recognition of caprock leakage in the snorre field norwegian north sea abstract the aim of this study was the evaluation of the distribution of hydrocarbons in the cretaceous caprock succession that unconformably overlies the triassic lower jurassic reservoir of the snorre field the snorre field is located in the tampen spur area of the norwegian north sea evaluation of the hydrocarbon distribution was based on data from hydrocarbon shows encountered during drilling and organic geochemical data from canned cuttings samples 27 dst oils and rock samples from two wells oil shows were recorded in the cretaceous shetland group over the crest of the structure oil shows were present up to 400m above the top of the reservoir the occurrence of these shows coincided with high 50 gas wetness values of c 2 c 4 c 1 c 4 100 the incidence of these high gas wetness values also showed evidence of a relationship with the thickness of the underlying oil column but showed a poorer correlation with evidence of undercompaction overpressuring in the cretaceous tertiary succession gas chromatography and combined gas chromatography mass spectrometry data from selected rock samples indicated that the liquid hydrocarbons in the caprock succession were similar in composition to the oil from the underlying reservoir although diffusion processes may play a part in the distribution of gaseous hydrocarbon compounds bulk flow processes provide a better explanation for the distribution of liquid hydrocarbons in the caprock succession the distribution pattern of the caprock hydrocarbons makes it unlikely that leakage along major fault planes represents the major emplacement pathway for these hydrocarbons a combination of relatively low pore entry pressures in the undercompacted cretaceous strata and extensive microfracturing of the caprock succession provide a more appropriate mechanism published estimates of hydrocarbon migration in the vicinity of the northern tampen spur suggest that the reservoirs of the snorre field began to receive a hydrocarbon charge during deposition of the shetland group or shortly afterwards development of undercompaction overpressuring in the argillaceous strata of the shetland rogaland and hordaland groups may therefore be directly related to the filling history of the underlying reservoir

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

a glacio isostatic facies model and amino acid stratigraphy for late quaternary events in spitsbergen and the arctic strong early holocene crustal uplift over the spitsbergen archipelago reflects disappearance of an ice mass centred just north east of the archipelago and which decayed rapidly just after 10 000 bp after a maximum extension between 12 600 and 10 000 bp from the lithofacies distributions associated with these events a glacio isostatic facies model can be defined which combined with analyses of amino acid racemization provides a valuable stratigraphic method for correlating pre holocene glacio isostatic events these are correlated with events in greenland and both are contrasted with weichselian glacial events at the southern margins of the two great northern hemisphere ice sheets and with contemporary water mass changes in the north atlantic and norwegian sea the geographical variation in glacier response through time is explained by three principal climatic circulation patterns

the late weichselian glacial maximum on western spitsbergen inferred from offshore sediment cores abstract the late weichselian glacial history of the continental shelf off western spitsbergen is discussed based on acoustic sub bottom records and sediment cores the outer part of isfjorden and the inner shelf to the west of this fjord are characterized by a thin veneer 10 20 m of glacigenic sediments and absence of ice marginal features towards the outer shelf the sediment thickness increases significantly and exceeds 500 m at the shelf edge possible moraine complexes were identified in this outer part sediment cores from the inner shelf sampled a firm diamicton interpreted as till beneath soft glaciomarine sediments radiocarbon dates on shells from the clay resting directly on the till suggest an age of around 12 500 yrs b p for the base of the marine sequence we argue that grounded ice covered the sites shortly before in contrast to suggestions that the fjords and coast were partly ice free during the late weischselian we conclude that the ice must have reached out onto the continental shelf

changes in gas composition during simulated maturation of sulfur rich type ii s source rock and related petroleum asphaltenes abstract asphaltenes extracted from crude oils are proposed to possess structural features of the related source rock kerogen for the present study micro scale sealed vessel pyrolysis mssv and combustion isotope ratio mass spectrometry gc c irms were used to compare gas generation from a whole rock type ii s kerogen from southern italy with that from related sulfur rich asphaltenes isolated from a low maturity heavy crude oil the purpose of was to determine whether experimental pyrolysis of oil asphaltenes can be used to predict the timing and the chemical and isotopic composition of hydrocarbon gases generated from genetically related kerogen in the source rock during burial maturation the results show that parameters such as gas to oil ratio gor and oil and gas formation timing are very similar for these two sample types whereas gas composition product aromaticity and sulfur content are remarkably different slight differences in gor are mainly due to differences in gas formation characteristics at very high levels of thermal alteration secondary gas formation from the whole rock covers a much broader temperature range under geological conditions than that from the asphaltene products however it is remarkable that both the onset and the maximum temperature are nearly identical under geological conditions the observed differences in gas generation characteristics are supported by discrepancies in the carbon isotopic characteristics of the gas range compounds and indicate different precursors and or mechanisms for gas generated from whole rock and asphaltenes

bioclastic carbonate sediments on the southwestern svalbard shelf the poleward continuation of one of the largest known arctic carbonate factories the western spitsbergenbank of the barents sea has been surveyed along the narrow sw svalbard shelf on this shelf formation of cold water carbonate sediments occurs under glaciomarine environmental conditions mya truncata and hiatella arctica colonized a soft glacio marine diamicton 3000 6000 years after the final retreat of the icedome from the sw svalbard shelf since 2600 yr b p an increase of along shelf bottom currents washed out the fine terrigenous deposits leaving behind a shelly lag deposit and winnowed boulders on a morainic shelf topography the most favourable depth interval promoting the establishment of an amalgamated bioclastic blanket is located in 50 80 m water depth in this interval strong bottom currents prevent sedimentation thus facilitating colonisation of filter feeding benthic communities dominated by balanus balanus and chlamys islandica additional skeletal components are supplied by echinoderms bryozoans serpulids brachiopods and gastropods in shallower water depths carbonate production is hampered by intense iceberg scouring and release of ice rafted debris from the still glaciated hinterland of svalbard in deeper water 80 m olive grey muds with dispersed pebbles rich in benthic foraminiferans clinocardium ciliatum and taxodont bivalves are present on all surveyed shelf banks the deepest unit is a blue mud in water depths 120 m with benthic foraminiferans taxodont bivalves and sipunculids compared to spitsbergenbank carbonate production is much more restricted and impoverished on the sw svalbard shelf but is still an instructive modern example for the formation of skeletal carbonates resting on tillites in the geological record

gravity induced soft sediment deformation in glaciomarine sequences of the upper proterozoic port askaig formation scotland large numbers of post depositional deformation structures in the form of downward penetrating sandstone bodies are identified on well exposed diamictite surfaces of the glaciogenic upper proterozoic port askaig formation scotland on the garvellach islands downfolds irregular dykes and a polygonal network of wedges are composed predominantly of massive fine to medium grained sandstone these structures occur towards the top of crude coarsening upward glaciomarine sequences of massive diamictite stratified diamictite variably cross stratified sandstone and conglomeratic lags massive diamictites record the dominance of pelagic sedimentation and ice rafting succeeding lithofacies indicate the increasing importance of marine traction currents these sequences are repeated in the port askaig formation and by comparison with late cenozoic glaciomarine sequences may have formed in response to changing water depths during basin subsidence downfolds dykes and a polygonal wedge network appear to be genetically related expressions of subaqueous gravitational loading and intrusion of sand into low strength diamict acting in response to reverse density gradients created by coarsening upward glaciomarine sedimentation analogues are provided by published laboratory investigations analysis of the regional tectonic setting of the formation suggests the importance of seismic shock as a triggering agent the subaqueous deformation model presented in this paper is of considerable significance for reconstruction of late proterozoic palaeoenvironments because the downward penetrating sandstone structures of the port askaig formation are widely reported to be indicative of the former presence of subaerial permafrost this paper stresses the importance of identifying the lithofacies sequence in which structures occur as a guide to deformational environment

