geological and oceanographic perspectives on event bed formation during hurricane katrina 1 storm deposits in ancient shelf sediments typically form thick sequences of interbedded sand and mud deposited during shoreline regression whereas modern shelf sediments are generally thin veneers deposited during shoreline transgression in this paper we present a preliminary comparison between ancient and modern storm beds deposited in these disparate contexts hurricane katrina deposited a storm bed on the louisiana shelf with a maximum observed thickness of 0 58 m which thinned to approximately 0 1 m at 200 km west of landfall this thickness is similar to event beds observed in both ancient and modern sediments using data for tropical cyclone landfalls in the gulf of mexico we estimate the return time for a storm of this size to be 40 50 years in this region this estimated frequency for deposition of storm beds is useful in evaluating ancient storm sequences that were deposited during similar climatic conditions

mica deformation fabrics and the seismic properties of the continental crust abstract seismic anisotropy originating within the continental crust is used to determine kinematic flow lines within active mountain belts and is widely attributed to regionally aligned mica however naturally deformed micaceous rocks commonly show composite e g s c fabrics it is necessary therefore to understand how both varying mica content and differing intensities of multiple foliations impact on seismic interpretations in terms of deformation fields an outcrop analogue for granitic mid crustal deformed zones is used here to calibrate the seismic response against both parameters seismic responses are modelled using crystallographic preferred orientations for polymineralic micaceous granitic gneisses measured using electron back scatter diffraction the sample results are generalised by modelling the effects of variations in modal composition and the relative importance of deformation fabrics of variable orientation so called rock and fabric recipes the maximum p and s anisotropy are calculated at 16 6 and 23 9 for single foliation gneisses but for mixed i e s c foliation gneisses these values reduce to 5 8 and 7 5 respectively furthermore mixtures of multiple foliations generate significant variations in the geometry of the seismic anisotropy this effect coupled with the geographical orientation of fabrics in nature can generate substantial variations in the orientation and magnitude of seismic anisotropy especially for shear waves as measured for the continental crust using existing receiver function and teleseismic near vertical incidence methods thus maps of seismic anisotropy varying with depth in deforming continents need not imply necessarily depth varying deformation kinematics and tectonic decoupling

long shelf sediment transport and storm bed formation by cyclone winifred central great barrier reef australia three major sediment facies belts occur on the great barrier reef shelf an inner shelf prism of holocene terrigenous sand and mud a patchy middle shelf veneer of palimpsest muddy shelly calcsand 1 m thick above a weathered pleistocene erosion surface and an apron of modern carbonate mud and sand around reefs of the main reef tract these sediments were mobilized and strongly affected by the passage of severe tropical cyclone winifred central pressure 958 hpa which traversed the central great barrier reef shelf on february 1 1986 re surveys after the passage of cyclone winifred showed that i a storm induced shell lag and or a normally graded bed of terrigenous fine sand mud had been deposited at depths down to 20 m ii middle shelf longitudinal bedforms were widespread at depths of 28 35 m and comprised a furrowed substrate of palimpsest muddy shell gravel surmounted by 40 150 m wide ribbons of quartzose and bioclastic sand up to 15 cm thick iii fields of northward facing 1 2 m wavelength megaripples were present adjacent to zones of ribbons and in the alleys between ribbons iv five days after the cyclone mud was still settling from suspension and large parts of the inner shelf were bathed in muddy hypopycnal river plumes some of which reached 30 km seaward to the inner edge of the reef tract and v suspended mud derived in part by unmixing of the seabed was present throughout the shelf water column and a seaward thinning mud drape up to 40 cm thick had accumulated on and seawards of the inshore sediment prism tapering seawards to a few mm thick only over most of the middle shelf it is inferred that storm waves and currents associated with the passage of cyclone winifred caused widespread unmixing of bottom sediments offshore long shelf transport of bedload sand ribbons and megaripples was affected by powerful shelf parallel currents of velocity 1 3 m s as the storm passed the graded seaward thinning sand mud bed was deposited over the inner middle shelf on the middle shelf bioturbation and downward mixing of the mud drape started immediately after the passage of the cyclone and was well advanced after 3 months in this way the ephemeral seabed features produced by passage of a cyclone are gradually degraded and the storm layer stratigraphy becomes incorporated within a thin middle shelf veneer of muddy shelly calcsand

compositional and metamorphic controls on velocity and reflectivity in the continental crust an example from the grenville province of eastern quebec we present velocity and density data for a suite of gabbros and metagabbros over a range of metamorphic grades from subgreenschist to the eclogite facies most of these rocks have a mesocratic protolith with overlapping bulk chemistry ranges providing an opportunity to investigate the systematics of mineralogy and physical properties across a wide range of metamorphic grades with minimal compositional variation in addition more mafic gabbros in the eclogite facies were also investigated in order to take into account variations in the extent of transformation of gabbro to eclogite controlled by bulk chemistry the physical properties data are used as the basis for a first order crustal model composed of granitic anorthositic and gabbroic components the objective of constructing the crustal model is to evaluate the relative contribution of compositional variation and metamorphism to the velocity density and reflectivity structure of the continental crust the model suggests that in the upper crust if fracture porosity is neglected composition dominates the velocity and density structure while in the middle and lower crust composition and metamorphism play equally important roles simulations designed to predict potential reflection coefficient size distributions for the various bulk chemistries and mineralogies in the crustal model indicate step increases in the potential for large reflection coefficients that are dominantly controlled by metamorphic grade step increases in reflectivity are predicted between the lower and upper amphibolite facies and between incompletely and completely eclogitized metagabbros in the eclogite facies we also consider several alternative mixing models which account for the effects of one of the three lithologic components occurring as isolated bodies rather than perfectly mixed with the other two components these models indicate a reduction of the potential for large reflection coefficients by as much as 50 emphasizing the importance of the degree of mixing for crustal reflectivity

the importance of cyclogenesis on the short term evolution of gulf coast barriers abstract over the past several years research has been conducted to determine the importance of cyclones on the morphodynamics and morphological maintenance of barrier islands along the northern gulf of mexico data are presented indicating the complexity and highly variable response of a 12 km stretch of barrier along the florida panhandle to cold front passage across the northern gulf in addition to the impacts of tropical storms hurricanes and winter storms in the gulf of mexico two temporal scales are used to evaluate short term response and adjustment to these events i e months and a near five year record of sediment volume change the combination of which have resulted in a time series of change for the subaerial and nearshore environments these data incorporate the morphological signature of six tropical storms hurricanes and approximately 100 frontal passages three important conclusions have been reached based on these data 1 low lying barrier islands which are vulnerable to overwash can conserve mass during catastrophic hurricanes e g hurricane opal a strong category 4 hurricane near landfall 2 less severe hurricanes can promote rapid dune and berm aggradation and contribute sediment to the entire barrier system and 3 cold fronts play a critical role in the post storm adjustment of the barrier by deflating the subaerial portion of the overwash terrace and eroding its marginal lobe the data presented also indicate that barrier systems along the northern gulf do not necessarily enter an immediate post storm recovery phase after catastrophic hurricanes even though they are nested in sediment rich nearshore environments it is anticipated that these findings will have important implications for better understanding the longer term evolution of barrier systems in mid latitude micro tidal settings elsewhere around the globe

