major pathways of atlantic water in the northern north atlantic and nordic seas toward arctic 1 the major pathways of near surface atlantic water in the northern north atlantic and nordic seas are identified as current speeds above 30 cm s using 1014 lagrangian drifters combined with previously published hydrography the inflow over the scotland greenland ridge and establishment of the two branch norwegian atlantic current nwac are described in light of the circulation in the northern north atlantic the western branch of the nwac appears as a jet in the polar front topographically guided from the iceland faroe front through the nordic seas toward fram strait the eastern branch starts as a shelf edge current above the irish scottish continental shelf and after passing through the faroe shetland channel it continues northward along the norwegian shelf edge toward the arctic with a branch bifurcating into the barents sea the nwac appears to maintain its two branch structure throughout the nordic seas with the atlantic water confined to a 200 600 km wide wedge

opening of the fram strait gateway a review of plate tectonic constraints abstract we have revised the regional crustal structure oceanic age distribution and conjugate margin segmentation in and around the lena trough the oceanic part of the fram strait between the norwegian greenland sea and the eurasia basin arctic ocean the lena trough started to open after eurasia greenland relative plate motions changed from right lateral shear to oblique divergence at chron 13 times 33 3 ma earliest oligocene a new bouguer gravity map supported by existing seismic data and aeromagnetic profiles has been applied to interpret the continent ocean transition and the influence of eocene shear structures on the timing of breakup and initial seafloor spreading assuming that the onset of deep water exchange depended on the formation of a narrow oceanic corridor the gateway formed during early miocene times 20 15 ma however if the initial lena trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep water circulation the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around chron 5 times 9 8 ma late miocene paleoceanographic changes at odp site 909 northern hovgard ridge are consistent with both hypotheses of gateway formation we cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the lena trough the gravity seismic and magnetic observations question the prevailing hypotheses on the yermak plateau and the morris jesup rise as eocene oceanic plateaus and the hovgard ridge as a microcontinent

late cenozoic geological development of the south voring margin mid norway abstract late cenozoic seismic stratigraphy of the voring continental margin has been studied in detail with emphasis on the geological development of the naust formation deposited during the last 3 million years the kai formation 15 3 ma comprises mainly biogenic ooze deposited in the more and voring basins in naust time there was a marked increase in supply of sediments from the inner shelf areas and the western part of the scandinavian mountain range and glaciers expanded to the shelf and reached the shelf edge several times during the last 1 5 2 million years during early to mid naust time the shelf was widened by westerly prograding sediment units but for a long period the shallowest part of the helland hansen arch hha formed a barrier preventing glacially derived debris from being distributed farther west west of the hha mainly stratified marine and glacimarine sediments were deposited a substantial part of these sediments were transported by the north flowing norwegian atlantic current which redistributed suspended particles from ice streams rivers coastal erosion and seabed winnowing after burial of the crest of the hha at c 0 5 ma glacial debris and slide deposits were also deposited west of this high in the north massive units of glacial debris were distributed beyond the crest of the hha also in mid naust time thinning westwards and interfingering with fine grained sediments on the lower slope the sklinnadjupet slide inferred to be c 250 000 years old corresponds in age with an earlier huge slide in the storegga area an elongated area of uneven seabed topography previously interpreted as diapirs vigrid diapirs on the slope west of the hha is shown to be formed by ooze eruption from the crest of the arch and submarine sliding

late cenozoic glacial history and evolution of the storegga slide area and adjacent slide flank regions norwegian continental margin abstract acoustic data and sediment cores collected from the storegga slide and its adjacent slide flanks i e the voring plateau to the north and the north sea fan to the south have been used to study the late cenozoic glacial history and geological development of this region age constrains obtained from the investigated cores show that the fennoscandian ice sheet reached the shelf edge during marine isotope stages mis 12 10 8 6 and 2 ice sheet fluctuations within each glaciation might have occurred as is evidenced for the last glacial maximum mis 2 the first extensive ice advance is identified in the early pleistocene at c 1 1 ma however between 2 6 and 0 5 ma the ice sheets were largely restricted to the fjords and inner shelf during each glacial maximum glacigenic debris flows gdfs transported basal till deposited at the shelf edge into the deep sea along the entire studied margin the most voluminous gdf sequences are found on the southern storegga slide flank north sea fan where the individual flows are found as far as 500 km from the shelf edge on the voring plateau glacimarine hemipelagic sedimentation has dominated the last c 250 000 yr during mis 2 such sediments were rapidly deposited covering the upper slope limited gdf units in this region between c 15 700 and 15 000 14c yr bp i e during the last deglaciation of the norwegian margin a presumed meltwater plume released from the disintegrating norwegian channel ice stream transported and rapidly deposited up to 20 m of fine grained sediments in the region north of the north sea fan the rapid deposition of large volumes of gdfs glacimarine and meltwater related sediments might have influenced the stability of the slope sediments in the studied region promoting conditions favorable for failure furthermore these high sedimentation rates also partly account for the high subsidence rates observed on the norwegian continental margin in the late cenozoic

green mosses date the storegga tsunami to the chilliest decades of the 8 2 ka cold event abstract chlorophyll in dead plants ordinarily decomposes completely before permanent burial through exposure to light water and oxygen here we describe 8000 year old terrestrial mosses that retain several percent of its original chlorophyll the mosses were ripped of the land surface carried 50 100 m off the norwegian coast of the time and deposited in depressions on the sea floor by the storegga tsunami a little of the chlorophyll survived because within hours after entraining it the tsunami buried the mosses in shell rich sediments these sediments preserved the chlorophyll by keeping out light and oxygen and by keeping the ph above 7 three factors known to favour chlorophyll s stability because the green mosses were buried alive their radiocarbon clock started ticking within hours after the storegga slide had set off the tsunami radiocarbon measurement of the mosses therefore give slide ages of uncommon geological precision and these together with a sequence of ages above and below the boundary date the storegga slide to the chilliest decades of the 8 2 ka cold event at 8120 8175 years before ad 1950 north atlantic coastal and fjord climatic records claimed to show evidence of the 8 2 cold event should be carefully examined for possible contamination and disturbance from the storegga tsunami

