and data from cores in the california continental borderland have defined active levee channel systems extending basinward from the lower fan of hueneme mugu submarine fan redondo submarine fan and santa cruz canyon fan in santa monica san pedro and santa cruz basins respectively the holocene distributaries have been created by a series of turbidity current events these distributaries range in length from 10 25 km and are wide 2 5 km and low relief 1 10 m in their distal parts they are also active conduits for nepheloid flows distributions of sedimentological parameters typically mimic the pattern of levee channel systems organic carbon and biogenic carbonate content roughly outline the systems channels are incised in the upper to middle fan areas and become constructional leveed channels in the lower fan and basin plain as the channel gradient adjusts to maintain a graded profile thus sediment gravity flows are generally confined to channels in the upper fan zones but deposit both channelized and over bank deposits on the lower fan and basin floor the deposits show that the canyon fan activity has continued during a rising sea level phase it is evident that canyon headward erosion rates have been equal to or greater than the transgression rate and that the canyon fan systems have remained linked with their sediment sources frequency of events was probably higher and volumes of the events were often larger during the glacially lowered sea level episodes however turbidity currents of sufficient volume to reach the basin floors continue to occur at century or multi century intervals as one progresses headward in each system the number of flows per length of core increases small flows that do not pass beyond the distributaries are much more frequent and may be decadal in frequency or even more frequent in the santa monica basin system these california borderland basins are probably typical of narrow active margins where rate of lateral sea level transgression is less than or equal to the rate of canyon headward erosion the canyons maintain connections with sediment sources during sea level rise and the systems therefore are active during the entire sea level cycle thus sediment supply is not a simple function of eustacy this contrasts with the simplified sequence model developed on passive margins where canyons turn off as sea level rises

210pb activities in and fluxes to sediments of the washington continental slope and shelf abstract surface sediments of the washington coast have 210 pb activites which average 104 48dpm g for submarine canyon and slope regimes and 18 12dpm g for the continental shelf regime 210 pb sedimentary fluxes are also higher in canyons averaging 18 13dpm cm 2 per yr compared to 5 2 3 1 dpm cm 2 per yr for slope and 4 8 1 8dpm cm 2 per year for shelf regions these 210 pb activities and fluxes are 2 7 times greater than those reported for other coastal regions inputs from the atmosphere and the columbia river are not sufficient to supply the 210 pb but advection of seawater containing dissolved 210 pb produced in situ from 226 ra provides an input several times larger than the sedimentary fluxes the sedimentary 210 pb flux is limited by scavenging reactions rather than by supply of dissolved 210 pb calculations of maximum biological uptake and fluxes of 210 pb and selective chemical leaching experiments all show that the primary scavenging processes are due to hydrous mn and fe oxides rather than biological phases the pattern of higher 210 pb depositional fluxes in canyons than in nearby open slope areas of comparable water depth is most reasonably explained by enhanced scavenging of dissolved 210 pb near the sea floor rather than by processes operating throughout the water column relatively rapid removal of dissolved 210 pb from the near bottom nepheloid layer to slope and canyon sediments is shown by its mean residence time of less than two years in this layer

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

sedimentary characteristics of late pleistocene bottom current deposits barents sea slope off northern norway abstract the barents sea slope off northern norway received large amounts of terrigenous sediments from an extensively glaciated norwegian continental margin during the late pleistocene a sedimentological study of seven gravity cores from the barents sea slope suggests that some terrigenous sediments were transported by both downslope currents and contour following bottom currents the bottom current deposits comprise four sedimentary facies 1 indistinctly laminated mud 2 layered mud 3 indistinctly layered mud and 4 bioturbated mud the indistinctly laminated mud on the mid to lower slope is characterized by a relatively low degree of bioturbation and consists of monotonous diffuse and discontinuous silt rich and silt depleted laminae 1 mm scale and or discontinuous trains of coarse grains these characteristics are suggestive of sedimentation from contour currents driven by water exchange with the north atlantic ocean these bottom current deposits can be distinguished from fine grained turbidites silt clay couplets and intensively bioturbated hemipelagites on the barents sea slope

solving the mystery of booming sand dunes desert booming can be heard after a natural slumping event or during a sand avalanche generated by humans sliding down the slip face of a large dune the sound is remarkable because it is composed of one dominant audible frequency 70 to 105 hz plus several higher harmonics this study challenges earlier reports that the dunes frequency is a function of average grain size by demonstrating through extensive field measurements that the booming frequency results from a natural waveguide associated with the dune the booming frequency is fixed by the depth of the surficial layer of dry loose sand that is sandwiched between two regions of higher compressional body wave velocity this letter presents measurements of the booming frequencies compressional wave velocities depth of surficial layer along with an analytical prediction of the frequency based on constructive interference of propagating waves generated by avalanching along the dune surface