seismic velocity anisotropy of phyllosilicate rich rocks characteristics inferred from experimental and crack model studies of biotite rich schist summary seismic velocity anisotropy of biotite schist 30 per cent mode biotite was measured under confining pressures up to 150 mpa the rock shows weak orthotropy which was altered from transverse isotropy ti generated by biotite preferred orientation the orthotropy was caused by microfolding in the rock the velocity increase under confining pressure indicates that most crack planes are aligned parallel to the cleavage planes silicate sheet of the oriented biotite minerals the anisotropy of the rock is basically ti due to both the aligned biotite minerals and cracks which have a common symmetry axis we found that other sheet silicate rich rocks have a similar anisotropy with the biotite schist in which the ti type anisotropy is characterized by the slow p and s wave velocities along the symmetry axis this is caused by the preferred orientation of sheet silicate minerals and the extremely slow p and s wave velocities along the axis perpendicular to the silicate sheet compared to the directions along the silicate sheet when rock contains a large percentage of highly oriented sheet silicates the fast and slow shear waves exchange their polarities at some off symmetry axis directions indicating that the qswave quasi s wave velocity exceeds the sh wave velocity the phase velocity distribution of qs wave shows an asymmetry with respect to the angle from the symmetry axis which is characterized by a bulge in this distribution located near the symmetric axis this is inherent to most sheet silicate minerals when crack density of aligned cracks increases the p wave velocity along the symmetry axis decreases considerably the qs wave phase velocity in the off axis directions also decreases in accordance with the decrease of the p velocity along the symmetry axis the asymmetry of the qs wave phase velocity distribution increases as the p wave velocity decreases along the symmetry axis this relationship can be well understood by means of berryman s extended thomsen approach

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

anisotropy of experimentally compressed kaolinite illite quartz mixtures the anisotropy of physical properties is a well known characteristic of many clay bearing rocks this anisotropy has important implications for elastic properties of rocks and must be considered in seismic modeling preferred orientation of clay minerals is an important factor causing anisotropy in clay bearing rocks such as shales and mudstones that are the main cap rocksofoilreservoirs thepreferredorientationofclaysdepends mostly on the amount of clays and the degree of compaction to studytheeffectoftheseparameters wepreparedseveralsamples compressingattwoeffectiveverticalstressesamixtureofclays illite and kaolinite and quartz silt with different clay quartz ratios the preferred orientation of the phases was quantified with rietveld analysis on synchrotron hard x ray images pole figures for kaolinite and illite display a preferred orientation of clay platelets perpendicular to the compaction direction increasing in strength with clay content and compaction pressure quartz particles have a random orientation distribution aggregate elastic properties can be estimated by averaging the singlecrystal properties over the orientation distribution obtained from the diffraction data analysis calculated p wave velocity anisotropy ranges from 0 pure quartz sample to 44 pure clay sample highly compacted but calculated velocities are much higher than measured velocities this is attributed to uncertainties about single crystal elastic properties and oriented micropores and limited grain contacts that are not accounted for in themodel inthiswork wepresentaneffectivemethodtoobtain quantitative data helping to evaluate the role of clay percentage and compaction pressure on the anisotropy of elastic properties ofclay bearingrocks

exploring typhoon variability over the mid to late holocene evidence of extreme coastal flooding from kamikoshiki japan sediment cores from two coastal lakes located on the island of kamikoshiki in southwestern japan lake namakoike and lake kaiike provide evidence for the response of a backbarrier beach system to episodic coastal inundation over the last 6400 years sub bottom seismic surveys exhibit acoustically laminated parallel to subparallel seismic reflectors intermittently truncated by erosional unconformities sediment cores collected from targeted depocenters in both lakes contain finely laminated organic mud interbedded with coarse grained units with depths of coarse deposits concurrent with prominent seismic reflectors the timing of the youngest deposit at kamikoshiki correlates to the most recently documented breach in the barrier during a typhoon in 1951 ad assuming that this modern deposit provides an analog for identifying past events paleo typhoons may be reconstructed from layers exhibiting an increase in grain size a break in fine scale stratigraphy and elevated sr concentrations

a suspended sediment stratification correction for combined wave and current flows a simple model for the near bottom combined wave and current flow over a moveable sediment bed is presented the model is an extension of the grant and madsen 1979 combined wave and current model with moveable bed effects on the physical bottom roughness included as by grant and madsen 1982 the unsteady conservation of fluid momentum and sediment mass equations which are coupled through an eddy diffusivity closure scheme are solved for the wave and current velocity profiles along with the suspended sediment concentration and transport profiles sample runs are presented to illustrate the effect of varying wave conditions on the current the mean sediment concentration and the mean sediment transport results show that for fine to medium sands self stratification of the flow can be important during storms owing to the large amount of sediment suspended by the waves and the enhanced turbulent mixing associated with the wave current interaction the theory easily can be generalized for inclusion in a full ekman layer model

impact of fabric microcracks and stress field on shale anisotropy summary few data are available on shales in terms of seismic to ultrasonic properties and anisotropy although all are important with regards to imaging problems often encountered in such lithologies additionally mechanisms causing changes in these properties are not well documented due to the fine grain size of such materials and time required for testing under controlled pore pressure conditions the results presented here are derived from a set of experiments run on muderong shale with pore pressure control in order to evaluate the effect of stress magnitude and stress anisotropy on ultrasonic response this shale was noted to have a linear velocitymean effective stress response and extremely high anisotropy both likely the result of the presence of fluid filled cracks in a low permeability porous medium changes in velocity and vp vs ratios are dependent on both stress and smectite content s wave velocity is significantly affected by the presence of smectite in this and other shales and at low stress 20 mpa is less sensitive to stress change than p wave velocity vp vs ratios are noted to increase in this shale up to 20 mpa effective stress then decrease slightly due to stress induced loss of interlayer water in smectite intrinsic anisotropy comes from composition a strong compaction fabric and the presence of microfractures changes to ultrasonic anisotropy are the result of the magnitude of the stresses their orientation with respect to the fractures and the degree of stress anisotropy

hurricane associated ebb tidal delta sediment dynamics bathymetric surveys conducted before and after the 2005 hurricane season at little pass timbalier in the mississippi river delta plain united states demonstrate that 9 1 2 4 10 6 m 3 of sediment was eroded from a 47 9 km 2 area between the two surveys hurricanes cindy katrina and rita passed within 300 km of the tidal inlet comparison of before and after bathymetric data sets shows that the distal portion of the ebb tidal delta etd was the site of 63 of the total erosion locally resulting in 400 m of shoreface retreat shoaling 0 75 1 0 m in the seawardmost portion of the ebb channel and erosion in the landward portion 1 5 m resulted in a 160 m landward shift of the inlet throat collectively these processes forced the landward migration of the entire tidal inlet and etd system there has been considerable discussion about large volumes of mineral sediment deposited on the mississippi river delta plain interior marsh surface as a result of hurricanes however the origin of this sediment is unknown we identify the distal portion of an etd as one possible sediment source and hypothesize that etd and shoreface sediment is mobilized by hurricane waves and transported landward by surge induced currents our results emphasize the role of frequent and intense hurricanes in long term coastal evolution and as a mechanism for regional sediment retention within the transgressive system beyond typical barrier overwash processes

