variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

gas hydrate systems in petroleum provinces of the sw barents sea abstract 3d seismic data of the sw barents sea provided information about the existence of structure ii gas hydrates and shallow gas in marine sediments gas hydrates and shallow gas exist in the sw barents sea in conjunction with deep hydrocarbon reservoir leakage available conventional 3d seismic data show acoustic chimneys that extend to depths 1700 ms two way travel time below the seafloor the location of the chimneys coincides with structural boundaries and fault complexes cutting through mostly jurassic and triassic strata vertical fluid flow through these chimneys transports thermogenic gas to the gas hydrate stability zone causing the formation of a bottom simulating reflector bsr in addition variations of fluid flux across deep seated fault complexes cause changes in heat flow which explains the shoaling of the bsr and the formation of a tilted bsr tbsr at the border between the ringvassoya fault complex and the loppa high the stability model using thermogenic gas composition type i and ii shows gas hydrates are stable at 225 m 345 m depth corresponding to variation in the geothermal gradient for upper bsr 28 7 c km and 37 c km and lower bsr levels 23 4 c km and 28 3 c km these lateral changes in the temperature gradient can be reconciled with changes in upward fluid flow rates of 1 8 2 2 mm yr 1 such gas hydrate and fluid flow systems on arctic continental margins especially in shallow water depths are potential gas emitters due to their sensitivity to warming ocean temperatures

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

seismic evidence for shallow gas escape features associated with a retreating gas hydrate zone offshore west svalbard active gas venting occurs on the uppermost continental slope off west svalbard close to and upslope from the present day intersection of the base of methane hydrate stability bmhs with the seabed in about 400 m water depth in the inter fan region between the kongsfjorden and isfjorden cross shelf troughs from an integrated analysis of high resolution two dimensional pre stack migrated seismic reflection profiles and multibeam bathymetric data we map out a bottom simulating reflector bsr in the inter fan region and analyze the subsurface gas migration and accumulation gas seeps mostly occur in the zone from which the bmhs at the seabed has retreated over the recent past 1975 2008 as a consequence of a bottom water temperature rise of 1 c the overall margin parallel alignment of the gas seeps is not related to fault controlled gas migration as seismic evidence of faults is absent there is no evidence for a bsr close to the gas flare region in the upper slope but numerous gas pockets exist directly below the predicted bmhs while the contour following trend of the gas seeps could be a consequence of retreat of the landward limit of the bmhs and gas hydrate dissociation the scattered distribution of seeps within the probable hydrate dissociation corridor and the occurrence of a cluster of seeps outside the predicted bmhs limit and near the shelf break indicate the role of lithological heterogeneity in focusing gas migration

neogene stratigraphy and the sedimentary and oceanographic development of the nw european atlantic margin a regional correlation of neogene stratigraphy has been attempted along and across the nw european atlantic continental margin between mid norway and sw ireland two unconformity bounded successions are recognised these are referred to as the lower and upper neogene successions and have been dated as miocene early pliocene and early pliocene holocene respectively in age their development is interpreted to reflect plate wide tectonically driven changes in the sedimentary oceanographic and latterly climatic evolution of the ne atlantic region the lower neogene succession mainly preserves a record of deep water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities within this succession on both sides of the eastern greenland scotland ridge from the mid miocene this is interpreted to record enhanced deep water exchange through the faroe conduit deepest part of the southern gateway and can be linked to compressive inversion of the wyville thomson ridge complex thus a pervasive interconnected arctic north atlantic deep water circulation system is a neogene phenomenon the upper neogene succession records a regional change at about 4 ma in the patterns of contourite sedimentation submarine erosion new depocentres coeval with the onset of rapid seaward progradation of the continental margin by up to 100 km this build out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin associated changes in deep water circulation may be part of an atlantic wide reorganisation of ocean bottom currents glacial sediments form a major component of the prograding shelf margin shelf slope sediment wedges but stratigraphic data indicate that the onset of progradation pre dates significant high latitude glaciation by at least 1 ma and expansive northern hemisphere glaciation by at least 3 ma

seismic stratigraphy and sedimentary processes at the norwegian sea margin northeast of the faeroe islands abstract sedimentary processes on the continental slope north of the faeroe islands during the cenozoic were studied in detail using high resolution multichannel reflection seismic data a wedge shaped succession of cenozoic sediments with a maximum thickness of approximately 2 km overlies the basaltic basement which forms the underlying structure of the slope the sedimentary succession represents four depositional sequences and a contourite deposition also some slump deposits are recognised the oldest sequence which is possibly of eocene late oligocene age was prone to repeated mass movements during the deposition of the sequence at the end of the oligocene the sediments on the slope stabilised and the depositional pattern was strongly influenced by sea level changes in the late pliocene a renewed instability of the slope occurred resulting in mass movements causing erosion at the middle of the slope and creating a major slide escarpment at the base of the slope subsequently the sedimentary processes change from mainly downslope progradational forms to along slope current induced contourite deposition this change most likely marks the formation of a norwegian sea deep water current pattern similar to the present variations of the current strength and sediment supply caused by glacial interglacial cycles probably results in an alternating sedimentation pattern of the contourite deposit another impact from the glaciation of the northern hemisphere is the presence of iceberg turbate at the upper parts of the northeastern faeroes slope

u pb zircon ages from the eastern savant lake crow lake metavolcanic metasedimentary belt northwest ontario five rocks from three areas in the eastern part of the savant lake crow lake metavolcanic metasedimentary belt have been dated by u pb analysis of zircons the sioux lookout area is composed of a sequence of generally fault bounded metavolcanic and metasedirnentary belts the age of a felsic tuff in the central volcanic belt is 2732 72 ma this is possibly the youngest sequence in the area the savant lake volcanic belt comprises the jutten volcanic unit at its base separated by an angular unconforrnity from the handy lake volcanic sequence the age of a dacitic tuff near the base of the handy lake volcanic sequence is 2745 22 i ma the south sturgeon lake volcanic belt is composed of four volcanic cycles the age of a felsic tuff from the top of the uppermost cycle is 2717 92 ma the felsic beidelman bay pluton and the mafic pike lake pluton which both intruded the lower art of the sequence give ages of 2733 82 and 2732 721 a respectively this establishes a minimum time span of 15 921 ma for deposition of the sequence this interval along with the 27 ma span between the ages of the handy lake sample and the volcanic sample from the south sturgeon lake area suggests that the sequences were laid down by a series of discrete volcanic episodes for samples subjected to multistage lead loss the reliability of ages has been greatly enhanced by air abrasion of zircons several cases of suspected biasing of analyses by the air abrasion process have been encountered it appears that this biasing problem can be overcome by selection and abrasion of low uranium grains that are free of imperfections

the free gas zone beneath gas hydrate bearing sediments and its link to fluid flow 3 d seismic imaging offshore mid norway abstract hydrate recycling and vertical migration of fluids from deep sources are processes evoked as controllers of the formation and stability of the free gas zone fgz beneath the base of the gas hydrate stability zone bghsz these processes have been often investigated through analytical and numerical modeling at some locations in continental margins however the seismic response of sediments deformed by such mechanisms has been poorly investigated due to the lack of reliable seismic resolution to clearly image anomalies confined to the fgz the present study is dedicated to the seismic characterization of the fgz beneath the bghsz at a hydrate site offshore mid norway using high resolution p cable 3d seismic data dim amplitude anomalies showing mainly lineations in a polygonal pattern of distribution 50 80 m vertical extension 150 300 m lateral extension and up to a few kilometers long are interpreted as evidence of sediment remobilization possibly aided by hydrate dissociation at focused fluid flow zones below former bases of the ghsz the exclusive occurrence of the anomalies within a depth range comprising estimated paleo bghszs during the last 200 kyr suggests that the anomalies are associated to paleo hydrate bearing sediment seals emplaced at depths controlled by overburden it also supports recently reported indications of main periods of fluid expulsion towards the seafloor occurring between 200 and 130 ka bp

towards an understanding of the neogene tectonostratigraphic framework of the ne atlantic margin between ireland and the faroe islands abstract the neogene succession preserved on the continental margin between ireland and the faroe islands can be divided into two megasequences of miocene and pliocene holocene age the base of each megasequence is marked by a regional unconformity these are of latest oligocene early miocene and early pliocene age respectively and reflect major phases of neogene margin evolution the megasequences and their bounding unconformities reflect a gross two stage depositional history predominantly a response to intra plate tectonism that modified sedimentation patterns and palaeoceanographic circulation the latest oligocene early miocene event marks a major change in the oceanographic regime and can be linked to the establishment of deep water exchange between the arctic and north atlantic oceans the submergence of the greenland scotland ridge which includes the iceland faroe rise and the wyville thomson ridge in the area of study resulted in locally vigorous deep water erosion as northern source deep water flowed through the faroe conduit which is part of the southern gateway for deep water exchange coeval deposition of sediment drifts occurred in the faroe shetland channel and rockall trough as the deep water currents stabilised the early pliocene event marked the widespread instigation of shelf margin progradation to the north west of britain and ireland and to the east of the faroe islands this event is linked to the uplift and erosion of britain ireland and the faroe islands and is part of a larger north atlantic scale uplift significant deep water erosion in the rockall trough suggests that the water circulation pattern was also modified by this event the formation of the key megasequence boundaries occurred during times of significant plate rearrangement and suggests that these events may be correlatable across the whole nw european margin

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

three dimensional seismic characterization of a complex sediment drift in the south china sea evidence for unsteady flow regime this study describes a previously unobserved reflection seismic configuration comprising a honeycomb planform and a repeated erosion infill cross section based on high resolution three dimensional two dimensional seismic data and bathymetric data the honeycomb structures cover an area of more than 5000km 2 and are developed within the late miocene to recent deep water sediments of the north western south china sea linear erosional troughs up to 10km long and 1km wide are widely developed in this area are intimately related to the particular seismic configuration and interpreted to represent a new type of sediment drift that is caused by unsteady bottom current regimes operating since the late miocene the unsteady bottom current regimes are suggested to be triggered by irregular seabed morphologies considerable sea floor topography was generated as a direct result of tectonic movements in the area since the late miocene and this topography then influenced the pathways of strong bottom currents this study highlights that i an unsteady bottom current regime can be laterally extensive and persist for millions of years ii structurally controlled sea floor relief plays an important role in controlling the depositional pattern and iii the bottom currents were active since the late miocene flowing from the south east through the xisha guangle gateway and crossing the honeycomb structure zone this study documents a new style of drift and will help to improve current knowledge of palaeoceanography and understanding of the south china sea deep water circulation which is at present still poorly understood

seismic geomorphology an overview seismic geomorphology the extraction of geomorphic insights using predominantly 3d seismic data is a rapidly evolving discipline that facilitates the study of the subsurface using plan view images a variety of analytical techniques is employed to image and visualize depositional elements and other geologically signi cant features this volume presents key technical papers presented at a recent research conference seismic geomorphology conference february 10 11 2005 co sponsored by the society for sedimentary geology and the geological society london these papers cover a broad range of topics from detailed depositional element analysis to big picture regional issues from lithology prediction to diagenetic modi cation of the stratigraphic section this discipline is only in its early stages of development and will henceforth expand rapidly in response to the growing availability to researchers of high quality 3d seismic data

introducing the vale formation in the southern central north sea basin offshore netherlands based on the re interpretation of well log data this study shows that the vale formation was deposited over large areas 100 km in the southern central north sea basin offshore netherlands up to now the vale formation and the lateral equivalent maureen formation were only described in the nearby offshore denmark norway and uk in the latter areas the vale formation consists of sandstones marlstones and marly mudstones the results of this study show that in the northern offshore netherlands the lithology of the vale formation ranges from marlstones to marly claystones biostratigraphic analyses by previous studies on samples within the newly interpreted vale formation indicate a similar age latest danian and selandian and depositional environment open marine in the offshore netherlands compared to the areas further north well correlation panels indicate that the vale formation obtains it highest thicknesses over 30 m in the western study area from where it thins to less than 10 m and changes its log signature towards the tectonically uplifted dutch central graben in the eastern study area on top of the dutch central graben the vale formation and overlying claystones locally seals off an oilfield in the underlying chalks

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

deep circulation change linked to heinrich event 1 and younger dryas in a middepth north atlantic core a core from the mid atlantic ridge at 43 5 n and 3 km water depth shows distinct evidence of the deglacial events known as heinrich event 1 probably the marine equivalent of oldest dryas cooling in europe and the younger dryas the heinrich event dated at three levels to between 14 3 and 15 0 ka is marked by a minimum in foraminifera per gram by maxima in rates of sedimentation ice rafted debris per gram and relative abundance of n pachyderma s and by a 18o minimum in planktonic foraminifera the younger dryas event is marked by peak abundance of n pachyderma s and a planktonic 18o maximum benthic foraminiferal 13c reaches minimum values during both the heinrich event and the younger dryas our data indicate pronounced changes in surface water properties were coupled with reduced production of north atlantic deep water at each of these times

late glacial and holocene palaeocurrents around rockall bank ne atlantic ocean core samples and hydrographic data from 50 to 60 n and 15 to 25 w in the northeast atlantic ocean are used to study changes in current activity from the last glacial to present we establish a new method to distinguish between the effects of changing bottom current speed and varying size input by drawing upon sediment flux data and detailed grain size analysis changes in current speed are recorded by the mean size of the sortable coarse noncarbonate silt component which increases with current vigor by winnowing away of fines our method involves the definition of an ideal sortable silt input function recorded at a site accumulating unmodified pelagic flux only the ideal profile is then compared with records from other sites to determine the history of current speed at a range of water depths the upper surface of southern source water ssw probably shoaled during the glacial as indicated by the covariation of sortable silt records from sites presently covered by ssw and lower north atlantic deep water lnadw the data suggest that production of lnadw was suppressed during the glacial increased following the last glacial maximum and declined at the start of termination 1a a second pulse of production occurred immediately before the younger dryas event intermediate waters were generally faster flowing during the glacial and may have expanded their depth domain such that a single glacial intermediate water mass covered depths from 1100 to more than 2000 m

plate reorganization a cause of rapid late neogene subsidence and sedimentation around the north atlantic subsidence analysis of wells in the central north sea and labrador grand banks and oft the west greenland scotian shelf and united states atlantic margin shows distinct quantitative stratigraphic correlation patterns of circum north atlantic sites a significant departure from the overall decrease in subsidence for the pliocene occurs in many wells when the rate is found to have increased one or more orders of magnitude from oligocence miocene rates wells were selected along transects from shore to basin to find if relative basin position is influenced by differential basin subsidence although stratigraphic resolution is not detailed more basinward sites experienced up to four times larger subsidence rates in the late neogene than in the oligocene miocene with a peak in the pliocene wells at the basin edge experienced much less subsidence or showed uplift the observations are consistent with a rapid change of intraplate stress at the cause for this observed transition in neogene subsidence major reorganizations of spreading direction and rate occurred during the pliocene along the entire atlantic spreading system possibly in conjunction with more global changes in plate motions we propose that the associated changes in intraplate stress caused the excess margin subsidence relative uplift along basin edges is consistent with this mechanism of relative movement and may explain apparent eustatic changes in sea level

3d seismic analysis of the west shetland drift system implications for late neogene palaeoceanography of the ne atlantic abstract detailed seismic stratigraphic analysis of the west shetland drift located on the shetland margin of the faeroe shetland channel has been undertaken using commercial 3d seismic data emphasis was placed on the interpretation of a significant plastered contourite drift body the west shetland drift slope section with the aim of reconstructing the palaeoceanographic regime of the west shetland slope during the past 5 ma although limited in areal extent the west shetland drift slope section provides a key record of the depositional environment and bottom current activity on the west shetland slope during the late neogene the drift body was divided into three seismic stratigraphic units and depositional processes responsible for each unit were interpreted resulting in proposal of an evolutionary model in which a mixed downslope alongslope depositional system was succeeded by alongslope current derived contourite drift deposition during the early pliocene to mid pleistocene during this time sw flowing alongslope currents impinged upon the west shetland slope between the basin floor and a mid to upper slope position the final stage of deposition consisted of slope wedge progradation associated with mid to late pleistocene glaciation contourite deposition on the west shetland slope was punctuated by periods of glaciation activity during which alongslope current activity appears to have been disrupted suggesting a link between alongslope current activity and glaciation detailed mapping of key smaller scale features including a spectacular bottom current sediment wave field and iceberg ploughmarks both of which were identified for the first time during this study was instrumental in constraining the palaeocurrent regime and would not have been possible without the high spatial resolution of the 3d seismic data this study therefore highlights the efficacy of 3d seismic data as a tool for large scale spatial and temporal analysis of contourite drifts palaeoceanographic research

danian selandian boundary criteria and north sea basin tethys correlations based on calcareous nannofossil and foraminiferal trends in sw france abstract high resolution calcareous nannofossil and foraminiferal investigations of the bidart and loubieng outcrop sections allow to define a time calibrated sequence of 47 bio events within the danian selandian d s boundary interval 61 2 59 7 ma of aquitaine sw france the d s boundary as originally defined in denmark start of clastic sedimentation at the base of the lellinge greensand formation is marked by the end of the acme of the nannofossil family braarudosphaeraceae this bio event dated at 59 9 ma has also been identified at the lithological change from limestone dominated lasseube formation to marly sedimentation latapy member of the pont labau formation in sw aquitaine and at the base of the red marls of the itzurun formation at zumaia spain recently designated as global stratotype section and point gssp for the d s boundary this implies contemporaneity of this lithological shift throughout europe and a gssp proposal which is consistent with the original boundary definition the braarudusphaeraceae event is believed to be due to the interruption of freshwater influx probably related to a sudden decrease in precipitation it is located at the top of nannofossil zone np4 and within planktonic foraminiferal zone p3b and bracketed between the lowest occurrence lo of morozovella velascoensis below and the lo of fasciculithus tympaniformis above it is coincident with the lo of bomolithus elegans the lcso cs consistent of fasciculithus janii and the lo of subbotina velascoensis the d s boundary as originally defined is 400 k y posterior to a major discontinuity recorded throughout the tethyan realm tunisia egypt and up to now erroneously considered to correspond to the d s boundary this break in sedimentation dated at 60 3 ma and coinciding with the p3a p3b boundary is due to a major sea level fall it is correlated with sedimentation changes in the aquitaine zumaia area start of development of marly interbeds and in the north sea basin transition bryozoan limestone calcisiltite in denmark transition shallow marine mons formation continental hainin formation in belgium the loubieng section supplements the zumaia section because of its rich and well preserved fossil content and continuous sedimentation it constitutes an excellent auxiliary section for the d s boundary

comparison of trends of iceberg scour marks with iceberg trajectories and evidence of paleocurrent trends on saglek bank northern labrador shelf high resolution seismic and sidescan sonar surveys on saglek bank indicate extensive areas of iceberg scoured sea bottom and provide data for an analysis of 6075 iceberg scour marks in 537 samples each of 0 25 km by 2 0 km area the general trends of iceberg scours measured on sidescan sonographs are comparable to iceberg trajectories which are mostly controlled by currents on saglek bank iceberg scour and iceberg drift directions are generally northwest southeast straight scours predominate on the shelf edge reflecting the influence of unidirectional oceanic labrador currents bank top scours are commonly curved reflecting the influence of slower moving water more subject to the effects of rotary tidal currents and storms this difference in dispersion of scour trends between the bank top and shelf edge is due to the relative strengths of variable tidal and storm driven currents and unidirectional oceanic currents pack ice forces may also influence iceberg movement modern icebergs scour the she

turbidity current sediment waves on irregular slopes observations from the orinoco sediment wave field abstract the orinoco sediment wave field covers an area of at least 29 000 km2 on the southern margin of the orinoco valley at a water depth of 4400 4825 m wave dimensions are highly variable across the wave field with wavelengths of 110 2600 m and wave heights of 1 15 m slope gradients are also very variable with values of 0 14 0 48 overall the sedimentary sequence on the upslope wave flanks is about 40 thicker than that on the downslope flanks leading to upslope wave migration in the manner of antidunes in addition reflectors on the upslope flanks generally display higher reflectivity than those on the downslope flanks suggesting that a higher proportion of coarser sediment occurs on the upslope flank an unconfined turbidity current origin is proposed for the orinoco sediment waves based upon detailed analysis of regional stratigraphic seismic facies and sediment wave distribution morphology and dimensions sediment waves are not related to flows passing along or spilling out of the orinoco valley or to bottom currents flowing parallel to the slope turbidity currents responsible for wave generation are interpreted as originating from slope failures on the adjacent venezuela guyana and suriname continental margins simple numerical modelling has enabled turbidity current flow characteristics across the orinoco sediment waves to be estimated internal froude number 0 7 1 1 flow thickness 24 645 m and flow velocity 31 82 cm s 1 a key finding of this study is that there appears to be a close relationship between the changes in slope gradient and those in wave dimensions across the wave field the irregular gradient of the present day wave field is partly a reflection of the irregular bounding surface of the sediment waves which is represented by mass flow deposits and associated mud diapirs the changes in slope gradient along this lower boundary lead to variations in the flow thickness and flow velocity of passing turbidity currents which in turn control the wave dimensions generally on lower gradients beyond minor breaks of slope flow thickness increases and flow velocity decreases leading to an increase in wavelength and a decrease in height

subdivision of precambrian time recommendations and suggestions by the subcommission on precambrian stratigraphy abstract the subcommission on precambrian stratigraphy consisting at the time of its last formal meeting in 1982 of 12 titular members and 30 correspondents has been actively working toward an acceptable subdivision of precambrian time for more than a decade comprehensive time rock charts have been prepared for major precambrian shields and this composite record has been analysed for patterns and events common to several or to all a geochronologic subdivision scheme has evolved that reflects these patterns of major events in earth history while still recognizing that those events are typically varied in intensity and timing from one region to another time unit boundaries have been selected so as to enclose or delimit principal cycles of sedimentation orogeny and magmatism but the boundaries are defined in years without specific reference to any bodies of rock several recommendations developed sequentially at formal meetings held at intervals of 2 4 years and announced in geologic journals with calls for comment and criticism are proposed 1 1 the recommendation to establish two major time units of eon rank proterozoic and archaean archean separated by a time boundary at 2500 ma is reaffirmed 2 2 the provisional recommendation to subdivide the proterozoic eon into three units of era rank provisionally labelled proterozoic i ii and iii with time boundaries at 2500 1600 900 and about 570 ma respectively is confirmed and 3 3 further subdivision of the proterozoic into eight time units of period rank as yet unnamed with time boundaries at 2500 2100 1800 1600 1400 1200 900 700 and about 570 ma respectively is provisionally recommended the nature of the subcommission s deliberations and the guidelines developed are described herein comment and criticism both on the procedure followed and on the recommendations themselves are invited

palaeoenvironmental changes across the danian selandian boundary in the north sea basin abstract the danian selandian boundary 60 ma marks the cessation of 40 million years of carbonate deposition in the north sea basin and a shift to siliciclastic deposition on the basis of variations in lithology benthic and planktonic foraminifera and calcareous nannofossils in three cores from storebaelt in the eastern part of the north sea basin we have reconstructed the palaeoenvironmental changes across the boundary the benthic foraminiferal faunas belong to the midway type fauna they are extremely rich and more than 260 taxa have been recognized q mode cluster analysis groups the benthic assemblages into four biofacies which correspond fairly closely to lithological units correlation of the storebaelt records with marine palaeorecords from the danish basin and the north sea basin indicate that the transformation of the north sea from a carbonate to a siliciclastic basin occurred in four steps separated by relatively long stable periods the most important external factors involved in the change are firstly a drop in the relative sea level during the late danian leading to the disappearance of bryozoans from the north sea basin and to non deposition and erosion in many areas secondly coinciding with the danian selandian boundary an uplift of the scotland shetland area resulting in a massive input of siliciclastic deposits to the north sea basin thirdly during the early selandian inversion of the sorgenfrei tornquist zone and mesozoic basins in the southern and eastern part of the north sea basin resulted in a huge influx of reworked cretaceous chalk and an almost complete stop of carbonate production finally later in the early selandian in connection to a general sea level rise and a reduction in the gateway between the north sea basin and the tethys sea the sea bottom conditions became colder and more acidic this resulted in partial dissolution of the carbonates and the deposition shifted from marl to clay comparison with records from the western pyrenees the nile basin and the eastern north america suggests that sea level changes across the danian selandian boundary are primarily of eustatic nature

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

sediment waves on the south china sea slope off southwestern taiwan implications for the intrusion of the northern pacific deep water into the south china sea abstract using an integrated multi beam bathymetry high resolution seismic profile piston core and ams 14 c dating data set the current study identified two sediment wave fields fields 1 and 2 on the south china sea slope off southwestern taiwan field 1 is located in the lower slope and sediment waves within it are overall oriented perpendicular to the direction of down slope gravity flows and canyon axis geometries morphology and internal seismic reflection configurations suggest that the sediment waves in field 1 underwent significant up slope migration field 2 in contrast is located more basinward on the continental rise instead of having asymmetrical morphology and discontinuous reflections as observed in field 1 the sediment waves in field 2 show more symmetrical morphology and continuous reflections that can be traced from one wave to another suggesting that vertical aggradation is more active and predominant than up slope migration three sediment wave evolution stages stage 1 through stage 3 are identified in both field 1 and field 2 during stage 1 the sediment waves are built upon a regional unconformity that separates the underlying mass transport complexes from the overlying sediment waves in both of these two fields there is progressive development of the sediment waves and increase in wave dimensions from the oldest stage 1 to the youngest stage 3 even though up slope migration is dominant in field 1 whereas vertical aggradation is predominant in field 2 throughout these three stages the integrated data and the depositional model show that the upper slope of the study area is strongly dissected and eroded by down slope gravity flows the net result of strong erosion is that significant amounts of sediment are transported further basinward into the lower slope by gravity flows and or turbidity currents the interactions of these currents with bottom contour currents induced by the intrusion of the northern pacific deep water into the south china sea and preexisting wavy topography in the lower slope result in the up slope migrating sediment waves in field 1 and the contourites as observed from cores ts01 and ts02 further basinward on the continental rise turbidity currents are waned and diluted whereas along slope bottom contour currents are vigorous and most likely dominate over the diluted turbidity currents resulting in the vertically aggraded sediment waves in field 2 the results from this study also provide the further evidence for the intrusion of the northern pacific deep water into the south china sea and suggest that this intrusion has probably existed and been capable of affecting sedimentation in south china sea at least since quaternary

glacial interglacial variability in lower north atlantic deep water inference from silt grain size analysis and carbonate preservation in the western equatorial atlantic abstract grain size records of the terrigenous and calcareous silt fraction preservation of planktic foraminifera and benthic foraminiferal stable isotope data 13c 18o values of c wuellerstorfi at odp site 927 on the ceara rise 5 27 7 n 44 28 8 w are used to reconstruct variations in the history of bottom current strength ventilation and carbonate corrosiveness of deep waters during the time interval from 0 8 to 0 3 ma glacial periods are characterized by generally smaller mean sizes of the terrigenous sortable silt fraction mean ss lower 13c values and poorer preservation of planktic foraminifera compared to interglacials this indicates lower bottom current speeds larger nutrient contents and more corrosive deep water by contrast larger mean ss sizes higher 13c values and well preserved planktic foraminifera indicate strong circulation and a well ventilated deep water mass during interglacials the observed changes are most likely related to the weakening and strengthening of circulation of lower north atlantic deep water lnadw cross spectral analysis between the mean ss and benthic 18o records reveals that minima in mean ss occur about 7 6 k y after the maximum in ice volume this indicates a considerable lag time between ice shield induced changes in lnadw production and subsequent changes in the velocity of lnadw flow in the western equatorial atlantic striking changes in bottom current speed occur regularly during glacial to interglacial transitions extremely fine mean ss minima point to an almost complete shutdown of bottom current vigor in response to a cessation of lnadw production caused by an enhanced melt water release during the initial phases of deglaciation however each of the fine minima extremes is followed by a rapid shift to very high mean ss values that indicate strong bottom currents and hence vigorous lnadw flow during the early interglacials after the onset of glacial stage 12 generally poorer carbonate preservation and higher variability is registered this coincides with a global decrease in carbonate preservation during the mid brunhes mid brunhes dissolution event detailed grain size analysis of the calcareous fine fraction

cretaceous early tertiary inversion tectonism in the danish central trough abstract the inversion of the danish central trough was heralded by a mild precursor during the late hauterivian before rifting had ended the main inversion took place during the late cretaceous it can be subdivided into several sub phases of which those occurring during the turonian santonian mid maastrichtian and post danian early tertiary are the most pronounced minor inversion tectonism occurred more or less continuously between these major events the turonian santonian event had the greatest impact in the northern part of the danish central trough whereas the effects of later events are most pronounced in the south throughout the late cretaceous danian a gradual change from more brittle deformation with faulting to more plastic deformation characterised by folding and flexuring can be seen

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

late cenozoic history of the polar north atlantic results from ocean drilling abstract dsdp odp drilling in the northern north atlantic reveals that so far the onset of northern hemisphere cooling deduced from the occurrence of ice rafted debris ird in deep sea sediments can be traced back to the middle miocene the greenland ice sheet has probably the longest history on the northern hemisphere leg 151 site 909 fram strait recovered a unique continuous sediment record dating from early middle miocene the composition of the coarse fraction indicates that the oldest ird pulses are documented around 14 ma in the fram strait site 909 and around 12 6 ma on the voring plateau leg 104 site 642 in the norwegian greenland sea fram strait site 909 indicates a further stepwise increase of northern hemisphere cooling by serveral ird pulses during late miocene between 10 8 and 8 6 ma around 7 2 6 8 and 6 3 ma which ultimately led to a drastic intensification of northern hemisphere glaciation during plio pleistocene the deep sea sediment records show that plio pleistocene strengthening of ird pulses have been observed since approximately 4 0 ma in the westernmost norwegian greenland sea and labrador sea by contrast strengthening of ird pulses are observed at approximately 3 2 2 7 ma on the eastern side of the norwegian greenland sea including the barents sea margin sediment composition and physical properties of the drilled mostly terrigenous sections reveal that orbital parameters have controlled major aspects of shallow and deep water environments with frequency domains related to 41 ka periods of obliquity dominant in the pre glacial miocene pliocene and early quaternary and to 100 ka periods of eccentricity dominant during the past 600 000 700 000 years the stratigraphy of ice rafted material reveals a frequently and rapidly changing history of the dynamics of various segments in ice sheets around the norwegian greenland sea it is particularly evident from the composition of the ice rafted material that the eurasian ice sheets delivered ird to the eastern part of the norwegian greenland sea whereas greenland source areas are represented in the drill sites of the east greenland continental margin and in the labrador sea the stratigraphic sequences on the yermak plateau suggest that the svalbard ice sheet may have extended far to the north prior to oxygen isope stage 16 but not since then invasions of temperate atlantic waters during interglacials can be observed as short lived and rather irregular events it never reached the area off eastern greenland except during the pliocene interval when tundra floras were able to develop on north eastern greenland and planktonic foraminifers suggesting the presence of temperate water masses in the fram strait as been documented in the drill sites from the yermak plateau

the rise and fall of the faroe shetland basin evidence from seismic mapping of the balder formation seismic mapping of the faroe shetland basin from three dimensional surveys provides striking evidence for uplift of the southern faroe shetland basin in the late palaeocene and rapid subsidence in the early eocene the seismic reflector at the base of the balder formation follows a regional unconformity surface which records erosion of a major branching drainage network into the underlying palaeocene section following a major base level fall the topography of this surface was subsequently in filled following marine transgression and deep water conditions returned to the basin in the early eocene we attribute base level changes to the influence of the proto iceland mantle plume beneath the lithosphere providing support until continental break up west of the faroe islands

on the origin of large shelf embayments on glaciated margins effects of lateral ice flux variations and glacio dynamics west of svalbard glaciated continental shelves are characterised by large amphitheatre like embayments between prominent cross shelf troughs the integration of swath bathymetry and high resolution seismic data 3d 2d collected across the western svalbard continental margin indicates how such embayments form although their bathymetric expression resembles headwall scarps of submarine slope failures the shelf embayments are the result of the interplay between sediment dynamics and transport underneath fast moving ice streams in the cross shelf troughs and the slower moving parts of the ice sheets on the adjacent shallower shelf banks during full glacial conditions this is supported by 1 the absence of major landslide deposits at their toe 2 continuous prograding shelf deposition and 3 absence of landslide related faulting instead the seismic data suggest a depositional origin of the shelf embayments that is characterised by continuous sediment input at lower rates off a slow moving ice mass in the centre of the embayment which is fringed by the lateral ice stream ridges these findings put into perspective the importance of submarine slope failure on glaciated margins

late cenozoic sediment drift complex northeast rockall trough north atlantic seismic reflection profiles and two shallow cores have revealed a sediment drift complex in the northeastern rockall trough the drift complex consists of an elongate drift with associated sediment waves a broad sheeted drift with a larger field of sediment waves and smaller moat related isolated drifts the internal reflection configuration of these features indicates consistent upslope migration throughout the late cenozoic the larger field of sediment waves has been described previously with a southerly migration a reevalution of these waves suggests a migration direction to the east conforming with the other drift complex features the most vigorous current activity probably occurred during the miocene with a more reduced current flow prevailing during the pliocene to holocene interval core evidence from the elongate drift and the moat has revealed upper pleistocene and lower holocene glaciomarine sediments reworked to produce muddy silty and sandy contourites sedimentation rates for the early holocene pre 7 5 ka are up to 4 times greater on the drift compared to the moat it is suggested that the sediment drift complex has formed through the interaction of a northward flowing slope current of north atlantic deep water origin with an area of complex bathymetry at the northeastern end of the rockall trough where the wyville thomson ridge intersects the hebridean margin

stratigraphic correlation of late palaeocene sand deposits in the sogne basin area of the danish and norwegian central north sea a stratigraphic analysis of late palaeocene sands of the sogne basin and the western part of the norwegian danish basin shows that the sand bodies are of differenct ages the geographic distribution of the sand deposits shows that they are related to underlying mesozoic structures suggesting a controlling effect of tertiary tectonics on the deposition of sand during the late palaeocene however the structural setting of various sand bodies varies from reactivation of older faults and reactivation of salt structures the local character of the structures active during the late palaeocene introduces minor depressions with no lateral connection the sand bodies which are interpreted as having been deposited in these depressions are thus in general separate bodies with no lateral connection the fennoscandian shield and eroded mesozoic sediments along the fennoscandian border zone are suggested as source area for the late palaeocene sand deposits

climatology glacial hiccups the climate instability of glacial times probably resulted from abrupt switches in ocean circulation a computer model simulation provides the first glimpse of the dynamics involved

repeated fluid expulsion through sub seabed chimneys offshore norway in response to glacial cycles abstract focused fluid flow through sub seabed sediments is a common phenomenon on continental margins worldwide however the governing controls and timing of this fluid release have been difficult to understand in particular for fluid flow features buried beneath sub surface sediments a link between fluid flow activity ensuing pockmark formation and the last glacial maximum has been hypothesized on the formerly glaciated norwegian margin new high resolution p cable 3d seismic data from the nyegga area on the mid norwegian margin reveal at least two more periods of fluid expulsion from sub seabed sediments the 3d seismic data show depositional patterns within chimney features expressed as truncations of seismic horizons against the flanks of the chimneys the truncations are interpreted by analogy with present day observations as evidence for buried carbonate mounds and or sediment wash out during formation of pockmarks in the past the truncations are hence an indicator and a chronological marker for fluid expulsion in the past the classification of chimneys results in three major groups 1 chimneys that have been formed and consecutively reactivated one or two times during the last 200 kyr and that have a fluid flow expression at the present seafloor 2 chimneys that are approx 125 160 ka bp old without any associated fluid flow expression at the present day seafloor 3 chimneys with no stratigraphical evidence for reactivation formed after the last glacial maximum 18 25 ka bp the observations suggest that each activity period was likely related to the last stages of maximum glaciations in the region the emplacement of thick sequences of glacigenic debris flow deposits during these maximum stages most likely caused rapid increase in overpressure and subsequently the formation of focused fluid flow features piercing through sediments of the naust formation at nyegga

submarine erosional troughs in the northern south china sea evidence for early miocene deepwater circulation and paleoceanographic change abstract the paleoceanography of the south china sea scs is poorly understood although recent cruises and an odp expedition leg 184 have provided a useful general framework here we report previously unrecognized multi km scale sedimentary structures consisting of coupled ridges and troughs within the early miocene strata using high resolution 3d seismic data from the northern scs margin the troughs are interpreted as linear and or arcuate erosional features which truncate the underlying strata they range in orientation from e w in the southern part of the study area to nearly ne sw in the northwestern part of the study area the spacing of erosional troughs varies from less than 0 1 km in the southern part to more than 3 km in the northern part and they are about 50 1500 m in width with a relief of 10 90 m the erosional troughs are parallel to the regional strike of the early miocene slope of the northern scs from their internal geometry context regional distribution and most importantly their orientation relative to the paleo slope gradient at the time of their formation it is argued that they formed due to the action of bottom currents linked to the broader paleo circulation regime in the basin we infer that the paleo bottom currents intruding from the pacific flowed along the northern scs slope resulting in the occurrence of localized erosional troughs as deep water masses impinged on and interacted with the sea floor topography this study provides new insights into the early miocene paleoceanography of the scs and demonstrates the utility of 3d seismic data to enhance our understanding of paleo bottom current circulation regimes

the deglaciation of the northern hemisphere a global perspective orbitally induced increase in northern summer insolation after growth of a large ice sheet triggered deglaciation and associated global warming ice albedo sealevel and greenhouse gas feedbacks together with tropical warming from weakening winds in response to polar amplification of warming caused regionalto global near synchronization of deglaciation effects were larger at orbital rather than millennial frequencies because ice sheets and carbon dioxide vary slowly ice sheet linked changes in freshwater delivery to the north atlantic and possibly free oscillations in the climate system forced millennial climate oscillations associated with changes in north atlantic deep water nadw flow the north atlantic typically operates in one of three modes modern glacial and heinrich deglaciation occurred from a glacial mode ocean that in comparison to modern had shallower depth of penetration of nadw formed further south causing strong northern cooling and the widespread cold dry and windy conditions associated with the glacial maximum and the cold phases of the millennial dansgaard oeschger oscillations the glacial mode was punctuated by meltwater forced heinrich conditions that caused only small additional cooling at high northern latitudes but greatly reduced the formation of nadw and triggered an oceanic seesaw that warmed some high latitude southern regions centered in the south atlantic

abyssal bedforms as indicators of changing bottom current flow examples from the u s east coast continental rise direct indications of circulation patterns in the deep sea especially along continental rises and sediment drifts can be obtained through the analysis of abyssal bedforms such as furrows and mud waves such direct evidence of current flow will supplement indirect indicators of circulation provide by paleochemical indicators preserved in ocean sediments water that sinks in the northern north atlantic forms part of the western boundary undercurrent along the continental rise of eastern north america and the understanding of temporal changes in the speed and depth of flow along this continental rise can provide important information on how the speed at which the global conveyor system is operating changes with time studies of furrows and mud waves along the blake bahama outer ridges show that they are active sedimentary features today and that bottom flow speeds near the time of the younger dryas were increased over later intervals a more detailed analysis of bedform structure and sediments is needed to more clearly show the timing and reason for this change in sedimentation pattern

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

precise u pb zircon ages from the gamitagama greenstone belt southern superior province volcanism in the gamitagama lake greenstone belt 50 km south of wawa ontario on the east shore of lake superior took place ago at the same time as similar volcanism in the much larger abitibi greenstone belt to the east two post orogenic intrusions in the metavolcanic metasedimentary terrain are coeval at and and could very well be comagmatic as suggested by ayres a granitic sill in a metasedimentary granitic migmatite terrain that borders the greenstone belt to the southwest has an age of 2615 10 ma and is much younger than the post orogenic plutons to the northeast this migmatite region represents either an uplifted deep zone that remained hot long after volcanism or a region that accumulated heat as a result of its sedimentary cover

changes in the strength of the iceland scotland overflow water in the last 200 000 years evidence from magnetic anisotropy analysis of core su90 33 abstract results from a high resolution study of magnetic anisotropy combined with mineral magnetic analysis clay analysis and oxygen isotopes stratigraphy are reported for core su90 33 located 60 34 4n 22 05 1w at 2400 m water depth along the iceland scotland overflow water isow a branch of the north atlantic deep water nadw this core covers the last 6 climatic stages the main magnetic mineral is low ti content magnetite with very slight changes in the grain size the susceptibility record corrected for the carbonate content indicates down core variations in the amount of magnetite which largely co vary with the changes in the proportion of smectite in the clay fraction both parameters are climatically controlled with lower values during glacial than during interglacial periods the measurements of the anisotropy of magnetic susceptibility document down core changes in the degree of anisotropy with significantly higher values during interglacial periods than during glacial times these changes appear to be related to differences in the degree of alignment of the magnetic particles and not to changes in grain shape providing evidence that they arise from changes in strength of the bottom water circulation therefore the strength of the contour current associated to the transport of the isow appears to have been significantly larger during climatic stages 5 3 and 1 than during stages 6 4 and 2

high resolution 3d seismic study of pockmarks and shallow fluid flow systems at the snohvit hydrocarbon field in the sw barents sea accepted manuscript version published version available at https doi org 10 1016 j margeo 2018 06 012 accepted manuscript version licensed cc by nc nd 4 0

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

seismic stratigraphy of the west shetland drift implications for late neogene paleocirculation in the faeroe shetland gateway 1 the morphology and anatomy of a late neogene contourite drift on the british margin of the faeroe shetland channel is investigated in unprecedented detail using industrial two dimensional and three dimensional seismic data the west shetland drift is constructed by a succession of mounded asymmetric strata that in the basin and on the midslope has accumulated on a regional unconformity of early pliocene age the midslope component of the drift system forms a 400 m thick convex elongate sedimentary body that can be traced from the outlet of the norwegian channel and 250 km southwest along the shetland margin contourite drifts occupying the basin are evident as a succession of sheeted mounded and wavy migrating units intercalated by three mega debrite sequences the seismic architecture of the west shetland drift and tentative age estimates of its bounding surfaces suggests that it formed rapidly 5 10 cm kyr 1 by alongslope transport of hemipelagic sediments derived from the nw european shelf the change from erosion nondeposition to enhanced contourite drift accumulation during the early pliocene suggests that a moderate thermohaline current regime prevailed in the faeroe shetland channel prior to the main phase of northern hemisphere glaciation at 3 0 2 5 ma a reduction in meridional heat transport associated with a decrease in the flux of north atlantic deep waters may have been an important factor for the growth of northern hemisphere ice sheets

contourite drift types and their distribution in the north and south atlantic ocean basins abstract patterns of sediment accumulation under the control of deep bottom currents depend on interacting factors intensity of the regional deep circulation morphology of the sea floor coriolis effects abundance of terrigenous and biogenic supplies subsequent turbidity of deep nepheloid layers and depth of the ccd based on many examples of bottom current deposits from the atlantic and from other oceans we recognise three major types of contourite accumulation 1 giant elongate drifts 2 contourite sheets and 3 channel related drifts they generally occur in distinct topographic settings and show different geometries facies and rates of deposition in the north atlantic strong bottom circulation an open basin system and high sediment supply have led to the construction of large elongate contourite drifts which have striking relief 200 1000 m above the surrounding sea floor and are composed of muddy contourites rich in calcareous pelagic material in the south atlantic strong bottom currents are often trapped in gyre like circulation patterns around topographically closed basins or are accelerated through deep narrow connecting passages the resulting deposits are mainly extensive contourite sheets covered by fields of large sediment waves and channel related drifts including contourite fans constructed at the downstream exit of deep passages

quaternary evolution of the northern north sea margin through glacigenic debris flow and contourite deposition the norwegian channel ice stream of the scandinavian ice sheet extended across the northern north sea margin during the mid to late quaternary eroding older sediment from the continental shelf consequently little is known about early quaternary sedimentation on this margin we use two and threedimensional seismic reflection data to investigate changing sediment volumes and sources in the northern north sea through the quaternary the northern north sea basin was infilled during the early quaternary by intercalated glacigenic debris flows and contourites which provide a record of the delivery of glacigenic sediment to the slope and the intensity of north atlantic thermohaline circulation during early quaternary glacial interglacial cycles the infilling of the basin reduced accommodation and led to the deflection of mid to late quaternary sediments into the norwegian sea forming the north sea fan close to the onset of the mid quaternary the south western scandinavian ice sheet margin was drained by an ice stream located beneath maluy plateau 60 km east of the last glacial maximum norwegian channel ice stream the southward flowing norwegian sea bottom water current was directed into the partially filled northern north sea basin during the early quaternary and deflected progressively northwards as the basin became infilled

deep marine seabed erosion and gravel lags in the northwestern rockall trough north atlantic ocean a zone of active seabed erosion has been identified in the northwestern rockall trough using seismic reflection profiles and cores the region from george bligh bank to rockall bank has been subject to vigorous bottom current activity for at least the last 35 ma bottom currents originate from southward flowing north atlantic deep water in water depths of 500 2000 m acoustic character mapping reveals a zone of erosion extending over 8500 km 2 along the northwestern margins of the trough the erosion surface is characterized by an acoustically reflective seabed with occasional parallel to transparent reflectors these are the result of strong bottom currents exposing the underlying volcanic basement drift sequences and fan sediments the erosion surface is covered by a

deep pleistocene iceberg plowmarks on the yermak plateau sidescan and 3 5 khz evidence for thick calving ice fronts and a possible marine ice sheet in the arctic ocean the southern yermak plateau northwest of spitsbergen was investigated with 11 12 khz sidescan sonar and 3 5 khz profiler to test whether thick pleistocene ice streams ever calved into the arctic ocean and or whether a continuous arctic ice sheet existed in either case the ice would have grounded on the plateau crest on its way out of the arctic several distinct sets of relict iceberg plowmarks were discovered at present water depths from less than 450 m to at least 850 m perhaps recording the deepest iceberg keels known the plateau crest 510 530 m is nearly bare of plowmarks perhaps because of beveling by an ice rise formed of grounding shelf ice this implies continuous 400 600 m thick grounded ice consistent with but not proving the postulated existence of an arctic ice sheet most plowmarks are probably late pleistocene products of the calving of barents kara ice sheets into the arctic ocean plowmarks in 450 850 m deep water require unusually deep ice sheet grounding lines e g svyataya anna trough and or drat increasing capsizing events even if sea levels were 100 50 m lower than today at water depths of 800 to 1800 m the sidescan texture and topography suggest bottom currents descending the northeast slope of the plateau

seismic geomorphology of offshore morocco s east margin safi haute mer area the lower continental slope of morocco s west coast consists of triassic age salt manifested in the form of diapirs tongues sheets canopies and toe thrusts active salt diapirism and regional tectonics greatly influence the morphology of the modern sea floor forming a severely rugose expression with ongoing minibasin development and episodic submarine failure detailed mapping of a 1064 km2 411 mi2 seismic survey acquired in the safi haute mer area revealed that jurassic to holocene salt mobilization continually affected distribution of sediment causing a range of depositional flow styles from slumps to sheet slides and mass transport complexes mtcs large sediment waves 20 km 12 mi long 1 5 km 0 9 mi wavelength were also documented at the end of the aptian an east west trending structural anticline downdip of the salt activated during initiation of the atlas uplift in the latest cretaceous to earliest tertiary and shaped much of the lower slope into the tertiary with a persistent canyon system and slope channels the largest of the debris flows is a cretaceous age mtc a 500 m 1640 ft thick flow that spans an area of up to 20 000 km2 7722 mi2 composing the mtc are 1 chaotic mounded seismic facies 2 internal syndepositional thrusts and 3 transported megablocks 3 3 km2 1 3 mi2 with preserved internal stratigraphy the mtc originated from an upslope collapse of a narrow shelf during the earliest phases of the alpine orogeny

post breakup compression of a passive margin and its impact on hydrocarbon prospectivity an example from the tertiary of the faeroe shetland basin united kingdom the faeroeshetland basin is part of a passive continental margin that formed as a result of multiphase extension associated with north atlantic rifting during the mesozoic and paleocene breakup was followed by postrift subsidence during the latest paleocene to late eocene and the development of at least three 70 150 km 43 93 mi long broadly north south orientated slope canyons and linked terminal fans during the middle eocene the terminal fans filled northeast southwest striking basin floor bathymetric depressions that had formed above the hanging walls of underlying dormant northeast southwest trending mesozoic extensional faults and adjacent half graben depocenters compression during the middle and late miocene caused contractional reactivation of the mesozoic extensional faults and folding of the overlying uppermost paleocene to middle miocene postrift sediments into a series of 17 northeast southwest striking anticlinal domes the switch from hanging wall bathymetric depression during terminal fan deposition to anticlinal domal high during and after the middle to late miocene compression has led to the present day spatial coincidence of a potential hydrocarbon reservoir and an effective trap the anticlines also acted as the foci for gas migration during or after compression 15 ma to present however the timing of compression and differential uplift of the basin margins during the past 15 m y approximately 45 m y after the main phase of oil migration may be a critical negative factor for oil exploration in this part of the basin this hydrocarbon phase may have spilled during the structural reorganization either updip into shallower traps or out of the hydrocarbon system via seeps

iceberg crater marks on the sea floor labrador shelf abstract sidescan sonograms of the labrador seabed show evidence of numerous subcircular iceberg generated impact craters some of these craters are found in linear associations crater chains having been formed by a single iceberg keel alternately impacting and rotating free of the seabed a three degrees of freedom iceberg model is used to generate crater chain configurations an unstable trapezoid shaped iceberg of 6 million t with a draft of 140 m in a water depth of 160 m is used in the simulations soil pressures acting on the penetrating keel introduce a vertical heave motion which depending on phase relationships with the swinging motions of the iceberg results in a variety of noncoherent crater depths and crater chain morphologies including chains with skips where craters appear to be missing on sidescan sonograms depending on the position of the final static orientation of the iceberg keel it may generate a crater chain if the keel comes to rest above the seabed or a crater chain may lead into a normal scour if the keel remains below the seabed both configurations are observed in nature

links between palaeoproterozoic palaeogeography and rise and decline of stromatolites fennoscandian shield through a review of literature and new data we have documented two major events in the palaeoproterozoic history of stromatolites as indicated by palaeontological and palaeoenvironmental studies with a time resolution of between 40 and 200 ma we confirm semikhatov and raaben s and awramik s albeit approximately maximum in diversity and abundance of stromatolites between 2330 and 2060 ma ago jatulian diversification we suggest that this taxonomic diversity was driven by a major phase of cratonisation formation of the karelian carbonate platform and numerous rift related shallow water carbonate basins supersaturated with ca 2 mg 2 and co2 the jatulian stromatolite explosion is synchronised with a positive 13ccarb shift of jatulian age carbonates we also document stromatolite decline which occurred on the fennoscandian shield somewhere between 2060 and 1900 ma ago this decline both in abundance and in taxonomic diversity is interpreted as having been caused by the first phase of oceanisation the oceanisation led to the considerable reduction in ecological niches that could be utilised by cyanobacteria the post jatulian decline of stromatolites coincides with an abrupt downward 13corg shift from 19 to 38 and is roughly coeval with the appearance of the first eukaryotic algae documented elsewhere the systematics of the fennoscandian diversity of palaeoproterozoic stromatolites is identical to that reported from india and china and reveals a dissimilarity with abundance and diversity patterns in australia and northern america

onset of north atlantic deep water production coincident with inception of the cenozoic global cooling trend here we show that the onset of deep water overflow from the norwegian greenland sea into the north atlantic interpreted to represent the onset of a modern style north atlantic deep water mass commenced close to the early to middle eocene boundary this finding is based on the identification of a large elongate contourite sediment drift the judd falls drift in the faeroe shetland basin through detailed mapping of high resolution two dimensional and three dimensional seismic data this sediment drift covers an area of 9000 km2 in one of the critical present day deep water gateways into the north atlantic ocean interpretation of the body as a contourite drift is based on standard seismic stratigraphic diagnostic criteria including tridirectional onlap lensoid sediment geometry upslope progradational configurations of stacked onlap units and an erosional base cut in a deepwater setting the internal reflection configuration indicates that the drift was deposited under a southwest flowing current regime which we propose represents the onset of north atlantic deep water production with continual deep water flow until at least the latest eocene ca 35 million years ago ma onset of drift deposition is dated by several key boreholes as occurring at ca 50 49 ma across the early to middle eocene boundary and is coincident with independent geochemical evidence for major changes in the configuration of deep sea circulation patterns global biological production and the onset of cenozoic climatic cooling these temporal concurrences suggest a strong link between the initiation of north atlantic deep water production and cenozoic global climate evolution

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

trends transitions and events in cryptozoic history and their calibration apropos recommendations by the subcommission on precambrian stratigraphy abstract here i examine the semifinal recommendations of the subcommission on precambrian stratigraphy of the international union of geological sciences plumb and james although stratigraphy is the subject the stated objective is subdivision of geologic time from that the subcommission derives a potentially workable set of eons eras and proterozoic systems arbitrarily separated by radiometric numbers seen as having the virtues of objectivity and stability the time transgressive transitions that actually separate the broad succession of prevailing stratigraphic and historical modes thereby become fixed globally synchronous boundaries by decree what kind of stratigraphy is that apart from its essential role in calibration what does geochronometry have to do with stratigraphy and historical geology how do practices proposed reconcile with those heretofore applied given radiometric boundaries are the numbers chosen the most appropriate just how is the system recommended to become useful to working geologists such reflections lead me to conclude that the proposed geochronometric subdivision is mistaken in principle confining in application and self contradictory particularly as concerns the grossly discordant but historically illuminating transition from the mantle dominated archean eon to continent dominated proterozoic history such matters are the foci of this brief paper

cenozoic bottom current sedimentation in the cape basin south atlantic the cape basin is located at a central location with respect to variouswater masses the coldest and densest of these water masses is thelower circumpolar deep water the location and topography of the agulhas ridge effectively blocks itsnorthward flowing branches and deflects them into a south westerndirection to follow the bathymetric contours of the agulhas ridge wheresuspended sediments accumulate in contourite drifts several hundred metres of sediments have accumulated since the onsetof antarctic bottom water intrusion into the basins of the south atlantic a present day like bottom current following agulhas ridge contours existssince an erosional event in the early oligocene took place which markeda prominent change in sedimentation strong and varying currents in the early oligocene formed a sheet likedeposition at high sedimentation rates the fluctuating types of sediments produce strong seismic reflections it was followed by a very stable unidirectional bottom current with mainlymuddy sediments this resulted in the formation of a more than 200 kmlong approx 30 km wide elongate contourite drift which shows fewinternal reflections on the seismic data an increase of well defined unitsis found after a period of non deposition in the middle miocene still the build up of the drift structure continued but at places erosion isfound especially in quaternary sediments and probably in relation toglaciation cycles

bottom current sediment waves sediment drifts and contourites in the northern rockall trough four types of large scale sediment bedform occur in the northeast rockall trough broad sheeted drifts elongate drifts sediment waves and thin contourite sheets a large sheeted drift occupies the northern basin its crest can be traced for 40 km perpendicular to the bottom current flow direction elongate drifts occur adjacent to steep areas of continental slope separated from the break of slope by a moat drift crests are oriented alongslope parallel to bottom current flow elongate drifts are asymmetric with the steeper flank facing upslope sedimentation rates are higher on the downslope flank sediment waves with a wavelength of 1 2 km and wave height up to 20 m occur locally on the flanks of sheeted and elongate drifts larger waves wavelength of 3 4 km and wave height of 50 100 m occur on the flank of the wyville thomson ridge wave crests are oblique to bathymetric contours to drift crests and to bottom current flow the association of sediment waves and drifts their orientation oblique to regional slopes and the presence of contourite sediments in cores indicate that these are bottom current rather than turbidity current waves a contourite sheet typically 10 25 cm in thickness and composed of well sorted sand covers the present day seafloor along the lower slope bedform evolution through time has involved a complex interaction between bottom currents of variable intensity sea level change and sediment input the present sea level highstand is characterised by minimal sediment input and redistribution of sediments by strong bottom currents giving active bedform growth and contourite development variability of sediment input is the main factor affecting sedimentation during sea level lowstands where input was high as when ice sheets reached the shelf edge downslope sediment transport dominated overwhelming any bottom currents that were active when input was low such as during the last lowstand some evidence for active currents can be observed although these were less energetic than those during highstands

paleoenvironmental changes in the norwegian sea and the northeast atlantic during the last 2 8 m y deep sea drilling project ocean drilling program sites 610 642 643 and 644 sedimentological isotopic and magnetostratigraphic investigations of ocean drilling program and deep sea drilling project sites 642 643 644 and 610 document the oceanographic and climatic evolution of the norwegian sea and the northeastern atlantic over the last 2 8 m y the results show that a major expansion of the scandinavian ice sheet to the coastal areas took place at about 2 56 ma relatively severe glacials appeared until about 2 ma the period 2 6 1 2 ma experienced in general cold surface water conditions with only a weak influx of temperate atlantic water as compared with late quaternary interglacials the norwegian sea was a sink of deep water through this period but deepwater ventilation was reduced and calcite dissolution was high compared with the holocene deep water formed by other mechanisms than it does today between 2 and 1 2 ma the glaciations in scandinavia were small a transition toward larger glacials took place during the period 1 2 to 0 6 ma corresponding to warmer interglacials and reduced calcite dissolution only during the last 0 6 m y has the oceanographic and climatic system of the norwegian sea varied in the manner described in previous studies of the late quaternary a strong thermal gradient was present between the norwegian sea and the northeastern atlantic during the matuyama 2 5 0 7 ma this is interpreted as a sign of a more zonal and less meridional climatic system over the region compared with the present situation

definition of archaean comment and a proposal on the recommendations of the international subcommission on precambrian stratigraphy abstract the proposed definition of the archaean proterozoic boundary at 2500 ma sims 1980 is unsatisfactory as it is difficult to use contravenes the international stratigraphic guide and does not allow for revisions of isotopic decay constants instead it is proposed that the boundary be set at the cooling age of the great dyke of zimbabwe 2 5 ga which provides an equivalent definition in the rock the division of the archaean at 2 9 ga and 3 5 ga sims 1980 is also unsatisfactory and instead reference successions are proposed in the rhodesian craton the pilbara block in australia and in greenland to serve as possible future stratotypes for archaean eras

morphology and pattern of quaternary sedimentation in the north sea basin 52 62 n abstract the quaternary north sea basin which extends from northwest mainland europe in the south 52 n to the norwegian sea in the north 62 n contains a thick up to 1 km sedimentary succession that records the changing nature of sediment supply from surrounding land areas during the last c 2 6 ma we use an extensive 2d and 3d seismic database to correlate major quaternary seismo stratigraphic surfaces and units across the north sea and reconstruct the broad scale infill pattern of the entire quaternary north sea basin the total volume of quaternary sediments in the north sea 350 000 km2 is c 140 000 km3 while the area inside the 500 m contour of the base quaternary surface has a volume of 109 000 km3 two largely independent depocentres developed in the north sea basin during the early quaternary the southern and central sub basin was infilled by shelf fluvio deltaic and prodeltaic sediments delivered from the east and south east whilst the northern sub basin was infilled mainly by prograding glacigenic debris flows deposited from an ice mass centred on the norwegian mainland contour currents were an important mechanism of sediment deposition and reworking with water circulation in the basin probably occurring in an anti clockwise direction whilst most of the southern north sea basin was infilled by around 1 6 1 7 ma a depression persisted in the central north sea until around 1 ma the analysis of landforms on 3d seismic data suggests that the fennoscandian ice sheet fis extended intermittently to the palaeo shelf break in the northern north sea during the earliest quaternary and expanded into the central north sea prior to the excavation of the norwegian channel