styles of failure in late holocene highstand prodelta wedges on the adriatic shelf on the continental shelves of the northern mediterranean basin the late holocene highstand systems tract hst prograded un der the influence of major rivers after the attainment of the present sea level highstand about 5 5 cal kyr bp on the adriatic shelf the thickness distribution of the late holocene hst reflects the location of major deltas on the western side of the basin and the geostrophic cir culation which prevents a more uniform sediment dispersal toward the center of the basin very high sediment accumulation rates 1 to 10 cm year resulted in the construction of a hst depocenter up to 35 m thick this shore parallel depocenter is affected by failure of limited displacement over as much as 40 of its extent gas impregnation is common in the topset region and occurs at very shallow levels a few meters below the sea floor five areas are characterized by a variety of sea floor and subsurface crenulations although locally some of these crenulations have an intriguingly regular geometry sediment failure is the most plausible mechanism for their formation sediment failure better explains the large variety of geometries that characterizes the coastal mud prism of the late holocene hst furthermore we observe that these crenulations occur only where the downlap surface at the base of the hst is disrupted and affected by geometries that are con sistent with fluid escape processes this relationship suggests that the basal surface acts as a weak layer for sediment failure failure occurred in variable water depths from the northern slope of the modern po prodelta 10 20 m water depth to the narrow shelf offshore bari 40 110 m water depth in all these areas the proximal part of the hst prodelta wedge is intensely gas charged the thickness and age of the sediment sections affected by failure are slightly differ ent from place to place but appear everywhere younger than 5 5 cal kyr bp where failure affects the entire hst the detachment occurs on the downlap surface at its base failure geometries characterize the head region whereas compressional features such as pressure ridges and mud diapirs dominate in the toe region ranging in depth between 70 and 110 m where failure is limited to the upper few meters of the hst there is a clear lithologic change decrease in carbonate fraction and grain size across the basal surface this lithological change reflects a switch in sediment supply from local apennine rivers below to po derived mud this change occurred at the onset of the little ice age documenting the indirect control of short term climate change and hu man impact on sediment architecture the deformations affecting the late holocene hst in the various areas show differences in internal geometry but appear everywhere to be characterized by limited downward displacement and can be attri buted to shear dominated retrogressive failure it is suggested that some degree of consolidation occurred immediately after mobilization possibly induced by the escape of fluids nowhere has failure evolved into disintegration and flow likely because the type of cyclic loading that triggered it was not prolonged over a long enough interval short lived radionuclides in the uppermost stratigraphic layers which postdate the failure in the area offshore ortona allowed us to quantify systematic changes in sediment accumulation rates as a func tion of the underlying deformed sea floor in areas of wavy sea floor troughs show sediment accumulation rates of greater than 16 mm yr a figure that is fourfold the rate measured on the flanks of the troughs

occurrence stratigraphy and geochemistry of late quaternary tephra layers in the aegean sea and the marmara sea abstract several discrete tephra layers occur in 2 5 10 3 m long cores from the aegean sea whereas a single tephra is identified in 3 5 9 7 m long cores from the marmara sea major and trace element data on these tephras delineate eight distinct groups the geochemical data and multivariate statistics allow the correlation of the tephra layers with six previously described marine tephras from the eastern mediterranean sea potential terrestrial sources are suggested for the others the chronostratigraphy of the tephra layers was established using several radiocarbon dates and the oxygen isotope stratigraphy from two long piston cores four widespread tephra layers occur within the upper quaternary sediments of the aegean sea the two youngest widespread tephra layers were derived from the santorini volcano of south central aegean sea z2 the minoan eruption ca 3 6 ka and y2 the cape riva eruption ca 21 7 ka the y2 tephra is also identified in three piston cores from the marmara sea the two older widespread tephra layers originated from the eruptions which emplaced the campanian ignimbrite of the italian volcanic provinces i e the y5 tephra ca 39 3 ka and from the nisyros volcano of the southeastern aegean sea the consistent occurrence of the nisyros tephra below the y5 tephra confirms similar findings in a lake core on the island of lesbos linear extrapolations using the oxygen isotope stratigraphy suggest an age of 42 44 ka for the nisyros eruption three additional tephra layers with a limited regional distribution are identified in the aegean sea cores two of these tephras originated from the yali volcano of the southeastern aegean sea and from the aeolian islands i e x1 tephra a series of six mugearite tephra beds in the south skiros basin is interpreted as a set of redeposited turbidites