the elastic anisotrophy of shales shales constitute about 75 of the clastic fill sedimentary basins and have a decisive effect on fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure the elastic stiffnesses of a shale with partially oriented clay particles is expressed in terms of the coefficients w sub lmn in an expansion of the clay particle orientation distribution function in generalized legendre functions application is made to the determination of the anellipticity of shales for transverse isotrophy the anellipticity quantifies the deviation of the p wave slowness curve from an ellipse and is shown to depend on a single coefficient w sub 400 in the expansion of the clay particle orientation distribution function if w sub 400 is small the anellipticity may be neglected as is apparently the case for a near surface late tertiary shale studied by winterstein and paulson strongly aligned clay particles result in a positive value of w sub 400 and a positive anellipticity in agreement with the majority of the field measurements however less well ordered shales could have a significantly positive second moment w sub 200 but only a small positive or even negative value of w sub 400 for such shales the anellipticity would be small or negative despite amore preferred alignment of clay particles in the bedding plane numerical examples of clay particle orientation distribution functions leading to zero or negative anellipticity are given less

effect of grain scale alignment on seismic anisotropy and reflectivity of shales the elastic properties and anisotropy of shales are strongly influenced by the degree of alignment of the grain scale texture in general an orientation distribution function odf can be used to describe this alignment which in practice can be characterized by two legendre coefficients we discuss various statistical odfs that define the alignment by spreading from a mean value in particular the gaussian fisher and bingham distributions we compare the statistical models with an odf resulting from pure vertical compaction no shear strain of a sediment the compaction odf may be used to estimate how the elastic properties and anisotropy evolve due to burial of clayey sediments our study shows that the three statistical odfs produce almost identical correspondence between the two legendre coefficients as a function of the spreading parameter so that the spreading parameter of one odf can be converted to the spreading parameter of another odf in most cases it is then sufficient to apply the spreading parameter for the odf instead of the two legendre coefficients the effect of compaction on the odf gives a slightly different correspondence between the two legendre coefficients from that for the other models in principle this opens up the possibility of distinguishing anisotropy effects due to compaction from those due to other processes we also study reflection amplitudes versus angle of incidence ava for all wave modes where shales having various odfs overlie an isotropic medium the ava responses are modelled using both exact and approximation formulae and their intercepts and gradients are compared the modelling shows that the s wave velocity is sensitive to any perturbation in the spreading parameter while the p wave velocity becomes increasingly sensitive to a perturbation of a less ordered system similar observations are found for the ava of the p p and p sv waves modelling indicates that a combined use of the amplitude versus offset of p p and p sv reflected waves may reveal certain grain scale alignment properties of shale like rocks

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

offshore transport of sediment during cyclonic storms hurricane ike 2008 texas gulf coast usa extreme storms can have a large impact on coastal sediment budgets and the character of strata preserved in the geologic record here we investigate the impact of a cyclonic storm surge flood and ebb on sediment transport in a microtidal beach barrier shelf system hurricane ike made landfall on the texas united states coast on 13 september 2008 the accompanying storm surge flooded galveston bay with up to 5 m of water above sea level the surge flood and ebb preferentially flowed over a low elevation bay fronting spit known as the bolivar peninsula destroying buildings and eroding sediments surge waters also flowed through bolivar roads tidal inlet the main passageway through the barrier system that separates the gulf and the bay bathymetry chirp data and samples were collected in bolivar roads tidal inlet 9 to 10 d after the storm and we compare them here to data collected 4 mo prior additional data were collected offshore of bolivar peninsula in october 2008 our results document the dominance of the storm surge ebb in forcing sediment transport through the inlet which is not considered in models of beach barrier evolution shoreface sands appear to have been incised by the storm and advected with beach barrier sediments sufficiently offshore by the storm surge ebb that they cannot be reincorporated indicating a significant loss to the barrier system9s sediment budget as a result of a single storm

new model for the emplacement bioturbation and preservation of fine scaled sedimentary strata we present a new quantitative model for the formation and preservation of sedimentary fabric based on interacting sedimentation and bioturbation the model is one dimensional and is forced by fluctuation of the sedimentation rate which affects deposition of sediment possessing primary depositional fabric primary fabric is modified by bioturbation which is represented as a depth limited reaction term model output includes depth in seabed and preservation quotient a measure of relative preservation of primary versus biogenic fabric at each depth the required parameters sedimentation rate and bioturbation rate can be derived from studies of seabed processes model output can be compared directly to observations of both modern and ancient sedimentary strata

probabilistic stability analysis of a tailings dyke on presheared clay shale probabilistic slope stability analysis offers an efficient framework for logical systematic incorporation of un certainty into slope design the slow integration of probabilistic slope analyses into practice is attributed among other factors to the lack of published studies illustrating the implementation and benefits of such techniques a spreadsheet based probabilistic slope analysis methodology is applied to evaluate the stability of a section of the syncrude tailings dyke in fort mcmurray canada the dyke is approximately 44 m high and is founded on presheared clay shale the performance of the dyke is governed by uncertainties about material properties and pore water pressures starting with field and laboratory data this study demonstrates the techniques used in quantifying the various components of param eter uncertainty conducting a probabilistic assessment and estimating the probability of unsatisfactory performance the probability of unsatisfactory performance of the dyke is estimated to be 1 6 10 3 field monitoring data indicate that the dyke performance is adequate the study thus provides a first link between probability figures and perfor mance the analysis also quantifies the relative contributions of the various sources of uncertainty to the overall uncer tainty in the factor of safety

evidence for regional dauphine twinning in quartz from the santa rosa mylonite zone in southern california a neutron diffraction study preferred orientation in granitic mylonites from the santa rosa mylonite zone in southern california is investigated with time of flight neutron diffraction quartz and biotite display strong preferred orientation whereas feldspar alignment is weak for quartz a c axis maximum in the intermediate fabric direction is consistent with dynamic recrystallization pole figures for positive and negative rhombs such as rz 10 11 and zz 01 11 are distinct over a wide region suggesting that the pattern reflects tectonic deformation and was not

mass wasting on the mississippi river subaqueous delta abstract the mississippi river delta front mrdf is an excellent natural laboratory for studying seafloor instability and evaluating the preconditioning factors and triggering mechanisms that lead to seafloor failures the occurrence of seafloor landslides on the mrdf has been recognized since the 1950s but the bulk of research on the topic was conducted in the 1970s 80s after seafloor landslides triggered by hurricane camille damaged offshore infrastructure through these efforts it was recognized that seafloor instability features are present across the entire delta front that rapid sediment delivery from the mississippi river is a primary preconditioning factor for failures and that cyclic loading from hurricane waves is the main triggering mechanism for deep seated catastrophic events however mounting evidence shows that mrdf seafloor motion occurs even during periods of no hurricane activity which could be attributed to creep like motion of underconsolidated sediment or smaller episodic flows triggered by winter storms or mississippi river floods given the extensive spatial distribution of instabilities on the mrdf the multiple mechanisms of failure and variety of resulting morphology and the range of potential triggering mechanisms with short recurrence the mrdf is an exceptional location to assess the complex problem of seafloor landslides an improved understanding of seafloor landslides is crucial for understanding global sediment budgets and associated biogeochemical cycling as they can evacuate large volumes of sediment into deep water over short time periods additionally seafloor landslides pose a hazard to offshore infrastructure and to coastal communities through possible tsunami inundation and advancing research on preconditioning factors and triggering mechanisms would improve hazard assessments this paper presents a review and synthesis of geological and geotechnical research on the mrdf particularly with respect to seafloor landslides their occurrence geological and geotechnical controls triggering mechanisms and knowledge gaps related thereto this synthesis is conducted at times of rapidly developing technologies for studying seafloor instability and as the mrdf enters a stage of degradation characterized by reduced sediment delivery and accumulation

