the influence of shelf crossing glaciation on continental slope sedimentation flemish pass eastern canadian continental margin abstract flemish pass is a small perched slope basin seaward of the grand banks on the eastern canadian continental margin glacial ice crossed the grand banks to reach the upper continental slope during some mid to late quaternary glaciations but terminated on the middle shelf 200 km distant at the last glacial maximum this study investigates the effect of ice extent on slope sedimentation processes sediment in flemish pass comprises muds of hemipelagic and proglacial plume origin minor thin bedded turbidite sands and thick bedded mass transport deposits mtds a regional stratigraphy based on 500 km of high resolution seismic profiles and 60 piston cores up to 11 m long was dated using 30 radiocarbon dates the presence of ash zone ii and oxygen isotope stratigraphy this provided stratigraphic control for till tongues in water depths

soft sediment deformation in the shallow submarine slope off nice france as a result of a variably charged pliocene aquifer and mass wasting processes abstract along the ligurian slope near nice southeastern france a combination of natural and man made factors govern slope stability and contributed to a devastating tsunamigenic landslide near nice airport in 1979 based on a total of 72 gravity and kullenberg cores we characterise the architecture and facies of the subbottom sediment a total of six sedimentary facies types were observed three of which represent the pliocene holocene background sediment in the wider nice area while another three are associated with the 1979 landslide and tsunami the three primary facies types are soft silty clay clayey silt somewhat indurated silt sand interbeds and pliocene conglomerates underlying the former the three other facies are poorly sorted mass wasting deposits up to pebble size silt representing the finer fraction of the mobilised mass and a tsunami related bed into which plant debris and artefacts got amalgamated accompanying geotechnical results attest that significant strength variations exist when comparing measurements from the narrow shelf shelf break and shallow slope as well as the 1979 slide scar factors such as groundwater charging in the more permeable horizons further lower the effective stress and in places approach lithostatic above such permeable silt sand beds deformation of soft clay is observed suggesting that leaching of ions from the clay mineral surfaces and frayed edges also facilitates weakening and creep micro slumping and folding elevated water supply as well as hydraulic fracturing of the clayey sediment is further attested by pipes of cm diameter and several decimeters length which entrained very soupy mud in the shallowmost deposits in and landward of the slide scar we also observe remnants from the catastrophic deposition associated with the 2 3 m high tsunami wave triggered in 1979 as attested by amalgamated sea grass and artefacts based on our observations and measurements on core scale and earlier models based on in situ cptu we suggest that a significant part of the quaternary delta and slope apron deposits are prone to being mobilised without a large external trigger so that all in all a high risk for a landslide event of considerable size off nice international airport is identified

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

correlation between rate of sea level change and frequency of explosive volcanism in the mediterranean volcanic activity has frequently been linked to quaternary environmental change either by driving climate modification1 2 or in response to environmental changes3 although a link has been established between large explosive eruptions and small 0 5 c brief 1 2 years falls in global temperatures4 both the evidence and mechanisms responsible for longer episodes of eruption induced planetary cooling remain questionable1 2 5 6 in contrast recent research based on ice core data suggests that rapid climate changes during the past 110 000 years increased explosive volcanic activity7 here we present a statistical analysis relating the frequency of explosive activity of mediterranean volcanoes based on dated8 9 10 11 tephra layers in deep sea sediment cores to the rate of late quaternary sea level change the nonlinear correlation between the two is tentatively explained in terms of dynamic responses of the volcanoes to stress related influences on various spatial scales the correlation supports a mechanism or mechanisms by which the climate driven growth and decay of large ice sheets can influence the eruptive chronologies of distant volcanic edifices via changes in global sea level

inferred gas hydrates and clay diapirs near the storegga slide on the southern edge of the voring plateau offshore norway this paper presents a new data set including single channel airgun seismic lines okean long range side scan sonar data and gravity cores acquired on the edge of the voring plateau and in the region of the storrega slide the data acquisition was part of the 8th training through research ttr 8 expedition with r v professor logachev the acoustic profiles clearly show two laterally separated zones characterised by the presence of bottom simulating reflectors bsrs at about 350 ms twt subbottom depth the lower bsr zone is located on the slope of the voring plateau in the immediate vicinity of the northern headwall of the storegga slide and in some places below the slide deposits this zone runs parallel to the general trend of the continental slope the spatial distribution of the upper bsr zone located upslope in an area where diapir like structures are found does not demonstrate any topographic control interpretation of high backscatter patches on the okean sonographs associates the observed structures with fluid escape features on the seabed most of them are pockmarks but in a few places diapirs are cropping out and form dome like elevations after analysing the behaviour of the bsr sometimes crosscutting and its acoustic characteristics reversed polarity and after applying seismic inversion processing to estimate the acoustic velocity change across the bsr this reflector is interpreted to represent the base of the local gas hydrate stability field ghsf this information was used to derive the regional geothermal gradient spatial variations of the inferred geothermal field appeared to be negligible the observation of two separated bsr zones suggests different environmental controls for the growth of the hydrates enhanced reflectors observed in the intermediate zone can be explained by the presence of strata bound free gas accumulations and migration combined with overlying permeability barriers therefore a model for gas hydrate formation in relation to directional fluid migration processes fluid escape features and the presence of diapiric structures is proposed in this paper our model is supported by sedimentological analyses of seafloor samples which demonstrate the presence of stiff clays with evidence of gas migration and by paleontological studies of the cores retrieved from the pockmarks the presence of a bsr in the sedimentary section within the slide scar area implies the repositioning of hydrates to newly established equilibrium conditions after the slide event this observation allows us to simply estimate an upper limit of the fluid migration velocity in the order of several cm year finally the effect of hydrate dissociation on slope instability is considered assuming that the in situ decomposition of hydrates due to instantaneous depressurisation is slow enough to permit the excess volume of released gas and water to be re distributed through the whole sedimentary section above the paleo bsr with consuming heat and increasing pore pressure dissociation tends to shift the pt conditions back to equilibrium values it appears that the dissociation of hydrates due to sliding would cause only 0 2 increase of the pore pressure which would hardly contribute to further slope instability

