a model for attenuation of backscatter due to sediment accumulations and its application to determine sediment thicknesses with gloria sidescan sonar where the seafloor consists of a highly backscattering surface covered with a drape of fine grained sediment and where the sediment does not contribute significantly to the backscattered signal the sediment thickness can potentially be inferred from the amount of signal attenuation in the sediment layer a first order acoustical model is proposed in which the signal strength is reduced by an amount proportional to the sediment thickness and attenuation rate in the sediments data collected with geological long range inclined azdic gloria are used to develop and test this model at an acoustic frequency of 6 5 khz the range of sediment thickness that the sonar can potentially recover is 0 20 m a range that is often below the resolution of vertical profilers in the first example the signal variation with grazing angle over a uniformly buried surface is analyzed for attenuation which is expected to increase toward shallow grazing angles and longer attenuating paths through the sediment layer the surface is a lava flow north of hawaii covered by 1 2 m of fine grained sediments clague et al 1990 and gloria data analyzed with the model suggest an attenuation coefficient of 0 2 0 4 db m a value consistent with results from laboratory and field measurements of sediment attenuation in the second example a rocky surface is buried by varying amounts of sediment which is analyzed at almost constant grazing angle the surface is the volcanic basement of the southeast indian ridge and gloria data reveal the thickening of the sediment cover with distance away from the spreading center this is used to derive an average sedimentation rate of 6 mm ka which is generally consistent with results from other studies and suggests that this technique may be used to study differences in sedimentation rates between different regions furthermore the model is used to calculate from image amplitude distributions the sediment thickness distribution which represents the accumulation of sediments in ponds and the exposure of abyssal hills these sedimentary processes are also reflected in the standard deviation of sediment thickness which increases with seafloor age i explore the various sources of error in estimating sediment thickness using this technique and propose a model for nonuniform sediment drapes the first order model assumes a uniform thickness at the subfootprint scale

deformational styles of the eastern mediterranean ridge and surroundings from combined swath mapping and seismic reflection profiling abstract recent swath mapping and seismic reflection profiling across the eastern levantine branch of the mediterranean ridge mr in the eastern mediterranean sea illustrate a strong variability of the deformational styles that characterize this precollisional accretionary prism along a north south cross section of the mr a structural analysis based on surface mapping combined with vertical seismic reflection data reveals two main structural domains a southern outer domain consists of a series of three disconnected distinct fold belts folding affects a sedimentary cover which includes an approximately 2 km thick pliocene and quaternary wedge in this domain resting on fairly thick messinian evaporitic sequences that act as probable decollement layers the mr inner domain includes three regions showing evidences of strong internal deformations and of numerous probable mud cones and mud flows but no seismic evidence of significant underlying messinian evaporites can be detected the inner sub regions are thrusting northwards over an area made of faulted and locally uplifted acoustic basement blocks that constitute the southernmost extension of the crete continental margin acting as a continental buttress for the mr this innermost domain is itself structurally disconnected from the crete continental margin by the en echelon pliny troughs system that shows evidence of left lateral displacement altogether the different structural and sedimentary cover patterns reveal a strong contrast between both mr inner and outer domains and important lateral variations within the inner mr itself strike slip faulting seams to characterizes both areas and large scale mud accumulations potentially exist in the northern one our results support a model of imbricated accretionary prisms including at least two stages 1 a pre messinian stage during which the inner mr probably developed in response to northward subduction of the african lithosphere beneath southern europe and 2 a messinian to post messinian period during which the kinematics of the aegean anatolian microplates and the presence of thick messinian deposits became prevalent and which led to the creation of the outer mr folded wedge piling against the previous one in our interpretation the occurrence of thick messinian evaporites in this area induces important local and regional modifications of the structural pattern strike slip activities reflect partitioning related to oblique subduction and likely lateral escape of the sedimentary cover in the whole studied area