the origin and preservation of a major hurricane event bed in the northern gulf of mexico hurricane camille 1969 cores collected from mississippi sound in the gulf of mexico were studied using 210 pbxs and 137 cs geochronology x radiography granulometry and a multi sensor core logger our results indicate the presence of a widespread sandy event layer that we attribute to hurricane camille 1969 an initial thickness of more than 10 cm is estimated from the cores which is large compared to the time averaged apparent accumulation rate of 0 29 0 47 cm y 31 physical and biological post depositional processes have reworked the sandy layer producing a regional discontinuity and localized truncation and resulting in an imperfect and biased record of sedimentary processes during the storm the oceanographic and sedimentological processes that would have produced an event bed during hurricane camille are simulated using a series of numerical models i e 1 a parametric cyclone wind model 2 the swan third generation wave model 3 the adcirc 2d finite element hydrodynamic model and 4 a wave current bottom boundary layer model that is coupled to transport and bed conservation equations trans98 the simulated bed ranges from 5 cm to over 100 cm within a tidal channel near the barrier islands seaward of the islands the bed is more than 10 cm in thickness with local variability the magnitude and local variability of the storm bed thickness are consistent with the observed stratigraphy and geochronology on both the landward and seaward sides of the barriers 2002 elsevier science b v all rights reserved

a nested grid ocean model with application to the simulation of meanders and eddies in the norwegian coastal current oceanic flow phenomena vary in such large ranges of time and spatial scales that even with the fastest and largest computer to date one cannot at reasonable costs compute large scale circulation and at the same time resolve mesoscale features like fronts and or eddies yet these features are dynamically important and their inclusion may determine how well we can model the mean flow including the deep ocean circulation a two way interactive nested grid primitive equation model is developed here for coastal ocean applications notable features of the model are 1 nesting can be specified on any subregion of a coarse grid large domain and there can be more than one nest if required 2 the nested region can be hot started from earlier calculation results of the coarse grid region that is the code automatically by a change of an input flag generates topography wind forcing climatology currents density and other prognostic variables in the nest and steps forward in time 3 a time splitting integration with small timesteps in the nest and large timesteps in the coarse grid domain is used and 4 nested variables are driven by coarse grid solutions around the nest s boundaries where a flow relaxation scheme may be used and at the same time drive the coarse grid evolution through its averaged action in the overlapped region to demonstrate its robustness the model is applied in a february march 1988 real time simulation of meanders and eddies in the norwegian coastal current initialized from a 585 days quasi equilibrium calculation the simulation includes meteorological forcings inflows outflows across the open boundaries inflow of the north atlantic warm water in particular tides coastal and baltic discharges and wintertime hydrography for depths 500 m from march 20 to 31 the development of a meander between the froya and the halten banks is simulated the timing and location of the meander agree well with observed hydrography

plagioclase preferred orientation by tof neutron diffraction and sem ebsd abstract the lattice preferred orientation lpo of an anorthosite composed of andesine sampled from a highly deformed anorthositic mylonite grenville province quebec was measured by tof neutron diffraction and sem ebsd the quantitative texture analysis of neutron data was accomplished by using the rietveld texture analysis with the wimv algorithm implemented in the program package materials analysis using diffraction maud the texture calculations of the ebsd data were performed by using the program beartex analyses from neutron and electron diffraction data gave similar results if ebsd data are smoothed to account for grain statistics the principal pole figures show 010 roughly parallel to the rock foliation 001 poles exhibiting a low angle 25 to the pole to foliation and 100 poles close to the y direction perpendicular to the lineation and foliation pole the 100 crystallographic direction shows a maximum in the lineation direction 010 directions concentrate near the foliation pole the geological deformation conditions and the constructed pole figure patterns indicate that the preferred orientation could be attributed to intracrystalline slip dominantly on 010 with 100 as slip direction elastic properties calculated by averaging document weak anisotropy that has implications for the seismic structure of the lower crust

seismic velocity anisotropy in mica rich rocks an inclusion model summary we calculated seismic wave velocity anisotropy caused by the preferred orientation of mica minerals by using the differential effective medium method dem spheroidal biotite crystals with their c axes coinciding with the symmetry axis of the spheroid are embedded in an isotropic matrix up to a volume ratio of 30 per cent all crystals are aligned with their c axes parallel to the symmetry axis of the effective homogeneous medium which shows transverse isotropy the effect of crystal shape on anisotropy was studied by changing the aspect ratio the ratio between the minor axis and the major axis of the spheroid from 0 01 flat spheroid to 1 sphere the s velocity anisotropy becomes large as the crystal shape becomes flat whereas the p velocity anisotropy shows only small changes with changes of the crystal shape in particular biotite generates large s wave anisotropy and the anisotropy becomes stronger as the aspect ratio of the biotite crystal becomes smaller when the volume ratio of the mica mineral is large the p wave phase velocity surface shows considerable deviation from the ellipse and the sv wave phase velocity surface forms a large bulge and crosses the sh wave phase velocity surface singularity in the plane including the symmetry axis these results show an interesting contrast when compared with the effect of crack or pore shape on seismic velocity anisotropy crack or pore shape affects the p velocity more than the s velocity we also calculated thomsen s anisotropic parameters e and as functions of the crystal aspect ratio and the mica volume ratio

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

p wave velocities of polymineralic rocks comparison of theory and experiment and test of elastic mixture rules abstract we compare the p wave velocities vp of 696 dry samples measured at pressures up to 0 6 1 0 gpa with values calculated from the volume fraction and room pressure elastic constants of each constituent mineral using 16 averaging methods the exceptional large number of samples covers almost all common lithologic types of igneous and metamorphic rocks the calculated vp data are in good agreement with laboratory values measured at about 300 mpa even though elastic constants of only 22 common minerals are used in the computation the mean vp of a polymineralic rock is exclusively controlled by the volume fractions of its constituent minerals while grain shape and crystallographic preferred orientations anisotropy and other perturbations have minimum effects the mean vp can be fairly well predicted as long as a relevant mixture rule is used and the volume fraction is accurately determined for each mineral however none of the mixture rules can simultaneously produce the best fit to measured p wave velocities for all the lithologic types one method may work well for one lithology but poor for other lithology even for a given lithology an averaging method may yield good agreement at moderate pressure but poor agreement at high pressure applications of an inappropriate mixture rule will potentially cause the misinterpretation of the crust and mantle vp data in terms of mineralogical compositions and structures

anisotropy in shale from mont terri anisotropy of shales is the subject of this report and we use an example of the jurassic opalinus clay from mont terri switzerland that is being investigated in the context of radioactive waste disposal the study is targeted at the geomechanical characterization of shale by laboratory testing the overall aim is to improve the constitutive material laws and their application in numerical models

sea bed mixing and particle residence times in biologically and physically dominated estuarine systems a comparison of lower chesapeake bay and the york river subestuary biologically dominated lower chesapeake bay and the physically dominated york river subestuary are contrasted in terms of the dynamics of sediment mixing strata formation and sea bed particle residence times two lower bay sites were examined both are located within the bay stem plains and are characterized by muddy sand and an abundance of large deep dwelling organisms x radiographs indicate extensive biological reworking of sediments with no long term preservation of physical stratification 210pb profiles reveal low sediment accumulation rates at both lower bay sites 80vs6 30 cm2year 1 in contrast the york river site located within a partially filled palaeochannel is predominantly mud with a depauperate benthic community dominated by small short lived shallow dwelling organisms although210pb accumulation rates at the york river site 0 2 cm year 1 are similar to those measured in the lower bay there is little bioturbation in addition transient bed forms at the york river site form laterally persistent linear ridges and furrows sub parallel to the channel spaced 10 20 m apart these observations coupled with evidence of episodic erosion and deposition from radioisotope and porosity profiles and x radiographs suggest that the upper 60 120 cm of the sea bed are dominated by physical mixing deep mixing and low accumulation rates result in long residence times of particles in the mixed upper portion of the sea bed 102year at both locations despite different mixing controls i e biological diffusive vsphysical advective

