seismic and structural characterization of fluid escape pipes using 3d and partial stack seismic from the loyal field uk a multiphase and repeated intrusive mechanism acknowledgements we thank an anonymous reviewer for the several constructive comments the seismic interpretation and image processing was carried out in the seislab facility at the university of aberdeen sponsored by bg bp and chevron seismic imaging analysis was performed using geoteric ffa and analysis of seismic amplitudes was performed in petrel 2016 schlumberger we would like to thank the tuscany phd regional program and the erasmus exchange for funding the aberdeen permanence of one of us d m gazprom for supporting a j phd bp for the release of the loyal field seismic dataset utilized in this research paper and also n vanden beukel bp and m gorling bp and his colleagues for their assistance

iceberg scours along the southern u s atlantic margin rapid climate fluctuations associated with ice sheet oscillations have resulted in pulses of iceberg discharge that are recorded by iceberg scour marks along continental shelves and ice rafted debris deposits across the north atlantic iceberg transport is largely controlled by ocean surface currents therefore iceberg trajectories can serve as a proxy for paleo circulation studies records of iceberg transport from ice rafted debris i e heinrich layers in the north atlantic suggest that most icebergs released during quaternary glaciations were entrained in a cyclonic subpolar gyre restricted to polar and mid latitudes however new data suggest that there may have been an additional southerly component of transport along the western atlantic margin here we present evidence of extensive iceberg scouring across the upper slope offshore of south carolina 1000 km south of the proximal ice margin during quaternary glacial maximums the location and orientation of the keel marks suggest that icebergs were entrained in a southwestward flowing coastal current at present warm waters of the rapid northeastward flowing gulf stream bathe the upper slope off the southeastern united states an offshore shift in the gulf stream axis during sea level lowstand may have allowed glacially fed coastal currents to penetrate farther south this may be the first evidence of iceberg rafting to subtropical latitudes in the north atlantic

ice stream dynamics of the sw barents sea revealed by high resolution 3d seismic imaging of glacial deposits in the hoop area abstract recent developments in seismic acquisition systems and seismic data visualization have contributed to improve the imaging of seismic geomorphologies over a broad range of topics this study focuses on a new high resolution p cable 3d seismic cube located in the hoop area in the sw barents sea the scientific motivations of the study are 1 to document glacial landforms on a meter scale 2 to study the link of these landforms with the subsurface and 3 to understand ice stream dynamics by detailed interpretation of main horizons including the seabed intra glacial horizons and upper regional unconformity uru the horizons are assessed using the concept of seismic geomorphology and compared with interpretations derived from conventional 3d seismic and state of the art multibeam echosounder technologies to discuss the benefits and limitations of the different geophysical technologies a well defined intra glacial seismic reflection is imaged in the eastern part of the p cable cube this reflection has an overall ne trending ridge shaped morphology which is up to 50 m high and 5 10 km wide and interpreted as a shear margin moraine the top of the moraine displays well defined iceberg ploughmarks and clear slope failure events along its eastern flank the seabed geomorphology which has been directly shaped by glacial processes related to multiple phases of ice streaming appears to be influenced by the buried shear margin moraine mega scale glacial lineations msgls indicative of fast flowing ice streams characterize the seabed west of the moraine infilled msgls and different sets of iceberg ploughmarks with large berms dominate the seabed geomorphology above the moraine the seabed east of the moraine characterized by a smooth morphology and few pockmarks is inferred to reflect more slowly moving ice not resolved by other geophysical techniques seismic attribute maps of p cable 3d allowed the identification of smaller ploughmarks and corrugated ridges related to paleo tides eroded by the larger iceberg ploughmarks these small ploughmarks are suggested to be linked to an earlier rapid disintegration of the barents sea ice stream the new high resolution 3d seismic data have led to the development of a revised ice stream model of the barents sea linking the glacial deposits to different ice stream events

seven glacial cycles in the middle late pleistocene of northwest europe geomorphic evidence from buried tunnel valleys the deep ocean marine isotope record and the antarctic and greenland ice caps record numerous glacial and interglacial cycles since the middle pleistocene and yet evidence for similar numbers of ice sheet advances over the continent and shallow shelves of northwest europe is absent here we document seven generations of regionally correlatable subglacial tunnel valleys that record the geomorphic imprint of ice sheets traversing the north sea basin between ca 500 and 40 ka consistent with that predicted by proxy records of glacial and interglacial climate change over 180 subglacial tunnel valleys that incise into pleistocene sediments in the north sea basin were mapped over 60 000 km 2 of three dimensional seismic reflection data using a subset of these data we identified seven separate episodes of subglacial erosion that can be correlated regionally in the uk sector of the central north sea the characteristics of the valley morphologies orientations and infill stratigraphy indicate that each set of tunnel valleys formed during a separate ice sheet advance and retreat cycle stratigraphic data suggest that the tunnel valleys formed significantly later than the brunhes matuyama reversal event at 780 ka and before the last glacial maximum marine isotope stage mis 2 21 ka these results imply a more complicated glacial history for northwest europe and more glaciations than the three glaciation model traditionally interpreted from the terrestrial record for the past 500 k y our data provide the most complete documentary evidence for repeated advance and retreat of the northwest european ice sheets since the middle pleistocene and for the first time indicate that terrestrial ice sheet advances in the north sea can be matched in number with the cold events recorded in oceanic and or ice core proxies of climate change over the past 500 k y