petroleum accumulation and leakage in a deeply buried carbonate reservoir nispero field mexico abstract the filling history of the nispero deeply buried lower cretaceous carbonate reservoir below 4000 m from the south part of gulf of mexico was studied using a combination of data from petrography stable isotopes and fluid inclusions and compared with a one dimensional burial model to derive timing a combination of techniques such as microthermometry confocal laser scanning microscopy clsm and raman microspectroscopy have been used to characterize the different fluid inclusion assemblages and discriminate between the reequilibrated and the preserved fluid inclusions the nispero reservoir is composed of a fractured finely crystalline replacement dolostone a first generation of fractures is filled by a non planar dolomite cement and a second generation by a planar e dolomite cement and a blocky sparite the reservoir is lastly stylolitised dolomite has 13c values between 0 9 and 4 0 pdb and 18o values between 4 5 and 10 8 pdb calcite has 13c values between 3 8 and 4 4 pdb and 18o values between 4 9 and 5 5 pdb these values suggest that the calcite represents a change in water composition and that dolomite and calcite cements do not precipitate from petroleum derived fluids however geological fluids are trapped as aqueous and oil inclusions in the calcite cements three petroleum aqueous inclusion assemblages were identified pseudo primary brown oil paired with brine inclusions and pseudo primary yellow oil paired with low salinity water inclusions distributed in local concentrations and secondary colourless oil paired with low salinity aqueous inclusions distributed in healed microfractures the burial model calibrated with bottom hole temperatures has been calculated using petromod 1d to generate the rock pt history under hydrostatic and lithostatic regimes reconstructed temperatures of initial trapping of fluid inclusion and calculated temperatures from 18o measured in dolomite and calcite cements are in good agreement data suggests that the reservoir was being filled at 97 c 315 bar by heavy black oils accompanied by high salinity water during the miocene period 11 6 m y the maximum estimated pressure of 700 bar at 130 c is reconstructed by petroleum inclusions trapping black oil and associated low salinity aqueous inclusions these pt conditions were reached during the pliocene 3 2m y present day reservoir conditions of 145 c and 500 bar are recorded by reequilibration of most of the fluid inclusions of the two assemblages and correspond to hydrostatic pressure the drop of pressure from 700 bar to 500 bar may be an explanation for the late stylolitisation

landscape imprints of changing glacial regimes during ice sheet build up and decay a conceptual model from svalbard the behaviour of ice sheets and their geologic imprints in fjord regions are often multifaceted fjords which were temporarily occupied by fast flowing ice streams during major glaciations and inter fjord areas which were covered by less active ice show different signatures of past glaciations the land and marine records of glaciations over the western svalbard fjord region have been extensively studied during the last few decades we have re examined ice flow records from stratigraphic and geomorphic settings and propose a succession of ice flow events that occurred repeatedly over glacial cycles the maximum the transitional and the local flow style the differently topographically constrained segments of the ice sheet switched behaviour as glacial dynamics developed through each glacial cycle these segments as well as the different flow styles are reflected differently in the offshore stratigraphic record we propose that the glacial geomorphological signatures in the inter ice stream areas mostly developed under warm based conditions during a late phase of the glaciations and that the overall glacial imprints in the landscape are strongly biased towards the youngest events

bulk kinetic parameters and structural moieties of asphaltenes and kerogens from a sulphur rich source rock sequence and related petroleums non isothermal open system pyrolysis gas chromatography and bulk petroleum generation experiments were performed on type ii s petroleum asphaltenes source rock asphaltenes and related kerogens to evaluate petroleum composition and generation timing the results show that contrary to convention there are significant differences in the reactivity between petroleum asphaltenes and their related kerogens in the studied type ii s petroleum system and these samples yield kinetic models that predict onset peak and completion of petroleum generation under different temperatures petroleum asphaltenes and source rock asphaltenes are less stable and show tighter petroleum formation windows than kerogens when extrapolated to geological heating rates source rock asphaltene related kerogen and oil asphaltene pyrolysates possess structural differences as revealed in the aromaticity and organic sulphur content aromaticity was highest in pyrolysates of source rock asphaltenes intermediate in kerogen pyrolysates and lowest in pyrolysates from petroleum asphaltenes in addition the highest organic sulphur content was identified in kerogen pyrolysates whereas pyrolysates of both source rock and petroleum asphaltenes are similar in organic sulphur content thus the amount of organic sulphur is not proportional to the reactivity of petroleum generation from asphaltenes at lower thermal stress it is more likely that kerogens and asphaltenes possess different configurations and types of sulphur bonds resulting in cracking of covalent bonds at different levels of thermal stress

late weichselian and holocene relative sea level history of broggerhalvoya spitsbergen abstract radiocarbon dated whalebones from raised beaches record a relative sea level history for broggerhalvoya western spitsbergen that suggest a two step deglaciation on svalbard at the end of the late weichselian glaciation the late weichselian marine limit was reached at about 13 000 yr b p and was followed by relatively slow emergence until about 10 000 yr b p either in response to ice unloading in the barents sea initial retreat of local fjord glaciers or some combination of the two rare whale skeletons dating between 13 000 and 10 000 yr b p indicate that the norwegian sea was at least seasonally ice free during that interval deglaciation of spitsbergen is recorded by the rapid emergence of broggerhalvoya after 10 000 yr b p this was followed by a transgression during the mid holocene here named the talavera transgression and another in modern times raised beach morphologies suggest striking differences in nearshore depositional processes before and after 10 000 yr b p that are probably related to changes in the rate of uplift and in sea ice conditions

milankovitch theory of ice ages hypothesis of ice sheet linkage between regional insolation and global climate abstract j d hays j imbrie and n j shackleton 1976 science 194 1121 1132 showed that the astronomical theory explained many features of late quaternary ice age climates but they did not specify the physical mechanisms involved here it is proposed that interlocked variations of ice sheet heat sinks in both polar hemispheres amplified and transmitted milankovitch summer half year insolation changes a version of the astronomical theory between 45 and 75 n into the globally synchronous climate changes recorded in geologic records it is suggested that late quaternary ice sheets had terrestrial components grounded above sea level melting margins fluctuations controlled by climate and marine components grounded below sea level drained largely by ice streams limited melting margins fluctuations controlled primarily by sea level and secondarily by climate interior surface elevations coupled to downdraw through ice streams northern hemisphere ice sheets were largely marine with minor melting margins in the arctic and terrestrial with major melting margins in the midlatitudes west antarctic and peripheral east antarctic ice was marine based and lacked melting margins because of their geographic array these terrestrial and marine components formed an ice sheet system whose variations were coupled on a global scale milankovitch summer isolation changes near midlatitude northern hemisphere melting margins controlled most variations of this system because advance or retreat of melting margins initiated concurrent eustatic sea level change such sea level change afforded the critical interlocking mechanism between terrestrial and marine components because it forced simultaneous expansion or contraction of marine margins in both polar hemispheres this initiated an amplifying feedback loop among all marine components and influenced interior downdraw through ice streams arctic summer insolation change was less important because northern melting margins were relatively minor its greatest influence was on surface ablation of ice streams that controlled interior downdraw this affected eustatic sea level and activated global linkage of marine sectors by analogy with present day antarctica late quaternary ice sheets were enormous planetary heat sinks due to their reflective and radiative surface characteristics it is suggested that the effectiveness of these ice sheet heat sinks varied with their areal extent and interior surface elevation thus it is postulated that concurrent growth or decay of these interlocked ice sheet heat sinks in both polar hemispheres served as the global amplifier of regional milankovitch summer insolation