fabric related velocity anisotropy and shear wave splitting in rocks from the santa rosa mylonite zone california the directional dependence of p and s wave velocities have been measured at pressures up to 600 mpa and temperatures up to 700 c in rocks from the santa rosa mylonite zone southern california during tectonism these were progressively deformed from granodiorite protolith to mylonite and ultimately phyllonite the mineralogical and chemical composition of protolith and mylonite is nearly identical thus these rocks provide excellent material for documenting the effect of microstructural and textural changes on rock anisotropy velocity anisotropy increases significantly with the degree of deformation whereas average velocities and densities do not change at low pressure 50 mpa the velocity anisotropy ranges from 1 7 in granodiorite up to 19 in phyllonite and is due to both oriented microfractures and crystallographic preferred orientation at high pressure 600 mpa the residual anisotropy up to 12 is mainly due to preferred mineral orientation in particular of biotite significant shear wave splitting is measured parallel to the foliation plane and shows a good correlation with the biotite texture these observations confirm that oriented microcracks and preferred orientation of minerals should be taken into account in the interpretation of seismic reflection and refraction data in terranes with deformed rocks

crystal chemistry of al rich biotites coexisting with muscovites in peraluminous granites a comparison was made between single crystal structure refinements electron microprobe analyses and octahedral site populations of seven biotite crystals and data obtained previously for coexisting muscovite in peraluminous granites using the same methods both micas from several plutons of northern victoria land antarctica and sardinia italy show significant octahedral substitutions biotite has a composition characterized by relatively high 6 al content 0 32 6 al 0 59 apfu whereas muscovite is characterized by phengite like substitutions 0 12 6 mg fe ti mn 0 35 mean bond lengths and electron count data for six biotites 1 m space group c 2 m agreement factor 2 7 r obs 3 6 and a biotite 2 m 1 space group c 2 c r obs 2 8 show that al substitutes for divalent cations in the octahedral m2 site and that the fe and mg distribution is disordered the mean tetrahedral bond lengths determined for biotite 2 m 1 reflect al si disorder in coexisting muscovite 2 m 1 crystals small positive electron density residuals close to m1 site position as well as the increase in m2 mean atomic number is in agreement with the presence of a significant phengitic component reduction in biotite unit cell dimensions with the increase of al follows a pattern similar to that of associated muscovites and the octahedral site volumes of both micas are influenced by the al saturation index asi of the rock these results and the calculated partition coefficients between biotite and muscovite for elements in m sites are consistent with continuous reaction and re equilibration of biotite and muscovite during crystallization of peraluminous granitic melts

texture and anisotropy analysis of qusaiba shales scanning and transmission electron microscopy synchrotron x ray diffraction microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried qusaiba shales from the rub alkhali basin saudi arabia kaolinite illite smectite illite mica and chlorite show strong preferred orientation with 001 pole figure maxima perpendicular to the bedding plane ranging from 2 4 6 8 multiples of a random distribution m r d quartz feldspars and pyrite crystals have a random orientation distribution elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution assuming a nonporous material the average calculated bulk p wave velocities are 6 2 km s maximum and 5 5 km s minimum resulting in a p wave anisotropy of 12 the calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample in the ultrasonic experiment which measures the effects of the shale matrix as well as the effects of porosity velocities are smaller p wave maximum 5 3 km s and minimum 4 1 km s the difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample which have not been taken into account in the matrix averaging

complete texture analysis of a deformed amphibolite comparison between neutron diffraction and u stage data abstract this paper describes a new technique of analysing complex neutron diffraction patterns allowing the quantitative texture analysis of each rock forming mineral up to trielinic lattice symmetry in polymineralic rocks the method is demonstrated using hornblende and plagioclase fabrics in alzenau amphibolite from the spessart mountains mid german crystalline rise hornblende and plagioclase exhibit a pronounced shape preferred orientation with respect to the macroscopic fabric elements for control purposes crystallographic preferred orientations were also determined independently by individual grain measurements using a u stage from the neutron texture analyses we obtain only superposed pole figures hornblende and hornblende hornblende and plagioclase and plagioclase with plagioclase of low indexed lattice planes therefore the critical crystallographic directions were recalculated by the orientation distribution function odf which is given by texture components the optical and neutron derived pole figures are in a good agreement all pole figures display strong preferred orientation although the plagioclase texture is less pronounced the hornblende texture consists of a 001 maximum parallel to the stretching lineation with 010 showing a tendency to develop a girdle around the lineation 100 axes are distributed with a clearly split maximum representing the monoclinic angle between 100 and 001 the plagioclase texture is a rare one with 001 subparallel within the foliation and 100 oriented subparallel to the lineation 010 of plagioclase is concentrated normal to lineation within the foliation the technique outlined here is potentially the most useful one for texture analysis of polyphase rocks independent of crystal symmetry

a detrital sediment budget of a maldivian reef platform abstract sediment dynamics are an important control on the morphology and development of reef systems by actively removing and redistributing excess detrital sediment this study presents quantitative data from direct point measurements of sediment transport on the platform surface and fore reef slope of vabbinfaru reef north male atoll maldives a suite of sediment traps were used to construct actual rates of platform sediment fluxes and off reef export over different spatial and temporal seasonal scales to establish key sediment transport pathways findings showed that high sediment fluxes occur on vabbinfaru platform in the absence of major storm activity up to 1905 g m 1 d 1 with 95 of annual transport occurring during the southwest monsoon as a result of increased wave energy climate driven changes in the platform process regime caused a reversal of net sediment transport pathways between each monsoon season off reef export rates were high reaching a maximum of 12 58 kg m 1 y 1 for gravel and 407 g m 1 d 1 for sand sized sediment an estimated 127 120 kg is exported from the platform annually equating to a significant loss from the reef sediment budget and contributing to the long term geomorphic development of the fore reef slope and atoll basin detrital sediment reservoirs on vabbinfaru are not purely depositional carbonate sinks but rather temporary stores that are important in the transfer of sediment between reef zones

an outflow event on the left side of hurricane harvey erosion of barrier sand and seaward transport through aransas pass texas abstract storm surge is a critical component in the evolution of barrier island systems eroding the shoreface and depositing sediment landward as overwash deposits this rollover process enables barrier islands to migrate landward during periods of rising sea level however cyclonic storms may also generate seaward directed flow and sediment transport which is not typically accounted for in barrier island modeling a strong outflow occurred at port aransas texas during hurricane harvey in 2017 as evidenced from field observations satellite photos and tide data modeling indicates that outflow was forced by offshore winds to the left of landfall to investigate the impact of this event on the barrier system we collected post storm multibeam bathymetry data and sediment samples within aransas pass and lydia ann channel important conduits linking the bays to the gulf of mexico and where such data were previously collected in 2009 and 2012 the 2009 2012 comparison provides a baseline against which to ascertain the storm impact contained in the 2012 2017 comparison both land and marine based evidence indicate that significant erosion accompanied the outflow event focused at the edges of the corpus christi ship channel and lydia ann channel large quantities of sand up to 6 5 m thick also accumulate in deeps of aransas pass and lydia ann channel presumably as the outflow event waned in strength we infer that the outflow event transported a large amount of barrier system sands offshore but do not have sufficient constraints at this time to quantify it