generalization of gas hydrate distribution and saturation in marine sediments by scaling of thermodynamic and transport processes gas hydrates dominated by methane naturally occur in deep marine sediment along continental margins these compounds form in pore space between the seafloor and a sub bottom depth where appropriate stability conditions prevail however the amount and distribution of gas hydrate within this zone and free gas below can vary significantly at different locations to understand this variability we develop a one dimensional numerical model that simulates the accumulation of gas hydrates in marine sediments due to upward and downward fluxes of methane over time the model contains rigorous thermodynamic and component mass balance equations that are solved using expressions for fluid flow in compacting sediments the effect of salinity on gas hydrate distribution is also included the simulations delineate basic modes of gas hydrate distribution in marine sediment including systems with no gas hydrate gas hydrate without underlying free gas and gas hydrate with underlying free gas below the gas hydrate stability zone for various methane sources the results are scaled using combinations of dimensionless variables particularly the peclet number and damkohler number such that the dependence of average hydrate saturation on numerous parameters can be summa rized using two contour maps one for a biogenic source and one for upward flux from a deeper source simulations also predict that for systems at steady state large differences in parameters like seafloor depth seafloor temperature and geothermal gradient cause only small differences in average hydrate saturation when examined with scaled variables although important caveats exist our model presents a unified picture of hydrate accumulations that can be used to understand well characterized gas hydrate systems or to predict steady state average hydrate saturation and distribution at locations for which seismic or core data are not available

the early holocene sea level rise the causes anatomy and consequences of the early holocene sea level rise ehslr are reviewed the rise of ca 60m took place over most of the earth as the volume of the oceans increased during deglaciation and is dated at 11 650 7000 cal bp the ehslr was largely driven by meltwater release from decaying ice masses and the break up of coastal ice streams the patterns of ice sheet decay and the evidence for meltwater pulses are reviewed and it is argued that the ehslr was a factor in the ca 8470 bp flood from lake agassiz ojibway patterns of relative sea level changes are examined and it is argued that in addition to regional variations temporal changes are indicated the impact of the ehslr on climate is reviewed and it is maintained that the event was a factor in the 8200 bp cooling event as well as in changes in ocean current patterns and their resultant effects the ehslr may also have enhanced volcanic activity but no clear evidence of a causal link with submarine sliding on continental slopes and shelves can yet be demonstrated the rise probably influenced rates and patterns of human migrations and cultural changes it is concluded that the ehslr was a major event of global significance knowledge of which is relevant to an understanding of the impacts of global climate change in the future

geochemical evidence for a large methane release during the last deglaciation from marmara sea sediments abstract recent methane inventories have revealed the potential impact of gas hydrates on the global carbon cycle and hence in climate change milkov 2004 however only a few studies have traced methane release in the geologic record here we show geochemical evidence for a large scale methane release at mid latitudes during the last deglaciation the sea of marmara an enclosed sea between the mediterranean and black seas is located in a tectonically active basin with gas hydrate expulsion and the formation of shallow gas hydrates since depths in the basin are shallower than 1100 m future global temperatures are expected to have a great influence in destabilizing methane clathrates among the suite of biomarkers we have focused on diplopterol and diploptene profiles in core md012430 retrieved from the central basin in the marmara sea our results indicate that during the last 15 000 years hopanoids showed important concentration variations with a pronounced peak during the deglaciation the lack of a relationship between diplopterol diploptene and phytoplanktonic biomarker concentrations as well as a depleted isotopic composition have linked the hopanoid maxima to methanotrophic activity suggesting that an intense methane release occurred at the onset of deglaciation in the marmara sea the vulnerability of the hydrate stability zone to changes in temperature and pressure under this range of shallow water depths as well as the relative timing of the hopanoid maxima and sea surface temperature rise points to thermal destabilization of hydrates as a trigger for methane release in the water column

character paleoenvironment rate of accumulation and evidence for seismic triggering of holocene turbidites canada abyssal plain arctic ocean abstract four box cores and one piston core show that holocene sedimentation on the southern canada abyssal plain for the last 8010 120 yr has consisted of a continuing rain of pelagic organic and ice rafted clastic sediment with a net accumulation rate during the late holocene of 10 mm 1000 yr and episodically emplaced turbidites 1 5 m thick deposited at intervals of 830 to 3450 yr average 2000 yr the average net accumulation rate of the mixed sequence of turbidites and thin pelagite interbeds in the cores is about 1 2 m 1000 yr physiography suggests that the turbidites originated on the mackenzie delta or its clinoform and 13c values of 27 to 25 in the turbidites are compatible with a provenance on a delta extant displaced neritic and lower slope to basin plain calcareous benthic foraminifers coexist in the turbidite units their joint occurence indicates that the turbidites originated on the modern continental shelf and entrained sediment from the slope and rise enroute to their final resting place on the canada abyssal plain the presence of middle pleistocene diatoms in the turbidites suggests in addition that the turbidites may have originated in shallow submarine slides beneath the upper slope or outer shelf small but consistent differences in organic carbon content and 13c values between the turbidite units suggest that they did not share an identical provenance which is at least compatible with an origin in slope failures the primary provenance of the ice rafted component of the pelagic beds was the glaciated terrane of northwestern canada and the provenance of the turbidite units was pleistocene and holocene sedimentary deposits on the outer continental shelf and upper slope of the mackenzie delta largely local derivation of the sediment of the canada abyssal plain indicates that sediment accumulation rates in the arctic ocean are valid only for regions with similar depositional sources and processes and that these rates cannot be extrapolated regionally the location of an elliptical zone of active seismicity over the inferred provenance of the turbidites suggests that they were triggered by large earthquakes distal turbidite sediment accumulation rates were more than two orders of magnitude greater than pelagic sediment accumulation rates on the canada abyssal plain during the last 8000 years this disparity reconciles the discrepancy between the high accumulation rates assumed by some for the arctic ocean because of the numerous major rivers and large ice sheets that discharge into this small mediterranean basin and the low pelagic sedimentation rates that have been reported from the arctic ocean

foraminiferal isotope anomalies from northwestern pacific marginal sediments 1 we evaluated the influence of methane release from methane hydrate reservoirs in the northwestern pacific continental margin on stable isotope values we analyzed stable isotopes of foraminifera from a piston core collected at 1066 m water depth off eastern hokkaido northern japan carbon isotope signals indicated that planktonic and benthic foraminifera in several glacial sediment layers in the core were highly depleted in 13c both the planktonic and benthic foraminiferal 13c values ranged from about 10 to 2 most foraminiferal tests in these horizons were brown as a result of postdepositional alteration foraminiferal oxygen isotopes fluctuated abnormally in the glacial sediment layers showing small about 0 5 positive shifts relative to normal glacial values we attributed the positive shifts to authigenic carbonate formation in the foraminiferal tests the authigenic carbonates have formed when rising methane from methane hydrate in the sediment became oxidized as it came in contact with dissolved sulfate near the seafloor episodic methane release events may be associated with great plate boundary earthquakes with epicenters near the coring site