cold seeps at the salt front in the lower congo basin ii the impact of spatial and temporal evolution of salt tectonics on hydrocarbon seepage abstract this study investigates the distribution and evolution of seafloor seepage in the vicinity of the salt front i e the seaward boundary of salt induced deformation in the lower congo basin lcb seafloor topography backscatter data and tv sled observations indicate active fluid seepage from the seafloor directly at the salt front whereas suspected seepage sites appear to be inactive at a distance of 10 km landward of the deformation front high resolution multichannel seismic data give detailed information on the structural development of the area and its influence on the activity of individual seeps during the geologic evolution of the salt front region the unimpeded migration of gas from fan deposits along sedimentary strata towards the base of the gas hydrate stability zone within topographic ridges associated with relatively young salt tectonic deformation facilitates seafloor seepage at the salt front bright and flat spots within sedimentary successions suggest geological trapping of gas on the flanks of mature salt structures in the eastern part of the study area onlap structures associated with fan deposits which were formed after the onset of salt tectonic deformation represent potential traps for gas which may hinder gas migration towards seafloor seeps faults related to the thrusting of salt bodies seawards also disrupt along strata gas migration pathways additionally the development of an effective gas hydrate seal after the cessation of active salt induced uplift and the near surface location of salt bodies may hamper or prohibit seafloor seepage in areas of advanced salt tectonic deformation this process of seaward shifting active seafloor seepage may propagate as seaward migrating deformation affects congo fan deposits on the abyssal plain these observations of the influence of the geologic evolution of the salt front area on seafloor seepage allows for a characterization of the large variety of hydrocarbon seepage activity throughout this compressional tectonic setting

liquid immiscibility and the evolution of basaltic magma this experimental study examines relationships between alternative evolution paths of basaltic liquids the so called bowen and fenner trends and silicate liquid immiscibility synthetic analogues of natural immiscible systems exhibited in volcanic glasses and melt inclusions were used as starting mixtures conventional quench experiments in 1atm gas mixing furnaces proved unable to reproduce unmixing of ferrobasaltic melts yielding instead either turbid opalescent glasses or crystallization of tridymite and pyroxenes in contrast experiments involving in situ high temperature centrifugation at 1000g g 1 4 9 8 m s did yield macroscopic unmixing and phase separation centrifugation for 3 4 h was insufficient to complete phase segregation and resulted in sub micron immiscible emulsions in quenched glasses for a model liquid composition of the middle zone of the skaergaard intrusion at super liquidus temperatures of 1110 11208c centrifugation produced a thin silicic layer 64 5 wt sio2 and 7 4 wt feo at the top of the main fe rich glass 46 wt sio2 and 21 wt feo the divergent compositions at the top and bottom were shown in a series of static runs to crystallize very similar crystal assemblages of plagioclase pyroxene olivine and fe ti oxides we infer from these results that unmixing of complex aluminosilicate liquids may be seriously kinetically hampered presumably by a nucleation barrier and thus conventional static experiments may not correctly reproduce it in the light of our centrifuge experiments immiscibility in the skaergaard intrusion could have started already at the transition from the lower to the middle zone thus magma unmixing might be an important factor in the development of the fe enrichment trend documented in the cumulates of the skaergaard layered series

mud volcanoes at the shelf margin of the east china sea abstract roughly circular sediment mounds varying from tens to hundreds of meters in diameter and from a few meters up to 40 m in height have been mapped for the first time at the shelf edge of the east china sea ecs high resolution seismic profiles together with swath bathymetric and acoustic data indicate that these features are common on the ecs outer shelf and on the upper western slope of the okinawa trough they are associated with unusually large pockmarks up to 40 m in depth and 600 m in diameter on seismic records bright spots phase inversions and other acoustic anomalies indicate that gas and or fluid escape plays an important role in the formation of these mounds they are often associated with normal faults that occur along the western slope of the okinawa trough these faults acting as conduits for migrating fluid based on regional stratigraphic correlation we propose that the source of mud and fluid is deeper older than 235 ka the seepage process is suspected to be very recent and probably still active based on the facts that 1 despite high sedimentation rate the mounds are not buried by recent sediments and 2 last glacial maximum deposits are reworked at the emplacement of the mounds carbonate cemented sediments and deep water reefs possibly associated with fluid seepage could be the origin of local patches of very high backscattering acoustic facies mapped with the swath bathymetric system

western mediterranean ridge mud belt correlates with active shear strain at the prism backstop geological contact a high resolution swath mapping survey conducted in the deep waters of the eastern mediterranean sea allowed mapping of active faults and mud volcanism along a sizable portion of the mediterranean ridge active shear is localized at the prism backstop con tact a major dextral flower structure and a site of massive mud expulsion we investigate the relationship between the mud output rate and horizontal strain rate by combining the mud volume estimate from sea bottom reflectivity with kinematic modeling based on far field global positioning system data and local fault and strain patterns we find a direct correlation between maxima of mud output and maxima of the shear component of strain at the backstop contact mud volcanism may reflect the abundance of solid mud and fluid methane sources combined with a favorable tectonic regime established at the prism backstop contact in post pliocene time in relation to plate tectonic changes

brine pools associated with mediterranean ridge mud diapirs an interpretation of echo free patches in deep tow sidescan sonar data abstract mak 1m deep tow sidescan sonar surveys have revealed two echo free patches in an area of mud diapirs on the mediterranean ridge the unusual shape of these patches and absence of returned signal can be explained more easily by the presence of brine pools rather than as a topography effect the high acoustic impedance contrast at the interface between brine and seawater a result of the salinity contrast there causing a relatively high contrast in sound velocity and water density acts as a screen preventing sidescan sonar sound signal at low grazing angles from reaching the seafloor sound is reflected and refracted away from the sonar towfish without any backscatter the inferred brine pools appear to be associated with faults recognized on sonographs and subbottom profiler records this first observation of brine pools related to mud volcanoes and mud diapirs suggests that salt is present in areas of mud diapirism possibly playing a role in that process or at least that the brines and mud may share flow paths within the mediterranean ridge

attenuation of sound in marine sediments a review with emphasis on new low frequency data in many situations the acoustic properties of the bottom are important and considerable effort has been directed at their elucidation over the whole frequency range of interest to underwater acoustics at low frequencies experimental measurement of these properties is particularly difficult and uncertainty exists in the values of some key parameters the determination of compressional and shear wave attenuation has been especially challenging and it is not surprising that debate has persisted as to the magnitude of this property and its overall dependence on frequency at low frequencies this paper attempts to examine this question through a review of the relevant literature from rock mechanics and underwater acoustics with a special emphasis on low frequency data

ground truthing 6 5 khz side scan sonographs what are we really imaging a 1000 km2 area on the distal lobe of monterey fan shows a digitate pattern of juxtaposed high and low backscatter on gloria side scan sonographs this area was investigated using stereo photography high resolution seismic profiles and measurements of physical properties of cores to quantitatively evaluate the causes of backscatter from the 6 5 khz side scan sonar stereo photography and bottom video were used to determine that the sediment water interface typically has a bed roughness less than 10 cm over the entire ground truth area consequently bed roughness is not a significant contributor to the sonar backscatter vertical incidence 3 5 khz profiles reveal that high backscatter areas allow less penetration and have slightly more relief than low backscatter areas closely spaced measurements of p wave velocity density and grain size made on transponder navigated cores are used to investigate the geoacoustic properties of the sediment with the aid of a numerical model the model results demonstrate that the sediment water interface is in most cases acoustically transparent to the sonar energy and that most or all of the energy is refracted into the sediment to depths of at least a few meters rather than scattered from the surface the variability of the dominant lithofacies sands with minor silty clays or silty clay with minor sands accounts for a regional correlation with backscatter when viewed over hundreds to thousands of square kilometers but at the detailed scale of hundreds to a few square meters we have not yet been able to identify a correlation of backscatter intensity with the angle of incidence surface lithology measured acoustic impedance or attenuation however there is a qualitative but unexpected correlation with lithostratigraphic variability in this area thick up to 50 cm sand deposits with thin interbeds of silty clay correlate with lower backscatter than do silty clay deposits with thin interbeds of sand this suggests that volume inhomogeneities and complex constructive and destructive interferences caused by the subsurface volume inhomogeneities within the top few meters of the sediment ultimately modulate the intensity of backscatter the ground truthing effort was further complicated by trying to compare the very large sonar footprint of a pixel 70 000 m2 relative to the area of an individual core 0 006 m2 bottom photograph 5 m2 or seismic profile although 6 5 khz sonographs appear easy to interpret in a conventional and simplistic manner caution should be used when interpreting lithofacies from backscatter intensities

a model data comparison for low frequency bottom backscatter this article describes a model for bottom backscattering strength applicable over the frequency range 100 1000 hz the model includes backscatter due to both a rough water sediment interface and internal sediment inhomogeneities i e sediment volume scattering within an upward refracting sediment the net result is predictions for bottom backscattering strength that depend on the following frequency sound speed of the water near the water sediment interface density ratio sound absorption within the sediment near surface sound speed gradient within the sediment two interfacial roughness parameters and a parameter proportional to the scattering cross section of a unit volume of sediment the sediment sound speed profile is specified in terms of near surface values for the sound speed ratio and gradient salient features of the modeled backscatter strength include marked departures from lambert s law for sediments with sound speed ratios greater than 1 1 5 db oscillations as a function of grazing an

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

sidescan sonar images of mud volcanoes from the mediterranean ridge possible causes of variations in backscatter intensity abstract a survey of a large field of mud diapirs on the mediterranean ridge south of crete was carried out using both okean 9 5 khz and mak 1m 30 khz sidescan sonar systems during leg 2 of the third training through research cruise of r v gelendzhik in june and july 1993 high backscatter intensities were recorded by both systems to different degrees over the mud diapirs and their immediate surroundings causes of variations in the backscatter intensity are considered to be the spatial distribution of mud breccia associated with the mud domes both the burial depth of the mud breccia beneath hemipelagic drape and its areal extent and its physical properties along with contributions from seafloor roughness and the topography of the mud domes significant sources of volume scattering of the sidescan sonar sound signal are considered to be mud breccia inhomogeneities represented by millimetric centimetric clasts of various lithologies and free gas bubbles distributed through the mud matrix a good general relationship is established between these sources and the observed backscatter variations through analysis of ground truth data from core samples with 5 khz deep tow subbottom profiler records and seafloor video observations as well as the sidescan sonar records but a fully quantitative assessment of this relationship would require acoustic modelling and additional ground truth data

structural features of mud volcanoes and the fold system of the mediterranean ridge south of crete abstract new information on the geometry of the mud volcanoes folds and faults located in the central part of the mediterranean ridge is provided from long range and deep tow sidescan sonar images high resolution seismic and low frequency echosounder profiles and gravity cores obtained on the r v gelendzhik during the 1993 unesco esf training through research cruise symmetrical gentle folds with a mean wavelength of 750 m deform predominantly pliocene quaternary sediments but also perhaps as old as messinian in most areas of the mediterranean ridge the north northeast directed subduction of the african plate below the eurasian plate at the hellenic arc produces folds with hinge lines subparallel to the trend of the ridge however the hinge lines of the folds curve around the southern part of the area with highest concentration of mud volcanoes and produce an irregular u shape fold belt some of the folds show an intrusive nucleus and in some of them mud breccia appears to have flowed from the flanks of the folds into the troughs the mud volcanoes consist of domes of interlayered pelagic sediments and mud breccias containing sediments and rock fragments of late aptian to pleistocene ages mud breccia flows are mainly extruded radially from vents although rare fissure extrusions are also observed the mud volcanoes have an irregular to elliptical shape with diameters up to 16 km the distribution of mud volcanoes in the area is irregular but they are more frequent in an area called the olimpi field faults in the uppermost part of the mediterranean ridge are rare most of the faults are normal and subparallel to fold limbs in addition n20 e and n100 e subvertical faults are found controlling the shape of the mud volcanoes

mud volcanoes in the alboran sea evidence from micropaleontological and geophysical data during the basacalb ttr9 cruise of the r v professor logachev 1999 two mud volcanoes called marrakech and granada were discovered in the southern sector of the mud diapir province in the west alboran basin wab this paper presents micropaleontological and geophysical data on these mud volcanoes from gravity core samples sidescan sonar okean images and high resolution seismic lines mud breccia recovered from the granada mud volcano is matrix supported with well consolidated clasts of limestone marlstone claystone siltstone sandstone and mudstone whereas mud breccia from the marrakech mud volcano contains unconsolidated clasts the mud breccia matrix contains abundant miocene calcareous nannofossils cn together with pliocene pleistocene species and reworked late cretaceous and paleocene eocene species cn dating indicates that clasts in the mud breccia derive from late cretaceous paleocene eocene and probable miocene sediments these data suggest that the mud diapirs and mud volcanoes in the wab can be derived from the olistostromes of unit vi the basal stratigraphic sequence in the alboran sea basin unit viconsists of lower miocene sediments that incorporated late cretaceous and paleocene eocene materials and basement derived rock fragments the mud volcanic deposits are covered by a thin drape of pelagic marls suggesting that these two volcanoes are currently inactive structures determined on highresolution seismic profiles across mud volcanoes and surrounding diapirs correspond to the late stage pliocene toquaternary diapir development this stage is thought to have developed during a compressional tectonic setting that produced folding and wrench tectonics throughout the basin mud ascent at that time resulted in active diapirism and mud volcanoes on the seafloor 2002 elsevier science b v all rights reserved

quantitative methods for analyzing the roughness of the seafloor the bathymetry of the world ocean has been mapped using a variety of acoustic sounding instruments and traditional contouring methods prior to this study relatively few quantitative studies have been focused on the detailed morphology of the seafloor the work of most investigators has generally dealt with the analysis of seafloor relief without regard to spatial frequency or concern for obvious morphologic anisotropies a brief review of previous work is presented and is accompanied by an identification of the specific applications and limitations of those approaches the availability of more precise digital sounding data coupled with the development of higher resolution sonar mapping instruments e g deeptow seamarc now make it possible to investigate quantitatively many important aspects of seafloor relief and the geological processes responsible for its formation typical bathymetric contour maps represent a low frequency deterministic model of the seafloor to describe the higher frequency variability or roughness of the seafloor requires the development of an appropriate statistical method for generating a valid stochastic model new methods are developed herein which allow valid statistical models of the variability of oceanic depths to be derived from existing digital bathymetric soundings the smooth contoured surface often preserved as a geographic grid of depths when supplemented by such a roughness model can provide an essentially complete statistical description of the relief statistical models of seafloor roughness are also valuable tools for predicting acoustic scattering and bottom loss and in addition contain a wealth of information for more comprehensive interpretations of deep sea relief forming geological processes to allow the variability of depths to be described as a function of scale spatial frequency the amplitude spectrum is employed as the fundamental statistic underlying the model since the validity of the amplitude spectrum depends upon the assumption of a statistically stationary sample space a computer algorithm operating in the spatial domain was developed which delineates geographic provinces of limited statistical heterogeneity within each of these provinces a spectral model is derived by fitting the amplitude estimates with one or two two parameter power law functions using specialized regression techniques the distribution of resultant model parameters is examined for a large test area adjacent to the coast of oregon 42 45 n 130 124 w which includes several contrasting geologic environments the distribution of roughness corresponds generally with the various physiographic provinces observed in the region within some provinces additional complexities are apparent in the roughness model which cannot be inferred by simply studying the bathymetry these patterns are related to a variety of geological processes operating in the region such as the convergence of the continental margin and the presence of a propagating rift on the northern gorda rise in contrast a very large area of the continental margin off the east coast of the united states was found to have in common a single distinct amplitude spectrum this amplitude spectrum is almost identical to that found from the tufts abyssal plain region off the west coast of the united states spectra from both of these areas can be clearly separated into two straight line segments of different slope the two segments of these spectra are interpreted as reflecting two dominant relief forming processes the higher frequency band representing a sedimentary regime and the lower frequency band representing an underlying tectonic volcanogenic regime in many cases the calculated roughness statistics are not constant for data collected along different ship track directions this is due to the anisotropic nature of the seafloor relief a simple model is developed which describes the roughness statistics as a function of azimuth the parameters of this model quantify the anistropy of the seafloor allowing insight into the directionality of the corresponding relief forming processes and the physical meaning of the derived model statistical parameters finally the model is used to successfully predict the roughness of a surface at scales much smaller than those resolvable by surface sonar systems the model regression line derived from a hull mounted sonar is compared to data from deep towed sonars and bottom photographs the amplitude of roughness is predicted to within half an order of magnitude over five decades of spatial frequency and this prediction capability can probably be improved even further the stochastic models presented also demonstrate the potential for closely approximating the full two dimensional nature of some areas of the seafloor with only four statistical parameters these parameters can be estimated from random ship track data given a sufficient number of tracks and range of headings