a numerical study of sediment transport and event bed genesis during tropical storm delia some event beds tempestites are thought to be emplaced on shallow marine shelves by the combined action of strong coastal currents and high waves during fairly short lived storms to test this hypothesis a storm sedimentation system has been constructed from six numerical models describing a cyclonic wind field three dimensional coastal circulation wind waves generated over the continental shelf the combined effect of steady and oscillatory currents within the benthic boundary layer suspended and bed load transport of sediment and conservation of the seafloor this model system is used to hindcast winds currents waves and resulting sedimentation during tropical storm delia which passed over the texas louisiana shelf on september 3 4 1973 sensitivity to the initial substrate is investigated in four experiments using uniform silt uniform sand a mud line at the 20 m isobath and a simplified modern sediment distribution modeled coastal currents are vertically uniform and do not reveal the structure predicted by the mid latitude geostrophic storm circulation model because the predicted depth of the wind mixed layer is greater than the water depth over the shelf shelf currents in excess of 2 m s flow predominantly along the coast to the southwest during most of the storm driven by the wind stress and the trapped coastal wave which peaks at 180 cm near galveston significant wave heights reach 8 m on the outer shelf but are less than 4 m over the inner shelf these waves combine with steady currents to produce bed shear velocities which locally exceed 20 cm s the region of highest stresses always lies to the right of the storm track viewed down the path and moves across the shelf with the eye of the storm three general sediment transport paths are evident 1 onshore transport of finer sediment over the outer shelf to the right of the storm track 2 westward directed along shelf transport of predominantly fine sediment between approximately 40 m and 20 m water depths and 3 minor offshore transport of sand from the shoreface to depths less than 30m the resulting event bed has a ragged appearance with a maximum thickness of about 20 cm in region 1 and covers an area of approximately 3 104 km2 to the right of the storm track aside from local transport associated with finer sediments these results are relatively insensitive to initial sediment type comparison of model results to observed data from buccaneer platform shows that the different models performed adequately during the peak of the storm except for a significant underprediction of the significant wave height by the wind sea model the estimated uncertainty in the calculated combined shear stresses u based on errors produced by the individual model components is most dependent on the wave bottom orbital amplitude the total uncertainty in u is estimated to be approximately 7

sedimentological and geoarchaeological evidence of multiple tsunamigenic imprint on the bay of palairos pogonia akarnania nw greece abstract this paper presents evidence of multiple tsunami impact on the bay of palairos pogonia nw greece during the holocene based on detailed geo scientific studies altogether 41 vibracores were drilled to detect high energy influence in the stratigraphical record layers of coarse grained allochthonous marine deposits were found intersecting autochthonous fine grained back beach sediments in the palairos coastal plain on top of beach or marly bedrock units at pogonia beach and along the pogonia cliff section high energy deposits are associated with specific sedimentary structures such as fining upward sequences rip up clasts basal erosional contact bi to multimodal grain size distribution lamination and co existence of both well rounded and angular sharply edged components all of them typical of tsunami impact macro and microfaunal analyses revealed tsunami related input of numerous ex situ marine species and mostly angular shell debris into quiescent fresh to brackish water environments by high energy and long distance transport geophysical methods helped to find subsurface structures and to seize the lateral extent of tsunami layers ca fe ratios derived from xrf measurements were used to trace tsunami influence inland most important is the widespread spatial distribution of the tsunamites with a lateral extent between 70 m at the pogonia cliff section 200 m at pogonia beach and 1 km in the central palairos plain and overall tendencies of fining and thinning towards inland highest elevations of tsunamites were found around pogonia village at ca 7 5 m a s l vibracore data give evidence that the overall coastal evolution has been strongly affected locally even controlled by multiple high energy impact a conspicuous geoarchaeological tsunamite up to 1 5 m thick was found at pogonia cliff consisting of mixed marine sand pebbles bio erosively altered stones shell debris foraminifers and terrigenous material abundant ceramic fragments bones building material it is directly associated with the submerged remains of an ancient mole which was destroyed and its building material partly dislocated by the same event dating of tsunamites was accomplished by archaeological age determination of diagnostic sherds and by radiocarbon and luminescence dating techniques strong tsunami events were dated to the beginning of the 6th the mid 5th the 4th 3rd and the late 2nd millennia bc as well as to the 4th 3rd century bc on a regional scale the recurrence interval for large events is ca 500 1000 years at least twice during the late holocene the palairos coastal plain was flooded quasi contemporaneously from both the northern and southern side

directional dependence of p and s wave propagation and polarization in foliated rocks from the kola superdeep well evidence from laboratory measurements and calculations based on tof neutron diffraction we have measured p and s wave velocities on two amphibolite and two gneiss samples from the kola superdeep borehole as a function of pressure up to 600 mpa and temperature up to 600 degrees c the velocity measurements include compressional vp and shear wave velocities vs1 vs2 propagating in three orthogonal directions which were in general not parallel to inherent rock symmetry axes or planes the measurements are accompanied by 3d velocities calculations based on lattice preferred orientation lpo obtained by tof time of flight neutron diffraction analysis which allows the investigation of bulk volumes up to several cubic centimetres due to the high penetration depth of neutrons the lpo based numerical velocity calculations give important information on the different contribution of the various rock forming minerals to bulk elastic anisotropy and on the relations of seismic anisotropy shear wave splitting and shear wave polarization to the structural reference frame foliation and lineation comparison with measured velocities obtained for the three propagation directions that were not in accordance with the structural frame of the rocks foliation and lineation demonstrate that for shear waves propagating through anisotropic rocks the vibration directions are as important as the propagation directions the study demonstrates that proper measurement of shear wave splitting by means of two orthogonal polarized sending and receiving shear wave transducers is only possible when their propagation and polarization directions are parallel and normal to foliation and lineation respectively c 2005 elsevier b v all rights reserved

3d velocity distribution of p and s waves in a biotite gneiss measured in oil as the pressure medium comparison with velocity measurements in a multi anvil pressure apparatus and with texture based calculated data abstract ultrasonic measurements of the 3d velocity distribution of p and s waves were performed on a spherical sample of a biotite gneiss from the outokumpu scientific drill hole measurements were done at room temperature and pressures up to 400 and 70 mpa respectively in a pressure vessel with oil as a pressure medium a modified transducer sample assembly and the installation of a new mechanical system allowed simultaneous measurements of p and s wave velocities in 132 independent directions of the sphere on a net in steps of 15 proper signals for p and s waves could be recorded by coating the sample surface with a high viscosity shear wave gel and by temporal point contacting of the transmitter and receiver transducers with the sample surface during the measurements the 3d seismic measurements revealed a strong foliation related directional dependence anisotropy of p and s wave velocities which is confirmed by measurements in a multi anvil apparatus on a cube shaped specimen of the same rock both experimental approaches show a marked pressure sensitivity of p and s wave velocities and velocity anisotropies with increasing pressure p and s wave velocities increase non linearly due to progressive closure of micro cracks the reverse is true for velocity anisotropy 3d velocity calculations based on neutron diffraction measurements of crystallographic preferred orientation cpo of major minerals show that the intrinsic bulk anisotropy is basically caused by the cpo of biotite constituting about 23 vol of the rock including the shape of biotite grains and oriented low aspect ratio microcracks into the modelling increases bulk anisotropy an important finding from this study is that the measurements on the sample sphere and on the sample cube displayed distinct differences particularly in shear wave velocities it is assumed that the differences are due to the different geometries of the samples and the configuration of the transducer sample assembly on the spherical sample with a point source and point receiver the first break at the velocity arrival time is suggested to define group velocities in most cases whereas the receivers in the multi anvil apparatus recorded the flat part of the wavefront that is phase velocities