late pliocene pleistocene environments and glacial history of the northern north sea abstract based on new geochronological amino acids and sr isotopes and lithological data combined with analyses of 3d seismic data the pliocene pleistocene development of the central northern north sea has been investigated at the start of the plio pleistocene transition the study area was dominated by a deltaic shallow marine or tidal depositional environment with sediments mainly sourced from the west these sand rich sediments include green glauconitic grains that belong to the utsira sand with a local provenance directly above the base quaternary r2 a 60 m thick layer of mud rich sediments of glacimarine origin were deposited at a rate of 12 cm ka between 2 1 5 ma and up to 80 cm ka between 1 5 and 1 2 ma possibly reflecting glacial ice advancing to the norwegian coastline the high rate of deposition in the early pleistocene occurred immediately before the initiation of the norwegian channel ice stream at 1 1 ma following this a large part of the sediment input from fennoscandia seems to have been directed away from the study area to the shelf break at the start of the mid pleistocene transition mpt subaerial conditions allowed the formation of a 50 km long fluvial channel across the study area draining water from the east to the south west the earliest evidence of grounded ice in the investigated area comes from mega scale glacial lineations formed during the mpt at or just after 1 2 ma following this a regional unconformity r4 was formed by one or more grounded ice advances across the study area possibly during or directly after the mpt and likely marks the boundary between the early and mid pleistocene glacimarine sediments the mid to late pleistocene stratigraphy is dominated by glacimarine sediments and tills and is associated with multiple generations of tunnel valleys observed within the seismic data a high shear strength till containing chalk clasts transported from the west and or south of the study area was likely deposited during mis6 and may have been more conducive to tunnel valley formation in comparison to lower shear strength tills deposited by later ice advances a thick till unit overlain by a sand layer in the study area was deposited by grounded ice during the last glacial maximum and subsequent drainage of an ice dammed lake in the southern north sea during the last deglaciation mis2 of the study area this study shows that much of the quaternary age sediments within the northern north sea were deposited relatively rapidly during short periods of time probably leaving significant hiatuses within the stratigraphic record this finding has implications for previous studies that use a chronological framework assuming a relatively continuous sedimentation rate and record for the early pleistocene within the north sea

pleistocene subglacial tunnel valleys in the central north sea basin 3 d morphology and evolution four phases of cross cutting tunnel valleys imaged on 3 d seismic datasets are mapped within the middle late pleistocene succession of the central north sea basin witch ground area in plan the tunnel valleys form complex anastomosing networks with tributary valleys joining main valleys at high angles the valleys have widths ranging from 250 to 2300 m and base to shoulder relief varying between 30 and 155 m with irregular long axis profiles characteristic of erosion by water driven by glaciostatic pressures the youngest phase of tunnel valleys are smaller and have a thinner infill than the older generations the fill of the larger valleys comprises three seismic facies the lowermost of which has high amplitudes and is discontinuous the middle facies consists of wedge shaped packages of low angle dipping reflectors and is overlain by a facies characterised by sub horizontal reflectors which onlap the valley margins the seismic character and comparison with lithologies identified in other northwest european pleistocene tunnel valleys both onshore and offshore suggests that the lower two seismic facies are most likely sand and gravel dominated while the uppermost facies consists of glaciolacustrine and marine muds the 3 d morphology of the valley margins combined with the geometry of the infill packages suggest that episodic discharge of subglacial meltwater was responsible for incising the valleys and depositing at least some of the infill proglacial glaciofluvial deposits are inferred to account for some of the fill overlying the subglacial deposits glaciolacustrine and marine muds filled remaining valley topography as the ice sheet retreated the preserved valley margins are shown to be time transgressive erosion surfaces that record changes in geometry of the tunnel valley system as it evolved through time implying that valleys associated with each ice sheet advance retreat cycle were dynamic and probably long lived within the constraints of the existing stratigraphy the oldest tunnel valleys in the witch ground area of the central north sea are most likely to be marine isotope stage mis 12 elsterian ca 470 ka in age and the youngest pre mis 5e last interglacial ca 120 ka if each tunnel valley phase was formed during the retreat of a major ice sheet then four glaciations with ice coverage of the central north sea are recorded in the pre weichselian middle late pleistocene stratigraphy copyright 2006 john wiley sons ltd

submarine glacial landforms and sedimentary environments in vaigattbogen northeastern spitsbergen abstract vaigattbogen is located in northern svalbard the area is currently affected by several tidewater glaciers this study uses multibeam sub bottom acoustic data and four sediment cores to reconstruct the late weichselian and holocene glacial history in vaigattbogen during the last glacial ice flowed northwards through vaigattbogen and fed into the hinlopen strait ice stream streamlined bedforms indicate relatively fast ice flow and their increasing elongation ratios towards the north suggest increasing flow velocities de geer moraines in the shallower parts of vaigattbogen imply that multiple halts and or re advances interrupted the ice retreat in these areas a sediment core suggests that the north basin deglaciated prior to 9 1 cal ka bp in the south basin two large moraine ridges and networks of crevasse squeeze ridges suggest that at least two surge type advances occurred during the holocene the hinlopenbreen glacier surged in the early 1970s and deposited the inner r 2 of the two large moraine ridges radiocarbon ages from a sediment core recovered from the crest of the outer r 1 ridge yield a basal age of 2 6 cal ka bp however the core did not sample subglacial diamict and the age of the ridge could be anything between 2 6 cal ka bp and early holocene the r 1 ridge formed prior to the little ice age lia implying that more than one tidewater glacier has experienced a pre lia surge on the east coast of spitsbergen suggesting that surging during the holocene was a regional phenomenon the r 1 ridge is double crested with small crevasse squeeze ridges between the crests suggesting that more than one surge type advance occurred during the holocene reaching approximately the same location data from eastern svalbard indicate differences in surge landform assemblages suggesting that different mechanisms could have governed surge cycles throughout the holocene