the geological interpretation of side scan sonar recent developments in side scan sonar these parameters play a critical role in our ability to technology have increased the potential for fundamental calibrate and ultimately to interpret the new pictures of the changes in our understanding of ocean basins developed ocean floor acoustic image processing is a new applica in the late 1960s side looking sonars have been widely tion of an old and well established technique digital used for the last two decades to obtain qualitative estimates optical images have benefited from several decades of of the acoustic properties of the materials of the seafloor modern developments in the ability to obtain spatially correct digital data from side scan sonar systems have resulted in images that can be subsequently processed enhanced and quantified with appropriate processing these acoustic images can be made to resemble easily recognizable optical photographs any geological interpretation of these images requires an understanding of the inherent limitations of the data acquisition system when imagery is collected these limitations are largely centered on the concept of resolution in side scan sonar images there are several different types of resolution including along and across track resolution display the geology of the seafloor resolution and absolute instrumental resolution all of development in processing techniques these relatively sophisticated techniques have been applied to photographic images from satellites and spacecraft images which are noisy and difficult to obtain but extremely valuable side scan sonar systems on the other hand have only recently been able to produce spatially correct digital images of the seafloor the application of digital signal processing techniques to side scan sonar data willnow allow us to quantify what had been previously very subjective and qualitative interpretations of images of the seafloor the goal of all this processing of acoustic images remains clear the development of an interpretable map of featureless static environment has undergone dramatic modification in the last 50 years early depth sounding with mechanical devices and even early wide beam acoustic echo sounders gave us an extremely low resolu tion picture of the ocean basins this early image of the ocean bottom consisted largely of a flat lying seafloor with few hills and ridges of any consequence completely covered with a thick layer of sediment and only an occasional inexplicable outcrop of hard rock the few recovered rock samples were of little value in understand ing the scientific processes of the deep sea because they could not be placed within any sort of geological and morphological context acceptance of seafloor spreading and the vine matthews hypothesis in the 1960s altered forever our perception that the floor of the ocean basins was unchang ing at least on a geological time scale the initial drilling efforts of the deep sea drilling project also modified our view about the uniformity of the seafloor even on a scale of a few hundreds and perhaps tens of kilometers higher resolution maps using multiple narrow beam echo sounders strongly reinforced this newperception of a nonuniform and scientifically interest ing seafloor tyce 1986 the initial interest grew to excitement as our perspective was extended by visual observation in a very few places down to the scale of a few meters by early submersible expeditions to mid ocean ridge spreading centers ballard and van andel 1977 clearly a new tool beyond the wide beam echo sounder was needed to map features of the seafloor and to understand the processes at work there to be effective this would have to be a tool which had both a sufficiently wide view for tectonic context and adequate resolution for interpretation in terms of geological processes the efficiency of sound transmission in seawater and the development of both electronic and digital techniques capable of rapidly processing the high data rates necessary to generate images dictated that this tool would be some form of acoustic swath mapping the scientific need for

life at cold seeps a synthesis of biogeochemical and ecological data from kazan mud volcano eastern mediterranean sea recent field observations have identified the widespread occurrence of fluid seepage through the eastern mediterranean sea floor in association with mud volcanism or along deep faults gas hydrates and methane seeps are frequently found in cold seep areas and were anticipated targets of the medinaut medineth initiatives the study presented herein has utilized a multi disciplinary approach incorporating observations and sampling of visually selected sites by the manned submersible nautile and by ship based sediment coring and geophysical surveys the study focuses on the biogeochemical and ecological processes and conditions related to methane seepage especially the anaerobic oxidation of methane aom associated with ascending fluids on kazan mud volcano in the eastern mediterranean sampling of adjacent box cores for studies on the microbiology biomarkers pore water and solid phase geochemistry allowed us to integrate different biogeochemical data within a spatially highly heterogeneous system geophysical results clearly indicate the spatial heterogeneity of mud volcano environments results from pore water geochemistry and modeling efforts indicate that the rate of aom is similar to 6 mol m 2 year 1 which is lower than at active seep sites associated with conditions of focused flow but greater than diffusion dominated sites furthermore under the non focused flow conditions at kazan mud volcano advective flow velocities are of the order of a few centimeters per year and gas hydrate formation is predicted to occur at a sediment depth of about 2 m and below the methane flux through these sediments supports a large and diverse community of micro and macrobiota as demonstrated by carbon isotopic measurements on bulk organic matter authigenic carbonates specific biomarker compounds and macrofaunal tissues because the aom community appears to be able to completely oxidize methane at the rate it is seeping through the sediments ultimate sinks for methane in this environment are authigenic carbonates and biomass significant differences in organic geochemical data between this site and those of other cold seep environments even within the eastern mediterranean mud volcanoes indicate that the microbiological communities carrying out aom varies depending on specific conditions such as methane flux and salinity c 2004 elsevier b v all rights reserved

morpho acoustic characterization of a shallow water mud volcano offshore scoglio d affrica northern tyrrhenian sea responsible for a violent gas outburst in 2017 abstract a violent gas outburst occurred offshore the scoglio d affrica islet tuscan archipelago northern tyrrhenian sea on march 16th 2017 with local fishermen observing columns of dirty water rising up to 10 m above the sea surface the integration of video footage and dissolved ch4 measurements collected 5 days after the event with high resolution multibeam data collected 4 months later allowed us to characterize the source area of the outburst corresponding to a shallow water mud volcano the mud volcano covers an area of ca 170 000 m2 has a vertical relief of ca 30 m with respect to the surrounding seafloor and an estimated volume of ca 1 106 m3 based on bathymetric reconstruction the elongated nnw sse shape of the mud volcano is compatible with local structural trends indicating a tectonic control for its development the mud volcano is made up of two mounds whose tops are located at a depth of ca 10 m the southern mound was responsible for the 2017 outburst as testified by a 15 20 m wide circular crater on its summit where a large amount of mud breccia and diffuse seepage from small pockmarks were observed in video footage the flanks of the mud volcano are steep and characterized in the upper part by a hummocky morphology and multiple sediment flows on the western flank the characterization of the mud volcano and the deposits associated with the 2017 gas outburst provides insight into seafloor shaping processes linked to fluid seepage in shallow water sectors this is a particularly relevant issue considering both the paucity of studies on shallow water mud volcanoes as well as the hazard associated with violent gas outbursts in such settings as witnessed by the march 16th 2017 event

geological evidence for mud diapirism on the mediterranean ridge accretionary complex abstract a mud breccia has been repeatedly cored from four mud diapir fields located on the crest of the mediterranean ridge this breccia is composed of subrounded clasts supported by a clay rich matrix and ranges in age from cretaceous to early miocene sedimentological analysis allows identification of a primitive intrusive and a reworked mud breccia the latter being formed by mud extrusion and gravitational reworking of the former homogeneous mud sorted by grain size which occurs at the top of the diapirs has been interpreted as a lake deposit based on composition and carbon isotopic ratios gases present within the diapiric material suggest a partial thermogenic origin and gas escape structures have been identified in the mud breccia and host sediments carbonate crusts occurring in the host sediments are not related to bacterial oxidation of methane and consequent authigenic calcite precipitation their carbon and oxygen isotopic ratios reveal that they are characteristic of early deep sea lithification in the mediterranean sea the presence of a marker bed composed of mn nodules and bacterial colonies the mud lake deposits showing lower carbonate content than primitive mud breccia and the gas escape structures suggest the presence of active fluid vents in the vicinity of the diapiric structures evidence of active mud diapirism can be found from about 300 000 yrs b p to the present

structural setting and tectonic control of mud volcanoes from the central mediterranean ridge eastern mediterranean based on a recent marine geophysical data set including swath bathymetry acoustic imagery and six channel seismics recorded over a large area of the mediterranean ridge mr in early 1998 during the prismed 2 survey this paper presents a study of the various relationships observed between tectonic features cutting across the central mediterranean ridge accretionary wedge and massive mud expulsions known as mud volcanoes identified over large areas of the ridge regional mapping of two of the mud volcano fields previously only partly investigated olimpi and united nations rise revealed the presence of many new mud expulsion centres and a third new mud volcano field has been identified all the mud features show great variability in morphology size and backscatter strength of their surrounding mud flows based on their contrasting morpho acoustic characteristics we propose a classification into three main groups of mud construction 1 mud volcanoes these consist of subcircular and prominent reliefs often associated with high backscatter mud flows 2 mud domes similar to mud volcano but smaller these occurrences correspond to weakly reflective mud constructions 3 mud plateaus represent a third category which appears as wide often highly reflective and rather flat mud extrusions from all available data an attempt to explain the different mud ascent processes and driving forces is discussed in relation to the initial collision structural setting of the central mediterranean ridge within this area most of the mud constructions have been observed to be associated with tectonic features and in particular with strike slip faulting for the first time as a hypothesis we propose in this paper two different ascent processes to explain the contrasting mud constructions 1 extrusion for the mud volcanoes and plateaus and 2 intrusion for the mud domes connected to two different mud levels controlled by the crustal geometry of this pre collision area and especially the southwards extension of the cretan continental crust below the mediterranean ridge accreted sediments

seafloor characterization and backscatter variability of the almeria margin alboran sea sw mediterranean based on high resolution acoustic data abstract an acoustic study of the almeria margin eastern alboran sea sw mediterranean was carried out by means of an integrated dataset comprising deep towed tobi sidescan sonar swath bathymetry topas high resolution seismics and sediment gravity cores the almeria margin is a complex system dominated by volcanic and tectonic features shaped by recent sedimentary processes in which a regional hemipelagic sedimentation is intercalated by sporadic gravitative events the aim of this work is twofold the first objective is to recognize the sedimentary and tectonic features that shape the almeria margin the main morpho sedimentary and morpho structural elements observed are the almeria canyon channel turbidite system the dalias tributary valley system landslides active faults and folds and volcanic banks the second aim is to explore and quantify the surface and subsurface seafloor parameters that characterize the backscatter of the study area sedimentary geomorphological and biological elements that play a role in the acoustic signature of the almeria margin were detected nevertheless it should be noted that seafloor acoustic backscatter is also affected by geometrical and instrumental factors despite the wide variability of the environments studied a low average acoustic backscatter reflects a diffused draping of hemipelagic sedimentation in the area higher backscatter values were observed at the top of some volcanic banks along the almeria canyon and in the shallower sector of the dalias tributary valley system the influence of subseafloor properties in the acoustic signature of the area was revealed by backscatter grain size correlations which were carried out for different depth intervals in sediment cores collected in the almeria turbidite system a poor relationship was found between backscatter and superficial silty sediments of the area whereas a higher correlation resulted in the upper 50 cm the presence of subsurface turbidites in the cores associated with the higher backscatter values suggests volume interface scattering of these sandy layers as a controlling factor of the acoustic signature obtained in the almeria margin on the other hand in rough settings such as the ones observed in the dalias tributary valley system topographic relief of up to 1 1 5 m strongly interacted with the tobi acoustic pulse this suggests that large scale roughness is an additional parameter that characterizes the acoustic strength of the area extremely high reflective patches distributed along some of the volcanic banks chella and pollux banks for depths ranging from 230 to 470 m coincide with areas where carbonate cold water coral mounds develop in the tobi images coral facies reach the maximum value of acoustic backscatter which is probably related to the rough morphology of coral ecosystems the position of coral mounds in the banks suggests that the occurrence of strong bottom currents and reduced sedimentary inputs are environmental factors that favour their settling and development in the almeria margin