deglacial and postglacial sedimentary architecture in a deeply incised paleovalley paleofjord the pennsylvanian late carboniferous jejenes formation san juan argentina quebrada de las lajas near san juan argentina preserves an early pennsylvanian deglacial postglacial succession in a highly confined paleofjord setting the sedimentary succession records four distinct stages in the evolution of the valley fill stage 1 is represented by the deposits of subglacial diamictites ice contact deltas and related deep water lacustrine environments including several subaqueous channels stage 2 records a glacio eustatic marine transgression and a slow down of the clastic supply into the paleofjord stage 3 records a sandy confined turbidite environment stage 4 consists of a coarse grained delta which represents a significant rejuvenation of the sedimentary system in the paleofjord the transition from stage 1 to stage 2 was abrupt and basinwide and has proven to be a good regional correlation marker in this paleovalley the glacio eustatic rise probably caused floating and consequent rapid melting of the valley glacier this resulted in a paleovalley wide turbidite event that is up to 5 m thick and indicates an overall waning character the rapid sediment emplacement in this event and resulting loading of the paleovalley sediments may have helped cause widespread mass transport events at the stage 1 2 boundary all stages show evidence of mass transport related deposits but stage 1 records the most widespread mass transport with a large spectrum of processes represented including coherently slumped material rafted blocks and completely mixed debris flow deposits these mass transport deposits range from a few meters to over 50 m thick and up to hundreds of meters wide and long most of the large mass transport deposits in the lower part of the fjord fill occurred at the transition to stage 2 implicating a rise in relative sea level as a possible trigger for the slope failures additionally stage 3 deposits were affected by several thrust sense dislocations that have large offsets relative to the scale of the sedimentary succession tens to over 50 m vertically and hundreds of meters laterally strata associated with the dislocations exhibit growth indicating very early movement and they are interpreted as the frontal ramp zones of mass transport deposits the abundance and size of mass transport deposits in stages 1 and 3 helped control sediment pathways throughout the paleofjord

changes in the atmospheric ch4 gradient between greenland and antarctica during the last glacial and the transition to the holocene significant variations in the interpolar difference of atmospheric ch4 concentration over the holocene period were observed by chappellaz et al 1997 here we extend this study to the last glacial and the transition to the holocene we observe a gradient of 3 4 parts per billion by volume ppbv during the last glacial maximum it increases to 26 10 ppbv during the bolling allerod and remains at 26 9 ppbv during the younger dryas cold period on average we find an interpolar difference of 14 4 ppbv during the cold phases and of 37 10 ppbv during the warm periods of the last glacial with a three box model we derive from the measured gradients the contributions of methane from the tropics and the mid to high latitudes of the northern hemisphere the tropics have been the largest source in all glacial epochs the contribution by the northern latitudes have been very small during the last glacial maximum but surprisingly large during the earlier part of the glacial epoch the model result suggests completely unexpected that the higher atmospheric ch4 concentration during the warm dansgaard oeschger events are caused by a higher source strength of the northern latitudes and not of the tropics

relative timing of the storegga submarine slide methane release and climate change during the 8 2 ka cold event this paper highlights the similarity in the timing between the 8 2 ka cold event across the north atlantic region and one of the world s largest underwater slides the storegga submarine landslide that took place on the continental slope west of norway we argue on the basis of a reinterpretation of the age of tsunami deposits that date the slide as well as published ages of sediment directly resting upon the slide surface that the slide occurred between 8100 and 8200 cal yr near the end of the 8 2 ka cold event because sediment exposed at the base of the slide contained less methane gas hydrate c 8200 years ago than exists today and because greenland ice cores do not show an increase in methane at the time of the slide it is argued here that the slide did not release significant volumes of methane to the atmosphere and did not contribute to any change in temperature during or after the 8 2 ka cold event

did two massive earthquakes in the holocene induce widespread landsliding and near surface deformation in part of the ottawa valley canada recent evidence based on ages of large landslides and the existence of severely disturbed terrain in champlain sea sediments to the east of ottawa suggests that this area may have been the site of two of the most geologically destructive earthquakes in eastern canada the walls of several paleochannels downcut into sensitive marine clayey silts are scarred by numerous large earthflows of sizes unequaled in historical time while radiocarbon ages of 15 landslides as much as 35 km apart range from ca 1870 to 5130 yr b p the majority of events cluster at ca 4550 yr b p the coincidence of numerous large failures in different paleovalleys occurring concurrently long after channel abandonment and at a time of drier climate suggests that the widespread landsliding was triggered by a strong earthquake close to the landslide area areas of very disturbed terrain in a flat erosional plain show severely deformed bedding and irregular ground subsidence and are attributed to a large earthquake ca 7060 yr b p that strongly shook a thick sequence of sensitive material filling deep steep sided bedrock basins

on the architecture of intra formational mass transport deposits insights from the carbonate slopes of great bahama bank and the apulian carbonate platform abstract large sub tropical carbonate platforms shed huge volumes of sediment onto their adjacent slopes resulting carbonate successions are comprised of gravity flow beds turbidites debrites which are occasionally reworked into mass transport deposits mtds by the failure of inconsistently lithified portions of slope strata despite their significance in the depositional record the internal architecture of mtds along relatively tectonically stable and sediment producing carbonate platforms is poorly understood in comparison with counterparts in active compressional tectonic settings this study compares carbonate slope derived mtds imaged in seismic reflection data with those observed in outcrop the internal architecture of mtds from two case studies is presented the seismically imaged mtds in miocene recent carbonate slope deposits from the bahamas and mtds off the cretaceous apulian carbonate margin exposed in outcrops of the ionian basin albania understanding the large scale kilometers to tens of kilometers internal architecture of mtds in seismic is crucial for identification of these structures in outcrop in turn only outcrop studies allow the detailed analysis of the reworking style within these massive sediment bodies at a smaller scale meters to kilometers the internal architecture of the studied carbonate mtds testifies to the existence of an along slope continuum of deformation structures characterized by vertical partitioning into distinct mass flows during single mass transport events mass wasting processes are inferred from strain partitioning structures recording along slope and slope parallel architectural heterogeneities three deformation domains are recognized extensional headwall domain translational body domain and contractional toe domain confined mtds are limited by steep and deep lateral margins and frontal ramps that mark the boundaries between failed deposits and undisturbed strata vertical strain partitioning is pronounced in the toe domain upward intensification of deformation within mtds is common and corresponds to a top down reorganization of failed strata during downslope transport intra formational mtds along carbonate slopes that are lacking exotics such as the ones studied here differ from extra formational mtds occurring in compressional tectonic settings that form sedimentary melanges ductile layer deformation structures are predominant in carbonate mtds as opposed to block in matrix fabrics in sedimentary melanges the development of shear surfaces rather than ductile shear zones in the body and toe domains presents predictive in modern environments and diagnostic criteria in fossil examples of mass wasting events along carbonate slopes