neogene tephra correlations in eastern idaho and wyoming implications for yellowstone hotspot related volcanism and tectonic activity the explosive rhyolitic eruptions that define the track of the snake river plain yellowstone volcanism have produced a large volume of tephra found in late miocene and younger basin fill sediments throughout the western united states here we use 40ar 39ar isotopic dating paleomagnetic analysis major and trace element geochemistry and standard optical techniques to establish regional tephra correlations we focus on tephra deposits in three neogene basins in spatially separated areas grand valley in eastern idaho jackson hole in northwestern wyoming and the granite mountains area in central wyoming these basins have experienced relatively continuous deposition from the late miocene to the holocene we found tephra layers that directly tie the stratigraphy between all three basins using these correlations we found that basins experienced discrete pulses of extension separated by long periods of relative quiescence the dates of which are staggered between basins an early pulse of extension occurred in grand valley and jackson hole between 10 3 ma and 16 33 ma with a second pulse initiating between 4 54 ma and 2 09 ma the granite mountains basin experienced a single pulse of extension sometime between 11 14 ma and 6 75 ma these pulses of accelerated extension along with evidence of similar pulses in other basins present a pattern of west to east migration that we suggest is related to the yellowstone hotspot the later pulse of activity in grand valley and jackson hole corresponds to the migration of the north american plate over the tail of the yellowstone hotspot we speculate that the earliest pulse in each basin is related to the more rapid movement of the sublithospheric hotspot head as it spreads out from its earliest known location where the columbia river plateau flood basalt province initiated in southeastern oregon to its outermost edge under central wyoming our results are consistent with this model of a plume head though not unique to it the results of our study also indicate that previous suggestions that the rate of snake river plain explosive volcanism has decreased by a factor of 2 or 3 since emplacement of the middle miocene trapper creek tuffs likely underestimate post trapper creek eruption rates we have discovered a large number of previously unidentified post middle miocene major eruptive events both as ash flow tuffs and as vitric air fall tuffs recalculation to include these newly discovered events results in a rate of major eruptions that is fairly uniform until ca 4 54 ma however there is a substantial gap in major silicic eruptions in the interval between 4 54 ma and 2 09 ma which we call the post heise eruptive gap with the exception of this gap the rate of major eruptions on the snake river plain has been roughly constant since inception of the eastern snake river plain yellowstone volcanic track between 16 ma and 17 ma

the norwegian greenland sea continental margins morphology and late quaternary sedimentary processes and environment the continental margins surrounding the norwegian greenland sea are to a large degree shaped by processes during the late quaternary the paper gives an overview of the morphology and the processes responsible for the formation of three main groups of morphological features slides trough mouth fans and channels several large late quaternary slides have been identified on the eastern norwegian greenland sea continental margin the origin of the slides may be due to high sedimentation rates leading to a build up of excess pore water pressure perhaps with additional pressure caused by gas bubbles triggering might have been prompted by earthquakes or by decomposition of gas hydrates trough mouth fans tmf are fans at the mouths of transverse troughs on presently or formerly glaciated continental shelves in the norwegian greenland sea seven tmfs have been identified varying in area from 2700 km2 to 215 000 km2 the trough mouth fans are depocentres of sediments which have accumulated in front of ice streams draining the large northwest european ice sheets the sediments deposited at the shelf break upper slope by the ice stream were remobilized and transported downslope mostly as debris flows the trough mouth fans hold the potential for giving information about the various ice streams feeding them with regard to velocity and ice discharge two large deep sea channel systems have been observed along the norwegian continental margin the lofoten basin channel and the inbis channel along the east greenland margin several channel systems have been identified the deep sea channels may have been formed by dense water originating from cooling sea ice formation and brine rejection close to the glacier margin or they may originate from small slides on the upper slope transforming into debris flows and turbidity currents

kinematics and timing of three superposed extensional systems east central idaho evidence for an eocene tectonic transition cenozoic crustal extension in east central idaho began about 50 ma and continues at present three distinct episodes characterize one of the longest intervals of cenozoic extension yet documented in the north america cordillera crosscutting relationships between ne striking normal faults and volcanic rocks regional dike trends and slickenline data indicate nw se extension during peak eocene volcanism about 49 48 ma episode 1 ne striking normal faults with at most a few kilometers of offset formed in an intraarc setting during rapid ne subduction of oceanic plates under the pacific northwest north to nnw striking and west dipping normal faults with offsets up to 10 15 km formed during a younger middle eocene to oligocene basin forming event episode 2 this newly documented episode was the most important extensional event in east central idaho and began during the waning phases of challis volcanism wsw ene to sw ne extension during episode 2 was nearly perpendicular to the extension direction during episode 1 and perpendicular to the grain of the idaho montana fold and thrust belt the flip in extension direction between episode 1 and episode 2 is tightly constrained by 40ar 39ar age determinations to have taken place at the end of eocene challis magmatism about 46 48 ma i infer that plate boundary forces controlled the geometry of normal faults and dikes during episode 1 whereas internal stresses within previously thickened crust drove major sw to wsw directed extension during episode 2 a drop in convergence rates between the north american and farallon plates between 59 ma and 42 ma stock and molnar 1988 may coincide with the onset of gravitational spreading during episode 2 and may also explain the abrupt end of eocene magmatism in the pacific northwest miocene and younger sw dipping basin and range faults episode 3 extended the region in a ne sw direction although faults formed during episode 2 and episode 3 are not parallel slickenlines indicate only small changes in slip vector trends suggesting little rotation of the extension direction in east central idaho since 46 ma

the plio pleistocene glaciation of the barents sea svalbard region a new model based on revised chronostratigraphy based on a revised chronostratigraphy and compilation of borehole data from the barents sea continental margin a coherent glaciation model is proposed for the barents sea ice sheet over the past 3 5 million years ma three phases of ice growth are suggested 1 the initial build up phase covering mountainous regions and reaching the coastline shelf edge in the northern barents sea during short term glacial intensification is concomitant with the onset of the northern hemisphere glaciation 3 6 2 4 ma 2 a transitional growth phase 2 4 1 0 ma during which the ice sheet expanded towards the southern barents sea and reached the northwestern kara sea this is inferred from step wise decrease of siberian river supplied smectite rich sediments likely caused by ice sheet blockade and possibly reduced sea ice formation in the kara sea as well as glacigenic wedge growth along the northwestern barents sea margin hampering entrainment and transport of sea ice sediments to the arctic atlantic gateway 3 finally large scale glaciation in the barents sea occurred after 1 ma with repeated advances to the shelf edge the timing is inferred from ice grounding on the yermak plateau at about 0 95 ma and higher frequencies of gravity driven mass movements along the western barents sea margin associated with expansive glacial growth

the magnetochronology of barstovian mammals in southwestern montana and implications for the initiation of neogene crustal extension in the northern rocky mountains magnetostratigraphic and biostratigraphic data have been used to construct a chronologic framework for the deposition of the hepburn9s mesa formation in the yellow stone valley of southwestern montana deposition spanned an interval from 16 8 ma to at least 14 3 ma and possibly to 13 8 ma the magnetic data help to constrain the barstovian land mammal age in the northern rocky mountains as well as two interval zones defined within it the major faunal boundary ages determined here are indistin guishable from ages for these same boundaries at the barstovian type locality in southern california consequently observed differences in generic and species composition between these regions are likely to reflect biogeographic and ecological variability rather than temporal separation when used in conjunction with biostratigraphic data from jackson hole wyoming these new dates improve the time constraints that can be placed on the duration 1 m y of the mid tertiary unconformity in the northern rockies and on the inception at 17 ma of the interval of crustal extension that led to extensive intermontane basin development during the neogene

non antipodal directions in magnetostratigraphy an overprint bias s u m m a r y paleomagnetic records show very often that the directions of normal and reverse polarity are not quite antipodal as one would expect for an axial geocentric dipole model specifically in magnetostratigraphic studies of tertiary sediments which include large data sets of paleomagnetic directions of both polarities it is commonly observed that reverse polarity inclinations are shallower than those of normal polarity such an inclination anomaly has important implications for both paleomagnetism and paleogeographic reconstructions we investigate the conventional explanation for such asymmetry which involves the presence of a persistent partially unremoved present day field magnetization in the studied rocks both plate motion history and inclination shallowing which we evaluate in detail can play an important role in the paleomagnetic record our analysis shows that alternatively it is plausible that the inclination anomaly is due to a contribution of an axial octupole in accordance with observations of the recent 0 5 ma geomagnetic field recorded in lava flows

postglacial seismicity offshore mid norway with emphasis on spatio temporal magnitudal variations abstract norway and its continental margin in spite of being located in an intraplate environment is of great interest from a neotectonic perspective influence on neotectonics stems both from the fact that this is a recently deglaciated region in which significant rebound is still occurring and from its proximity both to a rifted continental margin and to failed rift zones passive continental margins and rift related structures are the most seismically active ones within stable continental regions with a number of well documented earthquakes of magnitude 7 and higher as observed around the globe indeed the disparity in seismicity between such regions and plate boundary regions is greater in terms of return times than in terms of maximum magnitude a recent detailed assessment of neotectonics in fennoscandia has shown strong bedrock related evidence for several large magnitude m 7 earthquakes in the northern areas lapland while few if any similar observations have been made farther south a possible explanation for this is that postglacial earthquakes have been occurring on hidden thrusts in the south in fact several major structures have recently been mapped and shown to have capabilities to accommodate m 6 5 7 earthquakes without breaking the surface given that the largest historically known earthquake in fennoscandia is only of the order of m 5 8 it is likely therefore that the potentially largest magnitude in this region may be well above this

quaternary sedimentation margin architecture and ocean circulation variability around the faroe islands north atlantic abstract the quaternary development offshore the faroe islands has been studied using high resolution seismic and core data from the r v dana 2000 cruise and previous cruises several glacial related features and deposits are observed all bearing witness to former extensive glaciations of the faroe area on the shelves overlaying a mid pleistocene glacial erosional surface glacial and glacimarine deposits form a sheet geometry interrupted by ridges of sediment that are likely to represent ice front deposits an iceberg turbate north of the faroe islands provides evidence of large scale drift of ultra deep draft 600 m icebergs in the nordic seas at pre weichselian glacial stage s marginal and transverse troughs found on the eastern and western shelf are suggested to have formed during the same glacial period s as the iceberg turbate iceberg plough marks and abundant ice rafted material of non faroese origin together with the relict moraine ridges encircling the faroe islands at around the 100 and 200 m water depth contours indicate that the outer shelf was probably ice free during the weichselian ice age on the slopes and basinal parts the formation of fine grained contourites was favoured during weichselian glacial stages when bottom currents were reduced sediment overloading during these glacial stages resulted in repeated slope instability causing mass failures of the contourite deposits

hummock fields in the norway basin and eastern iceland plateau rayleigh taylor instabilities side scan imagery and 3 5 khz profiles in the norway basin reveal 3 4 10 4 km 2 of sea floor covered by regularly spaced 500 2000 m low relief hummocks previously attributed to bottom currents extrapolating from nearby borehole data i attribute these mound fields to gravitational rayleigh taylor instabilities resulting from superposition of 50 100 m of thick pliocene pleistocene glacigenic glacier derived sandy clays density 1800 kg m 3 on a several hundred metre thickness of miocene biosiliceous oozes having a density of 1300 kg m 3 this hypothesis predicts or explains similar hummock fields in many oceanic regions where such density inversions exist

seismotectonics of the norwegian continental margin the norwegian continental margin and surrounding areas are seismically less active than some other passive margins worldwide indicating a potential earthquake deficit the adjacent oceanic crust is mostly aseismic except for parts of the lofoten and norway basins which have experienced rapid deposition of glacial sediments the excess load has enhanced the local stress field and in turn the seismic activity the marginal highs along the continent ocean transition and the part of the more and voring basins which experienced crustal extension prior to the early tertiary breakup are practically aseismic this region is also underlain by high velocity lower crust emplaced during breakup suggesting crustal strengthening which also may increase the return periods for the largest events farther landward a spatial correlation of seismic activity and the glacial sediment wedge suggests a causal relationship expressed through preferential rejuvenation of late jurassic early cretaceous faults the locally high seismic activity in the coastal region occurs in areas where the continental crust is relatively thick 25 30 km but still thinner than in the shield area farther east 45 50 km although stress relations are complex we suggest that increased stress due to appreciable postglacial rebound gradients in the coastal region may be a contributing factor while the stress field along the margin complies in general with the ridge push force we infer that regional and local stress enhancement factors are not only present in this region but also necessary for explaining the earthquake activity the relative importance of local stress sources is supported by several cases of 90 stress rotations relative to the ridge push direction the superposition of regional and local stress together with the existence of weakness zones and faults yields potentials for earthquakes primarily through structural reactivation

pleistocene glacial history of the nw european continental margin abstract in this paper new and previously published data on the pleistocene glacial impact on the nw european margin from ireland to svalbard between c 48 n 80 n are compiled the morphology of the glaciated part of the european margin strongly reflects repeated occurrence of fast moving ice streams creating numerous glacial troughs channels that are separated by shallow bank areas end moraines have been identified at several locations on the shelf suggesting shelf edge glaciation along the major part of the margin during the last glacial maximum deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55 n and northwards whereas the margin to the south of this is characterised by the presence of submarine canyons glaciation curves based primarily on information from the glacial fed fan systems that depict the pleistocene trends in extent of glaciations along the margin have been compiled these curves suggest that extensive shelf glaciations started around svalbard at 1 6 1 3 ma while repeated periods of shelf edge glaciations on the uk margin started with mis 12 c 0 45 ma the available evidence for mis 2 suggest that shelf edge glaciation for the whole margin was reached between c 28 and 22 14 c ka bp and maximum positions after this were more limited in some regions north sea and lofoten the last glacial advance on the margin has been dated to 15 13 5 14 c ka bp and by c 13 14 c ka bp the shelf areas were completely deglaciated the younger dryas loch lomond advance reached the coastal areas in only a few regions

large scale development of the mid norwegian shelf over the last three million years and potential for hydrocarbon reservoirs in glacial sediments about 3 million years ago major ice sheets developed over scandinavia and began to deliverlargevolumesofsedimenttothemid norwegianshelf theshelfwasbuilt outina prograd ing pattern towards the west and more than 1000 m of sedimentswas deposited over large areas on the middle outer shelf the dominating large scale depositional pattern is a series of prograding wedges and flat lying sheet like units mainly of glacial origin on top of these units are flat lying till units deposited during the last few glaciations commonly separated from the underlying units by one or several erosional unconformities the lithology of these layers is generally fine grained mainly clay and silt but with sporadic clasts up to boulder size based on regional and detailed bathymetry the ice flow pattern from the last glaciation has been reconstructed on the shelf this involved a very dynamic ice sheet with fast flowing ice streams in the transverse cross shelf troughs separated by more passive ice domes on the intermediate shallow banks theicestreamsappeartofollowthecross shelftroughsfromglaciationtoglaciation butoccasion ally they switched to new flow paths the thick quaternary sediments on the outer part of the mid norwegian shelf represent a challenge for hydrocarbon exploration several large slides have occurred from the shelf break and down the continental slope during the last few years there has been an increased focus on investigating the quaternary succession in order to search for hydrocarbon prospects the potential for finding reservoirs in these sediments is discussed and a few examples of gas discoveries are shown the peon gas field c 250 km 2 is located in the gla cially eroded norwegian channel above the upper regional unconformity uru separating flat lying glaciogenic sediments from dipping sedimentary units the reservoir is developed in glacio fluvial sands a few hundred thousand years old and sealed by flat lying glaciomarine sediments and till units

the sklinnadjupet slide and its relation to the elsterian glaciation on the mid norwegian margin abstract the sklinnadjupet slide scar is a large buried feature on the continental slope southeast of the voring plateau the mass flow occurred ca 250 000 years ago on a slope angle of ca 0 5 and removed glacial debris from the up to 350 m thick naust s sequence on the upper slope this part of the mid norwegian margin appears to have been fairly stable throughout the last 2 8 million years naust s represents the third last glacial unit in the skjoldryggen region and was deposited during the elsterian ca 400 200 ka bp during this glaciation a wide depression was formed on the continental shelf between haltenbanken and traenabanken with the strongest glacial erosion in the west trending sklinnadjupet palaeo trough this trough leads directly towards the deep 90 km wide slide scar indicating that a local depocentre was formed here before the mass flow occurred the shallowest crest of the helland hansen arch is located below the southern part of the slide scar and two large craters were formed on the surface of this anticlinal structure our model suggests that the deposition of glacial sediments above the helland hansen arch caused high excess pore pressures along the shallowest crest of this structure and formed a high pore pressure gradient towards the sea floor on its western flank an earthquake possibly triggered the initial slide where the slope was steepest west of the crest most of the slide scar was already formed when the slide finally eroded into the anticline high excess fluid pressure subsequently mobilised the diatomaceous oozes in the helland hansen arch and formed the craters much of this material flowed down slope without being totally disintegrated and was deposited as levee ridges and mounds above slide deposits from the first phase of the mass flow they have previously been wrongly interpreted as diapirs

early oligocene initiation of north atlantic deep water formation dating the onset of deep water flow between the arctic and north atlantic oceans is critical for modelling climate change in the northern hemisphere1 2 and for explaining changes in global ocean circulation throughout the cenozoic era3 from about 65 million years ago to the present in the early cenozoic era exchange between these two ocean basins was inhibited by the greenland scotland ridge3 4 but a gateway through the faeroe shetland basin has been hypothesized3 5 previous estimates of the date marking the onset of deep water circulation through this basin on the basis of circumstantial evidence from neighbouring basins have been contradictory5 6 7 8 9 ranging from about 35 to 15 million years ago here we describe the newly discovered southeast faeroes drift which extends for 120 km parallel to the basin axis the onset of deposition in this drift has been dated to the early oligocene epoch 35 million years ago from a petroleum exploration borehole we show that the drift was deposited under a southerly flow regime and conclude that the initiation of deep water circulation from the norwegian sea into the north atlantic ocean took place much earlier than is currently assumed in most numerical models of ancient ocean circulation

rates of continental breakup magmatism and seafloor spreading in the norway basin iceland plume interaction 1 in year 2000 an ocean bottom seismometer obs profile was acquired across the more margin to the aegir ridge an extinct seafloor spreading axis the margin is an early eocene volcanic passive margin located between the faeroe iceland ridge fir and the east jan mayen fracture zone ejmfz the p wave data were modeled by ray tracing to give a crustal transect showing a 10 11 km thick igneous crust created by breakup magmatism tapering off to magma starved seafloor spreading by c23 time 51 4 ma the location of the ejmfz was reinterpreted from a satellite derived gravity map and spreading direction in the norway basin reevaluated no other fracture zones were confirmed and both thin oceanic crust 4 5 km and lack of fracture zones resemble ultraslow spreading on the arctic gakkel ridge magnetic seafloor spreading anomalies were identified from the magnetic track recorded with the obs profile and half spreading rates were derived early seafloor spreading was slow 15 32 mm yr 1 approaching ultraslow 6 8 mm yr 1 by c20 time 42 7 ma a v shaped pattern seen in the gravity field located only around the northern part of the aegir ridge corresponds to increased crustal thickness in the seismic model recording northeast transport 3 6 mm yr 1 of more melt fertile asthenosphere zones the magma starved character of the norwegian basin seen also during slow seafloor spreading may be the result of depletion of the asthenosphere when the iceland plume constructed the fir to the south as the asthenosphere is subsequently transported into the norway basin