the role of earthquakes in inducing sediment mass movements in the eastern korinthiakos gulf an example from the february 24 march 4 1981 activity abstract korinthiakos gulf is a narrow arm of the sea connecting the ionian and the aegean seas through the rion antirion strait and the korinth canal respectively the eastern part of korinthiakos was surveyed by the marine geology department of the institute of geology and mineral exploration of greece using a 3 5 khz subbottom profiler the survey was carried out a short time after intensive earthquake activity which occurred in the area from february 24 to march 4 1981 during this activity three major shocks of magnitudes ranging from 6 4 to 6 7 took place the subbottom profiles reveal a sediment mass which was deposited by submarine slumping in the alkyonides basin which lies at the eastern end of the studied area the slump is about 10 km long 1 5 to 2 0 km wide and its areal extent is about 16 km2 the scarp area occurs at a bathymetric depth of about 100 to 250 m in the northeastern part of the basin the scarp faces are from 10 to 15 m high and have a total areal extent of about 4 km2 the destruction of fishing nets of trawling boats and other evidence indicates that the triggering of the mass flow was effected by the earthquake activity and probably by the first major shock scarp areas and scarp faces from which sediment masses have been removed were detected in other shallow and deep sectors of the studied area indicating that mass transport processes are very common in this area of high seismicity

seismic geomorphological reconstructions of plio pleistocene bottom current variability at goban spur abstract high resolution single channel sparker reflection seismic data revealed the presence of large scale sediment waves nearby dsdp site 548 located on goban spur they developed in a gentle terraced environment which contrasts with the canyon incised celtic margin and the relatively smooth porcupine seabight to the north based upon the morphological characteristics of the observed seabed and buried sediment waves energetic alongslope bottom currents are thought to be the driving mechanism for the sediment wave development these currents are driven on their turn by an enhanced internal tide regime that could be attributed to the introduction of the mediterranean outflow water the dsdp site 548 downhole geophysical data and the seismic stratigraphic analysis allowed the differentiation of three sequences that relate to evolutionary stages since the lower pliocene the sequences are bounded by local erosional events associated with mass wasting events which seem to occur roughly synchronously to major northern hemisphere glaciations respectively during the lower pleistocene 2 5 to 2 15 ma and the middle pleistocene 0 45 ma the lower sequence from 4 5 to 2 15 ma shows no morphological evidence of bottom current driven sedimentation it is however settled over a smooth erosional surface which could indicate the introduction of the mediterranean outflow water the intermediate sequence is characterised by large scale sediment waves that have gradually developed in close association with palaeo seafloor irregularities it is inferred that the sedimentation resumed with a relative bottom current energy increase the youngest sequence recorded active sediment wave formation similar to the previous sequence although the goban spur sediment waves cannot be regarded as contourite drifts as such their stratigraphic evolution corresponds to other well documented contourite depositional systems influenced by the mediterranean outflow water

deep reaching liquefaction potential of marine slope sediments as a prerequisite for gravity mass flows results from the dsdp abstract plots of water content w and atterberg liquid limits wl versus depth coupled with measurements from young submarine mass flows support the concept that many fine grained but low cohesive slope sediments are susceptible to liquefaction and can as a result of dynamic loading earthquakes and storm waves be transformed into mud flows without the uptake of additional water the in situ water content w can be higher or approximately equal to wl boundary between the plastic and liquid state of a soil usually in the uppermost few meters but frequently also tens or even some hundreds of meters below the sea floor such a substantial liquefaction potential is particularly common in sediments rich in silt size biogenic particles and in regions of high sedimentation rates causing underconsolidation it is not clear whether changes in the salt concentration and chemistry of interstitial water versus depth in core exert some influence on wl and the liquefaction potential the average field liquid limit of the total mass flow can be even lower than wl of small only fine grained homogenized samples if part of the dislocated material is carried unchanged as lumps of mud by a liquefied matrix w and wl often decrease in a similar way versus depth in sediments rich in microfossils due to the onset of slight chemical diagenesis with increasing burial depth thus in spite of increasing compaction a high liquefaction potential may be maintained until finally substantial lithification reduces w to values lower than the plastic limit wp and completely alters all the mass physical properties