the andoya slide and the andoya canyon north eastern norwegian greenland sea based on gloria side scan sonar imagery echo sounder records 3 5 khz profiles multichannel seismics and gravity cores the andoya slide and andoya canyon north eastern norwegian greenland sea were mapped and interpreted the andoya slide covers an area of about 9700 km2 of which the slide scar area comprise ca 3600 km2 the slide has a total run out distance of about 190 km slope failure is inferred to have occurred during the holocene because the slide scar has prominent relief on the present sea floor the area of sediment removal is characterised by an irregular relief were relatively consolidated sediments are exposed at the sea floor little or no unconsolidated sediments overlies the slide deposits earthquake activity is inferred to have triggered the slide a holocene age of the andoya slide implies that three giant slides the storegga traenadjupet and andoya slides have occurred along the continental slope of norway during the last 10 000 years a large canyon the andoya canyon is located immediately south of the andoya slide on the upper slope the canyon has been incised about 1000 m in the bedrock and the maximum width at the bottom and between the canyon shoulders is 2 and 12 km respectively the andoya canyon represents the upper part of the lofoten basin channel based on analogy with other deep sea canyon channel systems the andoya canyon lofoten basin channel is possibly of pre quaternary age holocene sediments recovered from within the canyon and draping the flanking channel deposits indicate that the andoya canyon is not presently active and has probably not been active during the holocene during the holocene the canyon acted as a trap for sediments settling from the winnowing norwegian current

u th dating of cold seep carbonates an initial comparison authigenic carbonates from hydrocarbon seeps are unique archives of past seepage and associated environmental parameters in order to constrain the ages of a set of seep carbonates and the time involved in carbonate formation we applied uranium thorium u th dating to samples from the gulf of mexico the congo fan and the black sea the resulting u th ages indicate that environmental conditions must have been favorable for enhanced methane rich fluid seepage during the time intervals of 53 4 to 1 7 ka bp for the gulf of mexico and 45 5 to 3 0 ka bp for the congo fan the seep carbonates from the black sea formed at 1 6 to 1 1 ka bp our results suggest that enhanced fluid flow during these time intervals was closely related to 1 sea level variations associated with glacial interglacial cycles and 2 environmental alterations in the course of late quaternary climate change including variations in bottom water temperatures that affected the stability of gas hydrate reservoirs

late quaternary turbidite emplacement on the horseshoe abyssal plain iberian margin abstract the horseshoe abyssal plain hap is located on the iberian margin at approximately 4800 m water depth and is confined within topographic elevations with a relief of about 3000 m with the exception of gorringe bank which rises to only 20 m below sealevel the plain is built up by an alternation of turbidites of the order of meter thick beds numbered h2 h3 h8 and h13 contrasting with sets of thinner beds of the order of decimeters thick h4 5 6 7 and h9 10 11 12 and pelagites centimeters in thickness an intensive study of eight piston cores using visual observation color and thickness relative stratigraphic position of units magnetic susceptibility logs calcium carbonate content and mineralogy of turbid te bases concludes in a bed by bed correlation of all individual turbidites the major source of terrigenous material feeding the hap is the sao vicente canyon which incises the portuguese shelf while minor sources are the surrounding seamounts the elongate geometry of the abyssal plain with its single dominant source of sediments produced laterally continuous deposits from both large and small flows these covered the entire 356 km length of the plain grain size analysis of the four thickest turbidites h2 h3 h8 and h9 demonstrates only slight downcurrent fining and vertical grading expressed best in the ratio of coarse silt to fine silt plus clay a small amount of sand is carried the length of the plain the thicker units all show the same pattern of thickness with a maximum in the middle of the plain around a topographic constriction and bend this is most plausibly explained as due to reduction in flow speed of an initially supercritical flow causing enhanced deposition some of the beds appear to have a double coarse layer in the base which may indicate partial reflection of flows from the side of the basin it is suggested by application of equations for flow behavior that both thick 3 m and thin 0 3 m beds are due to supercritical flows a few tens of meters high however the thick beds resulted from high concentration flows cv 4 by volume whereas thinner beds require low concentration cv 1 to run out over the full length of the basin the stratigraphy is tied into the dated oceanic pelagic record by analysis of foraminifera in the pelagic layers above the turbidites and through recognition of two heinrich layers h 1 and h 2 ages 14 3 and 21 ka the resulting age framework shows higher turbidite frequency in the glacial 2 7 kyr than interglacial holocene 1 0 kyr this also gives higher mass flux during the glacial emplacement of turbidites cannot be clearly related to sea level changes but may well be due to seismic activity however one of the largest earthquakes in human experience lisbon in 1755 triggered only a thin turbidite invalidating the term seismite for thick turbidites

from marine bands to hybrid flows sedimentology of a mississippian black shale this study was funded by the natural environment research council nerc grant no ne l002493 1 within the central england training alliance centa consortium the study received case funding from the british geological survey nick riley carboniferous limited is thanked for sharing his expertise and assistance charlotte watts is thanked for providing field assistance nick marsh tom knott cheryl haidon and annika burns are thanked for offering expertise and laboratory assistance pete sadler university of california is thanked for compilation and provision of the background sediment accumulation rate dataset we thank all reviewers editor peir pufahl and elaine richardson editorial office for their valuable comments and advice which have significantly improved this manuscript

