continental oceanic crustal transition off southwest africa more than 1 426 mi 2 300 km of 48 trace 12 fold seismic reflection profiles were used to examine the nature of the continent ocean boundary off southwest africa south of the orange river faulted blocks which we interpret as rifted continental crust can be traced seaward to the 3 km isobath the transition to oceanic basement occurs in a zone 19 to 25 mi 30 to 40 km wide beneath the continental rise although structural details are obscured by a thick seaward dipping wedge of pre aii pre late early cretaceous overburden oceanic crust at the presumed contact is not older than magnetic anomaly m9 126 to 121 m y b p north of the orange river a pronounced hinge in continental crust correlates with magnetic anomaly g of rabinowitz 1976 seaward of the hinge a complex fault block terrane is evident oceanic basement can not be traced with any certainty landward of anomaly m4 intracontinental stretching and associated volcanism appear to have been important in the early history of the cape basin rifting and local dike intrusion may explain the presence of some lineated magnetic anomalies previously attributed to sea floor spreading related extrusives form at least part of the pre aii wedge just seaward of the hinge zone our interpretation of the seismic data suggests that the initiation of normal spreading in the cape basin postdates by 4 to 9 m y the valanginian age derived from prevailing plate tectonic reconstructions of the south atlantic

benthic foraminiferal evidence of deep sea sediment transport by the 2011 tohoku oki earthquake and tsunami abstract benthic foraminiferal assemblages within turbidites recovered from two upper slope stations off sendai bay northeast japan have been analyzed to estimate the source area of the turbidites resulting from the 2011 tohoku oki earthquake and tsunami the turbidite at one station st 5 893 m water depth is composed of a surface layer that contains foraminiferal species living on the outer shelf or inner bay and a lower part with bathyal species in the turbidite at the second station st 6 1446 m the assemblage consists of only bathyal species living in 800 1000 m the composition of the st 6 assemblage gradually changes from the base to the top of the turbidite consistent with the upward fining graded structure i e thin walled tiny species are increased in the upper layer the lower part of the turbidites at both sites st 5 and st 6 are considered to have originated from turbidity currents triggered by earthquake shaking in contrast the most probable generation mechanism for the turbidity current that formed the surface layer at st 5 is the tsunami related agitation of sediment in shallow water the relatively good preservation of benthic foraminiferal tests in the turbidites suggests transport processes with minimal internal friction and or collision of grains within the turbidity current these results show that benthic foraminifera are useful in turbidite paleoseismology

large submarine landslides in the japan trench a new scenario for additional tsunami generation 1 we describe in detail possible large submarine landslides several tens of kilometers in length and width on the trench landward slope of the japan trench on the basis of high resolution topographic surveys and detailed seafloor observations these slides stopped at the toe of the trench slope after initial movement of the toe along a basal decollement or thrust of the trench landward slope wedge during an earthquake the basal frictional condition s might change drastically from static to dynamic thus reducing the frictional strength as a result rapid submarine landsliding push downward on the toe generating large horizontal displacements for tsunamis this hypothesis should explain suitably the relation between large displacement of the thrust fault and tsunami generation by the 2011 tohoku earthquake as well as tsunami generation by the 1896 tohoku earthquake

extension of the parana basin to offshore brazil implications for coalbed methane evaluation abstract coalbed methane cbm is a worldwide exploration target of the petroleum industry in brazil the most important coal bearing succession is associated with the permian rio bonito formation of the parana basin the gas prone areas are located at the southeastern margin of the parana basin and possibly in the offshore region of the northern part of the pelotas basin coalfields end abruptly at the present day shoreline a result of rifting of gondwana and the evolution of the south atlantic ocean all geologic indicators suggest that in pre rift times the coal seams extended further eastwards probably now lying deeply buried below the sedimentary succession of the pelotas basin the present paper discusses structural stratigraphic seismic and aeromagenetic data that support the preservation of continental crust beneath ocean sediment if the coal beds had similar lateral extent to known onshore coals and coal beds extended across the projected extension of the parana basin and there was a conservative 5 m of cumulative coal thickness then a potential methane volume can be estimated for this newly inferred resource average onshore coal gas content is 32 scf ton 1 00 m 3 ton if this is similar in the offshore coal deposits then the hypothetical methane volume in the offshore area could be in excess of 1 9 10 12 scf 56 10 9 m 3 metamorphism from dikes associated with rifting are potential complicating factors in these deposits and since no borehole reaching the deep lying strata in the offshore area are available this is a hypothetical gas resource with a certain level of uncertainty which should be tested in the future by drilling a deep borehole

the tectonic evolution of the south atlantic from late jurassic to present an improved tectonic database for the south atlantic has been compiled by combining magnetic anomaly geosat altimetry and onshore geologic data we used this database to obtain a revised plate kinematic model starting with a new fit reconstruction for the continents around the south atlantic we present a high resolution isochron map from chron m4 to present fit reconstructions of south america and africa that require rigid continental plates result in substantial misfits either in the southern south atlantic or in the equatorial atlantic to achieve a fit without gaps we assume a combination of complex rift and strike slip movements 1 along the south american parana chacos basin deformation zone 2 within marginal basins in south america salado colorado basin and 3 along the benue trough niger rift system in africa these faults are presumed to have been active before or during the breakup of the continents our model describes a successive unzipping of rift zones starting in the southern south atlantic between 150 ma tithonian and approximately 130 ma hauterivian rifting propagated to 38 s causing tectonic movements within the colorado and salado basins subsequently between 130 ma and chron m4 126 5 ma the tip of the south atlantic rift moved to 28 s resulting in intracontinental deformation along the parana chacos basin deformation zone between chron m4 and chron mo 118 7 ma rifting propagated into the benue trough and niger rift inducing rift and strike slip motion after chron mo the equatorial atlantic began to open while rifting and strike slip motion still occurred in the benue trough and niger rift since chron 34 84 ma the opening of the south atlantic is characterized by simple divergence of two rigid continental plates

a slump in the trench tracking the impact of the 2011 tohoku oki earthquake we present differential bathymetry and sediment core data from the japan trench sampled after the 2011 tohoku oki offshore japan earthquake to document that prominent bathymetric and structural changes along the trench axis relate to a large 27 7 km 2 slump in the trench transient geochemical signals in the slump deposit and analysis of diffusive re equilibration of disturbed so 4 2 profiles over time constrain the triggering of the slump to the 2011 earthquake we propose a causal link between earthquake slip to the trench and rotational slumping above a subducting horst structure we conclude that the earthquake triggered slump is a leading agent for accretion of trench sediments into the forearc and hypothesize that forward growth of the prism and seaward advance of the deformation front by more than 2 km can occur episodically during a single event large mega thrust earthquake

interpreting soft sediment deformation and mass transport deposits as seismites in the dead sea depocenter we have studied the history of earthquakes over the past 70 kyr by analyzing disturbed sedimentary layers around the margins of the dead sea however we know little about disturbances in the basin depocenter where water depth is 300 m and accessible only by drilling in this study we compare disturbances from the dead sea depocenter with the contemporaneous earthquake record 56 30 ka that was recovered on the western margin of the lake this comparison allows us to discern the characteristics of disturbance in the different subaqueous environments and identify the source and sedimentary process of mass transport deposits our observations indicate that i the long disturbance sequences in the dead sea depocenter are composed of in situ deformation slump and chaotic deposits ii earthquake triggered kelvin helmholtz instability is a plausible mechanism for the in situ deformation in the lake center iii the slump is slope area sourced iv the unit of chaotic deposits is lakeshore sourced and v earthquake triggered slope instability is a viable mechanism for the slump and chaotic deposits we further suggest that long sequences of disturbance in seismically active lake depocenters can be used to infer earthquake clusters

tectonic evolution of the colorado basin offshore argentina inferred from seismo stratigraphy and depositional rates analysis abstract based on a dense 2d seismic reflection dataset and information from 8 exploration wells we reinterpreted the stratigraphic evolution of the colorado basin the basin is located on the continental shelf and slope within 50 to 2250 m of bathymetry the total sediment fill can be up to 16 000 m seismic to well log correlations provide a chrono stratigraphic framework for the interpreted seismic sequences we show that the colorado basin records the development of a permian pre rift period a triassic jurassic to early cretaceous rift phase and a lower cretaceous to tertiary drift phase this passive margin represents the evolution of lithospheric extension from active rifting to the thermal subsidence drift stage several cretaceous to cenozoic slumping episodes were identified and related to progradation of the sequences and sediment build up in the slope as well as to the development of seaward dipping extensional faults assuming an accumulation time span of 25 ma for the syn rift succession which corresponds to the duration of extensional phases preceding the final break up of the south atlantic sedimentation rates are in the order of 118 m ma by late cretaceous the gondwana break up had stopped in almost all areas and post rift thermal subsidence dominated the basin development during the early phase of subsidence high sedimentation rates of up to 122 m ma are recorded an important decrease of sediment supply 30 m ma occurred until the end of the sag phase during the deposition of the colorado formation and sedimentation took place in elongated depocenters with oceanward progradation a second phase of increased sediment supply takes place during the oligocene and miocene resulting in the development of large basinward prograding sedimentary wedges this event seems to be associated to the interaction between continental dynamics subsidence and increased continental erosion during climate shift from greenhouse to icehouse conditions

slump sheets as a record of regional tectonics and paleogeographic changes in south china abstract slumps of various scales are recognized in the late katian late ordovician mixed carbonate and siliciclastic slope successions in the changshan area western zhejiang province south china in order to understand their deformational processes triggering mechanisms paleo slope orientation and geological implications a detailed sedimentological study was carried out on four outcrop sections in the southern changshan the putangkou zhoutang and shikeng sections we recognized three slumping episodes ca 3 5 m 11 m and 73 m in thickness in stratigraphically ascending order and co occurred debris flows at the sanqushan section 11 5 km north of changshan thirteen slump units each being tens of cm to 6 m in thickness are recognized facies analyses and diagenetic characteristics of these slumps and their internal deformation structures suggest that they formed as a result of plastic and brittle deformation and liquefaction and fluidization during slumping the rip up blocks cracks and ruptured beds in the slumps of southern changshan indicate extensional features whereas recumbent and disharmonic folds in the slumps of northern changshan represent compressional features these spatially different features suggest that the slumps may have been generated on a paleo slope dipping generally to the north the case study of slumps and debris flows from the putangkou section indicates a significant mass flow transition from a slumped mass into debris flow deposits autogenic triggering mechanisms of these slumps e g rapid deposition storm wave loading and tidal shear are ruled out by the results of facies analysis instead the slumps might have been triggered by relative sea level changes or tectonically induced progressively steepening of the slope which is likely related to the contemporaneous kwangsian orogeny

slowdown of circumpolar deepwater flow during the late neogene evidence from a mudwave field at the argentine continental slope geochemical evidence from boreholes suggests enhanced transport of northern component water ncw to southern latitudes from about 6 ma onward however information on how this change in transport influenced the intensity and position of current systems is sparse here we use seismic reflection profiles interpreted together with bathymetric data to investigate current derived deposits at the central argentine margin upslope migrating mudwaves overlying a late miocene erosional unconformity provide evidence that circumpolar deepwater flow slowed down with the onset of ncw inflow during the last 3 ma changes in dimensions and migration rates of the waves are small indicating continuous bottom current flow conditions similar to today with only minor variations in flow speed suggesting that the deep western boundary current in the western south atlantic as observed today has been a pervasive feature of the global thermohaline circulation system during the plio pleistocene

mass transport deposits in the northern ecuador subduction trench result of frontal erosion over multiple seismic cycles article i nfo investigations of mass transport deposits mtds and turbidite deposition in the confined north ecuador subduction trench provide access to paleoseismic information and insights into long term mechanisms for frontal tectonic erosion at a convergent margin the studied trench has been the site of four great subduction earthquakes 7 7 mw 8 8 during the 20th century the trench is isolated from major continental sediment input so that investigated mtds and turbidites are considered of local origin swath bathymetry seismic reflection and chirp data together with sedimentary cores and 14 c dating revealed that seven mtds were emplaced in distinct trench sub basins since 23 kyr and 27 turbidites deposited in the southernmost trench sub basin since 4 9 kyr our analysis shows that six mtds were derived from the margin while a single one stemmed from the outer trench wall temporal correlations between mtds emplaced within trench sub basins separated by a structural saddle indicate that the seven mtds were emplaced during five main events three were triggered locally and tentatively dated 5 8 1 6 kyr and recent whereas four were emplaced in distinct trench sub basins as a result of two regional events at 22 6 and 15 4 kyr none of the mtds occurred during the fast stage of the last sea level rise 13 to 8 kyr however dissociation of gas hydrates during the last 8 kyr stage of slow sea level rise might have contributed to trigger the three youngest mtds the large 1 5 13 5 kyr return time of the mtds contrasts with that of 189 yr of the turbidites the later is consistent with the 73 yr return time of two local mw 8 2 earthquakes implying that turbidites might have been triggered by large earthquakes the very large mtds return time is attributed to long term deformation processes and mechanical weakening of the margin outer wedge in response to repeated variations in basal friction pore pressure and margin extensional contraction strain over multiple earthquake cycles this process contributes to short term frontal erosion the rate of which is estimated to be 8 6 10 3 km 3 kyr km since at least 15 4 kyr

birth of a volcanic margin off argentina south atlantic 1 based on a dense grid of multichannel reflection seismic lines we study the evolution of a volcanic rifted margin segment off argentina the segment under study is located between 44 s and 41 s we describe in detail the facies of the extrusive basaltic complexes across the margin these include single and multiple inner seaward dipping reflectors sdrs with varying architecture along the margin outer highs and outer sdr wedges a detailed interpretation of a transitional zone between the inner and outer sdr wedges is presented multiple inner sdrs are concentrated at the southern part of the margin segment while in the north only one steeply dipping wedge is present the dip of the inner sdr wedges changes along the margin and we propose subsidence by loading as main cause the transitional zone between the inner and outer sdr wedges becomes narrower toward the north by correlating with magnetic data we conclude that the emplacement of the 30 100 km wide multiple inner sdrs occurred episodically we propose an injection center which migrated in a seaward direction with proceeding extension as the origin for the multiple inner sdrs a scissor like opening of the margin segment resulted in different amounts of stretching along strike of the margin segment and is likely the cause for the varying distribution of the extrusive basaltic complexes the varying extension rates within the margin segment contribute to decreasing volumes of melts generated in a northward direction within this rift segment

reassembling gondwana a new high quality constraint from vibroseis exploration of the sub ice shelf geology of the east antarctic continental margin the breakup of gondwana is manifested by coeval early jurassic karoo magmatism in south africa and east antarctica in south africa the large volumes of volcanic rocks of the adjoining lebombo and mwenetzi save monoclines represent a volcanic rift margin and in east antarctica a corresponding feature the explora wedge is buried below sediments and floating ice shelves on the continental margin of dronning maud land we use the seismic vibrator source to explore the sub ice geology in antarctica and the new seismic reflection and available regional aeromagnetic data enable us to outline a dogleg landward extent of the explora wedge in dronning maud land the congruent inboard wedge geometries on the two continents define a high quality constraint which facilitate for the first time a geologically consistent and tight reconstruction of africa relative to east antarctica within gondwana the uncertainties in correlations of major geological features mobile belts from one continent to the other may now be of the order of ten s of kilometers rather than hundreds of kilometers

depth and age in the north pacific the concept of the oceanic lithosphere as a cooling thermal boundary layer on top of a viscous upper mantle accounts for the increase in depth with age of the ocean floor analyses of the exact nature of this relation provide constraints on the rheology and structure of this layer in past studies problems with uncertainties of age and in sediment thickness have limited the value of this relation on older ocean floor in this study we evaluate different tectonic histories for the quiet zones and construct a revised isochron chart for the north pacific we check and modify the current sediment thickness charts using new deep sea drilling data and revised ideas concerning reflectors in the southwestern north pacific averaging the synbaps digital data base into half by half degree elements and correcting for sediment load we plot basement depth versus age for the entire north pacific because of the skewness in the data associated with seamounts we present the data as contours about the mode and find that two thirds of the observations lie within 300 m of this value on crust between 0 and 80 ma the ocean floor subsides with the square root of age on ocean floor older than 100 ma the depths in general flatten with age with areally correlateable swells and valleys the hawaiian and line island swells correlate positively and the mariana basin valley negatively with geoid height the flattening in the depths indicates that the thermal boundary layer has reached equilibrium conditions under older ocean floor further the correlation of the swells and valleys with geoid height presents evidence for organized convection in the upper mantle beneath older lithosphere in the north pacific