kinetic modelling of petroleum formation and cracking implications from the high pressure high temperature elgin field uk north sea in this paper we use a case study to test the simulation of generation migration and cracking of petroleum fluids by a 2d compositional basin simulator using kinetic models based on chemical classes of compounds the selected area is the high pressure 1100 bar high temperature 190 c elgin field in the north sea this study is mainly focused on kinetic modelling of secondary cracking because in this zone paraffinic condensates with almost 50 c6 alkanes were recently discovered whereas only gas c5 was expected given the high temperature conditions the detailed hydrocarbon composition observed today in the fulmar sands reservoir of the elgin field is compared with the results of several simulations aimed at testing the influence of jurassic source rocks retention properties kinetic parameters and temperature variations on the predicted composition of fluids the influence of pressure was neglected in the modelling on the basis of results published in the literature results show that in this north sea area primary cracking of the kerogen into oil is completed whichever source rock is considered and that secondary cracking of accumulated petroleum compounds in the reservoir is presently in progress under these conditions source rock type and retention during primary and secondary migration have little influence on the present oil composition the occurrence of a monophasic paraffinic fluid in the elgin reservoir despite the high temperature is due to its very recent increase from 160 c to over 180 c in the last million years the fluid composition evolves rapidly and our compositional kinetic scheme accounts correctly for the presence of c6 hydrocarbons in these geological conditions first results using the compositional kinetic scheme of behar et al behar f kressman s rudkiewicz j l vandenbroucke m 1991 experimental simulation in a confined system and kinetic modelling of kerogen and oil cracking organic geochemistry 19 1 3 173 189 for secondary cracking showed a reasonably good fit between calculated and observed detailed fluid composition except for methylated aromatics which are overestimated and methane which is underestimated a recent comparison of kinetic parameters obtained from pyrolysis experiments on model compounds showed that it is not realistic to assume as done previously the same frequency factor for all chemical classes of compounds the higher stability of methylated aromatics relative to saturates observed under laboratory conditions would be extended to geological conditions a second set of simulations using frequency factors and activation energies obtained on these model compounds gave a better fit for methylated aromatics however methane is still strongly underestimated and reasons which could explain this discrepancy are discussed

late weichselian local ice dome configuration and chronology in northwestern svalbard early thinning late retreat the chronology and configuration of the svalbard barents sea ice sheet sbsis during the late weichselian lw are based on few and geographically scattered data thus the timing and configuration of the sbsis has been a subject of extensive debate we present provenance data of erratic boulders and cosmogenic 10be ages of bedrock and boulders from northwest spitsbergen nws svalbard to determine the thickness configuration and chronology during the lw we sampled bedrock and boulders of mountain summits and summit slopes along with erratic boulders from coastal locations around nws we suggest that a local ice dome over central nws during lw drained radially in all directions provenance data from erratic boulders from northern coastal lowland reinsdyrflya suggest northeastward ice flow through liefdefjorden 10be ages of high elevation erratic boulders in central nws 687 836 m above sea level ranging from 18 3 1 3 ka to 21 7 1 4 ka indicate that the centre of a local ice dome was at least 300 m thicker than at present 10be ages of all high elevation erratics 400 m above sea level central and coastal locations indicate the onset of ice dome thinning at 25 20 ka 10be ages from erratic boulders on reinsdyrflya ranging from 11 1 0 8 ka to 21 4 1 7 ka indicate an ice cover over the entire reinsdyrflya during lw and a complete deglaciation prior to the holocene but apparently later than the thinning in the mountains lack of moraine deposits but the preservation of beach terraces suggest that the ice covering this peninsula possibly was cold based and that reinsdyrflya was part of an inter ice stream area covered by slow flowing ice as opposed to the adjacent fjord which possibly was filled by a fast flowing ice stream despite the early thinning of the ice sheet 25 20 ka we find a later timing of deglaciation of the fjords and the distal lowlands several bedrock samples 10be from vertical transects in the central mountains of nws pre date the lw and suggest either ice free or pervasive cold based ice conditions our reconstruction is aligned with the previously suggested hypothesis that a complex multi dome ice sheet configuration occupied svalbard and the barents sea during lw with numerous drainage basins feeding fast ice streams separated by slow flowing possibly cold based inter ice stream areas

research on snow and ice this review unlike its predecessor martinelli et al 1979 is an intentionally selective survey of recent advances in selected areas of snow and ice research i have chosen to concentrate on studies relating to large scale aspects of the cryosphere and to consider their wider significance for other disciplines results obtained by new measurement techniques and the application of remote sensing methods are also stressed at the same time the broad lines of advance in glaciological research as represented in books conference themes and major field or laboratory programs are noted and a detailed bibliography is appended

amino acid geochronology of raised beaches in south west britain abstract based on 1 the epimerization of l isoleucine to d alloisoleucine d l ratios in patella vulgata littorina littorea l littoralis l saxatilis littorina species and nucella lapillus from raised beaches in south west britain 2 statistical analysis of the d l ratios and 3 lithostratigraphic and geomorphic evaluation three d l stages are proposed the d l ratios for all the species measured are converted to a patella vulgata standard the three d l stages are 1 1 the minchin hole d l stage d l ratios 0 175 0 014 defined at a stratotype in minchin hole cave gower wales 2 2 a provisionally defined but as yet unamed d l stage because of the current unavailability of a suitable stratotype with d l ratios of 0 135 0 014 3 3 the pennard d l stage d l ratios 0 105 0 016 defined at a stratotype in minchin hole cave gower wales two geochronological models of the three high sea level events representing the d l stages are constrained by uranium series age determinations on stalagmite interbedded with marine beds in minchin hole and bacon hole caves gower wales a potential fixed point in model evaluation is an age determination which is equivalent to oxygen isotope sub stage 5e 122 ka the two models are oxygen isotope stage and age ka bp d l stage d l ratio model 1a model 1b model 2 pennard 0 105 0 016 5a ca 80 5e 122 5e 122 5c ca 100 unnamed 0 135 0 014 5e 122 7 194 minchin hole 0 175 0 014 7 186 245 7 186 245 7 216 the ages of the raised beaches are used to constrain the timing and extent of glaciation in the area the extent of the late devensian glaciation is fixed by reference to localities where raised beaches of the pennard d l stage outcrop as well as by using unpublished data on molluscs incorporated into glacial deposits two pre devensian glaciations antedate the minchin hole d l stage the irish sea glaciation of the bristol channel irish sea older drift of south wales fremington till of north devon is ascribed to oxygen isotope 10 or earlier while the paviland welsh glaciation is ascribed to oxygen isotope stage 8 or earlier an earlier glaciation berwyn glaciation is inferred from erratics of known welsh provenance in essex