palaeomagnetic evidence for early pleistocene in the central and northern north sea the palaeomagnetic evidence presented here refutes the earlier hypothesis that most of the quaternary succession in the central north sea area is of middle to upper weichselian age a study of the quaternary seismic stratigraphy has been tied to 11 cored boreholes which are being examined for their physical properties and faunal content initial palaeomagnetic studies show a major reversely magnetized zone which can be correlated from borehole to borehole and with the seismic stratigraphy this reversely magnetized zone is thought to represent the matuyama epoch which ended 790 000 yr bp consequently this suggests the presence of early pleistocene strata in the central and northern north sea

the upper cainozoic of the norwegian continental shelf correlated with the deep sea record of the norwegian sea and the north atlantic a stratigraphic framework has been developed for the cainozoic succession of the norwegian continental shelf and margin this framework is consistent for the entire margin from the central north sea to the barents sea and also facilitates a correlation with the deep sea record of the norwegian sea and north atlantic a local system mainly utilising planktonic and benthic foraminiferal assemblages and bolboforma species is developed it can be potentially used for regional stratigraphic syntheses using this framework a more precise and detailed identification and age assignments of cainozoic and in particular neogene strata can be performed several revisions of previous age assignments and a more detailed dating of the various sediment packages are presented the most complete neogene succession is recorded in the central north sea further north the succession is interrupted by an increasing number of hiati of increasing duration after a period of erosion in the late middle to early late miocene there is a marked increase in the influx of terrigenous sediment in the late miocene a period of transgression in the early pliocene resulted in strongly reduced rates of deposition and sediments of this age are preserved mainly in the central north sea a period of regression in earliest late pliocene probably resulted in erosion of most of the norwegian continental shelf with the exception of the deeper areas of the central and viking grabens this period was immediately followed in the later part of late pliocene by rapid deposition of glacially derived sediment prograding along the entire shelf in general pleistocene development is a continuation of the late pliocene evolution but is marked by more extensive erosion of the inner shelf this is inferred from the flat truncation of underlying prograding strata and the extensive build up of debris flow sediments within glacial fan depocentres the entire neogene development is closely related to the climatic evolution of high latitude regions surrounding the north atlantic and the norwegian greenland sea

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

phased occupation and retreat of the last british irish ice sheet in the southern north sea geomorphic and seismostratigraphic evidence of a dynamic ice lobe along the terrestrial margin of the southern north sea previous studies of the mis 2 glaciation impacting eastern britain have played a significant role in the development of principles relating to ice sheet dynamics e g deformable beds and the practice of reconstructing the style timing and spatial configuration of palaeo ice sheets these detailed terrestrially based findings have however relied on observations made from only the outer edges of the former ice mass as the north sea lobe nsl of the british irish ice sheet biis occupied an area that is now almost entirely submarine c 21 15 ka compounded by the fact that marine acquired data have been primarily of insufficient quality and density the configuration and behaviour of the last biis in the southern north sea remains surprisingly poorly constrained this paper presents analysis of a new integrated set of extensive seabed geomorphological and seismo stratigraphic observations that both advances the principles developed previously onshore e g multiple advance and retreat cycles and provides a more detailed and accurate reconstruction of the biis at its southern most extent in the north sea a new bathymetry compilation of the region reveals a series of broad sedimentary wedges and associated moraines that represent several terminal positions of the nsl these former still stand ice margins 1 4 are also found to relate to newly identified architectural patterns shallow stacked sedimentary wedges in the region s seismic stratigraphy previously mapped singularly as the bolders bank formation with ground truthing constraint provided by sediment cores these wedges are interpreted as sub marginal till wedges formed by complex subglacial accretionary processes that resulted in till thickening towards the former ice sheet margins the newly sub divided shallow seismic stratigraphy at least five units also provides an indication of the relative event chronology of the nsl while there is a general record of south to north retreat seismic data also indicate episodes of ice sheet re advance suggestive of an oscillating margin e g mis 2 maximum not related to first incursion of ice into region demonstrating further landform interdependence geographically grouped sets of tunnel valleys are shown to be genetically related to these individual ice margins providing clear insight into how meltwater drainage was organised at the evolving termini of this dynamic ice lobe the newly reconstructed offshore ice margins are found to be well correlated with previously observed terrestrial limits in lincolnshire and e yorkshire holderness e g mis 2 maximum and withernsea till this reconstruction will hopefully provide a useful framework for studies targeting the climatic mass balance and external glaciological factors i e fennoscandian ice sheet that influenced late stage advance and deglaciation important for accurately characterising both modern and palaeo ice sheets

tunnel valleys of the central and northern north sea 56 n to 62 n distribution and characteristics abstract the analysis of buried tunnel valleys in the north sea can provide information about the past configuration and dynamics of the scandinavian and british ice sheets and the processes by which sediment and meltwater were transported at the ice sheet base however little is presently known about the distribution and characteristics of tunnel valleys in the norwegian sector of the north sea here we use an extensive database of 3d seismic and high resolution magnetic data to map 2200 tunnel valleys in the norwegian and british sectors of the north sea between 56 n and 62 n with the exception of the deep norwegian channel in which evidence for tunnel valleys is absent the geological setting of the north sea is interpreted to have been conducive to tunnel valley formation and preservation because of its poorly consolidated substrate and shallow water depths the highest density of tunnel valleys is located in the central part of the north sea where quaternary sediments are thickest the extreme length of some of the tunnel valleys which are up to 155 km long supports theories that tunnel valleys form in stages rather than catastrophically detailed analysis of the orientation of tunnel valleys and their relative age relationships within four representative subareas shows that tunnel valley orientation varies significantly across the central and northern north sea and between different generations of valleys this suggests that the pattern of subglacial meltwater drainage in the central and northern north sea was different between each deglacial event in which tunnel valleys were formed

