late cenozoic geological evolution of the northern north sea development of a miocene unconformity reshaped by large scale pleistocene sand intrusion despite hundreds of wells and extensive 3d seismic coverage the late cenozoic geological evolution is still not completely understood in the prolific northern north sea hydrocarbon province this is mainly due to post depositional modification of sediment body geometries by injections of large volumes of sand using high quality 3d seismic and well data above the snorre and visund fields we propose a new late cenozoic geological model that describes pre injection geomorphological forms and sand injection events the northern north sea was exposed during mid and late miocene times 10 myr simultaneously with the regional miocene compression phase subaerial and coastal cliff erosion formed escarpments up to 100 m high around the miocene pliocene boundary the northern north sea subsided below sea level and a layer of glauconitic sand was deposited during the early pleistocene glacial period high fluid pressures fractured the regional hordaland group seal fluidized sand either vented to the sea floor or was deposited in irregular sand bodies up to 150 m thick above them the injected sand lifted the overburden and formed irregular mounds that reshaped the top hordaland group unconformity regionally during the glacial period the area was tilted regionally by 0 3 towards the nne

a morphometric analysis of tunnel valleys in the eastern north sea based on 3d seismic data a 1250 km2 3d seismic volume is used to provide a detailed spatial and geometrical analysis of fifteen pleistocene tunnel valleys in the danish north sea all the valleys are buried they are up to 39 km long 3 4 km wide and up to 350 m deep the valleys are part of a vast tunnel valley province covering an area of some 0 5 million km2 of the formerly glaciated lowland areas of north west europe the valleys consist of non branching non anastomosing troughs they exhibit strongly undulating bottom profiles with numerous sub basins and thresholds and are characterised by adverse end slopes cross cutting relationships and theoretical considerations suggest the occurrence of seven major episodes of valley incision attributed to ice marginal oscillations within a few glacials calculations considering the valley end gradients and theoretical ice surface profiles suggest that the valleys were formed by pressurised subglacial meltwater erosion given a range of theoretical ice surface profiles the adverse end slopes are well beyond the supercooling threshold which suggests that the water was not in thermal equilibrium with the basal ice and that flow was concentrated in substantial conduits with sufficient mass and flux to maintain water temperature well above the freezing point copyright 2007 john wiley sons ltd

contrasting sources for glacial and interglacial shelf sediments used to interpret changing ice flow directions in the larsen basin northern antarctic peninsula abstract marine sediment cores from the former larsen a ice shelf area reveal three lithological units deposited during ice sheet advance and retreat from the continental shelf the uppermost unit 1 consists of a diatom bearing silty clay with sparse ice rafted debris ird clasts include rock types which can all be matched to onshore outcrops along the eastern side of the antarctic peninsula most clasts are very angular angular or subangular the clasts in this unit are interpreted as supraglacial or englacial debris deposited below an ice shelf distal from the grounding line and or by icebergs in an open marine setting during the holocene in the underlying units 2 and 3 clast lithologies are quite different and mainly comprise cretaceous and jurassic sedimentary rocks these lithologies were derived locally from the continental shelf the larsen basin rather than the limited onshore outcrops of the 2750 clasts studied in units 2 and 3 most are subrounded or subangular and some are striated unit 2 is interpreted as being deposited beneath an ice shelf proximal to the grounding line unit 3 is interpreted as subglacial diamict deposited by grounded ice flowing across the shelf during the last glacial period the availability of sedimentary rocks at the seabed may have facilitated the development of a deforming till layer with low shear strength i e soft or deformation till within unit 3 there are no consistent differences in clast composition or roundness between the deformation till which was probably deposited at the base of an ice stream and an underlying till with high shear strength i e stiff till on the inner shelf where the bedrock lies very close to the seabed clast composition in the subglacial diamicts affords a way of identifying the presence of mesozoic stratigraphic units the contrasting provenance of the coarse fraction between unit 1 and units 2 and 3 is used to interpret ice sheet basal thermal regime and produce a conceptual model of changing palaeo flow directions between glacial and interglacial periods grain roundness and petrology are shown to be a potent method for interpreting different glacial interglacial processes and environments

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

relating cenozoic north sea sediments to topography in southern norway the interplay between tectonics and climate abstract about 482 000 km 3 of sediment ca 24 m ma accumulated in the north sea during the cenozoic early cenozoic sedimentation was likely due to uplift of the circum north atlantic landmasses related to continental break up kilometre scale transient uplift and in some areas permanent uplift generated sources for progradational influx of clastic sediments from scotland the shetland platform and to a lesser degree southwestern norway the eocene sedimentation pattern was similar to the palaeocene with lower rates of accumulation associated with flooding and tectonic quiescence sediment influx from the shetland platform continued throughout the cenozoic while supply from southern norway increased markedly around the eocene oligocene coeval with the greenhouse icehouse transition mass balance calculations of sediment and eroded rock volumes suggest that while some topography along the western margin of norway may be pre cenozoic significant uplift of the main paleic surface in southern norway occurred around the early oligocene sedimentation rates were almost ten fold higher than the cenozoic average in the plio pleistocene slightly higher than the global average mass balance calculations indicate that plio pleistocene erosion over deepened a pre existing topography

the northern sector of the last british ice sheet maximum extent and demise abstract strongly divided opinion has led to competing apparently contradictory views on the timing extent flow configuration and decay mechanism of the last british ice sheet we review the existing literature and reconcile some of these differences using remarkable new sea bed imagery this bathymetric data provides unprecedented empirical evidence of confluence and subsequent separation of the last british and fennoscandian ice sheets critically it also allows a viable pattern of ice sheet disintegration to be proposed for the first time covering the continental shelf around the northern united kingdom extensive echosounder data reveals striking geomorphic evidence in the form of tunnel valleys and moraines relating to the former british and fennoscandian ice sheets the pattern of tunnel valleys in the northern north sea basin and the presence of large moraines on the west shetland shelf coupled with stratigraphic evidence from the witch ground basin all suggest that at its maximum extent a grounded ice sheet flowed from se to nw across the northern north sea basin terminating at the continental shelf edge the zone of confluence between the british and much larger fennoscandian ice sheets was probably across the northern orkney islands with fast flowing ice in the fair isle channel focusing sediment delivery to the rona and foula wedges this period of maximum confluent glaciation c 30 25 ka bp was followed by a remarkable period of large scale ice sheet re organisation we present evidence suggesting that as sea level rose a large marine embayment opened in the northern north sea basin as far south as the witch ground basin forcing the two ice sheets to decouple rapidly along a north south axis east of shetland as a result both ice sheets rapidly adjusted to new quasi stable margin positions forming a second distinct set of moraines c 24 18 ka bp the lobate overprinted morphology of these moraines on the mid shelf west of orkney and shetland indicates that the re organisation of the british ice sheet was extremely dynamic probably dominated by a series of internally forced readvances critically much of the ice in the low lying north sea basin may have disintegrated catastrophically as decoupling progressed in response to rising sea levels final stage deglaciation was marked by near shore ice streaming and increasing topographic control on ice flow direction punctuated retreat of the british ice sheet continued until c 16 ka bp when following the north atlantic iceberg discharge event heinrich 1 ice was situated at the present day coastline in nw scotland