microearthquakes in the tyrrhenian sea as revealed by joint land and sea bottom seismographs abstract five independent ocean bottom seismographs obs were operated from 17 to 28 may 1987 in the southeastern tyrrhenian sea at a depth range of 1000 2800 m these were concomitantly run with nine vesuvian observatory and university of calabria temporary digital seismic stations along the calabrian coast together with fifteen permanent seismic stations in southern italy the latter stations also belong to the university of calabria and to the italian national institute of geophysics about 200 local shocks mainly microearthquakes ml

the ebro continental shelf quaternary seismic stratigraphy and growth patterns abstract single channel seismic reflection profiles on the ebro shelf and upper slope between cap salou and the columbretes islands have been interpreted to outline the quarternary shelf evolution in this deltaic area three types of unconformity surfaces can be differentiated in the seismic records type 1 and 2 unconformities and toplap surfaces these surfaces are the stratigraphic expression of the difference between rate of eustatic sea level fall and subsidence on the outer shelf a type 1 unconformity forms if the rate of eustatic sea level fall is the more rapid a type 2 unconformity forms if subsidence is faster and toplap forms if subsidence and eustatic sea level fall are equal thirteen stratigraphic units can be differentiated on the basis of unconformities based on their relative location on the shelf these units are subdivided into inner and outer units the inner units occur on the inner and middle shelf and are characterized by an underlying transgressive surface while the outer units extend onto the middle to outer shelf and upper slope and show unconformities at their bases the inner units are interpreted to be stacked transgressive and highstand systems tracts bounded by a maximum flooding surface the outer units correspond to shelf deltas and shelf margin deltas that prograded southward and seaward over an unconformity in relatively stable water depths when sea level fall was compensated for by subsidence the progradation of these units ends with an episode of generalized erosion of the shelf and canyon cutting across the new shelf edge the growth pattern of the northern ebro shelf is characterized by important hiatuses condensed stratigraphic sections and units which are older than those on the southern shelf the depositional processes were mainly controlled by eustatic sea level oscillations subsidence and changes in sediment supply the subsidence during the late pleistocene was sufficient to compensate for the sea level falls and allow the development of shelf deltas and shelf margin deltas on the middle and outer shelf during low sea level stands

collapse and flow of lowstand shelf margin deposits an example from the eastern tyrrhenian sea italy abstract the upper slope of the eastern tyrrhenian sea margin has a complex morphology shaped by quaternary tectonism and by sedimentation phases controlled by changing sea levels sediment slides of widely varying size and shape are common in quaternary deposits of the upper slope particularly where gradients are steep our study of a large sediment failure in lowstand prograded coastal deposits west of cape licosa indicates that the nature of shelf margin deposition is an additional important control on failure the failure zone has a mobilization surface showing in situ deformation in the sediment above it an upper failure surface a head scarp and a zone of ponded sediment debris downslope from the exposed surface of failure the basal mobilization surface is roughly parallel to the seafloor and coincident with a major downlap surface the failed section is less that 20 m thick and local in extent but deformation on the basal mobilization surface extends outside the immediate area of the failure directly downslope of the slide scarp are internally stratified mounds that show no evidence of deformation or movement most of the prograded deposit experienced in situ deformation that evolved into the collapse of part of the sediment pile above the mobilization surface a portion of the mobilized sediment flowed a few kilometers basinward and accumulated at the base of a slope parallel ridge sediment failure occurred on the licosa shelf margin following a major pulse of coastal sedimentation along the lowstand shoreline on many continental margins sea level lowering is thought to be an important cause of failure unconsolidated sediment deposited during previous high stand conditions the licosa slide demonstrates that sea level fall has another equally important but indirect role in sediment failure as sea level falls and reaches its lowstand position streams are at their peak efficiency and a coarsening upward clastic coastal wedge is rapidly emplaced at relatively steep gradients on the shelf margin and these are conditions that inherently favor sediment instability and failure