keel depths of modern antarctic icebergs and implications for sea floor scouring in the geological record abstract icebergs affect the geological record through the scouring or ploughing action of their keels reworking sediments where they contact the sea floor satellite radar altimeter measurements of the surface elevation of the marine margins of the antarctic ice sheet are inverted to produce ice thickness values these data are assumed to represent the keel depths of newly calved icebergs there are three peaks in the frequency distribution of antarctic iceberg keel depths a about 140 200 m in thickness associated with smaller ice shelves fringing antarctica e g wilkins george vi and brunt ice shelves b about 250 300 m from large ice shelves e g ross ronne amery and c approximately 500 600 m from fast flowing ice sheet outlet glaciers e g pine island and dibble glaciers together with the filchner ice shelf controls on iceberg keel depth are ice thickness at the grounding line creep thinning and the rate of melting freezing at the floating ice shelf base with distance to the calving margin the distribution of sea floor scours produced by iceberg grounding is dependent on the changing form and flow of the glaciers and ice sheets from which icebergs are derived and on berg drift tracks and melt rates sea floor evidence for icebergs with particularly deep keels has sometimes been interpreted to indicate the presence of extensive former ice shelves however the largest modern antarctic ice shelves do not produce large numbers of icebergs thicker than about 350 m implying that sea floor scours found in deeper water are unlikely to be an indicator of extensive past ice shelf development iceberg scours found at water depths in excess of about 500 m in the geological record are instead probably indicative of either a the former presence of fast flowing ice sheet outlet glaciers b ice shelves fed from major interior basins where lateral spreading is constrained topographically or c a pulse of large icebergs released during major deglaciation or ice sheet collapse

glacial variability over the last two million years an extended depth derived agemodel continuous obliquity pacing and the pleistocene progression abstract an agemodel not relying upon orbital assumptions is estimated over the last 2 ma using depth in marine sediment cores as a proxy for time agemodel uncertainty averages 10 ka in the early pleistocene 2 1 ma and 7 ka in the late pleistocene 1 ma to the present twelve benthic and five planktic 18 o records are pinned to the agemodel and averaged together to provide a record of glacial variability major deglaciation features are identified over the last 2 ma and a remarkable 33 out of 36 occur when earth s obliquity is anomalously large during the early pleistocene deglaciations occur nearly every obliquity cycle giving a 40 ka timescale while late pleistocene deglaciations more often skip one or two obliquity beats corresponding to 80 or 120 ka glacial cycles which on average give the 100 ka variability this continuous obliquity pacing indicates that the glacial theory can be simplified an explanation for the 100 ka glacial cycles only requires a change in the likelihood of skipping an obliquity cycle rather than new sources of long period variability furthermore changes in glacial variability are not marked by any single transition so much as they exhibit a steady progression over the entire pleistocene the mean variance skewness and timescale associated with the glacial cycles all exhibit an approximately linear trend over the last 2 ma a simple model having an obliquity modulated threshold and only three adjustable parameters is shown to reproduce the trends timing and spectral evolution associated with the pleistocene glacial variability

evidence for late pleistocene ice stream activity in the witch ground basin central north sea from 3d seismic reflection data abstract buried submarine landforms mapped on 3d reflection seismic data sets provide the first glacial geomorphic evidence for glacial occupation of the central north sea by two palaeo ice streams between 58 59 n and 0 1 e streamlined subglacial bedforms mega scale glacial lineations and iceberg plough marks within the top 80 m of the quaternary sequence record the presence and subsequent break up of fast flowing grounded ice sheets in the region during the late pleistocene the lengths of individual mega scale glacial lineations vary from 5 to 20 km and the distance between lineations typically ranges from 100 to 1000 m the lineations incise to a depth of 10 12 m with trough widths of 100 m the most extensive and best preserved set of lineations is attributed to the action of a late weichselian ice stream which either drained the ne sector of the british irish ice sheet or was sourced from the sw within the fennoscandian ice sheet the 30 50 km wide palaeo ice stream is imaged along its flow direction for 90 km trending nw se an older set of less well preserved lineations is interpreted as an earlier weichselian or saalian ice stream and records ice flow in an sw ne orientation cored sedimentary records tied to 3d seismic observations support grounded ice sheet coverage in the central north sea during the last glaciation and indicate that ice flowed over a muddy substrate that is interpreted as a deformation till the identification of a late weichselian ice stream in the witch ground area of the north sea basin provides independent geomorphic evidence in support of ice sheet reconstructions that favour complete ice coverage of the north sea between scotland and norway during the last glacial maximum

relict sea floor ploughmarks record deep keeled antarctic icebergs to 45 s on the argentine margin abstract this paper reports ploughmarks on the argentine continental margin up to 44 50 s the most northerly morphological evidence of giant icebergs in the southern atlantic more than 2500 ploughmarks up to 32 km long 685 m wide and more than 20 m deep have been observed at modern water depths up to 646 m taking into account these iceberg sizes and ocean current directions which appear to have remained similar from the last full glacial to the present interglacial the icebergs that produced the ploughmarks are interpreted to be calved from fast flowing ice streams draining huge basins of the west antarctic ice sheet and the western antarctic peninsula during the last glacial maximum lgm about 20 000 years ago ploughmarks at the deepest water depths correspond to icebergs more than 500 m thick and at least 2 km wide given a sea level rise of 120 m since the lgm the icebergs after having drifted northeast in the antarctic circumpolar current were transported northward by the falklands malvinas current a total distance of 2000 to 4000 km the waters north of the falkland islands in particular were probably several degrees colder than today to prevent rapid iceberg melting and deterioration

giant iceberg plow marks at more than 1 km water depth offshore west greenland abstract during a recent 2006 cruise of rv dana high resolution side scan sonar and sub bottom profiling was carried out on selected shelf and slope transects offshore disko bugt central west greenland available commercial seismic data from the margin indicate here irregular seabed morphology with erosional features locally extending down to c 1100 m water depth the newly acquired side scan sonar data reveal the presence of giant iceberg plow marks extending sub parallel to the slope between about 800 and 1085 m water depth the height difference between bottom of the scours and rim crest is up to 40 m the largest plow marks are about 750 m wide to date no observed modern icebergs including those from antarctica have drafts in excess of c 500 m taking into account maximum glacial sea level lowering of c 120 m the paleo iceberg keel depth was at least 950 m due to the presence of the relatively shallow 1000 m and dimensions of the plow marks are concluded to be exceptional and comparable to glacial scouring features reported from the arctic ocean

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

metamorphism and kinematics of the early deformation in the variscan suture of sw iberia the early devonian collisional stage in sw iberia has been investigated through the analysis of deformation in the cubito moura schists the main lithology of an allochthonous complex putatively rooted in the suture between the ossa morena and south portuguese zones the first deformation in these schists d1 is recorded as a s1 l1 mylonitic fabric well preserved in early quartz veins subsequent d2 deformation caused the main folds and the main s2 foliation after restoration the stretching lineation l1 trends at a small angle with the ossa morena south portuguese suture this trend together with the top to the east kinematics determined from quartz microfabric is indicative of an oblique left lateral collisional scenario in sw iberia chlorite white k mica quartz chloritoid multi equilibrium calculations yield p t conditions in the range 0 9 1 2 gpa and 300 400 c during the first collisional stage p t conditions during d2 were 0 3 0 8 gpa and 400 450 c thus indicating an important stage of exhumation of the allochthonous complex during these two collisional events after subduction of the ossa morena zone margin under the south portuguese zone continental crust in the general context of the variscan orogen dominated by dextral collision the left lateral convergence in sw iberia can be explained in terms of the avalonian salient represented by the south portuguese zone which would impinge between iberia and morocco

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

high resolution geophysical observations of the yermak plateau and northern svalbard margin implications for ice sheet grounding and deep keeled icebergs high resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the yermak plateau and northern svalbard margin between 79 20 and 81 30 n and 5 and 22 e is presented

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

iceberg ploughmarks illuminated by shallow gas in the central north sea 2014 the authors published by elsevier ltd this is an open access article under the cc by nc salicense http creativecommons org licenses by nc sa 3 0

a relict ice scoured erosion surface in the central north sea abstract the interpretation of shallow seismic records from the central north sea has revealed the existence of an irregular erosion surface within late pleistocene sediments a morphological study of this surface has identified two main types of relief 1 an irregular rough topography with depressions varying in depth from 1 to 6 m and in width from 25 to 300 m and 2 a much smoother topography with relatively few depressions on a palaeobathymetric map the rough topography extends from ca 110 to 160 m below sea level od while the smoother topography extends beyond the 160 m below od contour this surface is interpreted as an ice scoured erosional feature formed by the grounding of sea ice in a shallow shelf environment the stratigraphic position of the ice scoured surface shows it to be a relict late weichselian feature formed at ca 17 000 18 000 b p

identification and preservation of landforms diagnostic of past ice sheet activity on continental shelves from three dimensional seismic evidence ice ages have occurred a number of times in earth9s history and are important in understanding changes in long term climate however it is difficult to demonstrate the presence of ice sheets in the ancient record because their sedimentary products can resemble those from nonglacial processes e g debris flows diagnostic large scale glacial landforms produced beneath ice sheets and preserved on continental shelves after deglaciation can establish a glacial origin three dimensional seismic evidence from the 2 7 ma naust formation norwegian margin illustrates several glacial landforms that are also commonly occurring features on modern high latitude shelves 1 streamlined mega scale lineations produced by fast flowing ice streams 2 ploughmarks formed by iceberg keels and 3 regularly spaced transverse ridges or push moraines formed during ice retreat we have found for example buried ice keel ploughmarks on a paleoshelf dating to ca 2 ma norwegian margin seismic stratigraphy data show that ice advanced and retreated many times and some paleoshelf surfaces were preserved such paleosurfaces must survive ocean basin destruction for glacial landforms to be useful in identification of ancient depositional environments

icebergs rework shelf sediments to 500 m off antarctica icebergs and sea ice rework the sediments of high latitude shelves producing modern diamicts ice keel turbates unrelated to glacial proximity off antarctica sidescan sonar data indicate the presence of ice gouge features formed by the physical interaction between ice keels and the sea bed these are recognized as incisions a few metres deep and tens of metres wide in water depths up to 500 m on the submarine bank tops and slopes off wilkes land and in the weddell sea subcircular depressions 30 to 150 m in diameter a washboard pattern and hummocky bed features also represent iceberg resting sites the freshness of sea bed morphology nearby holocene sediment ponding and active hydraulic sedimentary processes indicate that the sea floor is being reworked by iceberg keels tabular iceberg drafts in excess of 330 m have been measured and modeling studies suggest that nontabular iceberg drafts of 500 m are possible we conclude that a modern ice keel turbate deposit in the form of a poorly stratified diamicton is probably widespread on that part 54 of the antarctic shelf less than 500 m deep