localized rotation during paleogene extension in east central idaho paleomagnetic and geologic evidence we collected paleomagnetic data from 137 sites in middle eocene volcanic rocks of the northeastern basin and range province in order to characterize the three dimensional kinematics of continental extension in the lost river and lemhi ranges idaho and to test previous block rotation models statistically significant flattening of directions at three of 10 localities reflects either insufficient averaging of paleosecular variation or erroneous tilt corrections five of the seven remaining locality means are statistically indistinguishable from the middle eocene reference direction this indicates that vertical axis rotation did not accompany post 50 ma normal faulting discordant declinations from two localities in the northern lost river range indicate 30 40 of counterclockwise rotation of a large domain of nnw striking volcanic rocks inclination flattening at one of the two rotated localities is moderate but statistically significant f f 9 9 6 5 in total the paleomagnetic data conflict with earlier predictions of uniform clockwise rotation in response to right lateral transtension adjacent to the eastern snake river plain there is a close correspondence between counterclockwise rotated localities and domains of nnw striking volcanic rocks and between unrotated localities and domains of north striking volcanic rocks new mapping shows that counterclockwise rotated localities are all in the hanging wall of a major west dipping low angle normal fault the donkey fault named for the first time this fault loses displacement southwards was active in eocene oligocene time and is probably a tilted high angle fault the spatial distribution of rotated and unrotated localities is best explained by counterclockwise rotation of the hanging wall of the donkey fault during opening of a southward tapering half graben according to this hanging wall rotation model the footwall of the donkey fault remained fixed relative to its rotating hanging wall our proposed kinematic model is generally applicable to extending continental lithosphere and provides a mechanism for coeval crustal thinning and vertical axis rotation thus vertical axis rotation may occur in the absence of strike slip faults in extensional orogens

indications for control of the iceland plume on the eocene oligocene greenhouse icehouse climate transition the eocene oligocene boundary at about 33 5 myr ago marks the transition from greenhouse to icehouse world accompanied by a sudden cooling of ocean bottom water we show that this global event is simultaneous with a deep rooted mantle process an abrupt suppression of the iceland plume triggered rapid deepening of the greenland scotland ridge gsr the sill moderating deep circulation between the nordic seas and north atlantic striking coincidence of several sets of events reflects the abrupt suppression of the iceland plume and a rapid removal of its influence on the nearby reykjanes ridge rr 1 a sudden segmentation of the paleo rr seen on seafloor magnetic anomalies 2 a drop in spreading rate of the north atlantic 3 a transition from thick to normal oceanic crust and 4 a rapid deepening and accelerated subsidence of the gsr inferred from the sedimentary record of dsdp site 336 the plume suppression and the concomitant gsr deepening coincide with the initiation of north atlantic deep water nadw at the eocene oligocene e o transition attested by onset of drift sedimentation in the faroe shetland channel fsc the deepest spill point on the gsr and in the north atlantic the feni drift these processes have influenced global deepwater composition and temperature as indicated by the striking correlation with the jump in global 18o 1 measured on benthic foraminifers that reflects the e o global cooling and with enrichment of unradiogenic nd isotopes in the southeastern atlantic and southern ocean the initiation of atlantic thermohaline circulation at that time is inferred from the abrupt split between planktonic and benthic 18o indicating the building of ocean water stratification this scenario is further corroborated by a reversal in benthic 18o at the late oligocene coincident with the renewal of vigorous iceland plume some 25 myr ago causing a considerable retardation in nadw fluxes the plume renewal is inferred from the emergence of the iceland plateau the transition to oblique unsegmented rr axis the cessation in deepening of the gsr and rapid increase in spreading rate of the north atlantic these events coincide with decreasing difference in planktonic benthic in global 18o by the late oligocene all these inferences suggest the role of the nadw sourced at the nordic seas to form background cooler conditions in the long time scale since the early oligocene or to form permanent conditions of invigorated thermohaline circulation that forces co2 trap in the oceans

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

glacigenic debris flows on the north sea trough mouth fan during ice stream maxima abstract numerous short sediment cores which penetrate through the glacimarine section and into glacigenic debris flow debrites gdfs on the north sea fan are investigated the sampled gdfs represent the uppermost of several sequences of these stacked bodies many hundreds of metres thick the gdfs occurred over slopes from 0 3 to 0 7 and examples are found from the shelf break at the mouth of the norwegian channel to the norway basin floor 300 km distant the gdf diamicts are structureless and homogeneous in terms of grain size magnetic susceptibility nrm bulk density water carbonate foraminiferal and rock fragment content this applies both from gdf to gdf across the fan and in a proximal distal sense comparison of the investigated lithologic parameters with weichselian till from a borehole in the norwegian channel 200 km up ice shows striking similarity to the gdf debrites ams 14c dates at the gdf glacimarine contact and stratigraphic relationships indicate voluminous deposition before 18 ka continuing possibly uninterrupted until ca 16 ka and a final phase halting just before 15 ka when the norwegian channel became ice free this chronology the comparable lithologic character between till and gdf debrites and a seismic continuity confirms inferences that the gdfs are directly associated with glacial ice at the shelf break the glacial efflux has not been subject to subsequent sorting and the homogeneity of the gdf is thought to reflect thorough mixing in a deforming till layer beneath a fast flowing ice stream the glacimarine section subsequent to gdfs shows no indications of turbidity flow observations are compatible with a slow non disintegrating cohesive plug flow transport mechanism with little sediment water interaction on the upper surface minor distal differentiation might reflect a change in flow process deposition on the fan margins from water borne glacimarine processes simultaneous with gdf deposition is limited

buried iceberg ploughmarks in the early quaternary sediments of the central north sea a two million year record of glacial influence from 3d seismic data abstract buried linear to curvilinear depressions interpreted as iceberg ploughmarks were identified through most of the 2 ma long and about 700 m thick early quaternary sedimentary record in two 3d seismic cubes from the central north sea basin 56 58 n 2 3 e the mean width of 402 features measured at 6 time slices in cube c08 was between 49 and 63 m and mean length was 2 5 to 3 7 km mapping the

refining a pedogenic carbonate co2 paleobarometer to quantify a middle miocene greenhouse spike abstract estimates of respired soil co2 concentration in paleosols are needed to calculate past atmospheric co2 levels from the difference between organic and carbonate carbon isotopic values in paleosols a new compilation of co2 concentrations late in the growing season in modern calcareous soils can be used to estimate respired soil co2 by subtracting atmospheric co2 concentrations furthermore respired co2 shows a significant relationship with depth to calcic horizon and this relationship can be used to estimate respired co2 concentrations in paleosols these values as well as estimates of 13c of atmospheric co2 from 13c of soil organic matter and of paleotemperature from bw horizon chemical composition refine the cerling co2 paleobarometer these refinements are applied to quantify the middle miocene greenhouse which has been controversial because it was not detected by marine alkenone and boron paleobarometers new estimates of middle miocene atmospheric co2 from paleosols in railroad canyon idaho reveal levels at 16 ma of 852 86 ppmv this is similar to predicted values by 2100 and 3 times pre industrial values pil 280 ppmv

the norway basin revisited from continental breakup to spreading ridge extinction abstract we re evaluate the structure and spreading evolution of the southeastern norway basin nb based on a new high resolution aeromagnetic survey nb 07 the survey covers a complete oceanic spreading segment from the continental oceanic transition of the more margin off norway to the aborted aegir ridge the new survey documents a transform margin an orthogonally rifted segment and an oblique sheared volcanic margin formed during the onset of breakup observed from the east jan mayen fracture zone to the faroe platform the detailed fabric of the nb revealed by the new data indicates that two distinct tectonic phases have reshaped the basin before the cessation of seafloor spreading and abortion of the aegir ridge in the late oligocene after continental breakup phase i from c24 to c21r 52 to 49 ma marks the earliest phase of spreading probably initiated in the central and outer part of the more basin during this period competing oceanic segments led to the formation of overlapping systems and pseudo fault development we observe a significant change in the nb s oceanic spreading system in the late early eocene and based on observations from surrounding areas we suggest that this is a record of a major tectonic event in the norwegian greenland sea around c21r 49 47 9 ma during phase ii from c21r to c10 48 to 28 ma of nb s development spreading rates decreased spreading direction changed and the number of faulting with large displacement increased leading to the formation of unexpected n s oriented oceanic fracture zones the fan shaped development of the spreading system initiated around c21r 49 47 9 ma instead of c18 c17 40 38 ma or c24 53 3 52 3 ma as previously proposed these new observations were used to re evaluate the tectonic evolution of the norwegian greenland sea and discuss some implications on the syn and post breakup development of the surrounding continental margins and the evolution of the jan mayen microcontinent

the glacial north sea fan southern norwegian margin architecture and evolution from the upper continental slope to the deep sea basin abstract high resolution seismic data have been used to study the ice stream fed north sea fan deposited from approximately marine isotope stage mis 12 and onwards located at the outlet of the norwegian channel on the se nordic seas continental slope the 110 000 km2 fan is dominated by glacigenic debris flows and slide debrites the fan is divided in two provinces by the volcanic more marginal high the proximal province has been characterised by alternation between deposition and erosion while the distal province has been dominated by deposition from mis 12 until the present the fan has received 32 000 km3 of sediments age constraints on fan stratigraphy provided by core investigations indicate that the fennoscandian ice sheet advanced to the shelf edge during mis 2 6 8 10 and probably 12 the fan experienced megaslides in late mis 6 9 and during mis 11 12

neogene and quaternary depositional environments on the norwegian continental margin 62 n 68 n abstract 2d multichannel seismic and mini sleeve gun profiles reveal that an up to 1 5 s twt thick sedimentary succession has been deposited on the norwegian continental margin 62 n 68 n during neogene and quaternary well defined miocene depocentres have evolved both in the north sea fan region and along the flanks of structural highs in the voring basin miocene sediments are on the other hand mainly absent within the storegga slide scar seismic facies analyses show that these deposits locally are characterised by a mounded and or migration aggradation pattern which we relate to a current influenced depositional environment hence the early neogene sediments on the norwegian continental margin are classified as contourites the contourites have most likely been deposited in connection with the establishment of a deep water exchange in the norwegian greenland sea due to the opening of the fram strait and subsidence of the greenland scotland ridge at about 2 5 ma a significant change in this depositional environment took place down slope sedimentary processes became now more important and throughout the late plio pleistocene sediments were mainly sourced from the norwegian mainland and the adjacent continental shelf causing depocentres to evolve along the shelf edge

north atlantic ocean deep water processes and depositional environments a study of the cenozoic norway basin abstract despite the enormous areas deep water basins occupy in modern oceans our knowledge about them remains poor at depths of greater than 2000 m the cenozoic norway basin in the northernmost part of the atlantic ocean is one such basin interpretation of 2d multichannel seismic data suggests a three stage evolution for the norway basin 1 eocene pliocene this time period is characterised by deposition of ooze rich sediments in a widening and deepening basin 2 early middle pleistocene a significant shift in sedimentary processes and depositional environments took place in the early pleistocene mass failures initiated on the norwegian continental slope and three early and middle pleistocene slide debrites with maximum thicknesses of 600 m and sediment volumes of up to 25 10 3 km 3 were deposited with ages estimated at c 2 7 1 7 ma 1 7 1 1 ma and 0 5 ma these slide deposits are among the largest identified worldwide and among the oldest mapped along the entire ne atlantic continental margin 3 late pleistocene present since c 0 5 ma the norway basin has been effected by glacigenic debris flows the storegga slide and hemipelagic glacimarine sedimentation these sedimentary processes were active during a time of repeated shelf edge ice advances along the ne atlantic continental margin this study shows that deep water basins represent dynamic depositional environments reflecting regional tectonic and climatic changes trough time

stratigraphic development of the south voring margin mid norway since early cenozoic time and its influence on subsurface fluid flow abstract the cenozoic seismic stratigraphy and geological development of the south voring margin are analyzed to understand their relation to fluid flow and margin stability the regional stratigraphy and palaeomorphology of the more and voring basins indicate gradual changes in depositional environment and tectonic compression between 55 ma to 2 8 ma during brygge and kai periods and abrupt changes associated with glacial interglacial cycles from last 2 8 ma during naust period these changes resulted in deposition of various types of sediments and led to processes such as polygonal faulting and dewatering inter fingering of contouritic stratified and glacigenic sediments and margin progradation a gas hydrate related bottom simulating reflector bsr occurs at nyegga and within the central voring basin while pockmarks are observed at nyegga only diagentic reflectors due to opal a opal ct conversion dbsrs occur along a wider area beyond the shelf edge the dbsrs are located in oozes within the kai and late brygge formations the gas hydrate bsr occurrence is concentrated above eocene depocenters in hemipelagic and contouritic sediments deposited during late plio pleistocene the bsr overlies polygonal faults and dbsrs but are confined to the slope of anticlines indicating its formation being related to fluid pathways from methanogenic rocks through focused fluid flow microbial gas production in kai brygge and deeper formations may have supplied the gas for gas hydrate formation fluid expulsion due to dbsr formation and polygonal faulting in oozes may have created overpressure development in permeable layers belonging to the overlying naust formation slide headwalls are also located close to the anticlines in the study area implying that over pressured oozes and focussed fluid flow may have been important in creating weak surfaces in the overlying naust sediments promoting conditions for failures to occur

geometry and genesis of glacigenic debris flows on the north sea fan tobi imagery and deep tow boomer evidence abstract acoustic data have been used to study the upper sequence of glacigenic debris flows gdfs deposited during the last glacial maximum on the north sea fan the presumed gdf release area at the shelf break 450 m water depth exhibits a sequence up to 90 m thick thinning to less than 45 m basinward at approx 750 800 m depth on a low slope 0 6 0 8 a seismically featureless sequence at the shelf break changes distinctly the first kilometers basinward showing a significant occurrence of features interpreted as infilled transport chutes the straight or sinuous chutes feed into well defined relief building gdf lobes 10 40 km from the shelf break a lack of failure scarps at the shelf break suggests that the gdfs have been sourced by a relatively continuous release of material flow lines concentrated along the chutes and center of the gdfs suggest a laminar movement pattern in the gdf core supported by passive flanks based on the flow morphology high pore pressure and low sediment strength within a central core of the flow is assumed to have contributed to the mobility of the gdfs dissipation of pore pressure along the margins of the flow may have caused the margins freeze while the sediment in the core remained mobile

sediment deposition in the northern basins of the north atlantic and characteristic variations in shelf sedimentation along the east greenland margin abstract new seismic data off east greenland were acquired in the summer of 2002 between 77 n and 81 n north of the greenland fracture zone the data were combined with results from the greenland basin and odp site 909 and indicate a pronounced middle miocene unconformity within the deep sea basins between 72 n and 81 n seismic unit na 1 consists of sediments older than middle miocene age and unit na 2 contains sediments younger than the middle miocene classification of a thinly bedded succession in the molloy basin resulted in a subdivision into four units unit i unit ii unit iiia and unit iiib a comparison of volume estimations and sediment thickness maps between 72 n and 81 n indicates differences in sediment accumulation in the greenland boreas and molloy basins important controls on the variation of accumulation included different opening times of the basins as well as tectonic conditions and varying sources of sediment transport due to prominent basement structures and the varying reflection character of the sediments along the entire east greenland margin we defined an age model of shelf sediments on the basis of similar sediment deposit geometry and known results from other regions the seismic sequences on the shelf up to an age of middle miocene are divided into three sub units along the east greenland margin middle miocene middle late miocene su 3 middle late miocene pleistocene su 2 pleistocene su 1 the differences in the geometry of the sequences show more ice stream related sedimentation between 72 n and 77 n and more ice sheet related sedimentation north of 78 n the region south of 68 n is dominated by more aggradational sedimentary strata so that a glacio fluvial drainage seems the main transport mechanism due to the greenland inland ice borderlines we assume the glaciers between the scoresby sund and 68 n did not reach the shelf break a first comparison of the sediment structure of the northeast greenland margin with the southeast greenland margin made it possible to demonstrate significant differences in sedimentation along this margin

late quaternary glacial development of the mid norwegian margin 65 to 68 n abstract we have studied the younger part of the large plio pleistocene prograding wedge on the northern part of the mid norwegian margin using high resolution seismic data the wedge is mainly composed of thick glacigenic debris flow packages interbedded with hemipelagic and contouritic sediments age constraints of the seismic stratigraphy obtained through correlation to odp 644a show that the fennoscandian ice sheet advanced to the shelf break during marine isotope stages mis 2 ca 15 22 ka bp 6 128 186 ka bp 10 339 362 ka bp 12 423 478 ka bp and 14 524 565 ka bp and to the inner shelf during mis 8 245 303 ka bp the stratal geometry and sedimentary pattern locally indicate rapid subsidence up to ca 1 2 m ka of the outer shelf and slope area since 350 ka bp the subsidence is most likely a response to the rapid deposition of glacigenic sediments during the plio pleistocene it is inferred that sediment loading was an important factor behind the diapirism in the vema dome area

extreme sediment and ice discharge from marine based ice streams new evidence from the north sea a major problem for understanding the dynamics of ice streams has been a lack of precise data on ice streaming longevity and sediment transport efficacy here we present the first well constrained data on sediment flux from a paleoice stream this has been achieved by computing the volume of sediment deposited as debris flows on the fan located at the outlet of the norwegian channel ice stream and converting to a flux measurement by accounting for the duration of streaming in this episode between 20 and 19 ka during the last glacial stage in this period the ice stream delivered an average 1 1 gt of sediment per year equivalent to 8000 m 3 yr 1 per meter width of ice stream front the calculated flux is an order of magnitude higher than most previous estimates for other paleoice streams and is comparable to the present sediment flux from the world9s largest rivers the short period of debris flow deposition suggests that the norwegian channel ice stream underwent rapid on off switching with punctuated iceberg delivery to the north atlantic as a consequence

sedimentary and oceanographic responses to early neogene compression on the nw european margin the lower neogene stratigraphy of the nw european atlantic margin from the voring to the porcupine basins is interpreted to record a discrete phase of compressional tectonism that spanned at least 8 ma from the earliest to the early mid miocene this compressional tectonism may be coeval with a local reorganisation of the ne atlantic plate system with the transfer of the jan mayen micro plate from greenland to europe the compressional tectonics has resulted in a number of stratigraphic sequences of complex character bounded by regional base neogene and intra miocene unconformities these are traceable across a range of depths and record distortion of the basin margins and changes in deep water circulation patterns this episode of compressional tectonics has also resulted in the creation of a number of anticlinal domes along the norwegian faroese and uk atlantic margins the stratigraphic and structural evidence are interpreted to record two stages in the development of the margin the first being characterised by a prolonged period of regional flexure in response to the build up of compressive stresses the second stage is the development of anticlinal structures that led to a rapid release of stress in the wyville thomson faroes region compressional deformation influenced the creation of the present day deep water conduit of the faroe bank channel which is interpreted to be an early neogene syncline together the faroe bank and faroe shetland channels represent the deepest water passageway across the greenland scotland ridge the early neogene development of this conduit is considered to mark the onset of deep water exchange across this oceanic gateway

morphology sedimentary infill and depositional environments of the early quaternary north sea basin 56 62 n abstract the north sea basin has been subsiding during the quaternary and contains hundreds of metres of fill seismic surveys 170 000 km2 provide new evidence on early quaternary sedimentation from about 2 75 ma to around the brunhes matuyama boundary 0 78 ma we present an informal seismic stratigraphy for the early quaternary of the north sea and calculate sediment volumes for major units early quaternary sediment thickness is 1000 m in the northern basin and 700 m in the central basin total about 40 000 km3 northern north sea basin fill comprises several clinoform units prograding westward over 60 000 km2 architecture of the central basin also comprises clinoforms building from the southeast to the west an acoustically layered and mounded unit unit z was deposited remaining accommodation space was filled with fine grained sediments of two central basin units above these units an upper regional unconformity equivalent uru records a conformable surface with flat lying units that indicate stronger direct glacial influence than on the sediments below on the north sea plateau north of 59 n the upper regional unconformity uru is defined by a shift from westward to eastward dipping seismic reflectors recording a major change in sedimentation with the shetland platform becoming a significant source a model of early quaternary sediment delivery to the north sea shows sources from the scandinavian ice sheet and major european rivers clinoforms prograding west in the northern north sea basin representing glacigenic debris flows indicate an ice sheet on the western scandinavian margin in the central basin sediments are generally fine grained suggesting a distal fluvial or glacifluvial origin from european rivers ploughmarks also demonstrate that icebergs derived from an ice sheet to the north drifted into the central north sea basin by contrast sediments and glacial landforms above the uru provide evidence for the later presence of a grounded ice sheet

slope failure dynamics and impacts from seafloor and shallow sub seafloor geophysical data case studies from the costa project holocene and slightly pre holocene submarine landslide are found both in high latitude glacial dominated margins and in lower latitude river dominated margins this paper constitutes a major assessment on some of the best studied submarine instabilities in the world we review and update from original data and literature reports the current state of knowledge of storegga traenadjupet and finneidfjord slides from the mid norwegian margin afen slide from the faeroe shetland channel big 95 slide and central adriatic deformation belt cadeb from continental slope and inner continental shelf settings off the ebro and po rivers in the mediterranean sea canary slide west of the westernmost youngest canary islands and gebra slide off the northern tip of the antarctic peninsula in the southern hemisphere i e those studied in the continental slope stability costa project the investigated slides range in size from the gigantic 90 000 km2 and almost 3000 km3 storegga slide to the tiny 1 km2 and 0 001 km3 finneidfjord slide not only do individual submarine landslides rarely involve processes precisely fitting with pre established categories mostly based on subaerial research but also they display complex mechanical behaviors within the elastic and plastic fields individual events can involve simultaneous or successive vertical to translational movements including block detachment block gliding debris flow mud flow and turbidity currents the need for an in depth revision of the classification criteria and eventually for a new classification system based on the new imaging capabilities provided by modern techniques is more than obvious we suggest a new system which for the moment is restricted to debris flows and debris avalanches volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides the assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey cadeb a shore parallel prodelta detached from its source is the exception to the good correlation found between across slope width and alongslope length with slide area height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas which prevent farther forward expansion of the deposit such as gebra and big 95 in such cases over thickened deposits are found a particularly loose and fluid behavior can be deduced for slides showing an over thinned character such as the canary slide that traveled 600 km scar areas and slip planes have been investigated with particular emphasis although slide headwalls might present locally steep gradients up to 23 for storegga slide the slope gradients of both the failed segment margins and the main slip planes are very low max 2 and usually around 1 and less an exception is the finneidfjord slide 20 5 that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure mechanically distinct low permeable clayey weak layers often correspond to slip planes beyond the slide headwall since not only formation of these weak layers but also sedimentation rates are climatically controlled we can state that slide pre conditioning is climatically driven too run out distances reflect the degree of disintegration of the failed mass of sediment the total volume of initially failed material and transport mechanisms including hydroplanning commonly specific run outs could be attributed to distinct elements such as cohesive blocks and looser matrix as nicely illustrated by the big 95 slide total run outs usually correspond to matrix run outs since the coarser elements tend to rest at shorter distances outrunner blocks are finally a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass in addition to pre conditioning factors related to geological setting and sedimentation conditions a final trigger is required for submarine landslides to take place which is most often assumed to be an earthquake in high latitude margins earthquake magnitude intensification because of post glacial isostatic rebound has likely played a major role in triggering landslides although it cannot be totally ruled out there is little proof at least amongst the costa slides that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers

late cenozoic prograding wedges on the nw european continental margin their formation and relationship to tectonics and climate abstract during late pliocene to pleistocene times prominent prograding wedges were deposited along the continental margin of nw europe resulting in seaward shelf break migration of up to 150 km much of the sediment accumulation occurred marginal to the former mid to high latitude ice sheets the geographical distribution and stratigraphical and chronological data may suggest that the instigation of the wedges was variously related to tectonic uplift as well as a response to the late pliocene to pleistocene climate deterioration and onset of major northern hemisphere glaciations the onset of wedge growth on the nw uk and irish margins was initiated at about 4 ma in response to tectonic tilting of the margin in that region however glacially derived sediments here comprise a significant proportion of the wedges especially since 0 44 ma for the faroe margin no detailed chronology is available however it may be inferred that onset of glacigenic wedge growth here did not post date that observed on the nw uk and irish margins offshore norway wedge growth has largely occurred since ca 2 7 ma in response to northern hemisphere glaciations also recording a major change in sediments transport routes at 0 8 1 1 ma reflecting larger fennoscandian ice sheets presently it is uncertain whether the glacigenic wedge growth was preceded by a fluvial phase in response to uplift in this area in the western barents sea an early phase of wedge growth was glacio fluvial in character off western spitsbergen the development was similar to that of the barents sea although the glacigenic wedge growth phase may have started somewhat earlier the wedges commonly display gently inclined seaward prograding clinoforms and transparent to chaotic internal acoustic facies sampling of their sediments reveals that they are mainly composed of glacigenic diamicton interbedded with marine and glaciomarine sediments that to various extents have been affected by bottom current action the clinoforms of these wedges vary in geometry from oblique to sigmoidal and they also show varying degrees of aggradation throughout their development the resulting stratal stacking pattern can be attributed to a combination of variations in sediment supply sedimentary processes and accommodation space the latter being a function of tectonic movements and or loading induced subsidence as well as eustatic sea level fluctuations

large scale development of the mid norwegian margin during the last 3 million years abstract during the last c 2 7 my large quantities of glacially derived material were transported westwards from the norwegian mainland areas and inner shelf and deposited mainly as prograding sediment wedges into a basin of intermediate depth offshore mid norway the deposits are more than 1000 m thick in extensive areas and are defined as the naust formation in the haltenbanken traenabanken region the shelf edge migrated 100 150 km westwards the narrow more shelf was built out only in the order of 30 50 km mainly due to a steeper pre existing slope dipping towards a much deeper basin in this area the holocene storegga slide as well as older slides displaced slope sediments towards the deeper part of the basin in early naust time the most extensive progradation occurred in the northern area possibly due to the combined effect of land uplift and glaciations the importance of glaciations for the progradation of the more shelf and areas farther south increased through the pleistocene period the norwegian channel ice stream became very important during the last three glaciations and a thick succession of glacigenic debris flows was deposited on the north sea fan more than 400 m of sediments accumulated during the weichselian all the last three glaciations supplied glacial debris beyond the shelf edge the most extensive progradation in the north was in the skjoldryggen region particularly during the elsterian glaciation during ice free periods hemipelagic and contouritic sediments were deposited on the slope such sediments are most common in the storegga slide area where they hosted glide planes beneath the major slides