glacial terminations in the oxygen isotope record of deep sea cores hypothesis of massive antarctic ice shelf destruction abstract glacial terminations i and ii in the deep sea core foraminiferal oxygen isotope ratios though not similar in form are each characterized by a short interval of about 3 ka during which a large negative change occurred in the ratios after correcting for temperature effects we estimate that each change was equivalent to a glacial disintegration capable of causing a 50 60 m eustatic sea level rise in the termination i interval 16 13 ka b p the estimated equivalent sea level rise is much larger than that suggested by the best evidence of deglacial ice loss from the laurentide ice sheet which is thought to dominate pleistocene glacial ice volume changes moreover in termination ii about 125 ka b p the estimated equivalent sea level rise is much larger than that inferred from the stratigraphy of coral reefs and beaches on new guinea and other locations which suggests quite high sea levels for 10 ka prior to this termination to reconcile these severely conflicting lines of evidence we propose that the rapid negative isotope ratio changes were largely caused by the disintegration of massive floating antarctic ice shelves which masqueraded as land ice in the oceanic isotope ratios but which contributed no sea level change we propose that such shelves were formed when oceanic circulation changes in the north atlantic under glacial conditions greatly reduced the formation of relatively warmer north atlantic deep water and its injection into circumpolar antarctic regions and that the shelves disintegrated rapidly with the resumption of large scale formation of this deep water and its input into the antarctic we find that high sea levels in the 125 135 ka b p interval prior to termination ii which imply very little northern ice then are well supported by dated coral reef stratigraphy although these ages were not accepted by the climap study of the last interglacial ocean minimal northern ice volumes at that time imply that strong milankovitch summer insolation is not always required for northern deglaciation a promising additional deglacial mechanism is the prolonged viscous depression of the crust beneath the laurentide ice sheet combined with atmospheric oceanic circulation factors

the eurasian ice sheet formation and collapse resulting from natural atmospheric co2 concentration variations finite element model simulations of ice sheet dynamics are conducted to investigate the role of natural atmospheric co2 variations obtained from ice core bubbles in creating climatic conditions necessary to glaciate the eurasian arctic effects of co2 variations are sufficient to support extensive marine ice sheet and ice shelf development at the last glacial maximum and to deglaciate the region during the holocene from approximately 14 ka to 9 ka the ice sheet coverage simulated for the last glacial maximum agrees with evidence for extensive ice sheet grounding over the shallow continental shelves of the barents kara laptev and east siberian seas an ice shelf also forms over the arctic ocean and greenland and norwegian seas

northwest svalbard during the last glaciation ice free areas existed the possibility that ice free areas existed during the late weichselian glaciation of the svalbard archipelago has been debated for several decades this study reveals the first geologic evidence that nunataks existed on the islands of northwest svalbard several 10 be exposure ages were obtained from bedrock and glacial erratics on danskoya and amsterdamoya islands exposure ages for glacial erratics laid down in block field covered plateaus 300 m above sea level show that the last ice sheet that completely covered the islands deglaciated 80 k y ago dating of marine sediments close to sea level reveals that full ice free conditions were achieved by ca 50 ka during the late weichselian the coastal lowlands were glaciated and the major fjords and troughs controlled glacier flow the existence of nunataks at this time opens the possibility for glacial survival of plant species

pyrolysis gas chromatography of asphaltenes and kerogens from source rocks and coals a comparative structural study abstract pyrolysis gas chromatography of asphaltenes isolated from source rock and coal extracts and the corresponding kerogens show the same general pyrolysis characteristics while the pyrograms of asphaltenes associated with type i and ii kerogens are dominated by an aliphatic n alkene n alkane homology the pyrolysates of coal asphaltenes show a high abundance of aromatics the asphaltene pyrolysates differ from those of the related kerogens principally in that the relative abundance of isoprenoids and long chain hydrocarbons is higher in the asphaltene pyrograms these differences were minimized with increasing maturity suggesting comparable structures for mature asphaltenes and kerogens and that pyrolysis of asphaltenes should be integrated with other methods which are used in source rock geochemistry

quaternary deposits and glacial stratigraphy in ireland quaternary stratigraphic studies in ireland have been based largely on lithostratigraphy the division of complex sedimentary sequences into the traditional framework of munsterian and midlandian events has created a series of stratigraphic scenarios which cannot be fully substantiated either by biostratigraphy or by facies basin analysis many of the current problems of glacial stratigraphy in ireland therefore arise directly from the field procedures used and the frameworks used to subdivide sedimentary sequences these problems are centred on the selection of type sites the subdivision of sedimentary sequences into unnatural divisions the concepts of direct and indirect stratigraphy classical models of climatically determined ice advance retreat cycles and the genetic inferences of the term till the conceptual basis of various stratigraphic schemes has changed little since the work of farrington 1934 1966 it is argued that a more realistic approach to description and assessment of glacigenic sediments should be based on basinal facies analysis and must include a documentation of the composition and geometry of three dimensional facies variations palaeoenvironmental interpretations of complex glacigenic sequences especially in coastal locations should take account of the influences of marine ice sheets on the sedimentary record in the past most sequences were interpreted in terms of glacioterrestrial models a large body of sedimentary evidence now indicates that shallow glaciomarine environments occurred along the margins of the last ice sheet during its maximum and subsequent retreat phases the locations and patterns of associated icemarginal systems indicate that the magnitude of and patterns of crustal deformation were greater and more complex than formerly realised thus the primary control on sea level variation at successive ice sheet margins was largely a function of glacioisostatic disequilibrium although complex glacial and glacially related sequences are known it is argued here that most of the multiple glacigenic sequences in ireland can be accommodated within the midlandian cold stage the basal units from certain sequences and erratic fans have been attributed to events earlier than the midlandian however it is difficult to compare these traces of earlier events from different sectors of the island due to poor dating correlation and the fact that direct and indirect stratigraphy is not adequately defined or separated the age of the gortian style interglacial sequences the implications of their floristic composition and their relationships to drift stratigraphy remains a major problem in stratigraphic constructions of the irish quaternary the stratigraphic significance of many till units must remain largely unknown until these matters are resolved at present it is not clear if the gortian sequences represent more than one interglacial a series of exposures in ulster provide evidence for major environmental changes during the midlandian cold stage these include an early stadial an early forest biozone 48 1 ka bp an early herb biozone 41 5 ka bp a middle interstadial phase of cold but non glacial aspect 30 5 ka bp a late stadial max 24 22 ka bp and a late glacial climatic oscillation the late midlandian stadial comprises a major glaciation that almost covered the island and a later more restricted phase when drumlins formed in the northern and western parts of the island max 17 ka bp

analysis of petroleum fractions by tlc fid applications to petroleum reservoir description abstract thin layer chromatography and flame ionization detection iatroscan tlc fid offers a rapid and accurate method for quantifying saturated and aromatic hydrocarbons and resin asphaltene fractions in solvent extracts of petroleum source rocks reservoir rocks and crude oils while the instrument is superficially simple special precautions need to be taken in calibration and parameter setting due to complexities arising from the operational characteristics of the detector system nevertheless the technique offers superior speed and precision to conventional mplc analysis of petroleum fractions this paper describes the choice of operational parameters provides comparison with the traditional group type analysis technique mplc and presents some geochemical applications

biofacies and sediments in an emergent late pleistocene glaciomarine sequence skerries east central ireland abstract late devensian sedimentation ca 18 ka b p on the coastal margins of the irish sea basin occurred in shallow water glaciomarine environments around retreating tidewater ice margins high relative sea levels were the result of glacioisostatic crustal depression around the periphery of the last british ice sheet at skerries in east central ireland ice proximal glaciomarine diamict mud sand and gravel facies are selectively preserved in a bedrock depression the coastal exposure about 500 m long can be divided into three lithofacies associations 1 a diamict gravel association resting on bedrock was emplaced by sediment gravity flows and records the downslope reworking of glacial debris released from a retreating ice margin 2 an overlying mud association was deposited from suspended sediment plumes with minor ice rafting and records ice retreat and increasing distality of the site muds contain a mixed foraminiferal microfaunal assemblage typical of open water shallow marine shelves species can be grouped into reworked temperate cosmopolitan and well preserved boreo arctic elements and indicate mixing of derived and retransported temperate species with an in situ glaciomarine fauna 3 at the top of the section a gravel association derived from a nearshore fan delta rests on planated muds and is attributed to wave reworking and slumping of the fan delta front in shallow water during rapid basin rebound this and other sequences elsewhere in the irish sea basin is a record of rapid evacuation of the basin by calving tidewater glaciers and the uplift and erosion of glaciomarine sedimentary sequences in response to rapid late glacial crustal rebound

oxygen isotopes sea level changes and the temperature history of a coral reef environment in new guinea over the last 105 years abstract coral reef terraces consisting of an upward succession of fringing and barrier reef types are preserved on land along the raising coast of huon peninsula new guinea seven coral reef units i vii from the coast landwards spaced at about 20 kyr interval provide a rather complete record of sea levels oxygen isotopes and temperature of teh surface tropical ocean over the duration of the high sea level events of the last glacial cycle the systematic sampling of the coral reefs was restricted to the massive tridacna gigas species the giant clam which are about 0 7 0 enriched in 18o relative to calcite equilibrium value and the presence of symbionts seems to have no effect on the 18o of their aragonitic skeleton sea levels rose rapidly to 5 6 5 m above present during the last interglacial which on stratigraphic grounds and 18o compositions can be separated into an early phase whose 18o is similar to modern reef viia dated at 138 kyr and a late phase that is 0 6 0 heavier reef viib dated at 118 kyr fringing reefs vi v iv iii and ii record short lived high sea levels stands at 107 85 60 45 to 40 and 31 kyr respectively that stopped short of the present sea level 12 19 28 32 to 42 m the general decline of the high sea level stands corresponds to an average 18o enrichment of 1 7 0 measured between the early interstadials of isotope stage 5 vi and v and the late interstadials of isotope stage 3 iv iiia iiib and ii the maximum 18o enrichment of 1 7 0 relative to present was registered during a regressive phase of reef iiia stratigraphic evidence indicates that sea level lows in the range of 37 to 55 m below present have occurred in between the high sea level stands but those are unlikely to represent the lowest sea levels of the last glacial cycle sea levels and 18o ddta pair offer important clues regarding the partitioning of ice volume and temperature in 18o records the results suggest that the ice volume effect accounts for the observed 18o changes during the early interstadial culminations but only for 29 46 during the late interstadial culminations sea water cooling beyond the threshold limit of coral reef growth 18 c did not occur during the last glacial cycle the temperature of the surface tropical ocean was similar to present during the early interstadials of isotope stage 5 and cooler by 3 c below present during the later interstadials of isotope stage 3

climate sensitivity to continental ice sheet size and configuration abstract a version of the ncar community climate model ccm has been used to carry out a study of climate sensitivity to the size and distribution of continental ice sheets by comparing two perpetual season fixed sea surface temperature sst winter simulations of the climate at a glacial maximum the two simulations differ only in the size and configuration of the continental ice sheet boundary conditions these conditions represent minimum and maximum ice sheet extent for a glacial maximum as presently constrained by the geologic evidence all other boundary conditions are as specified by climap 1981 for winter surface conditions during the last glacial maximum lgm the ice sheets specified by climap 1981 used by many previous researchers to simulate ice age climate conditions are intermediate in size between the minimum and maximum ice sheets used for the simulations described here the maximum case simulation resulted in unexpected positive temperature anomalies over the northern hemisphere

mineral and fluid inclusions in diamonds from the urals placers russia evidence for solid molecular n2 and hydrocarbons in fluid inclusions abstract the compositions of mineral inclusions from a representative collection more than 140 samples of diamonds from the placer deposits in the ural mountains were studied to examine their compositional diversity the overwhelming majority of rounded octahedral and dodecahedral stones typical of placers contain eclogitic e type mineral inclusions up to 80 represented by garnets with mg 40 75 and ca 10 56 including the unique high calcic grospydite composition omphacitic pyroxenes containing up to 65 of jadeite as well as kyanite coesite sulfides and rutile peridotitic p type inclusions are represented by olivine subcalcic cr pyrope chrome diopside enstatite and magnesiochromite that are typical for diamonds worldwide comparing the chemical composition of olivine pyrope and magnesiochromite in diamonds of the urals north east of the siberian platform placers and arkhangelsk province kimberlites show striking similarity there are significant differences only in the variations of carbon isotopic composition of the diamonds from the placers of the urals and north east of the siberian platform one typical rounded dodecahedral diamond was found to contain abundant primary oriented submicrometer sized

ice proximal glaciomarine sedimentation and sea level change in the inverness area scotland a review of the deglaciation of a major ice stream of the british late devensian ice sheet abstract evidence of both rising and falling relative sea levels and glacitectonic movements is preserved in two formations of raised glaciomarine deposits that were laid down in front of an oscillating grounded tidewater glacier in the inverness firth these changes occurred during the latter stages of the disintegration of the moray firth ice stream one of the major ice streams that drained the british main late devensian ice sheet most of the glaciomarine deposits antedate a sequence of glacio isostatically tilted late devensian marine shorelines and associated littoral and estuarine deposits the shorelines began forming at about 13 000 bp and record a progressive fall in relative sea level a new model for the deglaciation of the moray firth region is proposed after a critical appraisal of published accounts of both onshore and offshore quaternary sequences the disintegration of the moray firth ice stream involved several rapid phases of retreat to pinning points caused by iceberg calving and triggered by rising global sea level each retreat was followed by minor readvances or stillstands possibly caused by short lived accelerated periods of glacio isostatic rebound and concomitant temporary falls in relative sea level two such events occurred in the inverness firth the ardersier oscillation and the alturlie stillstand substantial differences lower relative sea levels later deglaciation are apparent between the pattern of ice retreat in the moray firth region and published accounts of the deglaciation of the irish sea basin these differences require a reassessment of some current hypotheses concerning the disintegration of major ice streams associated with high relative sea levels furthermore geological and geomorphological evidence suggesting both rising and falling sea levels in the inverness area prior to ca 13 500 bp is not fully compatible with recently published computer simulations of the dissolution of the british main late devensian ice sheet

the last glacial maximum on spitsbergen svalbard most scientists have concluded previously that the west coast of spitsbergen svalbard remained ice free during the late weichselian between 25 000 and 10 000 yr b p we conclude that the glaciation was more extensive terraces that were postulated to have been ice free are covered by a thin late weichselian till sudden drop in the marine limit and basal radiocarbon dates of raised glaciomarine sediments demonstrates that the glaciers in the main fjords isfjorden and van mijenfjorden terminated west outside of the fjord mouths basal radiocarbon dates from glaciomarine clay above till in cores from the continental shelf west of spitsbergen yielded ages of about 12 500 yr b p from which we conclude that the ice extended to the shelf edge based on the extent of amino acid diagenesis in radiocarbon dated molluscs the duration of the maximum extension of the late weichselian glaciation was short certainly less than 10 000 years during the ice free period preceding that glaciation at least back to 40 000 yr b p the glaciers on svalbard were not significantly larger than at present as shown by marine deposits close to the glacier snouts many radiocarbon dates place deglaciation of the outer coast at about 12 500 yr b p at about 10 000 yr b p the rest of the archipelago rapidly became ice free

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

paleoclimatic inferences from glacial fluctuations on svalbard during the last 20 000 years the climate history of western spitsbergen svalbard is deduced from variations of glaciers during the last 20 000 years a major depression of the regional equilibrium line altitude ela occurred during the late weichselian glacial maximum 18000 13000y ago when low summer temperatures may have caused year round snow accumulation on the ground this rapid expansion of the glaciers also indicates nearby moisture sources suggesting partly open conditions in the norwegian sea during the summers a rapid glacial retreat around 13 000 12 500 y bp was caused by a sudden warming during the younger dryas the ela along the extreme western coast of spitsbergen was not significantly lower than at present in contrast to fennoscandia the british isles and the alps there is no evidence for readvance of local glaciers during younger dryas on western spitsbergen this difference is attributed to a much dryer climate on spitsbergen and probably only slight changes in sea surface temperatures in addition summer melting in this high arctic area is more sensitive to orbitally increased insolation around 10 000 y bp another rapid warming occurred and during early and mid holocene the summer temperatures were significantly higher than at present a temperature decline during the late holocene caused regrowth of the glaciers which reached their maximum holocene position during the last century

the caprock of the snorre field norway a possible leakage by hydraulic fracturing abstract the snorre field located on the tampen spur in the west of the viking graben presents a 300 m oil column in triassic and lower jurassic reservoirs and it is characterized by high pressures the caprock is formed by thick shale of cretaceous and palaeocene age some oil shows are found in the caprock up to a few hundred metres above the reservoir and have the same origin as the oil in the reservoirs the secondary migration process seems to be linked to high overpressures within the reservoir the pore pressure at the top of the reservoir reaches about 82 of the total vertical stress which is close to the minimum horizontal stress according to leak off test data hydraulic fracturing probably occurs increasing the shale permeability so that some oil escapes from the reservoirs the snorre field can be considered as a dynamic trap where a constant pressure regime is maintained by several processes linked to the local conditions and particularly to its structural situation and where regulation of the system occurs at the top of the reservoirs the pressure regime and the in situ stress conditions are the key factors in the prospectivity of the traps in this area

glaciomarine facies from the western sector of the last british ice sheet malin beg county donegal ireland the coastal margins and mountainous core of county donegal republic of ireland have been areally scoured and deeply eroded along structural lineaments by major late devensian ice streams which moved generally westwards onto the continental shelf a raised glaciomarine sequence is selectively preserved along a gully at malin beg and comprises mud muddy diamict sand and diamict 1 the mud which was deposited from suspended sediment plumes passes upwards into muddy diamict which reflects an increase in ice rafting the muds contain a redeposited foraminiferal assemblage of ice proximal origin pumped into the water column by jets reworking previously deposited outwash the presence of middle devensian shells have been identified from the mud by amino acid analysis this suggests a late devensian age for the succession 2 the overlying sand indicates an increase in traction current activity at the site 3 there is a sharp planar contact between the sands and the overlying tabular diamict unit 4 a surficial sheet of coarse grained breccia is attributed to intense periglacial weathering along the slopes of leahan mountain this sequence and those at other sites in western ireland e g belderg co mayo provide a record of deep isostatic depression and sedimentation in a peripheral trough at the north western margin of the last british ice sheet directional indicators including drumlin fields and major troughs indicate that the north western sector of the ice sheet was drained by major ice streams these ended in calving bays ice marginal response to ice wastage depended largely on catchment factors such as the magnitude of the ice reservoirs and the length of flow lines ultimately calving led to accelerated ice flow and areal down draw and collapse of the north western sector of the ice sheet

modeling subsurface flow in sedimentary basins groundwater flows that arise in sedimentary basins from the effects of topographic relief buoyant convection sediment compaction erosional unloading and combinations of these driving forces can be described using quantitative modeling techniques models can be constructed to consider the effects of heat and solute transport petroleum migration and the chemical interaction of water and rocks the accuracy of model predictions however is limited by the difficulty of predicting hydrologic properties of sediments on regional dimensions estimating past conditions such as topographic relief and knowledge of how physical and chemical processes interact over gelogic time scales progress in basin modeling will accelerate as hydrologic research efforts are better integrated with those of other specialities such as sedimentology rock mechanics and geochemistry

pvt and phase behaviour analysis in petroleum exploration abstract this paper describes the application of pvt data routinely determined for almost all conventional oil tests with respect to petroleum exploration in a broader context the use of pvt and phase behaviour analysis focuses on phase envelope evolution as a function of source rock maturity and secondary migration using both laboratory analyses and natural examples from the ekofisk eldfisk and snorre fields as well as data from the tampen spur area and barents sea in general pvt analysis is demonstrated to be applicable for relative maturity estimation recognition of mixing effects volumetric evaluation of complex reservoir filling histories and as a screening tool for oil population characterisation pvt analysis is used in this paper as a tool complementary to organic geochemistry allowing the integration and interpretation of data reflecting fluid response to geological conditions on a regional scale

constraints on the late weichselian ice sheet over the barents sea from observations of raised shorelines abstract direct evidence for late weichselian grounded glacier ice over extensive areas of the barents sea is based largely on indirect observations including elevations of old shorelines on svalbard and arguments of isostatic rebound such isostatic models are discussed here for two cases representing maximum and minimum ice sheet reconstructions in the former model the ice extends over the kara sea whereas in the latter the ice is limited to the barents sea and island archipelagos comparisons of predictions with observations from a number of areas including spitsbergen nordaustlandet edgeoya kong karls land franz josef land novaya zemlya and finnmark support arguments for the existence of a large ice sheet over the region at the time of the last glacial maximum this ice sheet is likely to have had the following characteristics conclusions that are independent of assumptions made about the earth s rheological parameters i the maximum thickness of this ice was about 1500 2000 m with the centre of the load occurring to the south and east of kong karls land ii the ice sheet extended out to the western edge of the continental shelf and its maximum thickness over western spitsbergen was about 800 m iii to the north of svalberg and frans josef land the ice sheet extended out to the northern shelf edge iv retreat of the grounded ice across the southern barents sea occurred relatively early such that this region was largely ice free by about 15 000 bp v by 12 000 bp the grounded ice had retreated to the northern archipelagos and was largely gone by 10 000 bp vi the ice sheet may have extended to the kara sea but ice thicknesses were only a fraction of those proposed in those reconstructions where the maximum ice thickness is centered on novaya zemlya models for the palaeobathymetry for the barents sea at the time of the last glacial maximum indicate that large parts of the barents sea were either very shallow or above sea level providing the opportunity for ice growth on the emerged plateaux as well as on the islands but only towards the end of the period of fennoscandian ice sheet build up

source rock quality and hydrocarbon migration pathways within the greater utsira high area viking graben norwegian north sea the greater utsira high area is located within the southern part of quadrants 24 and 25 and the northern part of quadrants 15 and 16 in the norwegian north sea in this part of the viking graben the main exploration play is the submarine fan sands of paleocene and eocene age these sands balder heimdal and ty formations pinch out to the east in blocks 25 8 jotun field and 25 11 balder and grane fields and along the western margin of the utsira high to form a combination of stratigraphic and structural traps marine sands of middle and late jurassic age typically present in rotated fault blocks constitute another important play geochemical analyses show that the upper jurassic draupne formation has a good potential for oil generation along the entire western margin and northern nose of the utsira high both upper and lower draupne source intervals along the western graben margin however contain more terrigenous kerogen than in the eastern part of the graben such change in organic facies within the draupne source interval naturally results in a higher proportion of gas generation and the possibility for generating a more waxy crude than typically encountered in the viking graben detection and characterization of oil and gas shows within the tertiary section permit mapping of migration entry points from the jurassic source rocks and help delineate secondary and tertiary migration pathways within the paleocene eocene play

simple kinetic models of petroleum formation part iii modelling an open system abstract the movement of petroleum from organic rich source beds to potential carrier beds is the net result of two processes expulsion the release of generated petroleum from kerogen within the source bed and primary migration flow of a petroleum phase through the inorganic void networks of the source bed and all other intervening fine grained rocks expulsion is by far the more important process within the source bed orgas a simple zero dimensional model of the source rock as an open system explicitly models expulsion concurrent with oil and gas generation and oi lgas cracking as a storage threshold problem oil and gas are retained adsorbed absorbed within kerogen until their concentrations exceed the respective sorptive capacity of the residual organic carbon 0 1 and 0 02 g g ck 1 the initial hydrogen index hl 0 controls the important balance between potential sorbate petroleum and sorbant residual carbon using simple geochemical measurements the initial organic carbon is divided into initial oil inert kerogen and oil and gas generative reactive kerogen components reactive kerogens are assigned to one of five global kinetic organofacies with pre determined kinetic parameter sets governing separately rates of oil and gas generation kinetic parameters governing the rates of oil cracking within the source rock are predicted from hl 0 the two most important determinants of source rock behaviour are organofacies and hl 0 at a reference constant heating rate of 2 c ma 1 the projected oil expulsion threshold for typical organofacies members increases in the order a de 100 110 120 135 c f typically expels no oil an order of magnitude increase decrease in heating rate increases decreases these thresholds by ca 15 c typical cumulative gas mass fractions in their ultimate expulsion products are a f 0 25 0 3 0 25 0 65 and 1 0 g g 1 a value of 200 mg hc g c 1 is an approximate minimum hl 0 prerequisite for oil expulsion irrespective of absolute petroleum potential p 0 as a family coals vary dramatically in their expulsion behaviour as their hl 0 ranges both above and velow this value primary migration is efficient for expulsive source rocks movement within the source bed is limited only at low p 0 a source rocks total genetic potential p 0 thickness becomes important during migration outside the source bed it potentially restricts the primary migration distance and the excess of petroleum available for secondary migration and entrapment we evaluate primary migration approximately using a small migration loss factor no more than about 10 saturation of porosity or 1 mg g 1 coupled with an understanding of fluid potential gradients which determine migration direction within the stratigraphic architecture ultimately kerogen degradation and oil to gas cracking in the source rock are the rate limiting processes in petroleum accumulation

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

improved understanding of mixed oil in nigeria based on pyrolysis of asphaltenes abstract crude oil from reservoirs in the onshore niger delta is a mixture of low and high maturity charge aromatic biomarkers in these oils such as alkylphenanthrenes and alkylnaphthalenes show relatively high thermal maturity whereas the saturated sterane and hopane biomarkers indicate lower maturity close to the peak of the oil window the high predicted maturity of the crude oils based on alkylphenanthrene and alkylnaphthalene indices is probably caused by mixing of high maturity condensate with less mature black oil this correlates with the gas washing phenomenon of studied nigerian oils caused by migrating condensate stream the results of our study indicate that asphaltenes can be used to infer the organofacies of the low maturity petroleum charge in mixed crude oils compositional characteristics of the asphaltene pyrolysates indicate an origin of the related oils from type ii iii or type iii source rock kerogen the n alkyl chain length distributions of the asphaltene pyrolysates predict source rocks that generated high wax paraffinic naphthenic aromatic oils or paraffinic oils the n alkyl chain length of asphaltene pyrolysates changes in proportion to oxicity and the relative input of terrigenous organic matter to the source rock

subaqueous outwash deposits in the ingraham ridge chazy new york a 1 5 km segment of ingraham ridge a stratified sand and gravel ridge in northeastern new york is composed dominantly of subaqueous outwash deposits the core of the ridge segment may include subordinate subglacial tunnel deposits the subaqueous outwash is composed mainly of interbedded sediment gravity flow bar dune and ripple deposits that occur in channels sheetlike cross stratified and cross laminated deposits also are common particularly on the distal western margin of the ridge segment the ridge segment is draped by glaciolacustrine laminated sand silt and clay and glaciomarine massive mud westward decrease in grain size and scale of sedimentary structures is attributed to confining ice walls of an asymmetric embayment sediments are deformed in part by the melting of adjacent and buried ice the ridge was modified during champlain sea regression and the reworked deposits were colonized by shallow water organisms reworking may have been minor and the broad low morphology of the ridge

state of the art of research in kinetic modelling of oil formation and expulsion abstract the last ten years have seen a rapid development in the understanding of petroleum generation and expulsion by a combined use of natural series and experimental simulation this knowledge is now used to develop mathematical models which reproduce the kinetics of petroleum generation and migration in the purpose of basin evaluation by a combination of observation of homogeneous geochemical series experimental simulation and mathematical modelling it has been now established that parameters governing the quantity and composition of petroleum are temperature type of organic matter time or heating rate catalysis by clay minerals which would produce important amounts of isoalkanes is not necessary to produce petroleum the role of minerals although still controversial is rather to retain the heavy fraction of petroleum pressure seems to have a limited influence within the range for effective source rocks kerogen is a tremendously complex macromolecule which is now insufficiently characterized to develop fundamental predictive models of thermal cracking i e involving intermediates such as radicals and olefins such models presently apply only to the cracking of simple molecules hexane hexadecane at limited degrees of cracking for this reason kinetic models are still empirically calibrated on pyrolysis experiments and or on natural maturation trends the most popular models involve a series or a continuous distribution of parallel reactions to describe primary cracking i e direct formation of mobile compounds from kerogen these are generally calibrated against open system pyrolysis with various temperature programs consideration of natural maturation trends i e decrease in petroleum potential may be used also for calibration but discrepancies of organic matter properties availability of deep samples and uncertainties on thermal history limit the effectiveness of such methods whatever the method main activation energies are found in the range 45 60 kcal mol secondary cracking which refers generally to cracking of mobile compounds cannot be modelled from open system pyrolysis nor from natural series unknown residence times but only from closed system pyrolysis although models of primary and secondary cracking still need experimental improvements and more realistic kinetic schemes their ability to predict quantities and composition of petroleum depends primarily on migration which is poorly known indeed migration controls the residence time of petroleum in hot zones of sedimentary basins and thus determines the extent of oil conversion into gas as reproduced by recent numerical models preliminary studies documenting the interactions between thermal cracking and expulsion are shown from haltenbanken area and paris basin in the last few years a kind of agreement has been reached that primary migration was most likely occuring in a separate phase from water and that a sufficient concentration of petroleum must be generated for expulsion to start indeed high expulsion efficiencies over 50 are systematically found for rich and mature source rocks a further understanding of primary migration requires observations of natural series petrophysical studies of source rocks porosities under 10 permeabilities in the nanodardy range thermodynamic investigation of unconventional multiphase organic systems kerogen liquid s gas and experimental simulation under stress this on going research should enable models to track correctly migration paths and thermal history of petroleum fluids as necessary to model their composition

sedimentation in an ice contact subaqueous setting the mid pleistocene north sea drifts of norfolk u k in east anglia the mid pleistocene north sea drifts extend over some 1500 km2 of the coastal zone of north norfolk they are the oldest pleistocene glacial sequences exposed in britain deposited during the anglian glaciation ca 450 ka bp laminated and stratified pebbly mud diamict facies of the north sea drifts are widely regarded as the product of subglacial deposition below a terrestrial ice margin in this paper these facies are identified as the product of subaqueous deposition in front of the margin of an ice sheet terminating in a large water body laminated stratified and massive diamict facies were deposited by the rain out of fine grained sediment from suspension and coarse debris from floating ice combined with downslope sediment gravity flow intraformational folds are the product of episodic downslope slumping and identify a regional paleoslope to the east away from a major ice marginal moraine ridge the cromer ridge exposures at cromer show bulldozed ice contact subaqueous sediments and ice thrust chalk rafts a fall in water level emplaced shelly shoreface sands and beach gravels which are loaded into the underlying diamicts as large pan shaped sag basins with diapiric structures at their margins comparable sedimentary sequences are exposed elsewhere around the southern north sea basin a glaciomarine setting in response to glacio isostatic depression around the anglian ice sheet is suggested

palaeoclimate of baffin bay from 300 000 year record of foraminifera dinoflagellates and pollen several different models1 5 have attempted to relate quaternary marine and terrestrial records of ice sheet growth in the north atlantic region the models are derived from either discontinuous terrestrial records including marine fossils in raised shorelines1 2 or from deep sea calcareous microfossils3 4 this study correlates arctic marine and terrestrial data directly by comparing 18o foraminiferal dinoflagellate and pollen records from a core taken in baffin bay the core contains an almost continuous sequence of sediments deposited during isotope stages 1 10 subarctic foraminifera and atlantic dinoflagellates in early isotope stages 2 4 6 and 8 show that subarctic water entered southern baffin bay before the glacial maxima boreal subarctic pollen suggest that atlantic air flowed into baffin bay during the ice sheet growth phases these data support models which postulate that open water in the labrador sea had an important role in supplying moisture to laurentide and greenland ice sheets

holocene glacial rebound and sea level change in nw europe summary observations of late pleistocene and holocene sea level change relative to the crust exhibit very considerable variations across nw europe in consequence of the response of the earth s crust to the deglaciation of fennoscandia and of the water added to the oceans from the melting of all late pleistocene ice sheets inversion of sea level observations from a site near the centre of the fennoscandian ice sheet and from three sites located beyond the margin of the ice sheet at the time of maximum glaciation yield a range of plausible models for the earth s response and for the ice models further constraints on this range of models is placed by a comparison of observed sea levels with predicted values at other sites near the former ice sheet margins the resulting mantle parameters are upper mantle viscosity 3 5 x 10 pa s lower mantle viscosity 2 7 x loz1 pa s lithospheric thickness 100150 km these values represent effective parameters that describe the response of the earth to surface loading of short to intermediate wavelengths on a time scale of 104yr the lower mantle viscosity is poorly constrained but the marked increase from upper to lower mantle is a characteristic of all plausible solutions the inversion places a constraint on the total volume of ice in the fennoscandian ice sheet such that the equivalent sea level rise from this contribution is about 13 14 m a less well determined constraint of about 10 m equivalent sea level rise is suggested for the barents kara ice sheet the inversion also indicates that a small amount of melt water from ice sheets far away from europe continued to be added into the oceans during late holocene time so as to raise the equivalent sea level by about 3 m during the past 6000 yr consistent with similar inversions of data from sites in the australian and pacific regions

enhanced age resolution of the marine quaternary record in the arctic using aspartic acid racemization dating of bivalve shells abstract aspartic acid asp racemization occurs at a significantly higher rate than isoleucine epimerization and consequently provides better temporal resolution of arctic marine deposits from alaska spitsbergen and baffin island heating experiments at 100 c on the bivalvesmyaandhiatellashow the asp racemization rate decreases with increasing d l values as is typical for biogenic carbonates based on these experimental racemization rates and rates determined from racemization of samples radiocarbon dated to ca 10 000 12 000 yr b p activation energies formyaandhiatellaare estimated to be 30 6 and 30 0 kcal mol respectively for asp racemization and 29 0 and 29 5 for isoleucine epimerization analysis of a time series of plio pleistocenehiatellafrom the north coast of alaska shows that last interglacial mollusks can be readily distinguished from modern samples by asp but not by isoleucine d l asp values indicate a younger age for the fishcreekian transgression than does isoleucine epimerization for spitsbergen d l asp shows a slight age difference ca 12 000 yr between two units of the episode b interstadial and suggests that the age of these units may be closer to 65 000 than to 80 000 yr b p two possible ages suggested by other evidence the age of the loks land interstadial on baffin island is likely to be greater than that indicated by radiocarbon ages within deposits from each region d l asp values are less variable among individual shells than isoleucine epimerization values this may indicate better reliability of asp for geochronology

postglacial emergence of western franz josef land russian and retreat of the barents sea ice sheet uncertainty remains on the timing and extent of late weichselian glaciers over the qsr barents and kara sea shelves franz josef land russia is a critical area for deciphering the record of glacier fluctuations and postglacial relative sea level change coastal forelands on the archipelago are covered by a well preserved raised beach sequence containing abundant and pristine driftwood whalebone and shell 4c dating of these materials provides site specific emergence records for the archipelago and some of the oldest ages on deglaciation of 10 400 bp three apparent still stands in emergence are inferred from morphology of the raised beach sequence and 4c dating between 9900 and 6200 bp and at ca 5500 bp and 3500 bp the earliest sea level arrest after formation of the marine limit reflects a balance between glacio isostasy and eustasy concomitant with the final phase of global sea level rise the latter two sea level arrests during the middle to late holocene are less pronounced and may indicate increased height of the ocean surface with greater storminess and extended open water conditions raised beaches at 1 2 m a s l and j4c dated at 1000 to 2000 bp give contemporary emergence rates of 1 to 2 mm year the low current rates of emergence on franz josef land are similar to areas in fennoscandinavia that sustained modest late weichselian glacier loads 1500 m within a few 100s of km of the inferred ice sheet margin the pattern of postglacial emergence and strandline tilts indicates that past glacier loads were greater over the adjacent barents sea than franz josef land marine and terrestrial records from franz josef land place retreat of glaciers from coastal areas by 10 400 bp whereas the adjacent franz victoria trough was deglaciated by 13 000 bp retreat of the barents sea ice sheet was probably underway by 13 500 bp coincident with rising global sea level and elevated summer insolation we infer that iceberg calving through the deep troughs bordering the barents sea particularly with rapidly rising sea level ca 12 000 bp was an important process controlling the demise of the barents sea ice sheet copyright 1996 elsevier science ltd

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

migration of hydrocarbons in the tampen spur area norwegian north sea a reservoir geochemical evaluation abstract this paper describes the application of reservoir geochemical protocols to a study of oil field and regional petroleum compositional variations in the major fields in the tampen spur area the tampen spur high is located in the middle of several oil mature to gas mature source rock kitchens and most of the structures might receive petroleum from several different directions based on the definition of several different petroleum populations within the tampen spur area we define five major petroleum charging systems correlating the petroleum population variations with geological information allows us to derive likely migration fill scenarios for many of the oil fields and requires us to invoke a new upper jurassic carrier system in parts of the area connecting brent group reservoirs across major faults based on this hypothesis two exploration wells were drilled on structures to test this carrier and petroleum was found in one of the structures an understanding of the migration pathways and petroleum drainage efficiency of the basins is of great economic interest because most of the smaller substructures are marginally economic thus it is important to provide an effective risk analysis and ranking of the satellite prospects prior to drilling this study has demonstrated that filling and migration in a geological province are controlled by a series of complex processes and that the filling history of the structures within the tampen spur is more complicated than suggested earlier