role of matric suction in collapse of compacted clay soil this paper examines the influence of variations in matric suction on the collapse behavior of compacted bangalore clay soil the astm filter paper method measured the matric suctions of the compacted soil specimens the matric suction of the compacted clay soil specimens ranged between 50 and 8 000 kpa at the as compacted s r values of 90 and 35 comparison of the matric suction gravimetric water content relations of various compacted soils showed that the soil with a higher liquid limit has a higher matric suction at a given gravimetric water content variations in as compacted degrees of saturation at a constant relative compaction or variations in relative compaction at a constant as compacted degree of saturation notably affected the matric suction of the bangalore clay soil experimental results also showed that the influence of matric suction on the collapse behavior of this compacted clay soil greatly depended on the relative compaction of the specimens and the pressure at which they were inundated

global risk from extreme geophysical events threat identification and assessment in an increasingly interconnected world any single geophysical hazard is capable of having consequences far beyond the range of immediate physical effects most recently this was demonstrated by the 2004 asian tsunami which took the lives of citizens from 57 different nations and by hurricane katrina in august 2005 which raised fuel prices worldwide and contributed to a record uk trade deficit in the month following the devastation of new orleans on an altogether wider scale global geophysical events gges are natural phenomena capable of having wholesale deleterious consequences for the world s environment economy and society these may arise i due to a global physical effect such as an episode of severe planetary cooling in response to a volcanic super eruption or large comet or asteroid impact or ii as a result of subsidiary ramifications for the global economy and social fabric of a cataclysmic regional event such as an atlantic or pacific wide mega tsunami or a more spatially confined event at a strategically sensitive location for example the awaited major tokyo earthquake while very infrequent the wide ranging and potentially ruinous consequences of a gge for the well being of the international community make it essential that they are seriously considered within any comprehensive assessment of natural threats

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

multi disciplinary investigation of fluid seepage on an unstable margin the case of the central nile deep sea fan we report on a multidisciplinary study of cold seeps explored in the central nile deep sea fan of the egyptian margin our approach combines in situ seafloor observation geophysics sedimentological data measurement of bottom water methane anomalies pore water and sediment geochemistry and 230 th u dating of authigenic carbonates two areas were investigated which correspond to different sedimentary provinces the lower slope at 2100 m water depth indicates deformation of sediments by gravitational processes exhibiting slope parallel elongated ridges and seafloor depressions in contrast the middle slope at not vert 1650 m water depth exhibits a series of debris flow deposits not remobilized by post depositional gravity processes significant differences exist between fluid escape structures from the two studied areas at the lower slope methane anomalies were detected in bottom waters above the depressions whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities carbonate u th age dates 8 kyr bp pore water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past in contrast large 1 km2 carbonate paved areas were discovered in the middle slope with u th isotope evidence for ongoing carbonate precipitation during the late holocene since 5 kyr bp at least our results suggest that fluid venting is closely related to sediment deformation in the central nile margin it is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of fossil carbonate ridges whereas pervasive diffuse flow prevails at the unfailed middle slope

tectonic activity evolution of the scotia antarctic plate boundary from mass transport deposit analysis the spatial distribution and temporal occurrence of mass transport deposits mtds in the sedimentary infill of basins and submerged banks near the scotia antarctic plate boundary allowed us to decode the evolution of the tectonic activity of the relevant structures in the region from the oligocene to present day the 1020 mtds identified in the available data set of multichannel seismic reflection profiles in the region are subdivided according to the geographic and chronological distributions of these features their spatial distribution reveals a preferential location along the eastern margins of the eastern basins this reflects local deformation due to the evolution of the scotia antarctic transcurrent plate boundary and the impact of oceanic spreading along the east scotia ridge esr the vertical distribution of the mtds in the sedimentary record evidences intensified regional tectonic deformation from the middle miocene to quaternary intensified deformation started at about 15 ma when the esr progressively replaces the west scotia ridge wsr as the main oceanic spreading center in the scotia sea coevally with the wsr demise at about 6 5 ma increased spreading rates of the esr and numerous mtds were formed the high frequency of mtds during the pliocene mainly along the western basins is also related to greater tectonic activity due to uplift of the shackleton fracture zone by tectonic inversion and extinction of the antarctic phoenix ridge and involved changes at late pliocene the presence of mtds in the southern scotia sea basins is a relevant indicator of the interplay between sedimentary instability and regional tectonics

influence of sea level and basin physiography on emplacement of the late pleistocene herodotus basin megaturbidite se mediterranean sea radiocarbon 14c dates from pelagic intervals above a megaturbidite in the herodotus basin give direct evidence of emplacement at the beginning of the last glacial period approximately 27 125 calendar years before present as sea level lowered rapidly and entered a low stand phase the herodotus basin megaturbidite is a basinwide deposit that forms a recognisable acoustically transparent layer on 3 5 khz high resolution seismic profiles and covers an area of approximately 40 000 km2 it thins from about 20 m in thickness proximally to some 10 m distally over a basin length in excess of 400 km the total volume is estimated at around 400 km3 which is significantly more than the volume of sediment that could have been displaced from its most likely source area the funnel shaped marginal embayment of the gulf of salum to the west of the nile cone the additional material may have been derived in part from synchronous failures on other parts of the libyan egyptian shelf and slope but most is believed to have come from large scale erosion at the base of the very large volume turbidity current that was generated from the original slide detailed sedimentary analyses of cores recovered from the megaturbidite show its distinctive characteristics graded sand silt mud and bioturbated mud units poorly developed structures proximally becoming more distinct and ordered distally variation in grain size and structures that suggest either flow separation reflection around topographic highs and or an inherently unstable flow and a mixed source bioclastic terrigenous composition these features together with its size and lateral extent would make any similar megabed an excellent marker horizon in basin analysis a combination of factors was responsible for triggering the initial slide debris flow event that evolved downslope into this mega turbidity current these include lowered sea level that destabilised the outer shelf upper slope sediments tectonic oversteepening of the margin relatively high rates of sedimentation and seismic activity