four storm event beds and the tropical cyclones that produced them a numerical hindcast a three dimensional numerical prediction system for storm sedimentation has been constructed to compute a cyclonic wind field coastal circulation storm waves generated over the continental shelf the combined effects of steady currents and waves on the benthic boundary layer both suspended and bed load transport of sediment and conservation of the sea floor it has been used to hindcast the oceanographic and sedimentological responses of the western gulf of mexico to four historical tropical cyclones in order to investigate the effects of coastal configuration and storm variability on event bed genesis the simulations reveal several common responses to these storms 1 onshore flow to the fight of the storm track generally transports fine sediment landward 2 off shore flow to the left transports coarser sediment seaward and 3 for an observer facing the coast right to left along shelf flow transports finer sediment in deep water and coarser sediment in shallow water the main source of sandy sediment on the inner shelf is the shoreface which is eroded by currents driven by wind stress geostrophy and offshore flows associated with collapse of the coastal setup coastal geometry is the dominant factor in determining sedimentation patterns along the coast in front of each storm the volume of sediment transported obliquely onshore or offshore is a function of shelf gradient and coastal configuration steeper gradients constrain flow to a more longshore pattern concave coastlines promote greater shoreface erosion because of increased coastal setup none of the simulations reveals the vertical current structure predicted by the geostrophic model for continental shelf circulation because the calculated depth of the wind mixed layer exceeded local water depth everywhere over the shelf thus in these experiments most of the continental shelf fell within the friction dominated zone in which the upper and lower boundary layers overlap resulting in vertically uniform along shelf flow

impacts of hurricane ike on the beaches of the bolivar peninsula tx usa abstract hurricane ike caused substantial beach erosion along the coast of the bolivar peninsula tx much of the erosion was caused by the offshore ebb flow of the ca 5 m storm surge that formed spatially discrete scour features using aerial photography and repeat lidar data we identify five types of scour features and describe the alongshore distribution in four flow environments type 1 scours are relatively small and compact features associated mainly with flow off a wide vegetated grasses shrubs trees surface across a wide beach type 2 scours are large and branching forms associated mainly with flow that was channeled by streets or gaps between structures type 3 scours are large and blocky features associated with flow off a marsh surface across a highway which removed almost all beach sands from the surface type 4 scours are elongated shore perpendicular channels associated with the same flow characteristics as type 3 scours type 5 scours are elongated shore perpendicular features sometimes branching associated with flow through gaps in a destroyed shore protection structure repeat imagery indicates that many of the features persisted for at least seven months recent aerial photography indicates that aspects of some features remained evident more than three years after ike s landfall

the generation and preservation of multiple hurricane beds in the northern gulf of mexico abstract cores collected from mississippi sound and the inner shelf of the northeast gulf of mexico have been examined using 210 pb and 137 cs geochronology x radiography granulometry and a multi sensor core logger the results indicate that widespread event layers were probably produced by an unnamed hurricane in 1947 and by hurricane camille in 1969 physical and biological post depositional processes have reworked the event layers producing regional discontinuities and localized truncation and resulting in an imperfect and biased record of sedimentary processes during the storms the oceanographic and sedimentological processes that produced these event beds have been simulated using a suite of numerical models 1 a parametric cyclone wind model 2 the swan third generation wave model 3 the adcirc 2d finite element hydrodynamic model 4 the princeton ocean model 5 a coupled wave current bottom boundary layer sedimentation model and 6 a model for bed preservation potential as a function of burial rate and bioturbation rate simulated cores from the mississippi sound region are consistent with the observed stratigraphy and geochronology on both the landward and seaward sides of the barrier islands

variations in storm response along a microtidal transgressive barrier island arc abstract storm response along the transgressive chandeleur barrier island arc southeast of the mississippi delta plain is variable because of local differences in sediment supply shoreline orientation and barrier morphology a study of the morphological impact of hurricane frederic 1979 affirmed that tropical storms are the primary agents causing erosion and migration of this barrier arc frederic s greatest impact was in the duneless southern chandeleurs where sheet flow overwash caused flattening of the barrier profile destruction of a strip of marsh 50 100 m wide and shoreline retreat of approximately 30 m in contrast overwash in the northern chandeleurs was confined between dunes in channels established by previous storms this channelized overwash breached the northern chandeleur barriers in nineteen places as frederic passed return flow through these channels transported overwashed sediment back to the nearshore zone these ebb deposits were a source for longshore drift sediments which quickly sealed storm channels reestablishing a coherent northern chandeleur barrier arc these storm response patterns may help explain long term changes in barrier morphology during an 84 yr period 1885 1969 the southern chandeleurs decreased 41 in area with an average retreat rate of 9 1 m yr 1 compared to a 15 increase in area and an average shoreline retreat rate of 7 2 m yr 1 for the northern chandeleurs

coherence of surf zone and shelf current flow on the texas u s a coastal margin implications for interpretation of paleo current measurements in ancient coastal sequences abstract measurements from the texas coastal margin a microtidal fetch limited wind dominated shallow sea reveal a strong correlation in timing and direction of surf zone and shelf flow during both fairweather and storm events coherence of current motion is statistically significant at many frequencies cycle lengths and is highest during storm events the lack of a significant lag between surf zone and shelf flow indicates that both respond rapidly to changes in the magnitude and direction of the wind field the alongshelf component of the wind stress is a major force in generating currents both on the shelf and in the surf zone as exhibited by comparison of numerical predictions and observed velocities during the 140 day study period current flow was mainly directed alongshelf to the northeast and southwest driven by southerly fairweather and northerly storm winds respectively however the threshold for generation and migration of megaripple bedforms in upper shoreface bar troughs was exceeded only during storm events when surf zone flow was oriented to the southwest along the coast this observation coupled with the knowledge that storm generated bedforms have the highest preservation potential imply that multi event traction bedding in upper shoreface bar troughs of analogous ancient environments will be dominated by unimodal alongshore current orientations large scale bedforms which respond to this time averaged flow on the shelf are expected to display a similar unimodal alongshelf orientation with a low angle deviation toward the offshore direction careful study of paleo current measurements in a well documented ancient shelf to shoreline sequence in the cretaceous of new mexico reflects this similarity in transport kinematics

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

lattice preferred orientation and seismic anisotropy in sedimentary rocks summary although it is well known that sedimentary rocks can be seismically anisotropic there have been few detailed investigations of the underlying cause of such anisotropy here we investigate anisotropy due to the preferred orientation of minerals or lattice preferred orientation lpo in a suite of sedimentary rocks seismic properties are predicted by averaging single crystal elastic constants of minerals according to their crystal orientation and modal volume fraction in the rock aggregate both electron backscattered diffraction ebsd and x ray texture goniometry xtg are tested as quantitative techniques for measuring the lpo of sedimentary rocks although ebsd has promise for future lpo measurements in polymineralic sedimentary rocks problems currently remain in measuring low symmetry phases e g feldspars and very small clay or mica particles however the lpo of very fine grained phyllosilicates can be measured using xtg and the lpo of low symmetry minerals can be measured using manual ebsd pattern analysis here we use such a hybrid approach to estimate lpo in a suite of sedimentary samples the seismic properties calculated from lpo data show anisotropy values for p waves ranging from 1 5 per cent in sandstones to over 3 5 per cent in a siltstone to 12 per cent in a shale the effect of thin multilayering on long wavelength propagation in a siltstone is predicted by applying backus type averaging the layering does not enhance the anisotropy because of the small differences in density and in elasticity between the two layer types the lpo of phyllosilicates and to a lesser extent dolomite and siderite seem to contribute significantly to the seismic anisotropy of phyllosilicate rich rocks siltstones and shales the weak lpo of quartz in sandstones causes a few per cent anisotropy cumulatively our results suggest that field observations of seismic anisotropy have the potential to be used as an indicator of rock lithology

the effect of oriented microcracks and crystallographic and shape preferred orientation on bulk elastic anisotropy of a foliated biotite gneiss from outokumpu abstract elastic anisotropy is an important property of crustal and mantle rocks this study investigates the contribution of oriented microcracks and crystallographic lpo and shape preferred orientation spo to the bulk elastic anisotropy of a strongly foliated biotite gneiss using different methodologies the rock is felsic in composition about 70 vol sio 2 and made up by about 40 vol quartz 37 vol plagioclase and 23 vol biotite measurements of compressional vp and shear wave vs velocities on a sample cube in the three foliation related structural directions up to 600 mpa and of the 3d p wave velocity distribution on a sample sphere up to 200 mpa revealed a strong pressure sensitivity of vp vs and p wave anisotropy in the low pressure range a major contribution to bulk anisotropy is from biotite importantly intercrystalline and intracrystalline cracks are closely linked to the morphologic sheet plane 001 of the biotite minerals leading to very high anisotropy at low pressure above about 150 mpa the effect of cracks is almost eliminated due to progressive closure of microcracks the residual pressure independent part of velocity anisotropy is mainly caused by the strong alignment of the platy biotite minerals displaying a strong spo and lpo calculation of the 3d velocity distribution based on neutron diffraction texture measurements of biotite quartz and plagioclase and their single crystal properties give evidence for an important contribution of the biotite lpo to the intrinsic velocity anisotropy confirming the experimental findings that maximum and minimum velocities and shear wave splitting are closely related to foliation comparison of the lpo based calculated anisotropy about 8 with measured intrinsic anisotropy about 15 at 600 mpa give hints for a major contribution of spo to the bulk anisotropy of the rock

revisiting elastic anisotropy of biotite gneiss from the outokumpu scientific drill hole based on new texture measurements and texture based velocity calculations abstract a sample of biotite gneiss from the outokumpu deep drilling project in finland was investigated by kern et al 2008 for crystal preferred orientation and elastic anisotropy considerable differences between measured acoustic velocities and velocities calculated on the basis of texture patterns were observed measured p wave anisotropy was 15 1 versus a voigt average yielding 7 9 here we investigate the same sample with different methods and using different averaging techniques analyzing time of flight neutron diffraction data from dubna skat and lansce hippo diffractometers with the rietveld technique much stronger preferred orientation for biotite is determined compared to conventional pole figure analysis reported previously the comparison reveals important differences hippo has much better counting statistics but pole figure coverage is poor skat has better angular resolution using the new preferred orientation data and applying a self consistent averaging method that takes grain shapes into account close agreement of calculated and measured p wave velocities is observed 12 6 this is further improved by adding 0 1 vol flat micropores parallel to the biotite platelets in the simulation 14 9

preferred orientation of phyllosilicates comparison of fault gouge shale and schist abstract samples of fault gouge from the san andreas fault drill hole safod a shale from the north sea sedimentary basin and schists from metamorphic rocks in the alps have been analyzed with high energy synchrotron x rays to determine preferred orientation of mica and clay minerals the method relies on obtaining 2d diffraction images which are then processed with the crystallographic rietveld method implemented in the software maud allowing for deconvolution of phases and extraction of their orientation distributions it is possible to distinguish between detrital illite muscovite and authigenic illite smectite kaolinite and chlorite and muscovite and biotite with strongly overlapping peaks in the diffraction pattern the results demonstrate that phyllosilicates show large texture variations in various environments where different mechanisms produce the rock microfabrics fault gouge fabrics are quite weak and asymmetric with maxima for 001 in the range of 1 5 2 5 multiples of random distribution m r d this is attributed to heterogeneous deformation with randomization as well as dissolution precipitation reactions shale fabrics have maxima ranging from 3 to 9 m r d and this is due to sedimentation and compaction the strongest fabrics were observed in metamorphic schists 10 14 m r d and developed by deformation as well as recrystallization in a stress field in the analyzed samples fabrics of co existing quartz are weak all phyllosilicate textures can be explained by orientation of 001 platelets with no additional constraints on a axes

assessing the suitability of holocene environments along the central belize coast central america for the reconstruction of hurricane records since the belize coast was repeatedly affected by hurricanes and the paleohurricane record for this region is poor sediment cores from coastal lagoon environments along the central belize coast have been examined in order to identify storm deposits the paleohurricane record presented in this study spans the past 8000 years and exhibits three periods with increased evidences of hurricane strikes occurring at 6000 4900 4200 3600 and 2200 1500 cal yr bp two earlier events around 7100 and 7900 cal yr bp and more recent events around 180 cal yr bp and during modern times have been detected sand layers redeposited corals and lagoon shell concentrations have been used as proxies for storm deposition additionally hiatuses and reversed ages may indicate storm influence while sand layers and corals represent overwash deposits the lagoon shell concentrations which mainly comprise the bivalve anomalocardia cuneimeris and cerithid gastropods have been deposited due to changes in lagoon salinity during and after storm landfalls comparison with other studies reveals similarities with one record from belize but hardly any matches with other published records the potential for paleotempestology reconstructions of the barrier lagoon complexes along the central belize coast differs depending on geomorphology and deposition of washovers in the lagoon basins is limited probably due to the interplay of biological geological and geomorphological processes

elastic wave velocities chemistry and modal mineralogy of crustal rocks sampled by the outokumpu scientific drill hole evidence from lab measurements and modeling the outokumpu scientific deep drill hole intersects a 2500 m deep precambrian crustal section comprising a 1300 m thick biotite gneiss series mica schists at top followed by a 200 m thick meta ophiolite sequence underlain again by biotite gneisses mica schists 500 m thick with intercalations of amphibolite and meta pegmatoids pegmatitic granite from 2000 m downward the dominating rock types are meta pegmatoids pegmatitic granite average isotropic intrinsic p and s wave velocities and densities of rocks were calculated on the basis of the volume fraction of the constituent minerals and their single crystal properties for 29 core samples covering the depth range 198 2491 m the modal composition of the rocks is obtained from bulk rock xrf and mineral chemistry microprobe using least squares fitting laboratory seismic measurements on 13 selected samples representing the main lithologies revealed strong anisotropy of p and s wave velocities and shear wave splitting seismic anisotropy is strongly related to foliation and is in particular an important property of the biotite gneisses which dominate the upper and lower gneiss series at in situ conditions velocity anisotropy is largely caused by oriented microcracks which are not completely closed at the pressures corresponding to the relatively shallow depth drilled by the borehole in addition to crystallographic preferred orientation cpo of the phyllosilicates the contribution of cpo to bulk anisotropy is confirmed by 3d velocity calculations based on neutron diffraction texture measurements for vertical incidence of the wave train the in situ velocities derived from the lab measurements are significantly lower than the measured and calculated intrinsic velocities the experimental results give evidence that the strong reflective nature of the ophiolite derived rock assemblages is largely affected by oriented microcracks and preferred crystallographic orientation of major minerals in addition to the lithologic control c 2009 elsevier b v all rights reserved