pliocene paleoenvironment evolution as interpreted from 3d seismic data in the southern north sea dutch offshore sector a high resolution 3d seismic survey from the dutch offshore sector has been interpreted and subsequently correlated with existing regional seismo stratigraphic concepts derived from conventional 2d seismic data sets the interpreted 13 seismic units have been related to a newly established chrono stratigraphic framework kuhlmann et al 2006a b chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 integrated chronostratigraphy of the pliocene pleistocene interval and its relation to the regional stratigraphical stages in the southern north sea region netherlands journal of geosciences geologie en mijnbouw 85 1 19 35 resulting in up dated age control for the seismic units the generation of amplitude maps time slices and isopach maps from the 3d seismic data enabled detailed spatial and temporal reconstruction regarding the paleoenvironmental and climatological development as depicted by kuhlmann et al 2006a chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 the lowermost seismic units s1 s4 comprise condensed middle miocene to piacencian sediments deposited under warm open marine conditions these sediments show a uniform seismic facies of low amplitude reflectors the boundary of seismic unit s4 s5 around 2 6 ma delineates a shift towards generally colder climate conditions that are connected to the onset of northern hemisphere glaciation seismic unit s5 includes alternations of warmer and colder periods during warmer periods bottom currents generated elongated structures 2 5 4 km long 300 500 m wide on the horizon display these layers show as well shallow gas accumulations with a more regional extent and are related to coarser grained sediments sealed by clayey sediments of the cold phases a homogenous seismic facies is characteristic for the colder periods within seismic units s6 and s7 internal fore set structures display the regressional trend related to the cooling of this interval seismic units s8 s11 display a pattern of unoriented lineaments which was probably caused by icebergs drifting into the north sea and souring the sea floor this finding is in accordance with the shallow marine arctic conditions of this interval within these units a bright spot of 3 by 7 km in size is interpreted to result from shallow gas accumulation related to a grounded iceberg this feature represents another more local area of gas accumulation that is closely related to iceberg activity within the study area the uppermost seismic units s12 and s13 belong to a fluvial paralic paleo environment that is characterised by aggradational seismic reflectors pleistocene glacial valleys were recognised in the upper 200 m below sea floor 2007 elsevier ltd all rights reserved

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

buried iceberg keel scouring on the southern spitsbergenbanken nw barents sea abstract parasound 3 5 khz subbottom echosounder profiles acquired on the southern spitsbergenbanken nw barents sea show iceberg keel scouring features which are buried by sediment that accumulated during the post last glacial maximum lgm sea level rise four acoustic units units 1 to 4 in stratigraphic order were differentiated based on the characterization of their acoustic facies and reflection surfaces unit 1 shows a chaotic internal structure and is interpreted as a glacial till whereas the laminated units 2 to 4 accumulated by sediment settling from suspension clouds and bottom currents during the last deglaciation phase the top of unit 2 was frequently incised by iceberg keels resulting in up to 12 m deep ploughmarks which were later filled and buried by unit 3 and 4 sediments three main paleo evironmental changes controlled the evolution of the facies succession 1 the major shift from till formation unit 1 below grounded ice to the accumulation of laminated sediments unit 2 which are inferred to reflect ice lifting and meltwater release 2 iceberg keel scouring after sedimentation of unit 2 3 the probable abrupt termination of iceberg keel scouring related to the glacio eustatic sea level rise a linkage between these episodes of changes and short lasting phases of rapid post lgm sea level rise such as meltwater pulses is inferred although further studies are needed to better understand the temporal and genetic relationships between the sedimentary events recognized in the barents sea and climate changes

sea floor scour at the mouth of hudson strait by deep keeled icebergs from the laurentide ice sheet physical evidence on the dimensions of icebergs released from the mouth of hudson strait into the northwest atlantic during the last heinrich event h 0 is presented side scan sonar imagery shows scour marks up to 700 m wide and longer than 28 km these scour marks were carved by gigantic icebergs megabergs with keel drafts possibly as great as 660 m capable of scouring trenches 20 to 25 m deep into the seabed these icebergs were likely calved from the grounding margin of a thick possibly as thick as 640 m rapidly flowing glacial margin during the h 0 heinrich event 11 ka bp along with the relatively few megabergs released were large numbers of smaller icebergs that calved from the ice margin at the same time and were also produced from break up of the megabergs scouring of the seabed by the large and smaller icebergs happened at the same time with megabergs scouring only in the deep waters of hatton basin and the smaller bergs scouring only on the eastern shallow margin of the basin at the continental shelf break