hotspots mantle plumes flood basalts and true polar wander persistent long lived stationary sites of excessive mantle melting are called hotspots hotspots leave volcanic trails on lithospheric plates passing across them the global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions through the orientations and age distributions of volcanic trails left by these melting anomalies hotspots appear to be maintained by whole mantle convection in the form of upward flow through narrow plumes evidence suggests that plumes are deflected little by horizontal flow of the upper mantle mantle plumes are largely thermal features and arise from a thermal boundary layer most likely the mantle layer just above the core mantle boundary experiments and theory show that gravitational instability drives flow beginning with the formation of diapirs such a diapir will grow as it rises fed by flow through the trailing conduit and entrainment of surrounding mantle the structure thus develops a large spherical plume head and a long narrow tail on arrival at the base of the lithosphere the plume head flattens and melts by decompression producing enormous quantities of magma which erupt in a short period these are flood basalt events that have occurred on continents and in ocean basins and that signal the beginning of major hotspot tracks the plume supported hotspot reference frame is fixed in the steady state convective flow of the mantle and is independent of the core generated axial dipole paleomagnetic reference frame comparison of plate motions measured in the two frames reveals small but systematic differences that indicate whole mantle motion relative to the earth s spin axis this is termed true polar wander and has amounted to some 12 since early tertiary time the direction and magnitude of true polar wander have varied sporadically through the mesozoic probably in response to major changes in plate motions particularly subduction zone location that change the planet s moments of inertia

risks inherent in the cenozoic stratigraphic plays in basins of the uruguayan continental margin abstract the genesis and evolution of the uruguayan continental margin are linked to the geological processes that resulted in the breakup of the western gondwana and the opening of the atlantic ocean intense hydrocarbon exploration over the last decade has identified several plays in the mesozoic cenozoic sedimentary basin infill the main exploration milestone was the drilling of the raya x 1 well in the pelotas basin which targets an oligocene turbidite deposit the well encountered no hydrocarbon accumulations but has contributed to the knowledge of a frontier area and has raised questions regarding the geological risks associated with the cenozoic prospects in the uruguayan continental margin in this study the exploratory potential of a set of stratigraphic plays identified in the cenozoic sedimentary succession of the uruguayan continental margin basins was analysed through the interpretation of 2d seismic sections a significant risk appears to be related to migration and charge of the cenozoic reservoirs from cretaceous source rocks because of the lack of major faults and the development of thick transgressive sedimentary packages especially in the pelotas basin the best areas for vertical charge of the cenozoic reservoirs resides on the southwest of the uruguayan continental margin distal part of the punta del este basin and in a portion of the central region southernmost part of the uruguayan pelotas basin

joint inversion of strong motion teleseismic geodetic and tsunami datasets for the rupture process of the 2011 tohoku earthquake 1 the 2011 tohoku earthquake was observed by dense strong motion teleseismic geodetic and tsunami networks we first inverted each of the datasets obtained by the networks separately for the rupture process of the earthquake we then performed checkerboard resolution tests for assessing the resolving power of these datasets in order to overcome the limited resolutions of the separate inversions and differences in their results we performed a quadruple joint inversion of all these data to determine a source model most suitable for explaining all the datasets in the obtained source model the maximum coseismic slip was approximately 35 m and the total seismic moment was calculated to be 4 2 1022 nm which yielded mw 9 0 the main rupture propagated not only in the strike direction but also in the dip direction and included both the deep area called the miyagi oki region and the compact shallow area near the japan trench

remobilization of surficial slope sediment triggered by the a d 2011 mw 9 tohoku oki earthquake and tsunami along the japan trench the a d 2011 tohoku oki m w 9 earthquake ruptured the megathrust up to the japan trench with a large displacement and caused a catastrophic tsunami this study is the first to use short lived radioisotopes including those emitted by the damaged nuclear reactors at the fukushima daiichi nuclear power plant japan to document the remobilization of the upper few centimeters of sediment as a highly significant process triggered by the earthquake and its aftershocks targeting the post earthquake environment allowed characterization of the sedimentary signature of this event for a better understanding of paleoearthquakes in japan and other tectonically active boundary areas the results stem from 23 piston cores recovered by the 2013 expedition nt13 19 of the japan agency for marine earth science and technology we document submarine homogeneous muddy flow deposits that were triggered by ground motion in 2011 they are highly enriched with excess xs xs 210 pb requiring only centimeters deep sediment remobilization over large areas of the seafloor some contain 134 cs and 137 cs radioisotopes derived from the fukushima nuclear reactors indicating that sedimentation persisted for at least 30 days after the main shock we found these deposits at all sampling sites in an 5000 km 2 area of the seafloor in 4000 6000 m of water depth the study area extends for 260 km parallel to the strike of the trench the thickness of this tohoku layer 3 200 cm increases toward the zone of maximum megathrust slip where deposits are thickest these results demonstrate that the shaking of the seafloor above large megathrust ruptures near the trench remobilized surficial unconsolidated sediment for hundreds of kilometers the characteristics of these deposits may typify deposits resulting from large fault slips like that of the tohoku oki earthquake but also other earthquake deposits contributing to their identification in the sedimentary record globally

early cenozoic crust at the norwegian continental margin and the conjugate jan mayen ridge multichannel seismic profiles at the voring plateau margin off norway and the northern jan mayen ridge have provided a framework for the early tertiary evolutionary history of these areas which were adjacent prior to the opening of the norwegian sea we propose that their paleogene evolution is quite similar and that the two acoustic basement reflectors ee and jo were formed in the early eocene by extrusion of flow basalts from the time of opening to about anomaly 23 time oceanic seafloor was generated by icelandic type spreading during that time the central jan mayen fracture was the main transform the seaward dipping reflector sequences are flow basalts generated by the icelandic spreading the existence of less well developed dipping sequences seaward of the primary ones probably reflects that these regions submerged later because of higher initial elevation during the early eocene subaerial spreading episode which is related to the north atlantic volcanic province basalt flows also covered the adjacent thinned and heavily intruded continental crust it is proposed that the continent ocean boundary is located just landward of anomaly 24b a short distance seaward of the voring plateau escarpment reflector k is only recognized landward of this boundary in a region of transitional crust the escarpment experienced syndepositional faulting and the most elevated parts of the voring marginal high did not subside below shallow water depths before oligocene miocene time we suggest that the voring margin and the jan mayen ridge represent volcanic passive margins the evolution of this margin type may relate to initial uplift due to rifting in previously thinned crust

insights from recent gravity satellite missions in the density structure of continental margins with focus on the passive margins of the south atlantic abstract we focus on new gravity and gravity gradient data sets from modern satellite missions goce grace and champ and their geophysical interpretation at passive continental margins of the south atlantic both sides south africa and south america have been targets of hydrocarbon exploration and academic research of the german priority program sample south atlantic margin processes and links with onshore evolution the achievable spatial resolution driven by goce is 70 80 km therefore most of the geological structures which cause a significant gravity effect by both size and density contrast can be resolved however one of the most important aspects is the evaluation of the omission error which is not always in the focus of interpreters it results from high frequency signals of very rough topographic and bathymetric structures which cannot be resolved by satellite gravimetry due to the exponential signal attenuation with altitude the omission error is estimated from the difference of the combined gravity model eigen 6c4 and the satellite only model goco05s it can be significantly reduced by topographic reductions simple 2d density models and their related mathematical formulas provide insights in the magnitude of the gravity effect of masses that form a passive continental margin they are contrasted with results from satellite only and combined gravity models example geophysical interpretations are given for the western and eastern margin of the south atlantic ocean where standard deviations vary from 25 to 16 mgal and 21 11 mgal respectively it could be demonstrated that modern satellite gravity data provide significant added value in the geophysical gravity data processing domain and in the validation of heterogeneous terrestrial data bases combined models derived from high resolution terrestrial gravity and homogeneous satellite data will lead to more detailed and better constrained lithospheric density models and hence will improve our knowledge about structure evolution and state of stress in the lithosphere

gravimetric determination of the continental oceanic boundary of the argentine continental margin from 36 s to 50 s fil arecco maria alejandra universidad de buenos aires facultad de ingenieria argentina

importance of submarine landslides for non steady state conditions in pore water systems lower zaire congo deep sea fan abstract most concentration profiles of sulfate in continental margin sediments show constant or continuously increasing gradients from the benthic boundary layer down to the deep sulfate reduction zone however a very marked change in this gradient has been observed several meters below the surface at many locations which has been attributed to anoxic sulfide oxidation or to non local transport mechanisms of pore waters the subject of this study is to investigate whether this feature could be better explained by non steady state conditions in the pore water system to this end data are presented from two gravity cores recovered from the zaire deep sea fan the sediments at this location can be subdivided into two sections the upper layer about 10 m thick consists of stratified pelagic deposits representing a period of continuous sedimentation over the last 190 kyr it is underlain by a turbidite sequence measuring several meters in thickness which contains large crystals of authigenic calcium carbonate ikaite caco3 6h2o ikaite 13c values are indicative of a methane carbon contribution to the co2 pool radiocarbon ages of these minerals as well as of the adjacent bulk sediments provide strong evidence that the pelagic sediments have overthrust the lower section as a coherent block therefore the emplacement of a relatively undisturbed sediment package is postulated pore water profiles show the depth of the sulfate methane transition zone within the turbiditic sediments by the adaptation of a simple transport reaction model it is shown that the change in the geochemical environmental conditions resulting from this slide emplacement and the development towards a new steady state are fully sufficient to explain all features related to the pore water profiles particularly so42 and dissolved inorganic carbon dic the model shows that the downslope transport took place about 300 yr ago

constraining the age and evolution of the tuaheni landslide complex hikurangi margin new zealand using pore water geochemistry and numerical modeling

analysis of submarine landsliding in the rupture area of the 27 february 2010 maule earthquake central chile the comparison of bathymetric datasets compiled before and after the mw 8 8 maule earthquake of the 27 february 2010 offshore central chile proves that no new submarine landslides on a size scale detectable with hull mounted bathymetric echosounders features of a horizontal size of 1 km formed as a direct consequence of the ground shaking gravity coring around a pre existing slide feature offshore concepcion biobio slide however documents that 1 a number of events occurred as retrogressive failures of the biobio slide wall the youngest of which is 700 1000 years old and that 2 a very recent small scale slide structure resulted from non destructive imbricate stacking of a thin sediment layer pore water geochemical data show that this event post dates the maule earthquake suggesting that it was triggered by one of the numerous aftershocks the absence of larger failures and the presence of a small slide let us propose that in contrast to apparent logic frequent violent earthquakes at convergent margins do not necessarily pose a particular tsunami risk by landslides the frequent shaking might even limit the slide volume and therefore their tsunami hazard as instead of rare and large slides frequent smaller slides are induced

geology and seismic structure of the northern section of the oman ophiolite in the north oman mountains a continuous ophiolite succession is exposed from tectonized harzburgites and dunites at the base through layered gabbros and peridotites high level gabbros and plagiogranite to a dike swarm and pillowed volcanics overlain by pelagic shales the upper part of this sequence possesses a static metamorphic overprint which passes downward from greenschist facies in the lowermost volcanics and most of the dike swarm to amphibolite facies in the lowermost dike swarm and in the high level intrusives these pervasively altered rocks are underlain by layered gabbros and peridotites where hydration is restricted to fractures compressional and shear wave velocities have been measured to confining pressures of 6 kbar for 139 water saturated cores from this sequence the samples were field oriented and collected from known stratigraphic levels which allows the construction of velocity depth profiles and an examination of anisotropy within the ophiolite compressional wave velocities measured for the basalt section are quite variable ranging from 4 5 to 6 0 km s at in situ pressures within the sheeted dike section compressional and shear wave velocities vary from 5 4 to 6 3 km s and from 2 9 to 3 6 km s respectively from the basalt sediment contact through the dike section velocities increase rapidly with depth this gradient is related to increasing metamorphic grade and a decrease in grain boundary porosity the top of seismic layer 3 is located near the lower boundary of the sheeted dike swarm and marks the transition from greenschist facies to amphibolite facies metamorphics the dikes decrease in abundance downward into the high level intrusives coarse grained gabbroic and granitoid rocks which often contain abundant hornblende with isotropic textures and lacking compositional layering mean compressional and shear wave velocities increase uniformly from 6 7 and 3 6 km s respectively in the highlevel intrusives to 7 5 and 3 9 km s respectively at the base of the layered sequence measured velocities of the ultramafic tectonites are highly variable because of the anisotropy and serpentinization petrofabrics of relic olivine in the wadi ragmi region show strong preferred fabrics for the tectonites and calculated compressional wave velocities for the serpentine free rocks range from 7 8 to 8 5 km s with the fast direction parallel to the direction of spreading inferred from dike orientations in excellent agreement with observed upper oceanic mantle seismic anisotropy the crust mantle boundary which is defined by the abrupt increase in seismic velocities coincides with the petrological contact between layered gabbros and peridotites and tectonized harzburgite and dunites

north atlantic volcanic margins dimensions and production rates early tertiary lithospheric breakup between eurasia and greenland was accompanied by a transient 3 m y igneous event emplacing both the onshore flood basalts of the north atlantic volcanic province navp and huge extrusive complexes along the continent ocean transition on the rifted continental margins seismic data show that volcanic margins extend 2600 km along the early eocene plate boundary in places underlain by high velocity 7 2 7 7 km s lower crustal bodies quantitative calculations of navp dimensions considered minimum estimates reveal an areal extent of 1 3 106 km2 and a volume of flood basalts of 1 8 106 km3 yielding a mean eruption rate of 0 6 km3 yr or 2 4 km3 yr if two thirds of the basalts were emplaced within 0 5 m y the total crustal volume is 6 6 106 km3 resulting in a mean crustal accretion rate of 2 2 km3 yr thus navp ranks among the world s larger igneous provinces if the volcanic margins are considered the velocity structure of the expanded crust seaward of the continent ocean boundary differs from standard oceanic and continental crustal models based on seismic velocities this volcanic margin crust can be divided into three units of which the upper unit corresponds to basaltic extrusives the regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust including the high velocity lower crust which extends some distance landward of the continent ocean boundary was emplaced during and subsequent to breakup the volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling probably reflecting the interaction of a mantle plume and a lithosphere already extending

the subantarctic front as a sedimentary conveyor belt for tsunamigenic submarine landslides abstract the subantarctic front saf one of the three main jets of the antarctic circumpolar current acc flows through a narrow gap in the north scotia ridge and then north westward across the continental slope of burdwood bank 150 km south of the falkland islands there the saf flows across a fold and thrust belt caused by oblique convergence at the active plate boundary between the scotia plate and south american plate we here use regional 2d and 3d seismic reflection data to show the interaction of the associated bottom currents with the active margin particularly to understand the causes and consequences of a number of large submarine landslides located in the adjacent foredeep kinematic indicators from the landslide deposits show that they are derived from a single point source located in an embayment on the northern slope of burdwood bank where we identify a large contourite drift deposit this drift forms the depositional sink for an along slope sediment routing system driven by currents associated with the saf with sediment being eroded from the burdwood terrace transported 200 km westward and plastered against the middle upper continental slope the contourite drift is undercut by the core of the current making the slope inherently unstable in this area numerical modelling of the landslides and resultant waves indicates the tsunamigenic potential of these events modelled peak wave elevations of up to 40 m inundate the southern coast of the falklands for a 100 km3 volume landslide with a recurrence interval of 1 ma or less this research highlights preconditioning mechanisms for submarine failure on continental slopes dominated by strong ocean currents and specifically oceanographic controls on the frequency magnitude and location of submarine landslides associated with contourite systems

tectonic erosion at the front of the japan trench convergent margin abstract the imaging of a multichannel seismic record was improved by reprocessing using pre stack techniques the reprocessed record shows structures that indicate tectonic erosion and gravity collapse at the front of the japan trench margin much of the lower slope appears to be underlain by a detached coherent block of continental crust the lower slope has failed by mass wasting and the resulting apron of slump debris at the base of the slope has become involved in thrust faulting at the front of the subduction zone slumping continues as long as debris is removed from the front of the margin by subduction and the apron cannot build up sufficiently to stabilize the failing lower slope truncated beds at the base of the upper plate indicate subcrustal erosion as well this probably being the main cause of massive subsidence of the margin subsidence was the cause of oversteepening destabilization and subsequent gravity collapse of the leading edge of the upper plate

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

the destructive 1946 unimak near field tsunami new evidence for a submarine slide source from reprocessed marine geophysical data the mw 8 6 earthquake in 1946 off the pacific shore of unimak island at the end of the alaska peninsula generated a far field tsunami that crossed the pacific to antarctica its tsunami magnitude 9 3 is comparable to the 9 1 magnitude of the 2011 tohoku tsunami on unimak island s pacific shore a runup of 42 m destroyed the lighthouse at scotch cap elsewhere localized tsunamis with such high runups have been interpreted as caused by large submarine landslides however previous to this study no landslide large enough to generate this runup was found in the area that is limited by the time interval between earthquake shaking and tsunami inundation at scotch cap reworking of a seismic reflection transect and colocated multibeam bathymetric surveys reveal a landslide block that may explain the 1946 high runup it is seaward of scotch cap on the midslope terrace and within the time limited area

high resolution chronology of sediment below ccd based on holocene paleomagnetic secular variations in the tohoku oki earthquake rupture zone using high resolution paleomagnetic data we examined the potential for obtaining precise ages from sediment core samples recovered from deep sea basins close to rupture zones of the 2011 and earlier earthquakes off tohoku japan obtaining detailed stratigraphic ages from deep sea sediments below the calcium compensation depth ccd is difficult but we found that the samples contain excellent paleomagnetic secular variation records to constrain age models variations in paleomagnetic directions obtained from the sediments reveal systematic changes in the cores a stacked paleomagnetic profile closely matches the lake biwa data sets in southwest japan for the past 7 000 years one can establish age models based on secular variations of the geomagnetic field on sediments recovered uniquely below the ccd comparison of paleomagnetic directions near a tephra and a paleomagnetic direction of contemporaneous pyroclastic flow deposits acquired by different magnetization processes shows precise depositional ages reflecting the magnetization delay of the marine sediment record

seismic slip propagation to the updip end of plate boundary subduction interface faults vitrinite reflectance geothermometry on integrated ocean drilling program nantro seize cores seismic faulting along subduction type plate boundaries plays a fundamental role in tsunami genesis during the integrated ocean drilling program iodp nankai trough seismogenic zone experiment nantro seize stage 1 the updip ends of plate boundary subduction faults were drilled and cored in the nankai trough offshore japan where repeated large earthquakes and tsunamis have occurred including the a d 1944 tonankai mw 8 1 earthquake samples were obtained from the frontal thrust which connects the deep plate boundary to the seafloor at the toe of the accretionary wedge and from a megasplay fault that branches from the plate boundary decollement the toe of the accretionary wedge has classically been considered aseismic but vitrinite reflectance geothermometry reveals that the two examined fault zones underwent localized temperatures of more than 380 c this suggests that frictional heating occurred along these two fault zones and implies that coseismic slip must have propagated at least one time to the updip end of the megasplay fault and to the toe of the accretionary wedge

a late cretaceous mixed turbidite contourite system along the uruguayan margin sedimentary and palaeoceanographic implications abstract the late cretaceous is a critical period in the evolution of the south atlantic significant changes in the tectonic configuration of continental landmasses and marine basins during this time lead to major shifts in the sedimentary and oceanographic regimes using a combination of 2d and 3d seismic data with well data from the uruguayan margin this work provides a new highly detailed description of the late cretaceous sedimentary evolution of the margin and its regional and global palaeoceanographic implications the polonio drift system pds occupies the middle to lower slope of the uruguayan margin the pds is characterised by four channel drifts which propagate obliquely 120 170 from the palaeoslope and exhibit over 800 m of local relief relative to the surrounding seafloor seismic interpretation identified four seismic units su 1 su 4 separated by five major discontinuities r 1 r 5 these record the onset albian upper turonian 113 89 8 ma growth coniacian upper maastrichtian 89 8 66 ma and burial paleocene 66 56 ma phases for the pds during the onset stage down slope processes dominate but three major shifts in the sedimentary stacking pattern occur these coincide with palaeoceanographic changes in the south atlantic during the cenomanian turonian 100 5 89 9 ma campanian maastrichtian 83 6 66 ma and paleocene 66 56 ma following the opening of the falkland malvinas agulhas seaway fas the subsidence of the walvis ridge and the opening of the vema channel bottom current influence first occurs during the growth stage coniacian campanian when mounded deposits shift from aggradational and slightly progradational towards the n su 2 to clear lateral migration towards the s su 3 this sedimentary pattern indicates a regional palaeoceanographic shift in bottom current flow from northerly to a subsequent southerly direction bottom currents do not appear to have actively eroded sediment although they apparently had the potential to pirate and entrain fine grained material from turbidity plumes which build on underlying bathymetric features such as basement horsts and channel levees these produce large mounded morphologies adjacent to channels drift growth ceases following the termination of shelf progradation r 4 enabling sluggish bottom currents contributed to a homogeneous sedimentary drape bottom currents intensify in the beginning of the paleocene forming contourite depositional systems with well developed contourite terrace along the middle slope further research can elucidate the nature and mechanics of turbidite contourites interactions along continental margins this work offers new insights for the implications and consequences of the interaction of turbidites and contourites which can improve the characterisation of deep water deposits and understanding palaeoceanographic interpretations

two dimensional seismic reflection modeling of the inferred fossil oceanic crust mantle transition in the bay of islands ophiolite we investigate the origin and character of oceanic moho reflections by computing two dimensional synthetic seismogram profiles of the inferred fossil oceanic crust mantle transition observed in the bay of islands ophiolite to simulate a seismic reflection experiment we calculated near vertical incidence seismograms at a horizontal spacing of 500 m for three separate sections of the ophiolite totaling 64 km in length in the synthetic profiles the moho reflection event varies from a single phase to two or more phases of up to 1 s two way travel time total duration individual phases show lateral variation in amplitude and their two way travel times vary by as much as 0 25 s over horizontal distances as short as 10 km lateral discontinuity of phases results in abrupt variations in the travel times of first arriving high amplitude moho phases the geological structures generating the highest amplitude moho reflections vary from high and low velocity lenses of mafic and ultramafic material in the lower crust and upper mantle to interlayered mafic and ultramafic lithologies in the moho transition zone reflection amplitudes from the residual upper mantle are insignificant and our modeling suggests that using the first arriving high amplitude moho phase to estimate thickness of magmatic material might result in errors of up to 1 s two way travel time 3 4 km multichannel seismic data from both the western pacific and western north atlantic show moho travel time variations similar to those observed in the synthetic profiles the western north atlantic data also show multiphase moho reflection events that are laterally discontinuous on a scale similar to that observed in the synthetic data suggesting that the structures observed in the inferred fossil crust mantle transition of the ophiolite are characteristic of oceanic lithosphere

crustal structure across the colorado basin offshore argentina summary the geology of the wide shelves surrounding the south atlantic is closely linked to the kinematics and history of the opening of the ocean however several wide sedimentary basins which developed along the margins show peculiarities that are not yet understood in the context of the evolution of the south atlantic the colorado basin a wide sedimentary basin on the broad shelf of argentina extends in ew direction the basin s evolution oblique or orthogonal to the continent ocean boundary indicates that it is not a product of simple progressive extension and crustal thinning in addition a basement high paralleling the continental margin and separating the colorado basin from the deep sea basin is a common interpretation these findings are hardly in accordance with the idea that the colorado basin is an extensional basin that developed in conjunction with the early e w opening phase of the south atlantic in the late jurassic early cretaceous the composition type and structure of the basement key points for the evaluation of the basins evolution are widely speculative in this context multichannel seismic reflection data from the argentine shelf and a 665 kmlong onshore offshore refraction profile running across the colorado basin onto the coast are discussed in combination with gravity data the stratigraphy for the sedimentary successions was adopted from the literature and the reflection seismic marker horizons formed besides the interval velocities the input for the starting model for refraction seismic traveltime modelling the modelling strategy was an iterative procedure between refraction seismic traveltime and gravity modelling the preparation of the density models was coarsely orientated on published velocity density relations the modelling results are in favour of a continuation of the main onshore geological features beneath the sedimentary infill of the colorado basin we interpret the basement along the line from west to east as offshore continuation of the ventana hills the

mass transport deposits and geo hazard assessment in the bradano foredeep southern apennines ionian sea abstract seafloor bathymetry combined with multi scale seismic reflection profiles were used to describe the morphostructural setting of the bradano foredeep gulf of taranto northern ionian sea where a submerged portion of the southern apennines is facing the apulia platform in the calabrian arc convergent margin in this complex area marine geophysical data highlight the presence of two mega slide deposits at the shelf slope transition which are most likely the largest ever described in the region these slid masses named the bradano basento megaslide bbms and bradano basento megaslide 1 bbms1 form a mass transport deposit complex mtdc affecting and eroding the topmost portion of the outer apennines deformation front and the apulian foreland ramp it was emplaced in late pleistocene times inside the narrow about 10 km wide bradano foredeep basin a plio pleistocene submarine trough developing at the chain front the youngest of these deposits bbms1 likely predates the last glacial maximum location of the mtdc within the subduction complex suggests that active tectonics and seismic shaking might represent the main triggering mechanisms for gravitative instability in this area although gravitational tectonics and sediment creeping mechanisms cannot be excluded on the other hand size and distribution of the mtdc in the sedimentary record of the bradano foredeep suggest the need of re evaluating the potential for large earthquakes tsunamis and more in general geological hazard related to submarine sliding masses along the coast of this highly populated area

constraints of c o s isotope compositions and the origin of the unlupinar volcanic hosted epithermal pb zn au deposit gumushane ne turkey abstract the eastern pontide orogenic belt epob constitutes one of the best examples of the metallogenic provinces in on the alpine himalayan belt this study focuses on the genesis of the unlupinar pb zn au deposit in the southern part of the eastern pontide orogenic belt the main lithological units in the study area are the early carboniferous kurtoglu metamorphic complex the late carboniferous kose granitoid and the early middle jurassic enkoy formation the studied deposit is hosted by the enkoy formation which consists predominantly of basaltic andesitic rocks and associated pyroclastic rocks that are calc alkaline in composition silicic sulfidic argillic chloritic hematitic carbonate and limonite are the most obvious alteration types observed in the deposit site ore microscopy studies exhibit that the mineral paragenesis in deposits includes pyrite chalcopyrite sphalerite galena gold quartz and calcite electron microprobe analyses conducted on sphalerite indicate that the zn cd ratio varies between 84 and 204 and these ratios point at a hydrothermal deposit related to granitic magmas fluid inclusion studies in calcite and quartz show that the homogenization temperature of the studied deposit ranges between 90 160 c and 120 330 c respectively the values of sulfur isotope analysis of pyrite sphalerite and galena minerals vary between 1 6 and 5 7 and the results of oxygen and carbon isotope analysis range between 8 4 and 18 and 5 and 3 6 respectively the average formation temperature of the ore was calculated as 264 c with a sulfur isotope geothermometer all of the data indicate that the unlupinar deposit is an epithermal vein type mineralization that was formed depending on the granitic magmatism

palaeogeographic consequences of conservational models in the south atlantic ocean conservational models like simple shear pure shear or polyphase models that exclude exchanges between the lower continental crust and upper mantle are usually proposed to explain the lithospheric stretching and consequent crustal thinning of passive continental margins these models need large amounts of horizontal movement and have therefore important implications for plate kinematic reconstructions and intraplate deformation in this paper we propose to show these implications in the central segment of the south atlantic ocean in the angola brazilian system these models imply about 240 km of horizontal movement this movement can be com pensated by two end member mechanisms 1 an intraplate deformation located in africa and 2 an intraplate deformation located in south america we detail for each solution the strong geological and geodynamical implications and discuss the consequences for the genesis of passive continental margins

convective partial melting 1 a model for the formation of thick basaltic sequences during the initiation of spreading stretching and thinning of continental lithosphere during rifting and initiation of seafloor spreading cause upwelling of mantle rocks into a pressure temperature environment where partial melting occurs the amount of melt liberated is however insufficient to account for the thickness of igneous crust emplaced near the continent ocean boundary at some passive margins these igneous structures are known from seismic reflection and deep refraction studies on numerous passive margins worldwide seismic studies also suggest that the transition from continental to oceanic crust on these volcanic margins is relatively abrupt their evolution apparently does not include a prolonged extensional phase preceding the inception of spreading to account for these observations we propose a model for the generation of partial melt in which the lateral temperature contrasts evoked by rifting and asthenospheric upwelling drive convection in the upper mantle deep hot mantle material is transported upward by the convection and hence much larger volumes flow through the region where partial melting occurs than during passive upwelling numerical calculations show that convective partial melting can provide substantial additions to melting due to passive upwelling alone using this model we propose an evolutionary scheme for volcanic passive margins emphasize the contrast with nonvolcanic margins and describe conditions which might lead to the development of both types

reef building and carbonate production modes in the west central tethys during the cenozoic abstract changing components rock textures lithofacies platform types and architecture throughout time are unique characteristics of carbonate rocks characterizing these attributes has been approached by 1 building reference models for specific phanerozoic intervals 2 recognizing the climatic impact in modulating carbonate production and 3 analyzing the influence of changing bio geochemical conditions the reference model approach is mostly based on biological evolution the climatic impact approach emphasizes temperature and the bio geochemical approach considers the changes in mg ca ratios and ca concentrations in the oceans to date however an analysis integrating all of these factors is still missing the analysis presented here includes all these factors but also co 2 which is fundamental for both photosynthesis and caco 3 precipitation here we analyze the waxing and waning of cenozoic reef limestones from the central tethys region through several steps 1 on the basis of rock volume rock textures associated sediments and light dependent skeletal components as records of light penetration and wave energy depth 2 on global environmental conditions 13 c 18 o p co 2 temperature and 3 on the basis of functionality nutritional requirements and available resources through the cenozoic water motion whether induced by surface or internal waves or by currents increased as the thermal gradients strengthened both with depth and with latitude active water motion is essential for plankton catchers such as corals but less so for many larger benthic foraminifers lbf pycnoclines in the meso oligophotic zone would then favor the benthic plankton catchers such as corals but would be detrimental for many lbf warm temperatures favored lbf the eocene lbf families predominated during lowering of atmospheric p co 2 by using respiratory co 2 to enhance the symbiont production of photosynthates under oligotrophic conditions and limited turbulence whereas the miocene families had to adapt to a progressive increase in turbulence the eurythermal coralline red algae however became preponderant producers in the mesophotic zone during times when the 13 c was relatively high this explains two apparent paradoxes 1 corals thrive best when the earth s high latitudes cool and 2 the dominance of corals and lbf is inversely correlated despite they both require tropical conditions and have similar trophic strategies mixotrophy

seafloor morphology of the sumatran subduction zone surface rupture during megathrust earthquakes high resolution multibeam bathymetry data from the sumatran subduction zone reveal the regional and local morphology including small scale fault related features and landslides that may be linked to earthquakes in the recent geological past the accretionary prism is steeply sloped and pervasively eroded with evidence of unusual landward vergence seaward fault dip of the frontal thrusts small scale 5 100 m height fault scarps folds and troughs are common along the seaward edge of the frontal thrust at the deformation front a model of back thrust fault slip or bending moment folding during plate boundary slip such as during the 2004 m9 2 megathrust earthquake can explain the position of these features on the seaward fold limb of a seaward dipping thrust we infer that in major sumatran and other similar settings plate boundary earthquakes coseismic surface rupture may occur at the prism toe

frontal wedge deformation near the source region of the 2011 tohoku oki earthquake 1 we report an uplift of 5 m with a horizontal displacement of more than 60 m due to the 2011 tohoku oki earthquake the uplift was measured by an ocean bottom pressure gauge installed before the earthquake on a frontal wedge which formed an uplift system near the japan trench horizontal displacements of the frontal wedge were measured using local benchmark displacements obtained by acoustic ranging before and after the earthquake the average displacements at the frontal wedge were 58 m east and 74 m east southeast these results strongly suggest a huge coseismic slip beneath the frontal wedge on the plate boundary the estimated magnitude of the slip along the main fault was 80 m near the trench our results suggest that the horizontal and vertical deformations of the frontal wedge due to the slip generated the tremendous tsunami that struck the coastal area of northeastern japan

isotopic and sedimentary signature of megathrust ruptures along the japan subduction margin abstract the m9 3 2004 sumatra and m9 0 2011 tohoku earthquakes and tsunamis had devastating consequences for the adjacent heavily populated coasts they had large shallow coseismic slip that reached the trench which is thought to be a key factor in generating the huge tsunamis the sedimentary record contains unique spatial and temporal information on the effects of megathrust earthquakes it can provide a better understanding of earthquake related tectono sedimentary processes and of the earthquakes themselves we present new results obtained from high resolution multibeam bathymetry subbottom profiles acquired with parasound and ten 10 m long piston cores recently collected from the japan trench margin during r v sonne so251 expedition we identify the 2011 tohoku event deposit extending for 250 km along the japan trench basins from the enrichment and concentrations of short lived radioisotopes excess xs210pb 137cs and 134cs in all ten cores the high enrichment of xs210pb points to surficial sediment remobilization as the main source in three cores from the northern central and southern segments of the japan trench for the first time we identify sediment remobilization by its 87 86sr end and pb isotope signatures and the composition and texture of the sediment with this new approach we fingerprint older sedimentation events potentially linked to earthquakes and infer processes responsible for their deposition thick acoustically transparent and homogeneous units we name homogenites characterize these event deposits physical geochemical and acoustic properties link homogenites to the 2011 tohoku and previous earthquakes we propose a multi stage entrainment and depositional process related with both the high frequency and the exceptionally large low frequency and long duration motions expected from ruptures of the shallow megathrust below the compliant outer upper plate these large long period motions could propagate along the outer upper plate beyond the rupture zone and could generate widespread entrainment of surficial sediment

origin of seaward dipping reflectors in oceanic crust off the norwegian margin by subaerial sea floor spreading a remarkable layered acoustic stratification is observed in the upper oceanic crust adjacent to the norwegian continental margin it comprises a seaward dipping complex of reflectors in the form of a wedge we suggest that it is a layered igneous sequence that results when crustal accretion occurs at a subaerial spreading axis and that this phenomenon may commonly occur during the earliest phase of ocean basin genesis

the crustal structure of the southern argentine margin summary multichannel reflection seismic profiles combined with gravimetric and magnetic data provide insight into the crustal structure of the southernmost argentine margin at the transition from a rifted to a transform margin and outline the extent of the north falkland graben based on these data we establish a regional stratigraphic model for the post rift sediments comprising six marker horizons with a new formation in the barremian lower cretaceous our observations support that a n s trending subsidiary branch of the north falkland graben continues along the continental shelf and slope to the argentine basin during the rift phase a wide shelf area was affected by the e w extension subsequently forming the north falkland graben and the subsidiary branch along which finally breakup occurred we propose the division of the margin in two segments a n s trending rifted margin and an e w trending transform margin this is further underpinned by crustal scale gravity modelling three different tectono dynamic processes shaped the study area 1 the triassic early jurassic extensional phase resulting in the formation of the north falkland graben and additional narrower rift grabens ended synchronously with the breakup of the south atlantic in the early valanginian 2 extensional phase related to the opening of the south atlantic 3 the transform margin was active in the study area from about hauterivian times and activity lasted until late cretaceous early cenozoic both the rifted margin and the transform margin are magma poor very limited structures may have a volcanic origin but are suggested to be post rift the oceanic crust was found to be unusually thin indicating a deficit in magma supply during formation these findings in combination with the proposed breakup age in the early valanginian that considerably predates the formation of the parana etendeka continental flood basalt provinces in brazil and namibia question the influence of the tristan da cunha hotspot during the initial formation of the south atlantic

multivariate statistical and multiproxy constraints on earthquake triggered sediment remobilization processes in the central japan trench understanding the impact of earthquakes on subaqueous environments is key for submarine paleoseismological investigations seeking to provide long term records of past earthquakes for this purpose event deposits e g turbidites are among others identified and stratigraphically correlated over broad areas to test for synchronous occurrence of gravity flows hence detailed spatiotemporal petrographic and geochemical fingerprints of such deposits are required to advance the knowledge about sediment source and the underlying remobilization processes induced by past earthquakes in this study we develop for the first time in paleoseismology a multivariate statistical approach using x ray fluorescence core scanning magnetic susceptibility and wet bulk density data that allow to test confirm and enhance the previous visual and lithostratigraphic correlation across two isolated basins in the central japan trench the statistical correlation is further confirmed by petrographic heavy grain analysis of the turbidites and additionally combined with our novel erosion model based on previously reported bulk organic carbon 14c dates we find surficial sediment remobilization a process whereby strong seismic shaking remobilizes the uppermost few centimeters of surficial slope sediment to be a predominant remobilization process which partly initiates deeper sediment remobilization downslope during strong earthquakes at the japan trench these findings shed new light on source to sink transport processes in hadal trenches during earthquakes and help to assess the completeness of the turbidite paleoseismic record our results further suggest that shallow buried tephra on the slope might significantly influence sediment remobilization and the geochemical and petrographic fingerprints of the resulting event deposits

kinematic keys of the santos namibe basins understanding the genesis of the very peculiar 600 km wide santos basin sa o paulo plateau system and its narrow conjugate namibe margin is a kinematic and structural problem several hypotheses have been proposed in order to explain the genesis of this system that imply the same amount of horizontal movement we investigate the consequences of the horizontal movement in the santos basin based in plate kinematic reconstructions the kinematic history of this system that we present here based on the interpretation of seismic profiles and kinematic constraints has the following consequences 1 there is no evidence of a ridge jump sensu stricto but rather a southwards propagation in the central segment of the south atlantic that starts in the northern part between the ne brazilian and gabonese margins 2 the namibe margin evolved as a transform passive margin 3 the opening direction of the santos basin sa o paulo plateau system is oblique to the general opening motions of the south american and african plates and 4 this opening is younger 6 ma than those of the other basins of the central segment of the south atlantic

potential tsunamigenic submarine landslides in active margins abstract a review of modern historical and submarine landslides from the geological record shows that landslides in active continental margins can generate tsunamis the tsunamis may damage coastal and seabed infrastructure and so represent an important element of marine geohazards research due to their potentially significant impacts on society the primary trigger mechanism of tsunamis in this type of setting was thought to be earthquake activity however there are also a number of alternative hypotheses regarding the likely initiation mechanism including the generation of submarine landslides in this paper we briefly review the geological features and trigger mechanisms of tsunamigenic submarine landslides on active margins large tsunamigenic submarine landslides appear to occur mostly on margins characterized by non accretion these observations have implications for tsunami warning systems as the japanese system does not consider the scenario of tsunami excitation by submarine landslides

ophiolites synthetic seismograms and ocean crustal structure 1 comparison of ocean bottom seismometer data and synthetic seismograms for the bay of islands ophiolite a series of synthetic seismograms based on the bay of islands ophiolite data are compared with ocean bottom seismometer seismic refraction observations which sample 60 m y crust in the northeastern pacific the general agreement between the synthetics for the ophiolite and the observations support the idea that some ophiolites are representative of normal ocean crust this support extends to similarities in complex second arrivals in the synthetics and observations which often are not used in the interpretation of marine seismic data the use of the ophiolite model also allows us to show how the interpretation of seismic data is affected by experimental design and interpretation procedures as the sampling density increases and as more phases in the observations are accounted for the velocity depth model more closely approaches that found for the ophiolite the results of this modeling support sharper p velocity transitions within the crust than are found in young 12 m y age oceanic crust the need for a thin approximately 1 km thick p low velocity zone at the base of the crust is interpreted as support for serpentinization at the crust mantle boundary serpentinization of the ultramafic component in the bay of islands ophiolite therefore may include a small preemplacement component

magmatism at rifted continental margins the intense volcanism and uplift observed on many rifted continental margins forming basaltic seaward dipping reflector sequences is accompanied by the emplacement of a thick igneous section at depth partial melting by decompression of passively upwelling asthenosphere that is hotter than normal because it is near a hotspot explains both the thickness of the new igneous crust and the initial elevation of the rifted margins

updip rupture of the 2004 sumatra earthquake extended by thick indurated sediments sediments accumulated in a subduction trench are usually unconsolidated and impede the updip propagation of fault rupture during an earthquake seismic images of the southern sumatra andaman trench reveal blocks of consolidated sediment that may have enabled fault rupture in 2004 to propagate up fault dip thus further seaward increasing the tsunami magnitude

tsunami triggered dispersal and deposition of microplastics in marine environments and their use in dating recent turbidite deposits microplastics have become widely dispersed throughout the marine environment in and around japan since the 1960s which correspond to the onset of mass plastic production and use in this country our study documents a possible abrupt microplastics depositional event in continental shelf and deep sea environments triggered by a tsunami the sediment layers contaminated by microplastics correspond with sedimentary horizons where 137cs signals were measured indicating deposition after 1960s nuclear tests the microplastics were observed in the 2011 tohoku oki tsunami deposits tsunamis can thus contribute to the wide dispersal of microplastics from coastal to deep sea areas and these anthropogenic particles can be used to date very recent turbidite deposits

meteoric 10 be reveals a young active accretionary prism and structurally complex decollement in the vicinity of the 2011 tohoku earthquake rupture

age progressive volcanism in the new england seamounts and the opening of the central atlantic ocean radiometric ages k ar and oar 39ar methods have been determined on dredged volcanic rocks from seven of the new england seamounts a prominent northwest southeast trend ing volcanic lineament in the northwestern atlantic ocean the oar 39ar total fusion and increnental heating ages show an increase in seamount construction age from southeast to northwest that is consistent with northwestward motion of the north american plate over a new england hot spot between 103 and 82 ma a linear volcano migration rate of 4 7 cm yr fits the seamount age distribution these ages fall within a longer age progression from the corner seamounts 70 to 75 ma at the eastern end of the new england seamounts to the youngest phase of volcanism in the white mountain igneous province new england 100 to 124 ma the new england hot spot estimated from the new radio metric ages and motion of north america in the hot spot reference frame to be near 28on 33ow probably generated a short line of mid to late tertiary age seamounts on the african plate but appears to be presently inactive the hot spot reference frame is used to calculate the motion of the north american plate away from the african plate from early cretaceous time to the present rominent magnetic anomalies recorded in the central atlantic seafloor give the positions of the spreading ridge for a bange of known ages hot spots that now underlie the african plate in the eastern central atlantic new england canary madeira cape verde azores could have produced cretaceous seamount and island chains on the north american plate during the early opening of the central atlantic each of these hot spots has been overridden by spreading ridges at pre dictable times some of these hot spot crossings are expressed as geochemical anomalies in the oceanic crust now far removed from spreading ridges

the argentine continental margin north of 48 s sedimentary successions volcanic activity during breakup abstract new seismic data and geophysical results from the outer argentine continental margin and from seismic flow line transects across the oceanic argentine brazil and cape angola basins are presented the results document that the early cretaceous south atlantic continental breakup and initial sea floor spreading were accompanied by large scale transient volcanism emplacing voluminous extrusive constructions on the conjugate outer continental margins of the south atlantic on the argentine margin we interpret three major tectono volcanic crustal units beneath a thick and tectonically undisturbed sedimentary succession of cretaceous and tertiary age 1 syn rift basins and even pre rift features are present on the outer shelf 2 a deeply buried 60 120 km wide and several thousand metres thick volcanic wedge occupies most of the slope the wedge is characterized by seaward dipping reflectors and is associated with the distinct magnetic anomaly g 3 the seaward adjacent oceanic crust of cretaceous age shows isochronous changes of the seismic images along our flow line transects suggesting some form of episodicity of rich magma and poor to moderate magma supply at the pre existing mid ocean ridge of the south atlantic during cretaceous time

probabilistic hazard of tsunamis generated by submarine landslides in the cook strait canyon new zealand cook strait canyon is a submarine canyon that lies within ten kilometres of wellington the capital city of new zealand the canyon walls are covered with scars from previous landslides which could have caused local tsunamis palaeotsunami evidence also points to past tsunamis in the wellington region furthermore the canyon s location in cook strait means that there is inhabited land in the path of both forward and backward propagating waves tsunamis induced by these submarine landslides pose hazard to coastal communities and infrastructure but major events are very uncommon and the historical record is not extensive enough to quantify this hazard the combination of infrequent but potentially very consequential events makes realistic assessment of the hazard challenging however information on both magnitude and frequency is very important for land use planning and civil defence purposes we use a multidisciplinary approach bringing together geological information with modelling to construct a probabilistic tsunami hazard assessment of submarine landslide generated tsunami although there are many simplifying assumptions used in this assessment it suggests that the cook strait open coast is exposed to considerable hazard due to submarine landslide generated tsunamis we emphasise the uncertainties involved and present opportunities for future research

south atlantic volcanic margins the early cretaceous south atlantic continental break up and initial sea floor spreading were accompanied by large scale transient volcanism emplacing the parana etendeka continental flood basalts and voluminous extrusive constructions on the conjugate margins south of the torres arch abutment plateau on the north namibia margin we interpret four main tectono magmatic crustal units 1 oceanic crust 2 thickened oceanic crust covered by huge seaward dipping wedges 3 a c 150 km wide break up related rift zone partly covered by the dipping wedges and 4 thicker continental crust partly deformed by palaeozoic extension east of the early cretaceous rift similar settings also characterize other south atlantic margin segments we infer an up to 300 km wide and 2400 km long rift zone representing lithospheric extension leading to breakup and formation of the south atlantic volcanic margins comparison with other volcanic margins demonstrates in spite of local and regional differences gross similarities in tectono magmatic style crustal units and dimensions

documenting large earthquakes similar to the 2011 tohoku oki earthquake from sediments deposited in the japan trench over the past 1500 years abstract the 2011 tohoku oki earthquake and tsunami was the most destructive geohazard in japanese history however little is known of the past recurrence of large earthquakes along the japan trench deep sea turbidites are potential candidates for understanding the history of such earthquakes core samples were collected from three thick turbidite units on the japan trench floor near the epicenter of the 2011 event the uppermost unit unit tt1 consists of amalgamated diatomaceous mud 30 60 cm thick that deposited from turbidity currents triggered by shallow subsurface instability on the lower trench slope associated with strong ground motion during the 2011 tohoku oki earthquake older thick turbidite units units tt2 and tt3 also consist of several amalgamated subunits that contain thick sand layers in their lower parts sedimentological characteristics and tectonic and bathymetric settings of the japan trench floor indicate that these turbidites also originated from two older large earthquakes of potentially similar to the 2011 tohoku oki earthquake a thin tephra layer between units tt2 and tt3 constrains the age of these earthquakes geochemical analysis of volcanic glass shards within the tephra layer indicates that it is correlative to the towada a tephra ad 915 from the towada volcano in northeastern japan the stratigraphy of the japan trench turbidites resembles that of onshore tsunami deposits on the sendai and ishinomaki plains indicating that the cored uppermost succession of the japan trench comprises a 1500 yr old record that includes the sedimentary fingerprint of the historical jogan earthquake of ad 869

tsunami source uncertainty estimation the 2011 japan tsunami this article was published in the journal of geophysical research solid earth 2016 american geophysical union and the definite version is available at http dx doi org 10 1002 2015jb012764 the journal s website is at http onlinelibrary wiley com doi 10 1002 2015jb012764 abstract jsessionid bf5813b61924fb094f31bc8f213840a1 f02t04

crustal structure of the southeast georgia embayment carolina trough preliminary results of a composite seismic image of a continental suture and a volcanic passive margin new deep penetration multichannel seismic reflection data combined with refraction results and magnetics modeling support a hypothesis that the carolina trough is a mesozoic volcanic passive margin exhibiting a seaward dipping wedge and associated underplating the structure of carolina platform continental crust is consistent with the late paleozoic continental collision that produced the appalachians but imbrication has had no obvious effect on shallower structures produced by mesozoic extension and volcanism the origin of prominent magnetic anomalies crossing the southeast georgia embayment can be explained by processes attending mesozoic separation of africa and north america and is not related to a paleozoic continental suture as previously postulated

backward modelling of the subsidence evolution of the colorado basin offshore argentina and its relation to the evolution of the conjugate orange basin offshore sw africa abstract in this study we focus on reconstructing the post rift subsidence evolution of the colorado basin offshore argentina we make use of detailed structural information about its present day configuration of the sedimentary infill and the crystalline crust this information is used as input in a backward modelling approach which relies on the assumption of local isostasy to reconstruct the amount of subsidence as induced by the sedimentary load through different time stages we also attempt a quantification of the thermal effects on the subsidence as induced by the rifting here included by following the uniform stretching model of lithosphere thinning and exponentially cooling through time based on the available information about the present day geological state of the system our modelling results indicate a rather continuous post rift subsidence for the colorado basin and give no significant evidence of any noticeable uplift phase in a second stage we compare the post rift evolution of the colorado basin with the subsidence evolution as constrained for its conjugate sw african passive margin the orange basin despite these two basins formed almost coevally and therefore in a similar large scale geodynamic context their post rift subsidence histories differ based on this result we discuss causative tectonic processes likely to provide an explanation to the observed differences we therefore conclude that it is most probable that additional tectonic components other than the ridge push from the spreading of the south atlantic ocean are required to explain the observed differences in the subsidence of the two basins along the conjugate passive margins such additional tectonic components might be related to a dynamic mantle component in the form of either plume activity africa or a subducting slab and the presence of an ongoing compressional stress system as revealed for different areas in south america