repeated advance and retreat of the east antarctic ice sheet on the continental shelf during the early pliocene warm period abstract diatom analysis of a sediment core recovered at iodp site u1358 on the continental shelf off the adelie coast indicated that the lower section of the core contained an assemblage dating back to the thalassiosira innura zone of the lower pliocene that ranges from 4 2 to 5 12 ma based on lithological descriptions at both a macro and micro scale of this early pliocene part of the core four facies were interpreted from the diamictons representing the progressive advance and retreat of the grounding line over the site facies 1a and 1b contain a distinct directional signal from the orientation of the a axis of clasts with several phases of fabric development along with both brittle and ductile deformation features that are common in sediments that have been subglacially deformed facies 1c and 1d are finely laminated and were deposited in open marine conditions the four facies within the depositional model provide for the first time direct evidence for ice advancing across the shelf adjacent to the wilkes subglacial basin on at least four occasions separated by three periods of open marine conditions indicating retreat of grounded ice inland of the site during a warmer than present early pliocene the times of open marine conditions are correlated with previous findings from the neighbouring rise sites that also indicated an oscillating ice margin this has significant implications because firstly it suggests a dynamic east antarctic ice sheet eais that is probably far more sensitive to climatic and oceanic forcing even during relatively short time periods than had previously been thought secondly it suggests that proxies used to interpret the advance and retreat of the grounding line from the rise can be linked with direct evidence of grounding line migration from the shelf it also has important implications for the future behaviour and sensitivity of the eais under present continuing warming conditions together with results from the rise this paper provides a crucial ice extent target for a new ice sheet model of this region during the pliocene

deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions earth has undergone profound changes since the late pliocene which led to the development 2 7 million years ago ma and intensification 0 9 ma of large scale northern hemisphere ice sheets recorded as transitions in the benthic foraminiferal oxygen isotope 18ob record here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium calcium ratios from the north atlantic which shows that temperature variations are a substantial portion of the global 18ob signal the record shows two distinct cooling events associated with the late pliocene lpt 2 5 to 3 ma and mid pleistocene mpt 1 2 to 0 85 ma climate transitions whereas the lpt increase in ice volume is attributed directly to global cooling the shift to 100 000 year cycles at the mpt is more likely to be a response to an additional change in ice sheet dynamics

plio pleistocene foraminiferal stratigraphy and correlation in the central north sea abstract a detailed foraminiferal stratigraphy is presented for the plio pleistocene sequence of the central north sea region these results are based on investigations carried out on seven boreholes and a detailed foraminiferal stratigraphy is presented here for the josephine borehole 30 13 2 x the pliocene pleistocene boundary is placed at the last common occurrence of cibicides grossa in the josephine hole at a depth of 700 m cassidulina teretis is the dominant species in the pliocene and it continues with decreasing frequencies into the early pleistocene the boundary between early and middle pleistocene occurs at a depth of about 210 m in the borehole correlation from west to east in the central north sea reveals an extremely thick pliocene 400 m and early pleistocene 500 m sequence at the josephine site this sequence thins out both to the west and to the east this together with the palaeoenvironmental evidence present at the josephine site indicates that continuous tectonic subsidence occurred during the pliocene and early pleistocene in the central graben variations in the thickness of the middle and late pleistocene units in the region is probably due to pronounced glacial chanelling

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

structural and seismic stratigrapic study in the center of the magdalena shelf in the western margin of baja california based on seismic reflection data the magdalena shelf is a shallow low relief surface located along the baja california pacific margin as part of a forearc basin the shelf was a convergent margin setting before the oblique divergent plate boundary formed in the gulf of california at 12 ma it is thought that since 12 8 ma this basin has been a transtensional or strike slip basin to constrain the geometry structural characteristics and some stratigraphic relationships an active source seismic reflection study was carried out in the central part of the shelf as a result the analyzed data show faults basins and unconformities two out of four observed basins are clearly controlled by the santa margarita and san lazaro faults that dip 40 ne a third basin is controlled by the tosco abreojos fault these three basins are part of the deformation zone that is associated with the tosco abreojos fault system the iray margarita basin on the other hand is a fourth basin located at the northeast sector of the study area an additional feature observed is a stepover lying between the overlapping ends of the santa margarita and san lazaro faults small faults oriented sub parallel to the above major faults are present mainly throughout the western sector of the study area some of those minor faults cut through the seafloor indicating recent tectonic activity santa margarita san lazaro and tosco abreojos are also the names given to half grabens controlled by the active faults that have the same names the first two basins are affected by many more small faults in comparison with what we see in the third basin tectonically this means that those two basins are the more active in the area of study in all four basins the upper seismic sequence consists of sediments controlled by faults of neogene age we found that the iray santa margarita basin is the deepest of all four basins beyond the resolution of the data 5 km and lack of minor faults there indicates that the basin is not tectonically active two unconformities are present in the region unconformity 1 of miocene age and unconformity 2 of paleocene eocene and cretaceous ages unconformity 1 is present in the entire region while unconformity 2 is present mainly in the iray magdalena and san lazaro basins in the iray magdalena basin the sedimentary sequences show an uplift that took place in late jurassic time along its western portion we also see that moderate compressive deformation increases gradually from west to east a chaotic reflector oriented nw se is observed with an irregular shape in all regions it shows very superficial in some places sub parallel to the major faults and in association with the subduction complex seismic activity reported for the region showed a strong correlation with the fault plane of the santa margarita fault indicating that the tosco abreojos deformation zone is 90 km wide in the area finally the santa margarita fault should be considered in future hazard risk assessments because of their proximity to puerto san carlos as it has been reported local seismic events m 4 have generated alarm in the local populace as well as soil liquefaction and minor damage to structures in the region

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

pre weichselian quaternary glaciations of the british isles the netherlands norway and adjacent marine areas south of 68 n implications for long term ice sheet development in northern europe within this paper we review the pre weichselian glacial history of northern europe focussing on evidence from the british isles netherlands norway and adjacent marine areas that record the activity of the british bis and scandinavian sis ice sheets the objective of the paper is to examine the long term evolution of the two ice sheets in order to determine their level of synchronicity and their relationship to the plio pleistocene record of northern hemisphere glaciation geological evidence demonstrates striking long term similarities between the behaviour of the bis and sis with a step wise intensification in the glacial signal 1 first ice rafted debris ird input onto the continental margin at ca 2 7 2 6 ma and restricted glaciation prior to ca 1 1 ma 2 initiation of more lowland style glaciation from 1 1 ma 3 repeated shelf edge glaciations from 0 45 ma these steps coincide with a major intensification of the northern hemisphere climate signal at the beginning of the quaternary and the mid pleistocene transition temporal and spatial variabilities in the behaviour of different sectors of the bis and sis appear to reflect regional scale geographic latitude elevation climatic moisture temperature and glaciological deformable beds controls that modulate the build up of ice volume in the main ice accumulation areas relative to global climate forcing and its subsequent lateral expansion 2010 nerc

quaternary glaciations in southern fennoscandia evidence from southwestern norway and the northern north sea region abstract based on records from the northern north sea and southern norway quaternary fennoscandian glaciations are described and discussed maximum glaciation defined as the presence of shelf edge glaciation an ice stream flowing out of the norwegian channel and most likely an ice divide over the central part of fennoscandia sweden gulf of bothnia occurred for the first time in the late cenozoic at ca 1 1 myr the fedje glaciation this glaciation was followed by a ca 600 kyr period with at least two glaciations with ice extension somewhat larger than the younger dryas event in the region the first maximum glaciation of the bruhnes chron was during isotope stage 12 and was followed by repeated maximum glaciations within each of the light isotopic stages until stage 2 during the weichselian the southwestern part of the fennoscandian ice sheet reached maximum position three times sometime between 22 and 28 37 and 50 and 60 and 80 ka limited glaciations probably occurred during stadials between the early and middle weichselian interstadials between 500 ka and 1 1 myr and most likely also prior to 1 1 myr deep norwegian sea ice rafted detritus ird records reflecting contributions from several different ice sheets fennoscandian barents sea iceland and greenland each with large variations in history of ice extent to their respective margins yet to some degree they reflect the glaciation of the northern north sea region with an increasing ird input around 1 1 myr and a relatively low input of north sea components during some cycles around the b m boundary maximum glaciations occurred during insolation minima in the earlier part of the middle pleistocene however not all such minima are reflected by maximum glaciation in southern parts of fennoscandia the relatively poor chronological control and non continuous character of the data on weichselian interstadials stadials precludes a clear relationship to atmospheric changes recorded in greenland ice cores as well as to precession and or obliquity cycles in insolation

quaternary stratigraphy of the fladen area central north sea a multidisciplinary study based on detailed stratigraphic investigations on a 200 6m long core bgs borehole no 81 26 from the fladen ground area british sector core material from the sleipner field norwegian sector and shallow seismic profiles between the core sites the following conclusions are drawn 1 the north sea was glaciated sometime during th elaterpart of matuyama reversed period a complete glacial interglacial glacial cycle is recorded in these sediments 2 in a period of marine sedimentation in the middle pleistocene a transgression regression cycle under boreal arctic regime is recorded 3 the fladen area has subsided between 0 9 and 0 6 m ka through the later parts of the quaternary 4 a major glacial event dated at between 130 and 200 ka is recorded as a thick till unit in 81 26 this till which was deposited by ice moving from the southwest scotland probably represents a period when the scandinavian and british ice sheets coalesced in the north sea 5 based on the seismic data and the stratigraphy of the sleipner core an ice free open embayment dry land is favoured for the central north sea during the late weichselian 6 from the amino acid data it is shown that there has been an episodic style of sedimentation through the quaternary 7 of the investigated sediments which span the last 1 mill year ca 98 have been deposited under arctic to boreal arctic conditions

modelling north american palaeo subglacial lakes and their meltwater drainage pathways this paper presents predictions of palaeo subglacial lakes and their drainage pathways beneath the north american ice sheet during the last glaciation we utilise data on the current topography and seafloor bathymetry and elevation models of the ice and ground surface topography from data calibrated glaciological modelling to calculate the hydraulic potential surface at the ice sheets bed given that specific ice surface elevations are only known from modelled outputs and thus contain significant uncertainty we utilise many such outputs to examine where on the bed that subglacial lakes are likely to have occurred our analysis demonstrates the potential for subglacial lake genesis particularly beneath the former cordilleran ice sheet along the suture zone between the laurentide and cordilleran ice sheets in hudson bay in the great lake basins and deep trenches of the canadian archipelago during the last glacial maximum we suggest that at least 1000 km3 of meltwater could have been stored subglacially as the ice sheet and the bed evolved subglacial lakes repeatedly formed and emptied particularly in hudson bay and the suture zone between the laurentide and cordilleran ice sheets where lakes were characteristically broad and shallow 10 m deep in contrast the cordilleran ice sheet was characterised by deep up to 90 m and persistent lake genesis significantly similar distributions and modes of predicted subglacial lakes are obtained irrespective of the model or model run which suggests the results are robust subglacial meltwater drainage varied between stable networks typically associated with strong topographic controls and convoluted networks that underwent considerable dynamism including repeated meltwater network capture these lake likelihood predictions could usefully form targets for detailed field and remote investigations and we hypothesise and explore the potential that numerous deposits and spillways previously interpreted as arising from ice marginal lakes may have emanated from their subglacial cousins

3d seismic analysis of buried tunnel valleys in the central north sea morphology cross cutting generations and glacial history abstract this work presents the results of morpho stratigraphic analyses carried out on more than 180 buried tunnel valleys imaged in the central north sea using 3d seismic data at a variety of resolutions the buried tunnel valleys form complex networks of multiple cross cutting generations in the northern part of the study area cross cutting relationships within higher resolution 3d seismic data are used to extrapolate seven generations of tunnel valleys over an area of 14 400 km 2 three generations of cross cutting tunnel valleys are also observed within higher resolution 3d seismic data in the southern part of the study area detailed morphological measurements of individual tunnel valleys reveal average widths between 300 m and 3000 m lengths in the region of tens of kilometres and relatively straight and simple planform geometries the majority of the tunnel valleys display undulating basal profiles which provide evidence for the uphill movement of water over distances greater than 10 km and indicate formation by meltwater under pressure tunnel valley geometries vary between generations and defy a simple link between formation process and end form detailed orientation measurements for the tunnel valley generations reveal an overall ne sw trend in the northern part of the study area and a nw se directionality in the south when considered in light of palaeoglaciological models for the british and scandinavian ice sheets during the pleistocene tunnel valley orientation and distribution are consistent with the majority of tunnel valley generations forming perpendicular to a retreating british ice sheet changes in orientations between generations in both northern and southern study areas provide evidence for changes in the dynamics of the british and scandinavian ice sheets between subsequent glaciations of the central north sea

formalising an inversion methodology for reconstructing ice sheet retreat patterns from meltwater channels application to the british ice sheet glacial meltwater channels yield important information regarding patterns of palaeo ice sheet retreat however it is important to distinguish between channels formed at different positions in relation to the ice mass e g lateral subglacial in britain whilst meltwater channels have been widely reported in the literature such categorisation is often lacking here we develop an inversion methodology for extracting ice margin retreat patterns from meltwater channels diagnostic geomorphological criteria are presented derived from published descriptions of meltwater channel form by which a channel of unknown origin may be assigned to its appropriate category these criteria are applied to channels recorded in the britice gis database of glacial landforms and we find most channels to be of lateral or subglacial origin the categorisation of channels enables palaeo margin positions and the direction of retreat stage ice flow to be approximated and a preliminary reconstruction is made of fragments of the ice sheet retreat pattern further mapping and integration of melt traces with other geomorphic data will permit a more complete palaeo glaciological reconstruction of the last british ice sheet copyright 2007 john wiley sons ltd

stratigraphy and facies distribution of the utsira formation and the pliocene sequences in the northern north sea abstract the upper cenozoic deposits of the northern north sea have been analysed in order to establish a regional and detailed stratigraphy the utsira formation is subdivided into four log units and mapped and two main depocentres are outlined the lower part of the utsira formation consists of thick marine mounded sand bodies interpreted as overall stacked lowstand fan deposits while the upper part of the formation consists of more clayey silty intervals indicating increased relative sea level the succeeding progradational pliocene deposits are subdivided into 13 high frequency depositional sequences and are mapped the sequences are grouped into four composite sequences each of the four pliocene composite sequences is composed of one or two rather locally distributed prograding sequences lowstand sequence set succeeded by one or two more widely distributed aggrading prograding sequences transgressive highstand sequence set boundaries between the composite sequences are recorded as marked changes in distribution of depocentres and sequence architecture the regional uplift of scandinavia is believed to be the main control on sediment input feeding the succeeding general prograding pliocene sequences oscillations of the eustatic sea level punctuated the tectonically controlled progradation and affected variations in the accommodation space and thus created the high frequency sequences

the jaeren area a border zone of the norwegian channel ice stream abstract the coastal lowlands of jaeren southwestern norway have an extensive cover of quaternary sediments lithological biostratigraphical and geochronological investigations of a series of boreholes across jaeren have allowed us to combine earlier and new information on these deposits into a temporal model of quaternary sedimentation the cores show evidence of at least four ice free episodes with marine deposition during mainly arctic conditions the oldest of these is considered to be ca 200 ka old and the youngest one is the sandnes interstadial which is 14 c ams dated to 32 ka bp interbedded between these units are 10 40 m thick units of till with components of marine material these findings together with a re evaluation of distinct morphological features on jaeren as well as earlier provenance studies strongly suggest that jaeren has been a boundary zone between an ice stream following the norwegian channel draining a substantial part of the southern region of the fennoscandian ice sheet and local ice from south western norway through multiple periods of glaciation starting ca 1 1 myr million years ago the norwegian channel ice stream has been the main conduit of erosion products from southern scandinavia to the deep norwegian sea comparison with ice stream profiles from antarctica suggests that the deposition of relatively young marine sediments as high as ca 200 m a s l on jaeren is a result of glacial isostasy rather than regional tectonic movements

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

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

distribution of the neogene utsira sand and the succeeding deposits in the viking graben area north sea abstract the sandy quartzose parts of the utsira formation the middle miocene to mid pliocene utsira sand extends north south along the viking graben near the uk norwegian median line for more than 450 km and 75 130 km east west the utsira sand is located in basin restricted seismic depocentres east of and below prograding sandy units from the shetland platform area with hutton sands the utsira sand reaches thicknesses up to ca 300 m in the southern depocentre and 200 m in the two northern depocentres with sedimentation rates up to 2 4 cm ka succeeding plio pleistocene is divided into seismic units including base upper pliocene shale drape prograding complex and pleistocene the units mainly consist of clay but locally minor sands occur especially at toes of prograding clinoforms bottom set sands and in the pleistocene parts and the total thickness covering the utsira sand is in most places more than 800 m but thins towards the margins

lithospheric dynamics and the rapid pliocene quaternary subsidence phase in the southern north sea basin abstract we present stratigraphic modeling and quantitative analysis of the pliocene and quaternary subsidence of the southern north sea basin during the late pliocene well before the onset of quaternary glaciation the subsidence rate in the southern part of the north sea basin showed a ten fold increase relative to previous tertiary rates the high pliocene quaternary subsidence rate is consistent with the direction and state of the present intraplate stress field in northwest europe one possible consequence of the modern compressional stress field in northwest europe is reactivation of faulting in the central graben resulting in localized stretching and the development of pull apart basins alternatively the acceleration in late pliocene subsidence rates could be due to localized flexural downwarping of the lithosphere in the central graben caused by an increase in the level of intraplate compression both mechanisms succesfully predict the major characteristics of the overall quaternary subsidence history and stratigraphy gravity modeling suggests that the mechanism of localized stretching dominates the recent tectonostratigraphic evolution of the southern north sea

origin of the middle pleistocene transition by ice sheet erosion of regolith the transition in the middle pleistocene 0 9 ma seen in 18o deep sea core records from relatively low amplitude high frequency 41 kyr to high amplitude low frequency 100 kyr ice volume variations under essentially the same orbital forcing can be attributed to a change from an all soft bedded to a mixed hard soft bedded laurentide ice sheet through glacial erosion of a thick regolith and resulting exposure of unweathered crystalline bedrock a one dimensional ice sheet and bedrock model which includes transport of sediment and ice by subglacial sediment deformation demonstrates that a widespread deforming sediment layer maintains thin ice sheets before the transition which respond linearly to the dominant 23 and 41 kyr orbital forcing progressive removal of the sediment layer eventually causes a transition to thicker ice sheets whose dominant timescale of change 100 kyr reflects nonlinear deglaciation processes in model simulations over the last 3 ma initialized with no ice and a uniform 50 m sediment layer the time series of ice volume and extent agree in several important aspects with the observed records

buried and open tunnel valleys in denmark erosion beneath multiple ice sheets abstract tunnel valleys are large elongate and irregular depressions cut beneath the margin of former ice sheets they are generally believed to play a substantial role for the entire hydraulic system beneath ice sheets and thus also for ice sheet behaviour their origin however remains poorly understood examination of newly collected danish hydrogeophysical and lithological data has revealed numerous systems of buried valleys 50 350 m deep and 0 5 4 km wide these valleys are similar to the open tunnel valleys found in the present day landscape infills comprise a variety of sediments often with subglacial clay till and meltwater deposits the incised substratum consists of limestone heavy paleogene clay sand and silt the tunnel valleys have preferred orientations and can be divided into several generations each ascribed individual ice advances or ice sheets occurring during multiple glaciations the processes forming the valleys appear to prefer pre existing open and buried valleys for the renewed erosion thus old subglacial erosion pathways have been re used several times and some of the present tunnel valleys may have been established in the middle or early quaternary or even earlier this valley re use effect causes apparently anastomosed valley systems to emerge in the data images the valleys were mainly eroded by meltwater supposed to have drained from subglacially stored reservoirs probably behind a frozen margin the water was most likely released in repeated jokulhlaups and flowed in relatively small channels on the floors of the tunnel valleys which gradually became ice filled with the lowering of the bed selective linear glacial erosion is also believed to have contributed to the erosion this however was most pronounced for the widest valleys and is supposed to have played a secondary role

the role of co2 decline for the onset of northern hemisphere glaciation the pliocene pleistocene transition ppt from around 3 2 to 2 5 million years ago ma represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern eurasia and north america paleo evidence indicates that the ppt was accompanied and possibly caused by a decrease in atmospheric co2 but the temporal resolution of co2 reconstructions is low for this period of time and uncertainties remain large therefore instead of applying existent co2 reconstructions we solved an inverse problem by finding a schematic co2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records to this end we performed an ensemble of transient simulations with an earth system model of intermediate complexity from which we derived a best guess transient co2 scenario for the interval from 3 2 to 2 4 ma that gives the best fit between the simulated and reconstructed benthic 18o and global sea surface temperature evolution our data constrained co2 scenarios are consistent with recent co2 reconstructions and suggest a gradual co2 decline from 375 425 to 275 300 ppm between 3 2 and 2 4 ma in addition to a gradual decline the best fit to paleoclimate data requires the existence of pronounced co2 variability coherent with the 41 kyr 1 kyr 1000 years obliquity cycle in our simulations the long term co2 decline is accompanied by a relatively abrupt intensification of northern hemisphere glaciation at around 2 7 ma this is the result of a threshold behaviour of the ice sheets response to gradual co2 decrease and orbital forcing the simulated northern hemisphere ice sheets during the early pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m both ice volume and benthic 18o are dominated by 41 kyr cyclicity our simulations suggest that before 2 7 ma greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation a fully glaciated greenland comparable to its present day ice volume is modelled only during glacial maxima after 2 7 ma and more continuously after 2 5 ma

amino acid geochronology resolution and precision in carbonate fossils changes in indigenous proteins preserved in carbonate skeletons can be used to estimate the time elapsed since death of the organism racemization the most widely used reaction in amino acid geochronology refers to the inversion of l amino acids to their d configuration for the protein amino acid l isoleucine racemization occurs about only one of the two chiral carbon atoms this reaction epimerization proceeds from an initial dl ratio near zero to an equilibrium ratio of about 1 30 the reaction rate is controlled primarily by temperature and to a lesser degree by the nature of the proteins themselves a variable related to taxonomy and the extent of protein degradation analyzing monospecific samples minimizes the taxonomic variable the resolving power of dl ratios as relative age indices is a function of the reaction rate degree of natural variability and analytical uncertainty natural variability is defined as the spread in ratios in five well preserved shells of the same age from a single stratum and is primarily related to taxonomy it can range from 20 or more in taxa of low reliability to 1 in taxa of greatest integrity 5 to 10 is to be expected analytical uncertainty within a single laboratory is relatively insignificant amounting to no more than 2 but interlaboratory comparisons suggest caution in comparing ratios determined at different laboratories or by different techniques sampling appropriate portions of a shell is essential to minimize variability in dl ratios site temperature exerts the greatest control on reaction rate hence resolving power for tropical sites 25 c age differences 1 ka can be resolved within the holocene and ca 5 to 10 ka for older samples as the rate decreases equilibrium is attained after 150 to 300 ka the reaction rate is substantially lower at mid latitude sites ca 10 c where equilibrium requires about 2 ma and resolution within the last glacial cycle is no better than 10 to 20 ka arctic sites 10 c show almost no measurable racemization within the holocene and in extreme cases even within the last 100 ka equilibrium is not attained in 10 ma the extent of amino acid racemization epimerization in carbonate fossils provides chronological information for the critical time period beyond radiocarbon dating dl ratios can be used directly as relative age indices and with suitable calibration can provide reasonable estimates of absolute age and or effective diagenetic temperature improving the accuracy of racemization based age estimates requires a better understanding of racemization kinetics in carbonate systems

temporal constraints on the growth and decay of large scale mobilized mud masses and implications for fluid flow mapping in sedimentary basins seismic stratigraphic analysis of the cretaceous to succession of the uer terrace north sea seabed basin norway demonstrates that the upper oligocene succession has undergone large scale mobilization of mudstone dominated units due to the upward migration of water and associated hydrocarbons into the interval which is in some way linked to a period of gas expulsion from adjacent deep basins seismic stratigraphic analysis of units overlying the mobilized zones indicates they created positive seafloor topography during the late miocene implying gaseous fluids were expelled at the seabed loading by the overlying pliocene succession caused the mobilized mud masses to deflate and resulted in the formation of low relief fault bounded craters the results of this study have implications for understanding the location and timing of fluid flow in sedimentary basins

late weichselian and holocene sediment fluxes of the northern north sea margin abstract an event chronology has been determined for temporal and lateral magnitudes of material fluxes across the northern north sea margin including the norwegian channel and the north sea fan this has allowed the governing factors for the sediment processes on the margin to be estimated the chronological model of selected cores is based on 14 c ams dates regional tephra layers and planktonic foraminiferal stratigraphy based on this chronological framework the core sediments across the north sea margin have been divided into four main climatostratigraphic intervals a oldest dryas 15 13 ka b bolling allerod 13 11 ka c younger dryas 11 10 ka and d holocene 10 0 ka further the holocene period has also been divided into two subperiods the preboreal 10 9 ka and the holocene interglacial 9 0 ka creating five well defined lithological units deposition phases in all of which the deglaciation units 15 9 ka usually constitute 90 of the sediment budget the recognition of an almost identical lithological succession both in the records on the fan and in the high resolution record of the channel suggests that sedimentation on the north sea margin must be governed dominantly by regional sedimentary processes for each time interval the sedimentation rate in the norwegian channel is on average an order of magnitude higher than on the north sea fan diminishing distally from the shelf edge sedimentation under the holocene interglacial period 9 0 ka contrasts totally from the deglaciation pattern controlled dominantly by pelagic productivity in the area close to 50 of the hemipelagic sediments on the north sea margin are of bolling allerod age 15 13 ka this extreme sedimentation resulted from a combination of a rapid sea level rise constantly exposing new areas for marine erosion winnowing and aggressive surface ocean current activity surface ocean currents and the associated bottom currents provide the dominant control on the pattern of deglacial sedimentation on the north sea margin 15 9 ka this is especially apparent during the oldest dryas and the bolling allerod periods where the distribution pattern across the margin is essentially hydrodynamically controlled only during the younger dryas period are the surface ocean processes overprinted by sedimentary processes from melting icebergs the high resolution records reveal that the shifts in the lithological style of sedimentation are directly linked to the rapid reorganisation of the surface ocean system frequently taking place during the deglacial and holocene time period suggesting a fairly regional type of sedimentation pattern as the shift between the different lithological styles of sediments is both abrupt and regional they should be detectable on the seismic high frequency records

sea level and deep sea temperature variability over the past 5 3 million years ice volume and hence sea level and deep sea temperature are key measures of global climate change sea level has been documented using several independent methods over the past 0 5 million years myr older periods however lack such independent validation all existing records are related to deep sea oxygen isotope 18o data that are influenced by processes unrelated to sea level for deep sea temperature only one continuous high resolution mg ca based record exists with related sea level estimates spanning the past 1 5 myr here we present a novel sea level reconstruction with associated estimates of deep sea temperature which independently validates the previous 0 1 5 myr reconstruction and extends it back to 5 3 myr ago we find that deep sea temperature and sea level generally decreased through time but distinctly out of synchrony which is remarkable given the importance of ice albedo feedbacks on the radiative forcing of climate in particular we observe a large temporal offset during the onset of plio pleistocene ice ages between a marked cooling step at 2 73 myr ago and the first major glaciation at 2 15 myr ago last we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep sea temperature a novel approach to the estimation of sea level and deep sea temperature has been used to determine these quantities over the past 5 3 million years this approach based on oxygen isotope records from the eastern mediterranean shows that temperature and sea level histories are broadly correlated but also show intriguing temporal offsets most records of past sea level variation and associated changes in ocean temperature rely on variations in oxygen isotopes recorded in deep sea marine microorganisms these signals unfortunately are confounded by other influences making it difficult to extract a clear climate related signal eelco rohling and colleagues now present a novel approach to estimating sea level and deep sea temperature variations for the past 5 3 million years the record based on oxygen isotope variations from the eastern mediterranean avoids the issues of the deep sea approach and generally corresponds to an independent record of the past 1 6 million years as expected temperature and sea level are broadly correlated but also show intriguing temporal discontinuities as at the initiation of plio pleistocene ice ages when a major sea level drop lagged a sharp temperature decline by several hundred thousand years

combined tide and wave influence on sedimentation patterns in the upper jurassic swift formation south eastern alberta in south eastern alberta the oxfordian swift formation comprises two unconformity bounded sequences sequence 1 consists of the shale member it unconformably overlies bathonian calcareous shale of the rierdon formation and consists dominantly of shale with uncommon hum mocky cross stratified siltstone the shale member comprises up to four parasequences that show a subtle upward fining stacking pattern suggesting overall deepening in a storm dominated fully marine basin deposition of the shale member was terminated by a fall in relative sea level which in turn initiated sequence 2 during lowstand a network of north east to south west trending meandering channels incised the top of sequence 1 despite the preserved morphology of these channels observations in core suggest that lowstand deposits are absent these strata were most likely thoroughly reworked by ravinement processes associated with the ensuing transgression and are recorded only by a thin chert pebble lag also associated with transgression were significant changes in the physical and ecological conditions in the local swift basin these changes were related to modifications in basin configuration and the development of a low energy strait which probably formed as a result of uplift of the sweetgrass arch within this newly configured basin brackish water conditions prevailed and sedimentation was dominated by suspension deposition of mud bed load sediment composed mostly of very fine and fine sand made up only a small part of the total sediment flux into the area and was transported principally by low energy combined flows with variable speed microtidal currents and a low energy oscillatory component related to storm waves sand was generally deposited in the form of small discontinuous sand ridges that developed locally throughout the study area it is these features that form the principal hydrocarbon reservoir bodies in the swift formation in the study area after initiation ridges built upwards and migrated laterally in response to transport and preferential local deposition of bed load sediment although common near the unconformity along the top of sequence 1 sand ridges also occur at several higher stratigraphic levels in sequence 2 these latter ridges however are not associated with regionally correlatable discontinuities but instead were initiated by local bed irregularities possibly related to breaking internal waves and were supplied with new sediment transported into the study area the origin of these sand ridges is therefore not related to changes in relative sea level but instead to intrabasinal processes in a low energy strait

