pleistocene pollen stratigraphy from borehole 81 34 devil s hole area central north sea abstract twelve pollen assemblage zones are identified in a 229 m deep borehole bh 81 34 from the devil s hole area in the central north sea british sector the sediment from this borehole is early to late pleistocene in age and the observation of massulae from azolla filiculoides in sediment with reversed polarity indicates an age younger than the olduvai geomagnetic event for the entire sequence the early pleistocene sediments were at least partly deposited in the vicinity of a river outlet and can be correlated either with the eburonian or the menapian cold stage and with the bavel interglacial and the linge glacial within the bavelian stage in the dutch stratigraphy the middle pleistocene sequence contains an interval rich in abies picea and pinus probably deposited during the end of either cromerian complex interglacial iv noordbergum or possibly the holsteinian the uppermost 80 m of the core contains high frequencies of pre quaternary and deteriorated palynomorphs indicating extensive glacial or glaciofluvially reworked sediment

time resolved seismic tomography detects magma intrusions at mount etna the continuous volcanic and seismic activity at mount etna makes this volcano an important laboratory for seismological and geophysical studies we used repeated three dimensional tomography to detect variations in elastic parameters during different volcanic cycles before and during the october 2002 january 2003 flank eruption well defined anomalous low p to s wave velocity ratio volumes were revealed absent during the pre eruptive period the anomalies trace the intrusion of volatile rich 4 weight percent basaltic magma most of which rose up only a few months before the onset of eruption the observed time changes of velocity anomalies suggest that four dimensional tomography provides a basis for more efficient volcano monitoring and short and midterm eruption forecasting of explosive activity

tomographic images and 3d earthquake locations of the seismic swarm preceding the 2001 mt etna eruption evidence for a dyke intrusion 1 on july 12 2001 mt etna experienced a sudden increase of seismic activity heralding one of the most intense eruptions of the past 30 years between july 12 and july 18 when the eruption started thousands of small magnitude earthquakes occurred and were recorded by a dense seismic network run by the istituto nazionale di geofisica e vulcanologia sezione di catania ingv ct hypocentral depths of earthquakes were very shallow mostly located above 3 km b s l and clustered near the summit area the high quality seismic dataset gives us the unique opportunity to study the process of magma migration before the eruption in this study we present the three dimensional earthquake locations and the velocity structure obtained by a tomographic inversion the shallowness of seismicity allowed us to enhance the details of the structure beneath the summit craters in a volume poorly defined by previous tomographic studies the presence of a high vp body previously observed at mt etna is confirmed at shallow depth beneath the southeastern part of the summit area the earthquakes preceding the eruption onset concentrated at its western border a low vp vs anomaly is found at 0 1 km depth just at the top of the volume where the magma intruded before the eruption this anomalous zone can be considered as molten material wealthy in gas the relocated seismicity occurs in a cylinder below the vents activated along the fracture system and exhibited an upward migration until the eruption all these results show evidence for the emplacement of a near vertical dyke striking about n s and a few kilometres south of the summit craters

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

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

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

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

middle pleistocene pollen biostratigraphy in the central north sea abstract middle pleistocene sequences from the northernmost fladen ground and the southernmost devil s hole area parts of the british sector of the central north sea are correlated on the basis of pollen biostratigraphy four pollen stratigraphies are compared with reference taken to existing borehole and seismic data the most pronounced influence of reworked pre quaternary sediments are present in an upper interval rich in pre neogene palynomorphs and in a lower interval rich in neogene palynomorphs this change can be related to middle pleistocene glacial periods the pollen content in the younger interval indicates a british provenance possibly correlated with the saalian stage the pollen content in the older interval indicates derivation from the scandinavian ice sheet and may correlate with the elsterian stage the pollen stratigraphies between these two intervals reflect a vegetational transition from dwarf shrub heaths and peatlands towards boreal forests possibly followed by a return to a more open landscape this pollen stratigraphical succession is best preserved in the devil s hole sequences in the fladen ground the upper part of the sequence may have been glacially eroded deposits of cromerian complex age occur at base of the middle pleistocene sequences

complex reservoir geometries in a deep water clastic sequence gryphon field ukcs injection structures geological modelling and reservoir simulation abstract the balder formation sandstone reservoir of the gryphon field was deposited during the late paleocene early eocene while the background sedimentation comprised pelagic shales and tuffs sediment gravity flows transported sands from the shelf area in the west the crawford ridge acted as a barrier to sediment transport in the east causing the sands to be deposited predominantly as massive sand bodies as flow velocities decreased during burial sand remobilisation and injection occurred possibly localised around faults cored intervals show a range of injection structures from thin cm scale dykes to more massive metre scale chaotic intrusive features the cross cutting nature of the injection structures as observed in core and in seismic sections accounts for the high degree of reservoir connectivity observed in the field a study was undertaken with the objective of constructing a 3d geological model for dynamic reservoir simulation in order to evaluate future development activities in the field as previous purely deterministic models had proven unsuitable the complex depositional and post depositional history of the gryphon field reservoir has resulted in a system for which there is no published analogue to aid in 3d reservoir modelling preliminary stochastic models based on analogues chosen to reflect the reservoir sand body geometries did not match the field production history the fact that both the deterministic and fully stochastic models were unsuitable suggested that a novel approach was required to model this field subsequent models constructed using a combination of stochastic and deterministic models have proven successful in matching the production history of the field and evaluating infill opportunities

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

pockmarks in the witch ground basin central north sea marine sediments host large amounts of methane ch4 which is a potent greenhouse gas quantitative estimates for methane release from marine sediments are scarce and a poorly constrained temporal variability leads to large uncertainties in methane emission scenarios here we use 2d and 3d seismic reflection multibeam bathymetric geochemical and sedimentological data to i map and describe pockmarks in the witch ground basin central north sea ii characterize associated sedimentological and fluid migration structures and iii analyze the related methane release more than 1500 pockmarks of two distinct morphological classes spread over an area of 225 km2 the two classes form independently from another and are corresponding to at least two different sources of fluids class 1 pockmarks are large in size 6 m deep 250 m long and 75 m wide show active venting and are located above vertical fluid conduits that hydraulically connect the seafloor with deep methane sources class 2 pockmarks which comprise 99 5 of all pockmarks are smaller 0 9 3 1 m deep 26 140 m long and 14 57 m wide and are limited to the soft fine grained sediments of the witch ground formation and possibly sourced by compaction related dewatering buried pockmarks within the witch ground formation document distinct phases of pockmark formation likely triggered by external forces related to environmental changes after deglaciation thus greenhouse gas emissions from pockmark fields cannot be based on pockmark numbers and present day fluxes but require an analysis of the pockmark forming processes through geological time

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

lower pleistocene dinoflagellate cyst foraminiferal and pollen assemblages in four boreholes in the southern north sea neogene and lower pleistocene stratigraphy in the southern north sea has been investigated in four i g s boreholes between east anglia and the netherlands the foraminifera of the red crag formation in borehole 81 51 are closely similar to upper pliocene assemblages in holland the overlying succession is clearly punctuated by unconformities in seismic profiles separating four early pleistocene formations in the boreholes and indicating intervals of significant stratigraphic hiatus offshore the westkapelle ground and smith s knoll formations correlate with thurnian and antian stage deposits in east anglia pollen spectra in the winterton shoal and yarmouth roads formations are similar to baventian and bramertonian assemblages in britain the autochthonous marine and allochthonous terrestrial microfauna and flora provide conflicting evidence of early pleistocene palaeoclimate the dinoflagellate cysts and foraminifera indicate that each formation was deposited in a warm temperate neritic environment the pollen record containing evidence of fluctuation between boreal and mixed coniferous deciduous regional forest cover suggests alternation between cool and warm temperate palaeoclimate

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

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

calculating quaternary glacial erosion rates in northeast scotland northeast scotland is an area exhibiting selective erosion by quatemary ice sheets in this area both glacial and preglacial landforms exist in close proximity the depths of erosion which this modification represents are calculated on the assumption of various depths of preglacial weathering a depth of erosion of between 34 and 62 m per unit area is indicated calculated rates of erosion are 0 021 nun a for the entire 2 3 m y of the quaternary and between 0 1 and 0 5 mm aa1 on the assumption that glacial conditions existed in this area for 500 000 years and 100 000 years respectively these figures are compared to the offshore sedimentary record in the adjacent west central north sea the volume of sediment deposited offshore is equivalent to a depth of erosion of 195 m per unit area yielding an average erosion rate of 0 085 mm a i over the entire quatemary rates of erosion were low in the preglacial pliocene 0 049 mm a 1 and early quatemary 0 063 mm a the expansion of ice sheets across the area in the middle quatematy was associated with a sharp increase in the rates of erosion 0 13 mm a but the last late devensian ice sheet in the area was less erosive 0 095 mm a the estimated rates of erosion represented by the offshore sedimentary record therefore exceed the estimated rates of glacial erosion from the onsho re geomorphological reconstruction

stable isotopic characterisation of francolite formation stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits values of 13c and 34s in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions the exceptions are concretionary francolite from namibia which has an isotopic composition in keeping with its formation within organic rich sediments and that from offshore morocco which has an isotopic signature of the anoxic suboxic interface onshore deposits from jordan mexico south africa and possibly the permian phosphoria formation in the western u s a are substantially depleted in18o they appear to be too altered for deductions to be made about their environments of formation in other onshore deposits which are unaltered or minimally altered the isotopic composition suggests that some formed within sulphate reducing sediments sedhura morocco whilst francolite from the georgina basin of australia formed at the oxic anoxic boundary where oxidation of biogenic h2s decreases the 34s of pore water in general pelletal samples show non oxic isotopic signatures whilst non pelletal samples show oxic isotopic signatures but samples from namibia peru ica plateau and the californian and moroccan margins are exceptions to this rule morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature

mid pleistocene thin skinned glaciotectonic thrusting of the aberdeen ground formation central graben region central north sea this paper presents the results of a high resolution 2d seismic survey of mid pleistocene glaciogenic sediments in the central graben region of the central north sea sediments have undergone major glaciotectonic thrusting and folding associated with the repeated southerly advance of a mid pleistocene ice sheet the total observed length of the thrust stacked section is approximately 5 6 km comprising a series of discrete thrust slices which range in length from 700 m the basal detachment of the thrust complex occurs at a depth of ca 220 m below the sea bed within the upper aberdeen ground formation a thin skinned glaciotectonic model involving proglacial to ice marginal glaciotectonic thrusting followed by post tectonic deposition is proposed initial ice advance led to the over pressurizing of groundwater within a laterally extensive sand sheet in the upper aberdeen ground formation promoting the formation of a major decollement surface at the base of the developing thrust stack over pressurization of the groundwater system is thought to have occurred in response to rapid ice advance suggesting that the development of large scale thrust complexes may be associated with surge type behaviour the proposed model evidences complex dynamics of mid pleistocene ice sheets within the central north sea

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

late weichselian to early holocene litho and biostratigraphy in the devil s hole area central north sea and its relation to glacial isostasy the 6 m long british geological survey vibrocore 56 01 170 from the devil s hole area central north sea comprises glaciomarine and marine sediments of late weichselian and holocene age besides the foraminiferal pollen and ams 14c data presented in this study amino acid and ostracod data exist for the core the accumulation of the sediment in the core began ca 15 7 14c ka bp on an erosional surface on overconsolidated saalian sediment when the lower part of the core facies 1 accumulated the core area is interpreted to have been around 40 m lower than present this interpretation is based on two assumptions first that the sediment is now ca 20 m above the global sea level at the time of deposition and second that the marine microfaunal content reflects a water depth of about 20 m at that time crustal downflexure caused by late weichselian glacial loading of the core area is considered as the most plausible explanation of this difference glacial overriding would also explain the overconsolidation of the underlying saalian sediment the erosional surface on the saalian sediment and the absence of weichselian sediment older than ca 15 7 ka bp at the core site indications of a regressional trend with a minimum age of 12 1 ka bp support the suggestion that the devil s hole area was glaciated during the weichselian as the fall in sea level at that time probably reflects local isostatic rebound

3 d density model of mt etna volcano southern italy a detailed density model of mt etna and its surrounding areas has been evaluated using a 3 d inversion of the gravimetric data acquired in the 1980 s several high density and low density bodies are found penetrating from shallow depths as far down as 12 km bsl a positive correlation in terms of location extent density and velocity is established between several anomalies of the density model and features identified in previously published seismic tomographies a prominent high density body extending down to 7 km bsl is recognized in the southern part of the valle del bove and interpreted as a solidified magmatic intrusion on the western boundary of this anomaly a low density body is interpreted as a bubble and liquid magma mixture outside the central area three other high density anomalies are imaged and attributed to the earliest phases of volcanic activity in the area several interesting low density anomalies are also identified and correlated with known fault lines and other structural features of the region

buoyancy controlled eruption of magmas at mt etna buoyancy controls the ability of magma to rise its ascent rate and the style of the eruptions geophysical geological and petrological data have been integrated to evaluate the buoyancy of magmas at mt etna the density difference between host rocks and magmas is mainly related to the amount of h2o dissolved in the magma and to the bubble liquid separation processes in the depth interval 22 2 km b s l highly hydrated h2o 3 basaltic magmas or mixtures of bubbles liquid have positive buoyancy and rise rapidly conversely bubble depleted liquids with an intermediate h2o content 1 5 having neutral buoyancy will spread out and form magmatic reservoirs at different depths until cooling crystallization further modify composition and density these different processes account for the magma compositions location of magmatic reservoirs as determined by geophysical methods and the complex eruptive cycles slow effusions fire fountains and plinian eruptions that have been observed in the history of the volcano