using ground penetrating radar to investigate a subsurface karst landscape in north central florida abstract doline formation in karst areas has been a major concern in florida recently there has been increased interest in investigating the subsurface conditions that influences preferential flow in these karst landscapes this information is necessary to improve transport and fate models of contaminants in addition there is interest in knowing if the formation and expansion of dolines can be predicted by studying subsurface conditions and flow patterns the soils on the newberry limestone plain are typically sandy above a thin or absent phosphatic clayey hawthorne formation underlying this formation is the crystal river limestone a field survey with ground penetrating radar gpr was conducted on the newberry limestone plain at a site with recently formed dolines the objectives were i to investigate the subsurface materials ii to ascertain subsurface landscape variability iii to relate the subsurface landscapes to subsurface flow patterns and iv to predict doline growth and formation in the study area the results of this study indicated that the subsurface features presence of clay over limestone location of solution pipes and paleo dolines are variable in general the subsurface landscape does not follow the surface topography subsurface solute movement can be estimated in these landscapes assuming the clay layer that drapes the limestone acts as an aquatarde thus subsurface modeling of flow at the study site is improved locations of paleo dolines and solution pipes were obvious in the radar data predictions though of future doline formation and growth at the study site were difficult with gpr fracture patterns e g dips in the limestone can be evaluated and weak zones where paleo dolines have formed can be identified this study would not have been possible without the use of the gpr the radar was able to obtain continuous information on 16 of the site to a depth of 3 m a highly detailed soil survey using conventional methods would have provided only 0 8 coverage of the site

intense earthquakes and seismotectonics as a function of glacial isostasy abstract old shields and plate interiors have often been assumed to exhibit a high crustal stability during the last decade or two we have learnt more and more about the fragility not to say untenability of this concept however high magnitude earthquakes and large scale fault movements have been recorded where they were not supposed to be able to occur within formerly glaciated areas like northern europe scotland and northern north america a rapidly increasing number of field observations indicates that the glacial isostatic readjustment process was linked to intense seismotectonic activity we will here investigate the fennoscandian situation and propose a novel causation model for the high deglaciation seismicity in comparison with the present day situation

what caused the march 25 1998 antarctic plate earthquake inferences from regional stress and strain rate fields we investigate possible driving forces behind the occurrence of the 1998 antarctic plate earthquake we determine first a regional strain rate field associated with the accommodation of relative plate motion and second a vertically averaged minimum deviatoric stress field associated with lithospheric gravitational potential energy differences and deglaciation of the antarctic ice cap we find that the mechanism of this event is inconsistent with strain orientations inferred from kinematic modeling of a diffuse zone of deformation within the triple junction region stress perturbations associated with deglaciation cannot be ruled out as a triggering mechanism for this event

time dependent response of the global ocean clathrate reservoir to climatic and anthropogenic forcing 1 buffett and archer 2004 showed a model of the steady state global ocean clathrate reservoir that reproduces drill data and predicts a global methane inventory of about 5000 gton c the model inventory is very sensitive to ocean temperature with factor of two changes in methane inventory in response to temperature changes of 1 5 c here we explore the potential time dependent behavior of the clathrate reservoir assuming simple first order rate constants for methane accumulation and meltdown in response to changes in the predicted steady state reservoir for melting we divide the reservoir into two parts one melting catastrophically and the other slowly evolution of clathrates through geologic time is very sensitive to the choice of these rate constants a positive feedback exists during a transient meltdown event stronger if the catastrophic melting fraction is high and its melting timescale is fast a clathrate reservoir governed by such kinetics would melt down periodically on a multimillion year timescale determined by the rate constant for clathrate accumulation ideally we would like a model that predicts runaway melting in the paleocene and stability in the pleistocene however the model is most unstable when climate is cold rather than warm opting for stability in the pleistocene constrains the melting kinetic parameters leaving one degree of freedom the grow in timescale must be 5 myr or longer to get the deglacial 13c right but shorter than 10 myr in order for clathrates to have built up through geologically recent cooling the model thus constrained predicts methane fluxes of 200 gton c or less on deglaciations but eventual releases of 2000 4000 gton c in response to a 2000 gton c anthropogenic carbon release anthropogenic climate change differs from a deglaciation in that it warms the ocean to temperatures not seen in millions of years

implications of reduced turbidity current and landslide activity for the initial eocene thermal maximum evidence from two distal deep water sites previous studies propose that submarine landslides and turbidity currents may become more likely due to future rapid global warming determining whether global warming increases likelihood assists in assessment of landslide triggered tsunami hazards and risk to seafloor structures other studies propose that landslides helped to trigger past rapid climate change due to sudden release of gas hydrates two deep water turbidite records show prolonged hiatuses in turbidity current activity during the initial eocene thermal maximum ietm at 55 ma the ietm represents a possible proxy for future anthropogenically induced climate change it is likely that our records mainly represent large and fast moving disintegrative submarine landslides statistical analysis of long term 2 3 myr records shows that turbidity current frequency significantly decreased after the ietm our results indicate that rapid climate change does not necessarily cause increased turbidity current activity and do not provide evidence for landslides as a primary trigger for the ietm

linking continental slope failures and climate change testing the clathrate gun hypothesis it has been suggested that the release of clathrates rather than expansion of wetlands is the primary cause of the rapid increases observed in the ice core atmospheric methane record during the pleistocene because submarine sediment failures can involve as much as 5000 gt of sediment and have the capacity to release vast quantities of methane hydrates one of the major tests of the clathrate gun hypothesis is determining whether the periods of enhanced continental slope failure and atmospheric methane correlate to test the clathrate gun hypothesis we have collated published dates for submarine sediment failures in the north atlantic sector and correlated them with climatic change for the past 45 k y more than 70 by volume of continental slope failures during the past 45 k y was displaced in two periods between 15 and 13 ka and between 11 and 8 ka both these intervals correlate with rising sea level and peaks in the methane record during the bolling allerod and preboreal periods these data support the clathrate gun hypothesis for glacial interglacial transitions the data do not however support the clathrate gun hypothesis for glacial millennial scale climate cycles because the occurrence of sediment failures correlates with heinrich events i e lows in sea level and atmospheric methane a secondary use of this data set is the insight into the possible cause of continental slope failures glacial period slope failures occur mainly in the low latitudes and are associated with lowering sea level this finding suggests that reduced hydrostatic pressure and the associated destabilization of gas hydrates may be the primary cause the bolling allerod sediment failures were predominantly low latitude suggesting an early tropical response to deglaciation e g enhanced precipitation and sediment load to the continental shelf or warming of intermediate waters in contrast sediment failures during the preboreal period and the majority of the holocene occurred in the high latitudes suggesting either isostatic rebound related earthquake activity or reduced hydrostatic pressure caused by isostatic rebound causing destabilization of gas hydrates