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

geomorphic implications of subglacial drainage configuration rates of basal sediment evacuation controlled by seasonal drainage system evolution abstract although basal sediment evacuation by subglacial meltwater is widely assumed to dominate the sediment budget of most temperate glaciers and ice caps its potential influence for glacial geomorphic processes and landforms has largely been overlooked in the glacial literature data collected at haut glacier d arolla switzerland during the 1998 ablation season are used to test theoretical predictions that subglacial drainage configuration should exert a primary control on rates of basal sediment evacuation by subglacial meltwater seasonal evolution of the subglacial drainage system enables observation of sediment evacuation from both distributed and channelised drainage systems daily suspended sediment load exhibits an extreme nonlinear increase with respect to discharge between winter and summer periods which correspond to periods of predominantly distributed and channelised subglacial drainage respectively these results suggest that subglacial drainage configuration should significantly impact upon a rates of subglacial erosion and debris production b the nature of debris transport and the proportion of sediment in glacial versus fluvioglacial transport pathways and c rates and styles of ice marginal sedimentation in contrast to their distributed counterparts channelised drainage configurations are predicted to encourage subglacial erosion through the removal of basal sediment from the ice bedrock interface and with the exception of supraglacial transport will discourage sediment transport by alternative glacial mechanisms direct sedimentation at the glacier margin may therefore be reduced resulting in smaller moraines despite an overall increase in sediment production an appreciation of the coupling between glacier hydrology and geomorphic processes suggests new frameworks for the understanding of rates and styles of glacial erosion sediment transfer and deposition and the complex geomorphology of ice marginal environments

latest caledonian to present tectonomorphological development of southern norway abstract the regional resultant stress field of the northeastern north atlantic has shifted significantly throughout the phanerozoic in fennoscandian parts of the caledonian orogen mountain building which was characterized by nw se contraction reference to present north was followed by a collapse with transport both parallel and transverse to the mountain chain the late palaeozoic mesozoic saw several stages of e w to nw se extension varying in time and position local episodes of inversion are traceable in some cases particularly in connection with deep seated and long lived zones of weakness the cenozoic has to a larger degree been affected by compression including folding and basin inversion again some of the more pronounced effects of local inversion are related to pre existing fault systems neogene uplift of the western mountainous area in scandinavia can be unravelled by potential field study aft data and reflection seismic sections assuming that the region is close to isostatic equilibrium the uplifted areas must be supported at depth by substantial volumes of low density material within the crust or the mantle close to the crust mantle interface or close to the lithosphere asthenosphere interfaces a series of nw se oriented cross sections representing successive stages of development from the late caledonian to present were prepared and used to analyse the tectonomorphological development as related to the shifting stress configurations three stages are inferred stage 1 devonian late permian denudation of the caledonian mountain chain during the latest stage of closing of the iapetus ocean in early to mid devonian times the caledonian mountain chain reached its maximum elevation of perhaps as much as 8 9 km including the foreland basins to the east the average topographic gradient of the eastern flank may have been in the order of 1 3 the denudation of the caledonian mountains continued into the permian and by the end of the permian the mountain system was more or less obliterated with a gradient of the eastern flank probably continued to fall to less than 0 1 stage 2 triassic late cretaceous tectono thermal uplift of central south norway uplift of central south norway was rejuvenated in triassic times and continued throughout the jurassic and early cretaceous the gradient of the eastern flank increased to a maximum of approximately 0 15 and master structural elements like the laerdal gjende olestol fault complex again played important roles in the development stage 3 tertiary present renewed tectono thermal activity and post glacial rebound a second phase of post caledonian tectono thermal uplift of south central norway started in oligocene time again increasing the gradient of the eastern flank of south norway around 0 2

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

sedimentation history of the northern north sea margin during the last 150 ka the norwegian channel ice stream ncis is one the defining features of the fennoscandian icesheet still little is known of the detailed dynamics of this ice stream in relation to regional changes in ice cover paleoceanographic and climatic changes sedimentological data from core md99 2283 in combination with seismic data allow a detailed chronological reconstruction of the outbuilding of the margin and the ice extent in southern scandinavia through the last 150 ka an integrated stratigraphy of the margin is presented and compared to the glacial history changes in the regional ice cover are reflected in the accumulation rates the clay mineralogy the coarse chalk fraction and the number of ird 2 mm in core md99 2283 while the sedimentation on the north sea fan as derived from seismic data provides direct evidence for the glacial activity at the shelf edge tentative evidence was found for two early weichselian glacial advances in southern scandinavia and possibly scotland at around 110 and 80 ka bp from 42 cal ka bp the ice cover expanded in southern fennoscandia and led to increased deposition on the margin and the occurrence of local melt water outbursts significantly increased accumulation rates coarse chalk local meltwater output and smectite occur during the ice expansion in the north sea from around 34 cal ka bp the main outbuilding phase of the nsf during the last glacial cycle occurred after 30 cal ka bp from around 24 cal ka bp the ncis became highly active and advanced at least three times prior to the final retreat from the shelf edge around 19 0 cal ka bp

removal of overburden velocity anomaly effects for depth conversion a method of compensating for the presence of discrete overburden velocity anomalies during depth conversion of time horizons interpreted on conventional post stack time migrated seismic data is presented positive and negative time delays are estimated either from the push down or pull up of reflectors directly beneath the anomalies or from interpreted time thickness of the anomalous body and interval velocities estimated from well data the critical steps are pre stack simulation of seismic acquisition across the velocity anomalies incorporating the effects of a fresnel volume which changes its width as a function of depth and simulation of commonmidpoint cmp stacking using a linear regression of time delay at versus offset squared x 2 the time correction method predicts the time distortion for any target horizon and the distortion is removed as a correction in time depth conversion is then performed using a background velocity function the final average velocity map is calculated from the resulting depth structure and the raw times at the target horizon the method is implemented by manipulating time grids within an industry standard mapping package the final average velocity map shows steep lateral velocity gradients which are constrained by the interpreted boundaries of the velocity anomalies