seismic velocities and poisson s ratio of shallow unconsolidated sands we determined p and s wave velocity depth profiles in shallow unconsolidated beach sand by analyzing three component surface seismic data p and s wave velocity profiles were calculated from traveltime measurements of vertical and tangential component seismograms respectively the results reveal two discrepancies between theory and data whereas both velocities were found to be proportional to the pressure raised to the power of 1 6 as predicted by the hertz mindlin contact theory the actual values of the velocities are less than half of those calculated from this theory we attribute this discrepancy to the angularity of the sand grains assuming that the average radii of curvature at the grain contacts are smaller than the average radii of the grains we modify the hertz mindlin theory accordingly we found that the ratio of the contact radius to the grain radius is about 0 086 the second disparity is between the observed poisson s ratio of 0 15 and the theoretical value 0 008 for random pack of quartz spheres this discrepancy can be reconciled by assuming slip at the grain contacts because slip decreases the shearing between grains poisson s ratio increases

comment on late holocene rupture of the northern san andreas fault and possible stress linkage to the cascadia subduction zone by chris goldfinger kelly grijalva roland burgmann ann e morey joel e johnson c hans nelson julia gutierrez pastor andrew ericsson eugene karabanov jason d chaytor jason patton and eulalia gracia goldfinger et al 2008 conclude that in the northern san andreas fault and cascadia margins holocene turbidites i e deposits of turbidity currents were triggered by earthquakes however their conclusion falters because of 1 selective data sets that were used for establishing seismicity as the sole triggering mechanism of turbidites 2 flawed sedimentological concepts and criteria that were applied for interpreting turbidites and 3 faulty methodologies that were employed for correlating turbidites over long distances this same turbidite i e sedimentological theme has also been published previously by goldfinger et al 2003a b 2006 2007 as with the recent article in bssa their previous publications on the subject matter were published in journals that are concerned primarily with geophysical topics as a result critical sedimentological conclusions which are an integral part of the articles by goldfinger et al have not been subjected to a rigorous scrutiny therefore i would like to comment on the following three issues along the washington oregon california margin potential triggering mechanisms of sediment failures and related turbidity currents are 1 earthquake adams 1990 2 tectonic oversteepening greene et al 2006 3 tsunami adams 1990 geist 2005 4 cyclone adams 1990 shanmugam 2008a fig 4 5 ebb tidal current puig et al 2003 6 submarine volcanic activity davis et al 2002 7 sediment loading adams 1990 and 8 gas hydrates chapman et al 2004 the link between gas hydrate decomposition and mass movements on the norwegian margin was discussed by mienert et al 2005 in the cascadia margin a total of 40 cyclones along the oregon coast were reported for the 1984 2006 period moritz and moritz 2006 a total of 24 tsunamis were reported along the oregon coast for the 1868 1994 period table 1 cyclones and tsunamis are powerful agents of sediment failures shanmugam 2008a on the outer continental shelf of the gulf of mexico for example the

displacement fields and finite strains in a sandbox model simulating a fold thrust belt this thesis uses geodetic satellite data to measure present day crustal deformation in the zagros fold thrust belt sw iran geodetic type measurements are also used in down scaled models that simulate the surface deformations seen in convergent settings like the zagros fold thrust belt global positioning system gps measurements of three surveys between 1998 and 2001 indicate 9 3 mm yr and 5 3 mm yr shortening across the se and nw zagros respectively gps results show that in addition to the different rates and directions of shortening on either side of the ns trending kazerun fault local along belt extension occurs to the east differential sar interferograms of ers1 2 images between 1992 and 1999 detect 8 4 mm yr uplift rate across a newly recognized fault in sw qeshm island this can be attributed to a steep imbricate thrust that may still represent the local zagros deformation front the salt diapirs in the zagros rise from a source layer that acts as a low frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern zagros whereas the cover to the west deforms above a high friction decollement physical models were prepared to simulate cover deformation in the zagros by shortening a sand pack above adjacent high and low frictional decollements represented by a ductile layer the strain distributions differed above the two types of decollements it was more heterogeneous above the salt where local extension in the shortening direction was dominant a separate work also investigated systematically the role of basal friction on cover deformation in convergent settings accurate height measurements of the model surface by laser scanner indicated a deformation front more distal than usual particularly in the low basal frictional models the volume reduction in our shortened sand models correlated directly with their basal friction