balancing the deglacial global carbon budget the hydrate factor abstract the discovery that methane from dissociation of gas hydrates could be an important factor in the global carbon cycle resolves the major discrepancy in estimates of the increase of terrestrial biomass from the last glacial period to the present carbon isotope budgeting using the marine carbon isotopic record results in an estimate centered around 500 gtc whereas palaeovegetation reconstruction with biosphere models gives averages around 1000 gtc the discrepancy may be resolved by considering release of isotopically light methane through destabilization of gas hydrates this provides a unique means of estimating the contribution of gas hydrates to the deglacial rise in atmospheric methane a release of 120 gtc methane makes a biospheric carbon transfer of 1000 gtc compatible with the marine carbon isotope data this however represents less than 30 of the enhanced atmospheric methane production between 18 and 8 ka observed in ice cores supporting the theory that glacial interglacial variations in atmospheric methane were driven primarily by changes in the extent of tropical and temperate wetlands and not by methane release from clathrates by balancing the deglacial carbon budget we demonstrate that global carbon models will have to incorporate glacial interglacial vegetation shifts of at least 1000 gtc which many currently find difficult

the end of the ice age methane gas hydrates may have contributed to the rapid rise in atmospheric ch4 co2 and global temperatures at the end of the last major glaciation about 13 500 years ago given suitable orbital conditions and insolation at high latitude a small triggering event such as the release of one or more arctic gas pools may have initiated massive release of methane from hydrate under ice and in permafrost the consequent greenhouse warming would have provided strong positive feedback amplifying emission this warming driven by ch4 may have induced the release of co2 from the oceans to the biosphere stabilizing the interglacial carbon cycle

archaeal and bacterial lipids in authigenic carbonate crusts from eastern mediterranean mud volcanoes abstract we investigated the distributions and 13 c values of lipid biomarkers in authigenic methane related carbonate crusts formed on eastern mediterranean mud volcanoes a highly diverse suite of microbial membrane lipids was detected strongly 13 c depleted lipids diagnostic for archaea include isoprenoid glycerol diethers isoprenoid glycerol dialkyl glycerol tetraethers and several c 20 c 35 isoprenoid hydrocarbons bacterial lipids mainly consist of dialkyl glycerol diethers branched fatty acids and hopanoids showing important 13 c depletions albeit less than archaeal lipids the data provide further evidence for the involvement of archaea and bacteria in the anaerobic oxidation of methane aom and in the sequestration of methane derived carbon in authigenic carbonate crusts varying distributions and isotopic compositions of 13 c depleted lipids argue for heterogeneous aom related microbial consortia expanding on existing work at cold seeps distinctive biomarker features and inferred microbial assemblages are observed in these crusts in agreement with available phylogenetic data for the samples our results support the potential of lipids for distinguishing methanotrophic communities despite the observed variances conservative features in the abundances and isotopic offsets of microbial biomarkers occur likely reflecting the overall relationships between archaea and bacteria and the nature of carbon flow between them

major controlling factors on hydrocarbon generation and leakage in south atlantic conjugate margins a comparative study of colorado orange campos and lower congo basins abstract we present a supra regional comparative study of the major internal and external factors controlling source rock sr maturation and hydrocarbon hc generation and leakage in two pairs of conjugate margins across the south atlantic the brazil campos basin angola lower congo basin margins located in the central segment and the argentina colorado basin south africa orange basin in the southern segment our approach is based on the analysis and integration of borehole data 1d numerical modeling 2d seismic reflection data and published reports coupling of modeling results sedimentation rate calculation and seal bypass system analysis reveal that 1 oil window is reached by syn rift srs in the southern segment during the early to late cretaceous when thermal subsidence is still active while in the central segment they reach it in late cretaceous neogene during a salt remobilization phase and 2 early hc generation from post rift srs in the southern segment and from all srs in the central segment appears to be controlled mainly by episodes of increased sedimentation rates the latter seems to be associated with the andes uplift history for the western south atlantic basins campos and colorado and to a possibly climate driven response for the eastern south atlantic basins orange and lower congo additionally we observe that the effect of volcanism on sr maturation in the southern segment is very local the comparison of cretaceous mass transport deposit mtd episodes with hc peak of generation and paleo leakage indicators in the southern segment revealed the possible causal effect that hc generation and leakage have over mtd development interestingly paleogene leakage indicators which were identified in the argentina south africa conjugate margins occur contemporaneously to low sedimentation rate periods nonetheless present day leakage indicators which were also identified in both pairs of conjugate margins might be related to seal failure events linked to eustatic sea level drops

toward the snowball earth deglaciation the current state of knowledge suggests that the neoproterozoic snowball earth is far from deglaciation even at 0 2 bars of co2 since understanding the termination of the fully ice covered state is essential to sustain or not the snowball earth theory we used an atmospheric general climate model agcm to explore some key factors which could induce deglaciation after testing the models sensitivity to their parameterizations of clouds co2 and snow we investigated the warming effect caused by a dusty surface associated with ash release during a mega volcanic eruption we found that the snow aging process its dirtiness and the ash deposition on the snow free ice are key factors for deglaciation our modelling study suggests that under a co2 enriched atmosphere a dusty snowball earth could reach the deglaciation threshold

evidence for long term instability in the storegga slide region off western norway abstract shallow seismic surveys around the storegga slide off western norway have allowed greater understanding of the development of this part of the european margin the northern flank of the scarp is formed of seismically well layered hemipelagic and distal glaciomarine deposits in which a variety of luid escape structures probably due to gas are locally abundant there is evidence of slides that substantially pre date the earliest slide previously recognized surveying on the north sea fan to the southwest of the storegga slide shows the markedly different nature of the autochthonous sediments on the southern flank of the storegga slide there is a predominance of glacigenic debris flows in the upper part of the sequence lesser maximum slopes and an apparent absence of interstitial gas and or hydrates this contrast has had considerable effect on slope stability and has influenced the position of the southwestern storegga slide boundary the north sea fan succession includes at least three major buried slides termed the vigra more and tampen slides all of which substantially pre date the storegga event and probably pre date predominantly glacigenic margin sedimentation post late weichselian slope failure is locally significant the region has a long but as yet chronologically poorly defined history of instability in which seismic triggering is considered to have been important

methane gas release from the storegga submarine landslide linked to earlyholocene climate change a speculative hypothesis the 3000 km3 storegga submarine landslide occurred c 8150 years ago from an area rich in gas hydrates off the western coast of norway a synchronous increase of 80 100 ppb in atmospheric methane c