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

pleistocene stratigraphy in the devils hole area central north sea foraminiferal and amino acid evidence a detailed study of the foraminiferal assemblages from the 229 1 m deep core 81 34 in the central north sea has been combined with a series of measurements of the isoleucine epimerisation of foraminiferal tests a total of 17 foraminiferal zones have been established and both the faunal compositions and the amino acid values suggest that a major part of the sequence represents deposits of early and middle pleistocene age only the uppermost zone is referred to the late pleistocene the sequence mainly comprises a series of marine zones from cold periods but with some barren possibly non marine intervals in between only two of the foraminiferal zones can be referred to interglacial periods the oldest one of these defined here as the devils hole interglacial may belong to the latter part of the cromerian complex while the upper warm interval is correlated with the holsteinian of northwest europe on the basis of its amino acid values a detailed stratigraphical correlation between core 81 34 and the neighbouring core 81 29 is suggested on the basis of their foraminiferal content palaeomagnetic evidence and amino acid measurements from both cores a characteristic feature of both sequences is that most of the quaternary record is missing similar episodic patterns of deposition and erosion have been reported previously from the north sea area

quaternary seismic stratigraphy of the north sea fan glacially fed gravity flow aprons hemipelagic sediments and large submarine slides abstract approximately 1000 km of high resolution sleeve gun array transects on the north sea fan located at the mouth of the norwegian channel reveal three dominant styles of sedimentation within a thick 900 m quaternary sediment wedge comprising numerous sequences these are interpreted as terrigenous hemipelagic sedimentation large scale translational slides and aprons of glaciogenic debris flow deposits contributing to considerable fan construction four large buried translational slides involved sediment volumes upwards of 3000 km 3 each and preceded the similarly dimensioned first storegga slide on the ne fan flank several thick 100 m terrigenous hemipelagic deposits apparently represent long lived 150 200 kyr periods of sedimentation whose distribution indicates fan input via the norwegian channel the upper sequences are each made upper sequences are each made up of one or several thick 100 m aprons comprising stacked lensoid and or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness they characterize debris flows attributed to periodic input from several phases of a norwegian channel ice stream reaching the shelf edge subsidence in the outer norwegian channel allowed preservation of several glaciation cycles represented by sheet erosion bounded tills and progradational units much of the shelf slope transition has been preserved allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the norwegian channel debris flows which signal the initial shelf edge glaciation are not recognized from the initial glaciation in the channel 1 1 myr but are associated with a middle pleistocene and all following glacial erosion surfaces ges in the outer norwegian channel this was followed by six further sequences probably totalling over 13 000 km 3 of sediment at least four of these were shelf edge ice maximum events the last of which was late weichselian age 14 c ams considering earlier glaciation related hemipelagic sedimentation material since removed by the large slides and extensive unmapped areas total quaternary fan sedimentation was in the vicinity of 20 000 km 3

palynological and foraminiferal biostratigraphy of upper pliocene nordland group mudstones at sleipner northern north sea abstract the nordland group is an important stratigraphical unit within the upper cenozoic of the northern north sea at its base lies the utsira sand a dominantly sandy regional saline aquifer that is currently being utilized for carbon dioxide sequestration from the sleipner gas and condensate field a mudstone drape immediately overlies the utsira sand forming the caprock for this aquifer the upper part of the utsira sand was recently dated as early pliocene but the precise age of the overlying nordland group mudstones has remained uncertain dinoflagellate cyst pollen and spore foraminiferal and stable isotopic analyses have been performed on these mudstones from a conventional core within the interval 913 10 906 00 m drilled depth in norwegian sector well 15 9 a 11 the samples lie closely above the utsira sand results give a gelasian late late pliocene age for this interval with a planktonic foraminiferal assemblage at 913 10 m indicating warm climatic conditions and an age between 2 4 and 1 8 ma an abundance of the cool tolerant dinoflagellate cysts filisphaera filifera and habibacysta tectata at 906 00 m along with evidence from pollen and foraminifera points to deposition during a cool phase of the gelasian dating the mudstone drape provides useful insights into depositional processes it seems likely that the utsira sand a basinal lowstand deposit became progressively starved of clastic input as sea level rose and shorelines retreated the mudstone drape is interpreted as a highstand deposit perhaps including a maximum flooding surface overlying prograding wedges of the nordland group form a regressive succession characterized by increased sedimentary input and rates of deposition of at least 25 cm per 1000 years which is more than five times that of the utsira sand this is the first published study of a dinoflagellate cyst assemblage from the upper pliocene of the northern north sea the new dinoflagellate cyst species echinidinium nordlandensis head sp nov and echinidinium sleipnerensis head riding sp nov are formally described

atmospheric carbon dioxide concentration across the mid pleistocene transition the dominant period of pleistocene glacial cycles changed during the mid pleistocene from 40 000 years to 100 000 years for as yet unknown reasons here we present a 2 1 million year record of sea surface partial pressure of co2 pco2 based on boron isotopes in planktic foraminifer shells which suggests that the atmospheric partial pressure of co2 pco2 was relatively stable before the mid pleistocene climate transition glacial pco2 was approximately 31 microatmospheres higher before the transition more than 1 million years ago but interglacial pco2 was similar to that of late pleistocene interglacial cycles 450 000 years ago these estimates are consistent with a close linkage between atmospheric co2 concentration and global climate but the lack of a gradual decrease in interglacial pco2 does not support the suggestion that a long term drawdown of atmospheric co2 was the main cause of the climate transition

cenozoic sequence stratigraphy of the central and northern north sea basin tectonic development sediment distribution and provenance areas the cenozoic succession in the central and northern north sea has been investigated to establish a regional sequence stratigraphic framework changes in sediment distribution indicate a complex pattern of regional vertical movements along older palaeozoic and mesozoic structures in cenozoic times these vertical movements mainly related to tectonic processes along the continental margin to the north and north west were responsible for the generation and removal of provenance areas for sediments delivered to the north sea basin through cenozoic time during the early through middle palaeogene sediments were mainly sourced from areas in the west and from the atlantic margin in the north uplift in the northern north sea in the late eocene was in the earliest oligocene followed by marked basin subsidence and tectonic uplift of southern norway a similar pattern of tectonic movements resulted in subaerial exposure of the northern north sea in the early miocene followed by significant tectonic subsidence in the basin and along the atlantic margin in late miocene pliocene times at the same time southern norway was uplifted and became a major sediment source after the miocene pliocene subsidence uplift events glacial processes in southern norway and fluvial processes in a large drainage area east and south east of the north sea were responsible for the main sediment influx to the north sea the cenozoic depositional sequences in the north sea developed in close interaction with regional tectonic movements and changes in provenance areas tectonic movements in north west europe overprinted global sea level changes so that the generation of depositional sequences and sequence boundaries apparently occurred independently of the rate of eustatic sea level change