earthquake induced sediment failures on a 0 25 slope klamath river delta california on november 8 1980 a major earthquake magnitude 6 5 to 7 2 occurred 60 km off the coast of northern california a survey of the area using high resolution seismic reflection and side scan sonar equipment revealed the presence of extensive sediment failure and flows in a zone about 1 km wide and 20 km long that trends parallel to the shelf on the very gently sloping c and a prominent 1 to 2 m high seaward facing toe scarp on the outer margin of the terrace this toe scarp is sinuous appears to be nearly continuous for a distance of 20 km and closely parallels the 60 m isobath evidence indicates that the toe scarp is the terminus of lateral spreads and lobes of sediment flows side scan sonar records show evidence of gas vents and small 10 3 0 5 m high pressure ridges formed seaward of and parallel to the sediment flow scarp indicators of liquefaction sand boils and collapse craters are present on the sediment flow terrace extensive sediment failure occurred on a sea floor slope of less than 0 25 and we can unequivocally pinpoint the cause as an earthquake of known location magnitude and time

sedimentary facies of the nova scotian upper and middle continental slope offshore eastern canada a detailed survey of the upper and middle nova scotian continental slope at 42 50 n and 63 30 w indicates a complex morphology dominated by mass movements on various scales and an immature turbidity current channel the range of sediment facies is diverse including hemipelagic and turbidite muds turbidite sands and gravelly sandy muds of debris flow origin deformed units interpreted as slump deposits are also observed several facies associations related to discrete morphological environments are recognized thick turbidite sand units with minor intervening mud beds are characteristic of the high relief uppermost slope and channel margin thinner turbidite sands deformed slump beds and various mud facies are associated with small scale hummocky mid slope topography sand beds are more abundant in the depressions than on intervening hummocks indicating the preferred transport paths of small turbidity currents at the lower end of the main turbidity current channel frequent turbidite sand beds with relatively minor mud beds are deposited on a depositional lobe in areas unaffected by mass movements alternating bioturbated mud and sandy muds make up the core sequences a local model of sedimentation is proposed for this area and illustrates that simple models of continental slope sedimentation only apply to a limited range of settings

sheet slides and rotational failures on a convergent margin the kidnappers slide new zealand the kidnappers slide on the upper continental slope of the convergent margin off eastern north island new zealand has been re examined using a grid of high resolution seismic reflection profiles the slide is not a single feature but a complex of sheet slides and rotational failures ranging from 20 to 140 m thick and covering a total area of 720 km2 failures occurred in several phases on slopes of 1 5 in late quaternary muddy shelf edge clinoforms that have prograded into an accretionary trench slope basin piston cores and seismic stratigraphy show that the main failure probably occurred in early holocene times but that movements ranged from mid last glacial to late holocene times the sheet slides exhibit tensional collapse via numerous listric normal faults that sole out on glide planes there is no clear evidence of compressional structures anywhere within the complex the glide planes occur at progressively deeper stratigraphic levels towards the northeastern end of the complex and near the steep slope that defines the seaward edge of the trench slope basin there is retrogressive failure at the top of the slope the surficial slides are being deformed by growth of active tectonic faults and folds associated with the convergent plate margin this type of slope failure may be partially related to metastable sandy layers within the last glacial age progradational sequence and possibly to formation of bubble phase gas at shallow depths failure was probably triggered by earthquake loading of sediments in this highly seismic region

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

gravity induced deformation on the north flank and floor of the sporadhes basin of the north aegean sea trough pdr and continuous seismic profiling surveys in the sporadhes basin the western part of the north aegean sea trough reveal active gravity induced deformation of the postorogenic sedimentary sequence different deformational patterns in the uppermost sedimentary layers of the flanks and floor of the basin suggest that the layers are deformed by several gravity induced processes including slumping sliding and creep contemporaneous with sediment deposition antithetic faulting on the northern flank of the basin the thermaicos slope results from downslope creep of surface layers over deeper tilted bedding planes this process is a consequence of progressive slope development associated with the evolution of the sporadhes basin the morphology of the sea floor and the deformation of the upper layers clearly reflect synsedimentary tectonics in a subsiding basin environment

empirical reflection travel time versus depth and velocity versus depth functions for the deep sea sediment column numerous correlations of one way reflection travel times and depths to reflecting horizons have been proposed in the initial reports of the deep sea drilling project dsdp having carefully reviewed proposed correlations we selected 233 correlated depths ranging from 27 m to 1 4 km and one way travel times ranging from 0 02 to 0 7 s from 154 dsdp sites worldwide assuming that the velocity depth function for deep sea sediments can be approximated by an exponential form we have used these data to establish statistically well constrained global models relating depth to travel time and velocity to depth there is remarkably little scatter in the data based on nonlinear least squares fits the best depth time function is z km 3 03 1n 1 0 52t s the rms error in depth is 26 m the corresponding average velocity depth function is v km s 1 59exp 0 33z we estimate that the real site to site variability of velocities at depth is less than 0 20 km s any dependence of velocity on composition is below the resolution of the data and available evidence suggests that age has no significant effect these results imply that to a depth of 1 4 km the physical state of sediments depends on in situ overburden pressure and temperature which are related to depth of burial and that chemical and mechanical equilibrium is achieved in a period of time that is geologically short our results are consistent with laboratory measurements of p wave velocities in deep sea sediments but velocity depth functions for terrigenous and calcareous sections derived from sonobuoy wide angle reflection surveys are incompatible with the time and depth data and overestimate velocities by as much as 10 and 30 respectively these systematic errors may result from the fact that the marked anisotropy of deep sea sediments is neglected in the interpretation of reflection data

late quaternary deltaic lowstand wedges on the rhone continental shelf france abstract shallow seismic profiles on the rhone continental shelf have shown the existence of stacked progradational lowstand wedges on the outer shelf accumulated during late quaternary glacioeustatic lowstands the wedges are bounded by sharp to erosional sequence boundaries and onlap onto the middle shelf the thickness of individual wedges attains 50 meters at the shelf edge where they are sheared by slumping the wedges exhibit well developed progradational clinoforms episodically interrupted by internal unconformities on which there is a downward shift of the succeeding clinoforms these represent small scale in the order of a few meters falls in sea level during the quaternary eustatic cycles the durations of the stable highstand conditions appear to have been too brief to permit the regressive highstand tract to prograde to the outer shelf therefore the shelf edge builds up entirely with lowstand wedges

structural and sedimentary features in the tyrrhenian margin off campania southern italy abstract the utilization of multichannel seismic reflection profiles permits the identification of the generally e w trending miocene orogenic and plio quaternary post orogenic features of apennine nw se and anti apennine ne sw trends in the campanian margin the former features are constituted by carbonate and or allochthonous sheets which were thrust mainly towards the north and northeast during the miocene tectogenetic phases the latter are represented by extensional structures which affected the orogenic features during plio quaternary times the anti apennine tectonic trend is responsible for the recent late pliocene quaternary and remarkable block faulting differential subsidence of the southern margin as well as for its present morphology the ragged and disconnected pattern of the allochthonous units over the present day slope and their accumulation underneath the shelf area suggest that they are the result of gravitational gliding tectonics gravity cores and 3 5 khz subbottom profiles indicate that the salerno trough and capri basin areas are characterized by a particular neotectonic mobility this is proved by the thick and coarse grained sediment accumulation from steep relief produced by block faulting this faulting created uplift belts serving as sediment source

tectonic and volcanic evolution of panarea aeolian islands italy abstract based on new geophysical volcanological structural and radiometric data a morphological structural reconstruction of the submarine part of the panarea volcanic edifice is provided and a model for the evolution of the entire complex is proposed panarea is a small part of a much larger submarine edifice whose overall shape is one of a truncated cone with an eastern protrusion the base of the cone is about 1500 m below sea level it has a diameter of about 23 km and an area of 460 km2 several lobes are present on the steep eastern slopes of the cone and the wide submarine top is of a morphology which is more complex than previously thought the evolution of the panarea volcanic complex occurred in three stages 1 1 development of a central volcano in the western sector of the complex the island of panarea represents the top of this volcano 2 2 eastward shifting of volcanic activity producing development of the lobed eastern sector of the complex 3 3 extensive caldera collapse of the central part of the complex and emplacement within the collapsed area of domes and lava bodies of various affinities some of which are basaltic ne sw oriented structures seem to have had a fundamental role during the development of the panarea volcanic complex these structures have been active until recent times and are of regional significance indeed the evolution of nearby stromboli has been controlled by the ne sw trending structures panarea and stromboli also display similar magnetic anomaly trends geochemical affinities and temporal relationships in volcanism

pleistocene suvero slide paola basin southern italy abstract the suvero slide covers an area of about 225 km 2 in the paola slope basin on the eastern tyrrhenian margin the shape and lateral extent of the deposit reflect topographic confinement of the slide between the continental slope and a morphologic barrier formed by a margin parallel slope ridge no headwall or slide plane comparable in scale with the slide deposit were found suggesting that quasi in situ deformation of semi consolidated sediments took place when the failed materials reached the floor of the slope basin the failure occurred downslope from a basement high originating from local uplift continued uplift after the suvero slide occurred is documented by the presence of steep upper slope gradients within the study area and by the presence of small scale creep and failure events that postdate the suvero slide

estimating spatially variable representative elementary scales in fractured architecture using hydraulic head observations 1 water resources within large scale fractured aquifers are typically evaluated using continuum models while any arbitrary scale of continuum can be imposed to represent fracture architecture using the representative elementary volume eliminates errors that result from estimating network connectivity in traditional theory representative elementary scales res are equal in magnitude and geometry throughout a domain and are normally determined using a structural indicator such as porosity or effective hydraulic conductivity we present a fluid based methodology analyzing scale dependent energy variation to estimate res using relatively low cost readily available hydraulic head data hydraulic head predictions of res hyres reveal a spatial variation in elementary scale consistent with the flow field and fracture architecture porosity predictions of res porres incorporate the structural effect of disconnected fracture regions but do not account for fluid behavior res estimated from hydraulic conductivity kres are sensitive to fracture connectivity which controls fluid movement but are difficult to quantify because of scale and spatial variability hyres may be the superior approach for evaluating water resources because it is sensitive to fracture connectivity and avoids complications with scale and spatially dependent averaging our method is sensitive to fracture density clustering connectivity and flow direction but is insensitive to the magnitude of hydraulic gradient hyres is a novel approach to estimating spatially variable res that improves water resource evaluation and flow characterization in fractured aquifers

odp leg 107 in the tyrrhenian sea insights into passive margin and back arc basin evolution leg 107 of the ocean drilling program drilled a west northwest east southeast transect of seven sites across the tyrrhenian sea the youngest of the sub basins of the mediterranean sea sites 654 653 652 and 656 document the rifting and subsidence of the sardinia passive continental margin on the upper margin site 654 we cored a classic transgressive sequence subaerial conglomerates overlain by oyster bearing sands overlain by marine marl comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are tortonian late miocene to messinian latest miocene in age whereas synrift sediments on the lower margin are messinian to pliocene in age during the messinian desiccation of the mediterranean sites 654 and 653 now on the upper sardinian margin apparently occupied a basinal setting where they received nannoplankton bearing clays interbedded with laminated gypsum sites 656 and 652 now on the lower sardinia margin were apparently higher standing during the desiccation event their messinian facies are subaerial and lacustrine respectively we infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a rolling back subduction zone or in terms of extension of continental crust by shear along a deep detachment fault sites 655 651 and 650 were drilled into two small basalt floored basins of the central and eastern tyrrhenian emplacement of basaltic crust in the central tyrrhenian vavilov basin apparently began more than a million years before emplacement of basaltic crust in the eastern tyrrhenian marsili basin this observation is compatible with previous suggestions that the tyrrhenian has grown southeastward in response to rollback of the down going slab that currently dips northwestward under the toe of italy at the easternmost site high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2 500 m it has apparently subsequently subsided to its present depth of 4 100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid ocean ridge

the upper and lower nisyros pumices revisions to the mediterranean tephrostratigraphic record based on micron beam glass geochemistry abstract the greek island of nisyros is the source of tephra found in distal settings throughout the aegean in this contribution we define geochemical fingerprints for the lower and upper pumice eruptions of nisyros based on micron beam major empa and trace la icp ms element data these two eruptions are compositionally distinct from each other the high phenocryst content of proximal lower and upper pumice tephra means that the differences between the two magmas are masked in whole rock analyses we demonstrate that all previous reports of distal marine and continental tephras correspond to the younger upper pumice not the older lower pumice this has important implications for the marine tephrochronology of the mediterranean and for the age of the upper and lower pumice eruptions we suggest an age of at least 47 ka for the upper pumice and an older unconstrained age for the lower pumice

seafloor gas seeps triggered by a northern california earthquake abstract a series of marine surveys using high resolution seismic reflection and side scan sonar profiling was conducted on the klamath river delta from 1977 to 1985 in november 1980 near the middle of this 8 year time period a major earthquake magnitude 7 occurred in the area the earthquake caused liquefaction of shelf deposits off the klamath river and while mapping the sediment failures we observed an inordinate number of gas vents and acoustic anomalies in the sediment gas charging and water column gas clouds our analyses indicate that a change in gas seepage occurred after the earthquake there was a marked increase in gas abundance immediately after the earthquake a gradual decrease over the next year and stabilization at pre earthquake gas levels within five years or less the acoustic anomalies were observed in pre quaternary rocks as well as in surficial holocene deposits and gas seeps overlay truncated anticlines faults and syncline exposures thus the gas released may have been in part thermogenic in origin a large area 20 km 2 on the delta failed during the earthquake and the abundance of gas seeps and craters in the area suggests that sediment degassing may have been an important process contributing to failure

geometry lateral variation and preservation of downlapping regressive shelf deposits eastern tyrrhenian sea margin italy abstract the shelf of the eastern tyrrhenian sea margin changes substantially in width shelf break depth and sea floor steepness over relatively short distances largely owing to pronounced lateral changes in subsurface geologic structure remnants of late pleistocene prograded coastal deposits are locally preserved on the middle and outer parts of the shelf we recognize two major controls on the distribution lateral extent thickness and preservation potential of these prograded deposits first prograded downlapping deposits formed only where the physiographic shelf break was deeper than the lowstand shoreline thus providing accommodation space for the lowstand deposits second the proximity and relative size of sediment sources and the local coastal dispersal system apparently infl enced the geometry of the deposit midshelf and shelf margin bodies composed of seaward steepening downlapping reflectors were deposited as thin to thick continuous prograding sheets over an irregular eroded shelf surface and onto the shelf edge during the latest fall and lowstand of sea level decreased sedimentation at the end of this lowstand resulted in net erosion during sea level rise shoreface erosion created a major marine erosional ravinement surface landward of the 120 m isobath and much of the downlapping deposits were removed preservation of these downlapping deposits is largely a function of their thickness thick continuous deposits are common on the shelf edge whereas on the midshelf only thin remnants are preserved locally where depressions or morphologic steps were present in the shelf surface

current modification of a mass failure deposit on the continental shelf north canterbury new zealand abstract the holocene mud blanket on the nearly flat 0 4 middle to outer shelf off canterbury contains a 255 km 2 zone of ridges and gullies exhibiting up to 10 m relief ridges are mantled by cohesive mud in various stages of dissection whereas gullies mainly have a flat sandy floor morphologic and seismic evidence suggests that the topography initially formed by mass failure along an unconsolidated sand horizon which presumably acted as a failure plane a number of mechanisms are readily available to favour such movement earthquake shock sediment overloading subsurface instability due to gas and wave loading since formation the topography has been modified by currents which have eroded mud from gullies as well as locally scouring ridge crests current meter measurements from 1 m above a ridge crest indicate that erosion most likely occurs under storm conditions when currents reach a laboratory determined threshold speed of 100 37 cm s 1 in contrast undissected crests may be resistant to erosion as a consequence of biological stabilization by dense colonies of chaetopterid worm tubes or associated biota