paleoseismicity and geodynamics in sweden abstract paleoseismicity denotes past pre instrumental earthquakes as recorded by bedrock structures morphological features and sedimentological criteria glacial varves eskers and deltas are excellent records of paleoseismic events data from sweden are presented faults fractures and various types of sedimentary disturbances of late pleistocene and holocene age frequently occur it is concluded that the seismic activity was very intensive in connection with the peak rates of glacial isostatic uplift and that this was a natural effect of the geodynamic processes operating

assessing methane release from the colossal storegga submarine landslide 1 marine slope failure involving methane gas hydrate bearing sediments is one mechanism for releasing enormous quantities of methane to the ocean and atmosphere the storegga slide on the norwegian margin is the largest known holocene aged continental margin slope failure complex and is believed to have occurred in sediments that may have initially contained gas hydrate here we report pore water sulfate gradient measurements that are used as a proxy for the relative amounts of methane that exist in continental margin sediments associated with the colossal storegga slide these measurements suggest that a considerable inventory of methane occurs in sediments adjacent to and unaffected by the storegga slide events but indicate that methane is notably absent from sediments on the sole of the slide and distal deposits created by the slide events either methane was lost during previous pleistocene failure events or was never present in significant concentrations within the sediments that failed

sea level induced seismicity and submarine landslide occurrence the temporal coincidence between rapid late pleistocene sea level rise and large scale slope failures is widely documented nevertheless the physical mechanisms that link these phenomena are poorly understood particularly along nonglaciated margins here we investigate the causal relationships between rapid sea level rise flexural stress loading and increased seismicity rates along passive margins we find that coulomb failure stress across fault systems of passive continental margins may have increased more than 1 mpa during rapid late pleistocene early holocene sea level rise an amount sufficient to trigger fault reactivation and rupture these results suggest that sea level modulated seismicity may have contributed to a number of poorly understood but widely observed phenomena including 1 increased frequency of large scale submarine landslides during rapid late pleistocene sea level rise 2 emplacement of coarse grained mass transport deposits on deep sea fans during the early stages of marine transgression and 3 the unroofing and release of methane gas sequestered in continental slope sediments

laboratory experiment and numerical simulation on authigenic mineral formation induced by seabed methane seeps abstract in natural gas hydrate marine settings cold seepage of methane fluid is a widely observed phenomenon where authigenic minerals serve as an indication of potential gas hydrate bearing reservoirs at depth in this study based on the data from the site hd196 near dongsha island northern continental slope of south china sea laboratory experiments and numerical simulation studies were conducted to investigate the biogeochemical processes of authigenic mineral formation induced by methane seepage the bioreactor experimental results show that in response to methane flux ph increased to 8 5 after 20 days of reaction and eh declined rapidly first and then remained unchanged at about 100 mv the decrease in so42 hs and hco3 concentrations indicated the occurrence of anaerobic oxidation of methane coupled with sulfate reduction aom sr the depletion of fe2 implied the formation of iron bearing minerals e g iron sulfides carbonate minerals were also identified in the experimental phase of this study most iron sulfides existed as massive pieces and in some cases as spherical or rod shape pieces the calcium carbonates were observed as blocky pieces numerical simulations were also performed to reproduce the biogeochemical reactions that occurred in the reactor experiments based on experimental data kinetic parameters associated with the observed reactions were calibrated the model simulated results are general consistent with those obtained by the experiments conducted in this study the combination of simulation and experimental studies provided a powerful tool to investigate the biogeochemical processes in the methane leakage environment at different temporal and spatial scales this study gave a new perspective to understand the formation of cold seep authigenic minerals in marine sediments and was significant for future investigations on the effects of hydrate decomposition

characterization of microbial activity in pockmark fields of the sw barents sea abstract multibeam bathymetry revealed the occurrence of numerous craterlike depressions so called pockmarks on the sea floor of the hammerfest basin and the loppa high south western barents sea to investigate whether these pockmarks are related to ongoing gas seepage microbial processes associated with methane metabolism were analyzed using geochemical biogeochemical and microbiological techniques gravity cores were collected along transects crossing individual pockmarks allowing a direct comparison between different locations inside assumed activity center on the rim and outside of a pockmark reference sites concentrations of hydrocarbons in the sediment particularly methane were measured as headspace free gas and in the occluded and adsorbed gas fraction down to a depth of 2 6 m below sea floor mbsf sulfate reduction rates were quantified by radiotracer incubations concentrations of dissolved sulfate in the porewater were determined as well neither the sulfate profiles nor the gas measurements show any evidence of microbial activity or active fluid venting methane concentrations and sulfate reduction rates were extremely low or even below the detection limit the results show that the observed sediment structures are most likely paleo pockmarks their formation probably occurred during the last deglaciation

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

carbon isotope excursions and microfacies changes in marine permian triassic boundary sections in hungary abstract several permian triassic boundary sections occur in various structural units within hungary these sections represent different facies zones of the western palaeotethys margin the gardony core in the ne part of the transdanubian range typically represents the inner ramp while the balvany section in the bukk mountains of northern hungary represents an outer ramp setting the two sections have different patterns for their 13 c values the balvany section shows a continuous change towards more negative 13 c values starting at the first biotic decline followed by a sharp quasi symmetric negative peak at the second decline the appearance of the 13 c peak has no relationship to the lithology and occurs within a shale with low overall carbonate content indicating that the peak is not related to diagenesis or other secondary influences instead the shift and the peak reflect primary processes related to changes in environmental conditions the continuous shift in 13 c values is most probably related to a decrease in bioproductivity whereas the sharp peak can be attributed to an addition of c strongly depleted in 13 c to the ocean atmosphere system the most plausible model is a massive release of methane hydrate the quasi symmetric pattern suggests a rapid warming cooling cycle or physical unroofing of sediments through slope failure and releasing methane hydrate the gardony 1 core shows a continuous negative 13 c shift starting below the p t boundary however the detailed analyses revealed a sharp 13 c peak in the boundary interval just below the major biotic decline although its magnitude doesn t reach that observed in the balvany section based on careful textural examination and high resolution stable isotope microanalyses we suggest that the suppression of the 13 c peak that is common in the oolitic boundary sections is due to combined effects of condensed sedimentation sediment reworking and erosion as well as perhaps diagenesis

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete