reflection and reverberation in normal incidence echo sounding a mathematical model of normal incidence sediment backscatter based on the helmholtz integral and the kirchhoff approximation was developed this model is different from existing models in that it is able to account for the effects of sonar beamwidth and wavefront curvature including a first order correction for the effects of local slope bottom roughness was modeled as a spatial correlation function constructed from a distribution of gaussian functions a probabilistic measure of the validity of the kirchhoff approximation was also developed two bottom models for a sand and a mud sediment based on measured roughness spectra of real sediments in situ were used to generate numerical results the results confirm the ability of current narrow beam high frequency systems to detect sub bottom interfaces in mud and the ability of most systems to estimate the magnitude of the reflection coefficient of the sediment surface they also predict that measurement of the phase of the reflection coefficient w

predictive mapping of seabed substrata using high resolution multibeam sonar data a case study from a shelf with complex geomorphology abstract this study explores the full potential of high resolution multibeam data for the automated and accurate mapping of complex seabed features under a predictive modelling framework for an area of seabed on the carnarvon shelf in western australia morphometric variables and textural measures were derived from multibeam bathymetry and backscatter data several feature extraction approaches were applied to backscatter angular response curves to obtain new features these derivatives and new features were used separately and in combination in the predictions despite the complex distribution of various hard substrata within the study area we achieved a nearly perfect prediction of hard vs soft seabed types with an auc area under curve close to 1 0 the predictions were also satisfactory for gravel sand and mud content with r 2 values that range from 0 55 to 0 73 this study demonstrates that using a full range of derivatives and new features from both multibeam bathymetry and backscatter data optimises the accuracy of seabed mapping from the modelled relationships between sediment properties and multibeam data we confirmed that coarser sediment generally generates stronger backscatter return importantly the results again highlight the advantages of applying proper feature extraction approaches over using original backscatter angular response curves

model for the precambrian evolution of the avalon terrane in southern new brunswick canada the tectonostratigraphic record of the avalon terrane in southern new brunswick is interpreted as that of a wilson cycle that followed the grenvillian and preceded the opening of lapetus development of a late precambrian continental shelf is attributed to the cadomian ocean whose initial subduction at 800 ma led to platform collapse regional metamorphism and minor mafic to ultramafic plutonism in response to back arc extension and crustal separation oblique subduction of the resulting back arc basin at 600 630 ma produced calcalkaline plutonism and cogenetic volcanism that ended in dextral transtension and the emplacement of a bimodal dike complex initial rifting of lapetus which isolated this record from cratonic north america is recorded in eocambrian redbeds and bimodal volcanics and produced a cambro ordovician overlap sequence bearing acado baltic fauna

stratigraphy and genesis of a modern shoreface attached sand ridge peahala ridge new jersey abstract we investigated the genesis and evolution of peahala ridge a modern shoreface attached sand ridge 1 km 6 km in size and 4 7 m in bathymetric relief through an integrated sedimentologic and stratigraphic study involving vibracoring box coring grab samples high resolution seismic paleontology radiocarbon dating and oceanographic measurements near surface strata of peahala ridge include six important stratigraphic units modern shoreface upper ridge sand lower ridge sand swale inlet fill middle holocene back barrier and late pleistocene strandplain radiocarbon dating and determination of the stratigraphic relationships indicates that peahala ridge formed initially from an ebb tidal delta associated with a tidal inlet so thwestward migration of the inlet channel a vector resultant of landward coastal retreat and southerly longshore drift cut and then filled the swale separating peahala ridge from long beach island following inlet closure peahala ridge developed its present form as a shoreface attached shoreline oblique bathymetric feature hydrodynamic processes have played a major role in evolution of the ridge including considerable growth and accretion this combination of long term eustatic and short term hydrodynamic factors is the best explanation for the present morphology and internal stratigraphy of peahala ridge

tracking the last sea level cycle seafloor morphology and shallow stratigraphy of the latest quaternary new jersey middle continental shelf seafloor geomorphology and surficial stratigraphy of the new jersey middle continental shelf provide a detailed record of sea level change during the last advance and retreat of the laurentide ice sheet 120 kyr b p to present a nw se oriented corridor on the middle shelf between water depths of 40 m the mid shelf paleo shore and 100 m the franklin paleo shore encompasses 500 line km of 2d huntec boomer profiles 500 3500 hz an embedded 4 6 km2 3d volume and a 490 km2 swath bathymetry map we use these data to develop a relative stratigraphy core samples from published studies also provide some chronological and sedimentological constraints on the upper 5 m of the stratigraphic succession the following stratigraphic units and surfaces occur from bottom to top 1 r a high amplitude reflection that separates sediment 46 5 kyr old by ams 14c dating from overlying sediment wedges 2 the outer shelf wedge a marine unit up to 50 m thick that onlaps r 3 channels a reflection sub parallel to the seafloor that incises r and appears as a dendritic system of channels in map view 4 channels fill the upper portion of which is sampled and known to represent deepening upward marine sediments 12 3 kyr in age 5 the t horizon a seismically discontinuous surface that caps channels fill 6 oblique ridge deposits coarse grained shelly units comprised of km scale shallow shelf bedforms and 7 ribbon floored swales bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits we interpret this succession of features in light of a global eustatic sea level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr the morphology of the new jersey middle shelf shows a discrete sequence of stratigraphic elements and reflects the pulsed episodicity of the last sea level cycle r is a complicated marine non marine erosional surface formed during the last regression while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum wisconsin lowstand i e marine oxygen isotope stage 3 1 channels is a widespread fluvial subarial erosion surface formed at the late wisconsin glacial maximum 22 kyr b p the shoreline migrated back across the mid shelf corridor non uniformly during the period represented by channels fill oblique ridges are relict features on the new jersey middle shelf while the ribbon floored swales represent modern shelf erosion there is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession

petrology and age of the mechanic settlement pluton avalon terrane southern new brunswick the mechanic settlement pluton located at the northern margin of the caledonian highlands in southern new brunswick is composed of rocks ranging from ultramafic lherzolite plagioclase bearing lherzolite through mafic mainly olivine gabbronorite and gabbro to intermediate quartz diorite and monzodiorite spatial distribution of these lithologies textural features and geochemistry are consistent with evolution of a tholeiitic mafic parent magma by crystal fractionation processes with some evidence for magma mingling between evolved gabbroic and quartz dioritic magmas the dioritic rocks form most of the southwestern upper part of the pluton whereas the varied gabbroic rocks with ultramafic layers form the northeastern part u pb zircon dating of a quartz diorite sample from the southwestern part of the pluton indicates crystallization at 557 3 ma amphibole and phlogopite in two lherzolite samples from the northeastern part of the pluton gave 40ar 39ar dates of 550 5 and 539 5 ma re

strataform overview of its design and synthesis of its results abstract the strata formed on continental margins record the history of both marine and terrestrial events occurring on earth the strataform program was created to develop a better understanding of relationships between these events and margin stratigraphy in order to obtain the maximum information from strata they are being examined simultaneously on various temporal and spatial scales and their formation is being studied where events and accumulation are known to be active the general objectives of strataform are to add geological perspective to studies of sedimentary processes to constrain stratigraphic interpretations better and to develop numerical models relating processes and stratigraphy this research is being undertaken on margins off northern california and new jersey which provide unique opportunities for investigation of short term and long term stratigraphy respectively this volume and paper focus upon studies undertaken off northern california north of cape mendocino this area is tectonically active with a coastal mountain range narrow shelf and input of sediment primarily from the eel river recent estimates indicate that 1 to 3 10 7 t yr of mud silt and clay are supplied to the continental shelf sand accumulates on the inner shelf 70 reaches the continental slope or deeper during the previous lowstand of sea level sediment discharge was 25 greater and probably led to hyperpycnal debris and other flows transporting sediment down the slope on the eel shelf flood and storm events combine to create normally stratified fine grained layers with basal sand and much terrestrial organic debris these layers are modified through time but some can be buried and preserved subsurface flood layers seem to impact observations of acoustic backscatter on the middle shelf and subsurface fluids gas freshwater affect electromagnetic measurements on the inner shelf budgets of eel river mud accumulation for the past century indicate 20 trapped on the adjacent shelf and 20 on the upper slope 150 600 m the remaining 60 is dispersed to more distal locations over holocene time scales eel river sediment has built a small sandy subaqueous delta and a subtle bulge of muddy sediment on the middle shelf north of the river gullies have been eroded on the open slope during lowstands of sea level and have accreted upward during highstands a massive failure has formed the humboldt slide due to earthquake activity and unstable substrates possibly from excess pore pressures and gas the tectonic setting has impacted margin stratigraphy from small scales fluid expulsion pockmarks to large scales spatial variation of late cenozoic sedimentation the broad dispersal of eel sediment demonstrates the three dimensional character of the resulting stratigraphy including the large scale clinoform structure developed on the shelf upper slope the rollover point topset foreset boundary for this feature is the shelf break i e below sea level which is important information for stratigraphic interpretations of sea level change

high resolution swath sonar investigation of sand ridge dune and ribbon morphology in the offshore environment of the new jersey margin abstract sand ridges on the northeast us atlantic shelf form in the near shore environment most likely in response to storm driven flows as the holocene transgression has continued the ridges have been transferred to an offshore hydrodynamic regime where currents are not constrained by the coast and storms do not influence bottom currents as frequently or as strongly here we qualitatively and quantitatively investigate the morphology of offshore sand ridges and smaller scale features in an effort to place constraints on bedform development in these deeper waters a recent high resolution swath sonar survey mapped a portion of the new jersey shelf from 20 m water depth to the shelf break 120 m imaging both sand ridges and smaller scaled dunes and ribbons in far greater detail than has been previously possible using a robust statistical analysis we find that the gross morphology of ridges height width length does not change with depth beyond 20 m water depth and changes in ridge orientation generally mirror changes in regional contour orientation hence ridges have not continued to grow since transgression has brought them into the offshore hydrodynamic regime however on the inner shelf 20 m water depth to the mid shelf shore we do find evidence in the ridge shape which has an asymmetry opposite to that seen near shore and in the complex backscatter response that some important modifications to ridges are taking place at these water depths in contrast on the mid shelf from the mid shelf shore to the franklin shore ridges tend to have higher backscatter at the crests implying that these are largely winnowed relict features lineated smaller scale 100 500 m wavelength

finite difference simulations of seismic scattering implications for the propagation of short period seismic waves in the crust and models of crustal heterogeneity synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two dimensional media with random spatial variations in seismic velocity the results of this study provide important insights about the propagation of short period 5 the self similar medium is characterized by a scattering q that is constant with frequency whereas theory predicts that the apparent q in an exponential medium is proportional to frequency these alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal q at frequencies greater than about 1 hz assuming that scattering is responsible for most of the attenuation at these frequencies measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation scattering q 200 in these cases q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission q of the medium the cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium the self similar random medium proposed here for the crust produces waveform variations at high frequencies 15 30 hz similar to those reported for actual small scale seismic arrays with apertures of hundreds of meters

geochemical and isotopic characteristics of granitoids of the avalon zone southern new brunswick possible evidence for repeated delamination events nd o and pb isotope data from southern new brunswick suggest that 625 to 360 ma granitoid plutons contain a major juvenile component and small amounts of middle proterozoic or older crustal material plutons fall into four major age groups 600 630 540 560 422 430 and 367 396 ma the first and third groups can be related to subduction in other parts of the appalachian orogen but most of the second and fourth magmatic pulses have lithologic associations and chemistry not readily reconciled to subduction the timing and volume of magmatism presence of mafic end members and juvenile signatures in the plutons suggest that crustal delamination may have been involved little evidence exists for extensive middle proterozoic or older continental crust beneath the avalon zone which consists mainly of late proterozoic continental margin arc material intruded by younger granitoid plutons that include a major mantle component this differs from contiguous gander and meguma zones in which plutons contain a ma

evolution of a classic sand ridge field maryland sector north american inner shelf the ridge and swale topography of the middle atlantic bight is best developed on the delaware maryland inner shelf here sand ridges can be seen in all stages of formation several aspects of the ridge field are pertinent to the problem of ridge genesis the first is ridge morphology there is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges which reflects the changing hydraulic regime as successively more seaward ridges are examined maximum side slope decreases the ratio of maximum seaward slope to maximum landward slope decreases and the cross sectional area increases these changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the holocene transgression a second aspect is the change in bottom sediment characteristics that accompanies these large scale morphologic changes megaripples sand waves and mud lenses appear in the troughs between nearshore and offshore ridges these changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector and that the role of high frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea floor a third aspect is the systematic relationship of grain size to topography grain size is 90 out of phase with topography so that the coarsest sand lies between the axis of the landward trough and the ridge crest while the finest sand lies between the ridge crest and the axis of the seaward trough this relationship is characteristic of large scale bedforms finally flow was measured and transport calculated on the same ridge during a one month period november 1976 threshold was exceeded only during storm events mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline these flow measurements are in conformity with the pattern of smaller bedforms a 43 year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion seaward flank deposition and seaward crest migration sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress the relationship between grain size and topography supports this model but does not account directly for the oblique angle of the ridge with respect to the coastline this feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge and the relationship between this migration rate and the rate of shoreface retreat

paleoenvironmental evidence for latest pleistocene sea level fluctuations on the new jersey outer continental shelf combining high resolution sequence stratigraphy and foraminiferal analysis foraminiferal assemblages in vibracored sediments within 5 m of the seafloor document high resolution sea level fluctuations and confirm the complex quaternary depositional history of the new jersey margin biostratigraphic data have been integrated with ongoing 2 d 3 d high resolution seismic analyses to interpret paleoenvironments of surficial stratigraphy beneath the modern middle to outer shelf cluster analysis of foraminiferal assemblages sampled every 20 cm average define four sample groups a d dominated by benthic species group a characterized by cibicides lobatulus is a middle to outer shelf assemblage 60 100 m water depths group b is composed of middle shelf species 30 60 m water depths and is characterized by low abundances and a fairly uniform distribution of foraminifera which suggests reworking and or a high rate of sediment accumulation group c dominated by elphidium excavatum is an inner to middle shelf assemblage 10 40 m water depths group d present in only one core and dominated by ammonia beccarii represents marginal marine environments 0 10 m water depths with fluctuations in salinity in general the modern sedimentary veneer i e the upper 20 cm is characterized by the deeper water fauna of group a sediments below these modern deposits are characterized by groups b and c reflecting shallower water depths and variable sediment accumulation rates on the inner and middle shelf taken together the group succession in the cores suggests an overall se to nw landward transgression in these latest pleistocene holocene deposits seismic analysis indicates that one core 27 penetrates the flank of a buried channel including its fill and the pre channel section within the channel three alternations of groups c and d suggest fluctuations between marginal marine and middle shelf paleoenvironments high frequency perhaps very small 10 m changes in base level are indicated using previously published ams 14c dates these fluctuations can be constrained as having occurred between 45 000 yr b p channel incision and 12 500 yr b p channel filling suggesting the non uniform nature of the last wisconsinan deglaciation

seabed characterization on the new jersey middle and outer shelf correlatability and spatial variability of seafloor sediment properties abstract nearly 100 collocated grab samples and in situ 65 khz acoustic measurements were collected on the new jersey middle and outer shelf within an area that had previously been mapped with multibeam backscatter and bathymetry data and more recently with chirp seismic reflection profiling eighteen short cores were also collected and probed for resistivity based porosity measurements the combined data set provides a basis for empirically exploring the relationship among the remotely sensed data such as backscatter and reflection coefficients and directly measured seabed properties such as grain size distribution velocity attenuation and porosity we also investigate the spatial variability of these properties through semi variogram analysis to facilitate acoustic modeling of natural environmental variability grain size distributions on the new jersey shelf are commonly multi modal leading us to separately characterize coarse 4 mm fine

anomalous compaction due to silica diagenesis textural and mineralogical evidence from hemipelagic deep sea sediments of the japan sea abstract although anomalous compaction dramatic physical property changes is widely recognised from scientific drilling of sections of marine biosiliceous sediments that have undergone silica diagenesis the precise mechanisms governing vertically abrupt compaction are poorly understood to better understand relationships between silica diagenesis and anomalous compaction the microfabric and composition of hemipelagic sediments at the ocean drilling program sites 794 and 795 in the sea of japan were analysed in detail textural and mineralogical examination of core samples from these stations shows that dissolution of opal a and precipitation of opal ct are the two major controls on anomalous compaction other observed components of the diagenetic history such as structural ordering of diagenetic opal and precipitation of authigenic phases clay minerals and pyrite do not strongly affect physical properties above the opal a to opal ct transition zone anomalous compaction interval opal a deposits impart significant porosity to the sediments because of this high porosity and the relative incompressibility of siliceous tests normal mechanical compaction of biosiliceous units is retarded and mainly postdates silica diagenesis across the transition zone a sharp reduction in opal a content under dissolution from 35 to 12 in site 794 and from 45 to 7 in site 795 leads to a significant reduction in sediment framework stability which makes it vulnerable to sudden collapse abrupt reduction in intergranular and intragranular porosity and increasing bulk density and a decrease in pore water content although later opal ct precipitation does influence the petrophysical response mineralogical analyses suggest a lesser role for opal ct precipitation on host porosity than precursor opal a dissolution this is attributed to the inhibiting effects of high abundance of clay sized components that have restricted significant precipitation of opal ct

the role of erosion by fish in shaping topography around hudson submarine canyon abstract an 800 km2 area of rough topography around the head of hudson canyon off the eastern united states is attributed to erosion by tilefish lopholatilus chamaeleonticeps and associated species of crustaceans the rough topography has a relief of 1 10 m occurs in water depths of 120 500 m and has been cut into a semilithified silty clay substrate since the onset of the holocene transgression commercial fishing activity indicates that a large population of tilefish which dig burrows in the sea floor occupy the area of the rough topography average tilefish burrows are 1 6 m in diameter and 1 7 m in depth they have a clustered not uniform distribution and their average density is 2 500 per km2 the close match of areas of rough topography and high til fish populations the active burrowing of the sea floor and the clustered distribution of the burrows suggest that the hummocky topography in this area may be the result of continuous erosion by tilefish and associated crustaceans during the holocene an erosion rate of 13 cm per 1 000 years is necessary to create this topography during the past 13 000 years and 18 cm per 1 000 years if as is more likely based on the depths at which tilefish presently are found the erosion started 9 000 years ago

magmatic history of the avalon terrane of southern new brunswick canada based on u pb zircon geochronology u pb zircon dates from volcanic and plutonic units confirm that igneous activity throughout the caledonian highlands of southern new brunswick occurred in two main episodes ca 620 ma and ca 560 550 ma the ca 620 ma episode is represented by mainly metatuffaceous rocks of the broad river group and associated dioritic to granitic plutons that form most of the eastern highlands igneous rocks of similar age and type have been documented in avalonian areas throughout the northern appalachian orogen and are interpreted generally to have formed during subduction at a continental margin in contrast the ca 560 550 ma igneous episode may be unique to the caledonian highlands it is represented by tuffs and bimodal flows of the coldbrook group and co genetic gabbroic and granitic plutons that occur mainly in the western highlands this voluminous magmatism may have taken place in a volcanic arc and intra arc extensional setting perhaps like that represented by older but lithologically similar rocks of th

relict iceberg keel marks on the new jersey outer shelf southern hudson apron swath sonar bathymetry reveals sinuous furrows 400 m wide kilometers long and 4 m deep inscribed in semilithified clays on the southern hudson apron we interpret these as keel marks created by floating icebergs detached from the retreating laurentide ice sheet since ca 25 ka keel mark orientations suggest two phases of iceberg rafting these phases could correlate with heinrich meltwater events h2 and h1 ca 25 and 17 ka bracketing the late wisconsinan glacial maximum ca 22 ka during holocene transgression some keel marks were reworked and reformed into oblique ridges where older sandier sediments crop out at the seafloor relict glacial features on the new jersey outer shelf provide a tie between the timing of laurentide glacial retreat and the evolution of shallow stratigraphy on this mid latitude shelf during the last global sea level cycle ca 120 ka to present

two and three dimensional heterogeneity in carbonate sediments using resistivity imaging abstract volume heterogeneity was investigated in carbonate sediments using fine scale electrical resistivity data which are sensitive to porosity and to sediment macrostructure and microstructure variability in sediment density and porosity was assessed by x radiographic and two dimensional 2d electrical resistivity measurements in 3 cm thick slabs collected from the dry tortugas in the lower florida keys a comparison of the 2d correlation lengths calculated from each assessment indicates that using methods that differ in resolution these two methods measure quite different horizontal and vertical fluctuations in sediment density and porosity other electrical resistivity experiments were conducted using a 2d network of resistivity electrodes on the surface of freshly collected box cores the resulting three dimensional 3d resistivity data provide a unique insight into the spatial variability of sediment porosity and structure at the cm scale complementary x radiograph cores provide 2d datasets of resistivity and porosity at higher resolution these data are used to establish the porosity resistivity microstructure relationships for these carbonate sediments with microstructure being described in terms of tortuosity these relationships are used to extend our interpretation in terms of porosity and tortuosity to the corresponding 3d box core resistivity datasets sediment tortuosity is investigated by numerically modeling the flow of electrical currents through a range of pore morphologies in three dimensions the results show particular sensitivity to the intra particle porosity particle shape and the relative sizes of pores and throats the 3d methodology shows promise as a non invasive measurement of buried inhomogeneities that could lead to improving models for predicting acoustic backscattering from the sediment volume

late quaternary sedimentation on the outer and middle new jersey continental shelf result of two local deglaciations high resolution seismic profiles show two prominent late quaternary sediment wedges on the outer and middle new jersey continental shelf an extensive wedge along the outermost shelf and upper slope up to 50 m thick appears to have been deposited on the hudson apron during an early melting of the late wisconsin laurentide ice sheet subsequent southward transport of this sediment occurred during sea level regression still stand and transgression a mid shelf sediment wedge which forms the fortune shore probably was deposited during a second melt event 11 to 12 ka as sea level was transgressing over the shelf

observations of the r reflector and sediment interface reflection at the shallow water 06 central site acoustic bottom interacting measurements from the shallow water 06 experiment experiment frequency range 1 20khz are presented these are co located with coring and stratigraphic studies showing a thin 20cm higher sound speed layer overlaying a thicker 20m lower sound speed layer ending at a high impedance reflector r reflector reflections from the r reflector and analysis of the bottom reflection coefficient magnitude for the upper two sediment layers confirm both these features geoacoustic parameters are estimated dispersion effects addressed and forward modeling using the parabolic wave equation undertaken the reflection coefficient measurements suggest a nonlinear attenuation law for the thin layer of sandy sediments

tectonic setting of avalonian volcanic and plutonic rocks in the caledonian highlands southern new brunswick canada the caledonian highlands of southern new brunswick consist of late proterozoic to cambrian rocks generally considered typical of the avalon terrane of the northern appalachian orogen mainly tuffaceous volcanic and sedimentary rocks of the broad river group and cogenetic dioritic to granitic plutons with ages ca 620 ma form most of the eastern caledonian highlands they have petrological features indicative of origin in a continental margin subduction zone significantly younger ca 560 550 ma dacitic to rhyolitic lapilli tuffs and flows laminated tuffaceous siltstone basaltic and rhyolitic flows and clastic sedimentary rocks of the coldbrook group form most of the western highlands and occur locally throughout the highlands the mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group this voluminous subaerial magmatism may have formed during postorogenic ex

extreme tectonic rotations within an eastern mediterranean ophiolite baer bassit syria palaeomagnetic results from 27 sites at five localities within the dismembered bae r bassit ophiolite of northern syria are presented the ophiolite forms part of a series of thrust sheets emplaced over mesozoic carbonates of the arabian platform in the middle maastrichtian a positive inclination only area wide tilt test applied to four locality mean remanences and positive fold and reversal tests from palaeohorizontal units pillow lavas lava flows within one of these localities indicate that the ophiolite preserves pre deformation magnetisations variable directions of remanence between localities demonstrate that the ophiolite has experienced extreme relative anticlockwise rotations on a kilometric scale within the most extensively sampled ophiolite massif bassit sheet there is a progressive increase in rotation from north to south the southernmost units at the lowest structural level in the imbricate thrust stack record the highest rotation exceeding 200 although tectonic rotation during imbricate thrusting has been reported in a number of orogenic belts the pattern of rotations in the bassit sheet is difficult to explain by differential thrust sheet rotation instead regional comparisons with the hatay ophiolite of southern turkey and the troodos ophiolite of cyprus suggest that a significant component of rotation may be ascribed to intraoceanic deformation of a coherent region of oceanic crust within the southern neotethyan basin prior to ophiolite emplacement the partially rotated bae r bassit ophiolite was then emplaced and structurally dismembered by thrust faulting during the late tertiary the ophiolitic units were further rotated during the initiation and development of a major sinistral strike slip fault zone linking the cyprus subduction zone to the dead sea transform system the extreme rotations observed in the study are therefore of composite origin and reflect the complex development of structural fabrics within the ophiolite 2002 elsevier science b v all rights reserved

u pb geochronology of late proterozoic rocks of the eastern cobequid highlands avalon composite terrane nova scotia in the cobequid highlands of nova scotia low grade late precambrian arc related volcano sedimentry rocks typical of the avalon composite terrane overlie platformal metasedimentry rocks and are spatially associated with gneisses previously considered to be basement to both these units u pb zircon dates of 580 587 ma from an orthogneiss and an amphibolite are similar to the u pb zircon dates of 580 610 ma from both syntectonic granites in ductile shear zones and high level posttectonic plutons that intruded the avalonian successions hence the gneisses do not represent basement but are an integral part of the avalonian orogenic cycle the geochronological data indicate that penetrative fabrics in the gneisses syntectonic granites and volcano sedimentary successions are penecontemporaneous ca 580 620 ma and not sequential as previously interpreted the gneisses have a metamorphic fabric s1a crystallized under amphibolite facies conditions and may represent the deeper roots of a late precambrian

short range travel time geoacoustic inversion with vertical line array this paper presents travel time geoacoustic inversion of broadband data collected on a vertical line array at short range of 230 m during the shallow water 2006 experiments a ray tracing method combined with a hybrid optimization algorithm that utilizes differential evolution and downhill simplex was used for the inversion of sediment properties the ocean sound speed profile and geometric parameters were inverted prior to the sea bottom properties to account for the temporally variable ocean environment the sediment sound speed and thickness estimates are consistent with in situ measurements and matched field inversion results of longer range data from the experiment

late quaternary sedimentation off new jersey new results using 3 d seismic profiles and cores abstract regional seismic reflection surveys have delineated a wedge of late quaternary sediment extending 150 km south from the hudson apron along the edge of the continental shelf off new jersey the bottom of the sediment wedge is defined by a prominent reflector r assumed to represent an erosional surface carved during a low stand of sea level probably corresponding to the wisconsinan maximum glaciation a 3 d reflection survey of a 5 0 5 km area of the southern part of the wedge was carried out in october 1989 line spacing was 10 m and shot spacing 2 5 m navigation achieved position accuracies to the survey shows that the outer shelf sediment wedge has a complex internal structure unrelated to the present seafloor morphology the sedimentary sequence appears to have been formed by a series of depositional events related to glacial melting and interrupted by at least one erosional episode marked by a seismic surface that defines a system of meandering channels faunal studies of samples from cores indicate that the sediments were deposited at shallower depths than at present but there is no evidence for deposition in shallower water or closer proximity to land than the modern mid shelf it appears that the history of periglacial marine sedimentation which accompanied the post wisconsinan deglaciation is no less complex than its continental counterpart

anatomy of rapid margin progradation three dimensional geometries of miocene clinoforms new jersey margin documentation of along strike variations in the morphologies of continental margin clinoforms is essential for understanding mechanisms of progradation one of the fundamental relationships between depositional processes and preserved stratigraphy maps based on a grid of commercial multichannel seismic data offshore new jersey extending more than 70 km along strike and approximately 50 km downdip reveal the three dimensional morphology and evolution of four buried surfaces correlated with middle upper miocene sequence boundaries calibrated by drilling on the adjacent continental slope miocene clinoform breakpoints are not depositional analogs of the modern shelf edge they are linear to gently arcuate breakpoint and slope trends indicate a systematic southward displacement of depocenters over about 5 6 m y progradation responded to point fluvial sediment sources but efficient along strike sediment dispersal muted their influence canyons are absent on three of four clinoform slopes the fourth slope has one v shaped canyon and a broad erosional area possible slope failure planar floored canyons also occur albeit rarely seaward of clinoform toes apparently v shaped and planar floored canyons previously ascribed to downslope erosion vs slope failure headward erosion respectively can coexist the accretionary northern slope of little bahama bank is a possible morphologic analog by analogy with pleistocene shelf slope geometries an absence of canyons breaching clinoform breakpoints suggests that rivers did not discharge at paleoshelf edges indicating that sea level lowstands postulated for the middle upper miocene did not expose breakpoints reconstruction of breakpoint paleoelevations supports this conclusion for three of the four mapped surfaces suggesting that elevations of some miocene lowstands on the global sea level curve are too high by up to 60 m

geology and geochemistry of the late precambrian coldbrook group near saint john new brunswick the late precambrian coldbrook group comprises basal basaltic flows and pyroclastic rocks fragmental andesitic to rhyolitic rocks and minor capping sedimentary strata all deformed and metamorpho

stochastic modeling of the reflective lower crust petrophysical and geological evidence from the ivera zone northern italy crustal scale seismic wave equation modeling demonstrates that wavelength scale velocity fluctuations can dominate the seismic response over a wide range of offsets and that a wide range of velocity distributions qualitatively can explain deep seismic data this range can be narrowed by studying the detailed petrophysical and structural properties of middle and lower crustal exposures the ivrea zone in the southern alps is a well studied sliver of extended lower continental crust brought into its present upright position as a result of late alpine lithospheric shortening the high degree of structural and petrophysical complexity and in particular the limited exposure of the ivrea zone favor a statistical rather than deterministic approach to develop a two dimensional crustal scale seismic model for this purpose we digitized two 1 25 000 geological maps from the central ivrea zone on a 60 m grid we find that the ivrea zone is characterized by a bimodal velocity distribution and a band limited self affine structure having a fractal dimension of 2 7 a characteristic horizontal scale of 500 to 1000 m and an aspect ratio around 4 0 assuming statistical stationarity a realization of this stochastic model was used to develop synthetic seismograms typical of ivrea type lower continental crust our results indicate that 1 ivrea type lower crust can explain qualitatively commonly observed lower crustal reflectivity 2 relatively minor changes in bulk composition and or metamorphic grade may lead to dramatic changes in reflectivity which cannot be explained by current generic models on the origin of lower crustal reflections and 3 travel time interpretation of the synthetic wide angle data may lead to erroneous large scale velocity structures

inversion of acoustical data from the shallow water 06 experiment by statistical signal characterization this paper presents an application to validate an acoustic signal characterization scheme for ocean acoustic tomography and geoacoustic inversions proposed by taroudakis tzagkarakis and tsakalides j acoust soc am 119 1396 1405 2006 using data from an experiment at sea the data were collected during the shallow water 06 sw06 experiment off the new jersey continental shelf and the inversion results sea bed geoacoustic parameters and source range are compared with those reported from the same data by bonnel and chapman j acoust soc am 130 2 el101 el107 2011 the comparison and the signal reconstruction using estimated values of the model parameters are satisfactory indicating that the new signal characterization method is useful for practical applications of acoustical oceanography

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

quantitative analysis of sea ice draft 1 methods for stochastic modeling this paper seeks to develop a robust set of tools for estimating the stochastic properties of sea ice drafts five parameters are estimated along with their formal uncertainties mean draft rms topographic variation characteristic length fractal dimension and normalized skewness these provide an objective basis for terrain classification a recent 10 km by 10 km upward looking submarine sonar survey serves as a test case data profiles are compared with synthetic profiles generated from the statistical parameters estimated from the data these provide a means of qualitatively assessing the success of the stochastic model at characterizing the principal morphological properties in general the comparisons are good providing confidence in the applicability and versatility of the stochastic model a few exceptions are notable but these also provide valuable insight into our understanding of the morphology of sea ice draft

the effects of fine scale surface roughness and grain size on 300 khz multibeam backscatter intensity in sandy marine sedimentary environments abstract high frequency acoustic backscatter intensity that is returned from sediment is affected by a number of seabed characteristics including sediment grain size distribution the nature and magnitude of seabed surface roughness and volume scattering by subsurface scatterers in order to develop quantitative remote sediment classification techniques it is important to determine the relative and combined effects of the dominant variables to which the acoustic signal is sensitive data used in this study were collected at two sandy sites off the south shore of long island new york and include 300 khz multibeam simrad em 3000 backscatter intensity data as well as grab samples and stereo bottom photographs multivariate statistical analyses were used to investigate the relationships between grain size properties seabed roughness and backscatter intensity at a number of sample locations at each study site encompassing a moderate range of backscatter intensities from 32 5 to 24 db the results of this study demonstrate that the relative importance of variables that affect backscatter intensity varies at different sites suggesting that backscatter intensity alone cannot be used to quantitatively predict seabed characteristics however our study indicates that in sandy sediments the median grain size the standardized magnitude of seabed roughness and the sorting of sediment can together be used to predict 300 khz backscatter intensity with high significance and that the relative importance of these variables varies from site to site we present an empirical model derived from a combined dataset that includes two sites of similar sedimentary and hydrodynamic conditions to predict the magnitude of seabed roughness based on backscatter intensity and sediment grain size characteristics the spatially coherent patterns in predicted seabed surface roughness revealed through the use of this kind of model greatly improve our understanding of variations in backscatter intensity in sandy marine sedimentary environments as a result the multivariate statistical approach that we employ improves our overall ability to remotely assess the details of the sedimentary environment that are significant with respect to benthic habitats and physical processes and are applicable to other geophysical datasets including sidescan sonar data

acoustic propagation in the ocean with a poro elastic bottom the acoustic normal modes in a homogeneous ocean overlying a homogeneous porous elastic bottom half space are obtained in closed form the biot theory is used to model the bottom the effects of sediment properties on the dispersion and attenuation of acoustic waves are examined numerically it is found that the shear modulus and the poro viscous frequency number ksf are the two most critical bottom parameters for acoustic attenuation here ks is permeability f is frequency is porosity and is the kinematic viscosity for sediment and rocks having shear modulus larger than 5 107 n m2 the shear waves and the slow compressional waves become important in acoustic propagation for hard porous rocks such as sandstones and corals the attenuation of acoustic waves by a porous rock increases with frequency for a given soft sediment the acoustic wave attenuation decreases with frequency for a given frequency the acoustic attenuation becomes maximum when the sediment properties are such that ksf

seabed acoustics of a sand ridge on the new jersey continental shelf acoustic measurements were made on a sand ridge on the new jersey continental shelf data collected on two l arrays separated by 20km from a single multi frequency tow suggest small horizontal environmental variability values for the sound speed structure of the seabed are extracted by first applying a geo acoustic inversion method to broadband and narrowband acoustic data from short range sources then a parabolic equation algorithm is used to properly include the bathymetry and sub bottom layering finally the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long range transmission loss data in the 50 3000hz band

stochastic modeling of seafloor morphology inversion of sea beam data for second order statistics at scale lengths less than 100 km or so statistical descriptions of seafloor morphology can be usefully employed to characterize ridge crest processes off ridge tectonics and vulcanism sedimentation and postdepositional transport we seek to develop methods for the estimation of seafloor statistics that take into account the finite precision resolution and sampling obtained by actual echo sounding systems in this initial paper we restrict our attention to the problem of recovering second order statistics from data sets collected by multibeam devices such as sea beam the seafloor is modeled as a stationary zero mean gaussian random field completely specified by its two point covariance function we introduce an anisotropic two point covariance function that has five free parameters describing the amplitude orientation characteristic wave numbers and hausdorff fractal dimension of seafloor topography we formulate the general forward problem relating this model to the statistics of an ideal multibeam echo sounder in particular the along track autocovariance functions of individual beams and the cross covariance functions between beams of arbitrary separation using these second moments as data functionals we then pose the inverse problem of estimating the seafloor parameters from realistic noisy data sets with finite sampling and beamwidth and we solve this inverse problem by an iterative linearized least squares method the inversion method is applied to sea beam transit data from both the pacific and atlantic oceans sea beam system noise stands out as a sharp spike on the along track autocovariance function and can be modeled as a white noise process whose amplitude generally increases with beam angle the five parameters in our second order model can be estimated from the inversion of data sets comprising 100 200 km of track length in general the cross track wave number is the most poorly determined although uncertainties in the assumed sea beam response may bias the values of the fractal dimension using the assumed beamwidth the measured noise values and the seafloor parameters recovered from the inversion we generate sea beam synthetics whose statistical character can be directly compared with raw sea beam data for most of the track segments we have processed thus far the synthetics are similar to the data in the case of one atlantic profile however the comparison clearly indicates the necessity of incorporating higher order statistics the space domain procedures described in this paper can be extended for this purpose

measurements of diffusivity near the sediment water interface with a fine scale resistivity probe fine scale profiles of the sedimentary formation factor f were obtained from measurements of resistivity at millimetre intervals in marine sediments these profiles demonstrated that rapid decreases in diffusivity occurred in the upper few centimeters of both compact intertidal sands and fine silty muds in the compact sands a 70 decrease in the formation factor was observed within 2 cm of the interface close correlations were found between the formation factor and sediment porosity for both sediment types profiles of 1f predicted from these correlations and porosity profiles were very similar to those obtained from measurements of resistivity these correlations also suggested that 3 is a better approximation of the formation factor in fine muds than the archie relation 2 in both sediments the interfacial value of the diffusion coefficient was estimated to be between 74 and 87 of its value in free solution a value much higher than is normally assumed

range dependent waveguide scattering model calibrated for bottom reverberation in a continental shelf environment an analytic model is developed for scattering from random inhomogeneities in range dependent ocean waveguides using the rayleigh born approximation to green s theorem the expected scattered intensity depends on statistical moments of fractional changes in compressibility and density which scatter as monopoles and dipoles respectively and the coherence volume of the inhomogeneities the model is calibrated for ocean bottom scattering using data acquired by instantaneous wide area ocean acoustic waveguide remote sensing oawrs and geophysical surveys of the onr geoclutter program the scattering strength of the seafloor on the new jersey shelf a typical continental shelf environment is found to depend on wave number k medium coherence volume vc and seabed depth penetration factor fp following a 10log10 fpvck4 dependence a computationally efficient numerical approach is developed to rapidly compute bottom reverberation over wide areas using the parabolic equation by exploiting correlation between

the influence of geomorphology and sedimentary processes on benthic habitat distribution and littoral sediment dynamics geraldton western australia abstract understanding of the processes regulating sediment transport accumulation and erosion requires an appropriate mapping of coastal geomorphology seabed sediments and benthic habitat distribution to allow management issues to be identified understood and addressed in this study multibeam echo sounder data were used to map shallow water geomorphological features and the spatial distribution of benthic habitats with the support of underwater imagery for ground truthing the acoustic data at geraldton sediment analyses have revealed a dominant biogenic nature with modern carbonate sedimentation linked to the seagrass and macroalgal carbonate factories colonising these shallow