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

the history of quaternary sedimentation in the uk sector of the north sea basin reconnaissance seismic and sampling surveys have shown that up to 500 m of lower and early middle pleistocene deltaic sediments are preserved in the uk sector of the north sea the distributions of delta related facies record the progressive expansion of peripheral delta systems northwards across the southern north sea during the early pleistocene a late middle pleistocene unconformity is present throughout the uk sector and sedimentation above the unconformity was dominated by glacial erosional and depositional processes a complex system of deeply incised valleys was eroded during each of three regional middle and upper pleistocene glaciations and the valleys have been filled or partially filled by glaciolacustrine or glaciomarine and interglacial marine sediments the valleys of the earliest elsterian glaciation are up to 400 m deep in the southern north sea the saalian and weichselian valleys are commonly more than 100 m deep they are eroded through their contemporary tills nearshore but occur well beyond the limits of these tills offshore the origins of these valleys are attributed to a combination of fluvial subglacial and periglacial processes

lower pleistocene deltaic and marine sediments in boreholes from the central north sea lower pleistocene sediments recovered in boreholes from the aberdeen ground formation in the central north sea indicate that the unit was deposited in a delta front to prodelta shallow open shelf marine setting possible estuarine and clastic nearshore marine deposits have been identified on the western margin of the basin the delta front sediments consist of interbedded structureless to laminated sands and muds with organic debris ferruginous nodules and common soft sediment deformation structures sporadic rippled and graded beds basal scours to beds and starved ripples suggest periodic wave current reworking prodelta shelf marine sediments are predominantly argillaceous with only occasional thin sand beds and rare phosphatic bands one exceptionally thick sand body or submarine channel fill although this remains uncertain the estuarine clastic nearshore marine sediments include coarse channel lag deposits and rippled and laminated subtidal sands a rich microfossil assemblage recovered from the prodelta shelf marine sequence indicates that deposition occurred under fluctuating climatic conditions

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

sea ice scouring on the inner shelf of the southeastern canadian beaufort sea abstract about 2200 ice scours were observed and analyzed over a distance of approximately 500 km on the inner shelf of the southeastern canadian beaufort sea ice scours were divided into two types based on their morphology multiple scours consisting of a series of parallel scours and ridges and single scours single scours are the dominant type representing more than 85 of the total observations the mean scour depth and width are 0 3 m and 11 m respectively but scour depths of more than 2 m and a scour width up to 345 m were documented the magnitude of ice scouring processes increases with water depth in water depths less than 10 m less than 25 of the seafloor surface is reworked by ice scours this percentage increases significantly seaward of the 10 m isobath being more than 75 in water depths in excess of 12 m a break in the seabed slope at about 10 to 12 m water depth marks a boundary between a nearshore zone moderately influenced by ice processes and an outer zone affected by intense ice scouring this morphological boundary could be due to intense erosion by the keels of pressure ice ridges at the inner edge of a zone of grounded ice ridges most of the observed ice scours appear to be reworked especially in water depths of less than 10 m and represent small scale sediment sinks inshore of the 10 m isobath scour reworking is believed to be mainly due to frequent bottom disturbance by wave orbital currents and mean near bottom flows during the open water season scour orientations show that the dominant motion of ice during scouring events is east or west which is subparallel to the bathymetric contours and coastline scour terminal push mounds however suggest a dominant east to southeast movement that may contribute to onshore sediment transport during ice push events

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

increased fluid flow activity in shallow sediments at the 3 km long hugin fracture in the central north sea the north sea hosts a wide variety of seafloor seeps that may be important for transfer of chemical species such as methane from the earth s interior to its exterior here we provide geochemical and geophysical evidence for fluid flow within shallow sediments at the recently discovered 3 km long hugin fracture in the central north sea although venting of gas bubbles was not observed concentrations of dissolved methane were significantly elevated up to six times background values in the water column at various locations above the fracture and microbial mats that form in the presence of methane were observed at the seafloor seismic amplitude anomalies revealed a bright spot at a fault bend that may be the source of the water column methane sediment porewaters recovered in close proximity to the hugin fracture indicate the presence of fluids from two different shallow 500m sources i a reduced fluid characterized by elevated methane concentrations and or high levels of dissolved sulfide up to 6 mmol l 1 and ii a low chlorinity fluid cl 305 mmol l 1 that has low levels of dissolved methane and or sulfide the area of the seafloor affected by the presence of methane enriched fluids is similar to the footprint of seepage from other morphological features in the north sea

origin transport and emplacement of an exotic island arc terrane exposed in eastern kamchatka russia the regional stratigraphy of eastern kamchatka includes an exotic early late cretaceous ophiolite and late cretaceous island arc volcanic sequence integrating the existing geologic and geophysical data we examine the origin transport emplacement and postemplacement deformation of the island arc terrane which is named the olyutorsky island arc results from several paleomagnetic studies consistently indicate that the island arc terrane originated 1000 km to the south of where it is presently exposed although the formative paleolatitudes of the island arc rocks approximately correspond to the location of the izanagi farallon subduction zone the age of the volcanic rocks postdates the cessation of izanagi farallon convergence thus indicating that an unnamed plate or back arc basin existed in the northwest pacific during late cretaceous time we examine two possible models for northward transport of the island arc terrane to kamchatka 1 infra oceanic transport with the pacific or kula plates and 2 coastwise translation of the island arc terrane after accretion to the eurasian margin far to the south of kamchatka for both models the dominant eocene and miocene deformation ages observed in eastern kamchatka are used as two possible age limits for the cessation of northward transport although the observed paleolatitudes from paleomagnetic data correspond best with the infra oceanic transport model the provenance of the paleogene transport stratigraphy indicates a near shore sediment supply our preferred interpretation is that the island arc terrane 1 accreted onto the eurasian margin concurrent with cessation of island arc volcanism maastrichtian danian and 2 underwent northward coastwise translation along a major strike slip fault zone ending by middle late eocene time 43 50 ma it is unclear whether the ophiolite was exposed during arc continent collision or whether the ophiolite was obducted onto the island arc prior to collision a consequence of either infra oceanic transport or coastwise translation is that an open corridor between the western terminus of the aleutian arc and kamchatka must have existed until middle to late eocene time spreading within the komandorsky basin subduction of sea mounts and collision of the aleutian arc with kamchatka are proposed to have instigated the second miocene phase of deformation which uplifted and reexposed the island arc terrane

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

mid pleistocene ice drainage pattern in the norwegian channel imaged by 3d seismic abstract several investigations have shown that a huge late weichselian ice stream flowed along the norwegian channel and deposited thick debris flow deposits at the north sea fan the development of the channel is probably mainly a result of several cycles of ice stream activity during the quaternary a merged 3d seismic image shows a lineated relief pattern interpreted as a uniquely well preserved footprint of a moving ice sheet this deep quaternary horizon corresponds to a slightly irregular reflector on top of a parallel layered seismic sequence seismic tie to the troll core 8903 south of the study area shows that the sequence comprises early middle pleistocene marine sediments the pattern of lineations the seismic stratigraphy as well as the chronostratigraphic investigations of the troll core strongly indicate that the image reflects the initial phase of an extensive middle pleistocene glaciation inferred age ca 0 5 ma prior to the development of a massive norwegian channel ice stream the northwesterly oriented pattern seen in the southeastern part of the study area demonstrates that the ice flowed into the channel mainly from the coastal zone north of bergen farther west various sets of fan shaped lineations partly cross each other showing that the 3d image represents a certain short time window in the northern study area the ice flow was dominantly northwards and directed towards the area below the present shallow maloy plateau there are no indications that the glaciers north of sognefjorden affected the marine ice sheet

3d seismic analysis of buried tunnel valleys in the central north sea tunnel valley fill sedimentary architecture fourteen overlapping 3d seismic reflection data sets originally acquired by the oil and gas industry were used to image and investigate complex networks of buried tunnel valleys in the uk sector of the central north sea more than 180 individual tunnel valleys were observed and mapped to horizontal resolutions of 12 50 m and vertical resolutions of 8 10 m the results presented here identify three recurring seismic facies that locally define stratigraphic organization from base to top of the buried tunnel valley fills i high amplitude disrupted units ii a unit containing gently dipping disrupted reflections or transparent facies and iii well layered continuous reflections a comparison to similar works in the region is used to infer tunnel valley infill during changing depositional conditions from high energy subglacial meltwater to quiet glaciolacustrine or glaciomarine environments

seafloor glacial features reveal the extent and decay of the last british ice sheet east of scotland three dimensional 3d seismic datasets 2d seismic reflection profiles and shallow cores provide insights into the geometry and composition of glacial features on the continental shelf offshore eastern scotland 58 n 1 2 w the relic features are related to the activity of the last british ice sheet bis in the outer moray firth a landsystem assemblage consisting of four types of subglacial and ice marginal morphology is mapped at the seafloor the assemblage comprises i large seabed banks interpreted as end moraines coeval with the bosies bank moraine ii morainic ridges hummocky push and end moraine formed beneath and at the margins of the ice sheet iii an incised valley a subglacial meltwater channel recording meltwater drainage beneath former ice sheets and iv elongate ridges and grooves subglacial bedforms overprinted by transverse ridges grounding line moraines the bedforms suggest that fast flowing grounded ice advanced eastward of the previously proposed terminus of the offshore late weichselian bis increasing the size and extent of the ice sheet beyond traditional limits complex moraine formation at the margins of less active ice characterised subsequent retreat with periodic stillstands and readvances observations are consistent with interpretations of a dynamic and oscillating ice margin during bis deglaciation and with an extensive ice sheet in the north sea basin at the last glacial maximum final ice margin retreat was rapid manifested in stagnant ice topography which aided preservation of the landsystem record

architecture and sedimentary processes on the mid norwegian continental slope a 2 7 myr record from extensive seismic evidence abstract quaternary architectural evolution and sedimentary processes on the mid norwegian continental slope are investigated using margin wide three and two dimensional seismic datasets of 100 000 km3 sediments delivered to the mid norwegian shelf and slope over the quaternary 75 000 km3 comprise the slope succession the structural high of the voring plateau characterised by initially low 1 2 slope gradients and reduced accommodation space exerted a strong control over the long term architectural evolution of the margin slope sediment fluxes were higher on the voring plateau area increasing up to 32 km3 ka 1 during the middle pleistocene when fast flowing ice streams advanced to the palaeo shelf edge resulted in a more rapid slope progradation on the voring plateau these rates of sediment delivery are high compared to the maximum of 7 km3 ka 1 in the adjacent sectors of the slope characterised by steeper slope 3 5 more available accommodation space and smaller or no palaeo ice streams on the adjacent shelves in addition to the broad scale architectural evolution identification of more than 300 buried slope landforms provides an unprecedented level of detailed process based palaeoenvironmental reconstruction channels dominate the early pleistocene record 2 7 0 8 ma during which glacimarine sedimentation on the slope was influenced by dense bottom water flow and turbidity currents morphologic signature of glacigenic debris flows appear within the middle late pleistocene 0 8 0 ma succession their abundance increases towards late pleistocene marking a decreasing role for channelized turbidity currents and dense water flows this broad scale palaeo environmental shift coincides with the intensification of northern hemispheric glaciations highlighting first order climate control on the sedimentary processes in high latitude continental slopes

past ice flow in wahlenbergfjorden and its implications for late quaternary ice sheet dynamics in northeastern svalbard wahlenbergfjorden is a fjord situated in the western part of nordaustlandet in northern svalbard it leads into the 400 m deep hinlopen strait located between nordaustlandet and spitsbergen high r