mean and tidal currents in baltimore canyon the mean and tidal current fields within baltimore canyon and on the shelf and slope around it were observed with instrumented moorings at 12 sites currents on the shelf are similar to those observed elsewhere over the northeastern u s outer shelf with mean flow southwestward at 10 to 15 cm s 1 parallel to the shelf break tidal current velocity in the direction of the major axis of the m2 ellipse over the shelf is about 9 cm s 1 currents within the canyon are complex mean flow near the bottom along the canyon axis is downcanyon at 5 cm s at a depth of 275 m but upcanyon at 7 cm s 1 at 600 m depth and negligible at depths of 1000 m and 1500 m at 50 m above the bottom mean flow at each of these sites is less than it is at 6 m above the bottom the m2 tidal currents in the canyon tend to be aligned with topography and have velocities ranging up to 22 cm s 1 maximum instantaneous current speeds were found near the bottom in the canyon axis with a peak speed for the entire survey of 106 cm s 1 near the bottom at the 275 m level

the tsunamite problem the genetic term tsunamite is used for a potpourri of deposits formed from a wide range of processes overwash surges backwash flows oscillatory flows combined flows soft sediment deformation slides slumps debris flows and turbidity currents related to tsunamis in lacustrine coastal shallow marine and deep marine environments tsunamites exhibit enormous variability of features e g normally graded sand floating mudstone clasts hummocky cross stratification etc these sedimentary features may also be interpreted as deposits of turbidity currents turbidites debris flows debrites or storms tempestites however sedimentary features play a passive role when these same deposits are reinterpreted as tsunamites on the basis of historical evidence for tsunamis and their triggering mechanisms e g earthquakes volcanic explosions landslides and meteorite impacts this bipartite sedimentological vs historical approach which allows here classification of the same deposit as both turbidite and tsunamite has blurred the distinction between shallow marine and deep marine facies a solution to this problem is to classify deposits solely by a descriptive sedimentological approach the notion that tsunami waves can directly deposit sediment in the deep sea is unrealistic because tsunami waves represent transfer of energy and they are sediment starved during tsunamis and major storms submarine canyons serve as the physical link between shallow water and deep water environments for sediment transport tsunami related deposition involves four progressive steps 1 triggering stage offshore 2 tsunami stage incoming waves 3 transformation stage near the coast and 4 depositional stage outgoing sediment flows in this progression deep water deposition can commence only after the demise of incoming tsunami waves due to their transformation into outgoing sediment flows deposits of these sediment flows already have established names e g debrite and turbidite therefore the term tsunamite for these deposits is obsolete

reply to shanmugam g comment on internal waves an underexplored source of turbulence events in the sedimentary record by pomar et al earth science reviews 111 2012 56 81 earth science reviews 2012

sand curve facelift empirical to polynomial model and the effect on the tomogram abstractan empirical thickness versus time relationship sand curve has been established in the rub al khali desert and verified by a theoretical curve from the direct measurements of sand the empirical sand curve has variable success in other areas of saudi arabia we established a theoretical sand curve model to determine the single way time in dry sand tomographic modeling of a higher resolution 3d seismic survey contributes more data to refine the relationship polynomial curves were used in the calculation of near surface static corrections to improve the solution for low relief structures

synchronous and velocity partitioned thrusting and thrust polarity reversal in experimentally produced doubly vergent thrust wedges implications for natural orogens a sandbox analog modeling research program was used to study the detailed evolution of doubly vergent thrust wedges high resolution multilayers of thin alternating sand and mica layers were used in contractional coulomb wedge experiments to simulate deformation of anisotropic brittle upper crustal strata in doubly vergent orogens experiments incorporating syntectonic sedimentation in foreland basins and in piggyback basins were also carried out our laboratory models evolved in two main stages 1 initial high velocity thrusting in the retrowedge and high frequency together with low displacement folding and thrusting in the prowedge and 2 low frequency high displacement synchronous thrusting in the prowedge and low velocity thrusting in the retrowedge transition from stage i to stage ii occurred when the growing wedges reached the critical height at which they behaved as a backstop for further prowedge accretion addition of syntectonic sediments increased the persistence of stage i and triggered out of sequence thrusting in the axial zone of the experimental orogens thrust motion was stick slip retrovergent thrusting occurred along a long lived ramp whose lower tip was located at the subduction slot provergent kink bands nucleated at the subduction slot in stage i in contrast during the second stage of wedge evolution kink bands nucleated in a piggyback fashion in the foreland far from the subduction slot and then evolved into high displacement faults that remained active up until the end of the experiments at progressively decreasing rates of thrusting the axial zones of the model wedges were characterized by fast uplift rates during stage i due to backward translation of the belt along the retrovergent long lived ramp and due to the localization of deformation close to the subduction slot outward migration of the deformation front in the prowedge region during stage ii caused the progressive decrease in the rate of the wedge uplift until it eventually stopped analytical models to quantify the coulomb behavior in the wedges validated the reversal of thrust polarity with increasing shortening triggered by the buildup of the topographic load during deformation this thrust polarity reversal highlights problems with the classic concept of back thrusting as a reflection of a significant change in the deformation regime our results compare well with the kinematic evolution of natural accretionary prisms and of thrust and fold belts such as the lesser antilles arc system the mediterranean ridge and the pyrenees