glacial geomorphic features in the northern barents sea direct evidence for grounded ice and implications for the pattern of deglaciation and late glacial sedimentation

sequence stratigraphic significance of sedimentary cycles and shell concentrations in the upper jurassic lower cretaceous of kachchh western india abstract upper jurassic and lower cretaceous siliciclastic shallow water sediments of the kachchh basin western india form strongly asymmetric coarsening upward cycles which are interpreted as recording changes in relative sea level deepening shallowing cycles these cycles correspond to depositional sequences in which deposits of the lowstand systems tract are not present the sequence boundary coinciding with the transgressive surface shell concentrations are found in the transgressive lags at the base of the transgressive systems tract tst in the maximum flooding zone mfz and at or close to the top of the highstand systems tract they belong to six assemblages five of them dominated by large bivalves such as seebachia herzogina gryphaea gervillella megacucullaea pisotrigonia and indotrigonia the sixth by the coral amphiastraea three types of shell concentrations can be distinguished that differ from each other in a number of ecological and taphonomic features such as species diversity preservation quality orientation in cross section percentage of disarticulation and degree of biogenic alteration characteristic features of concentrations at the base of the tsts are moderate time averaging sorting a preferred convex up orientation and nearly total disarticulation of shells they are suggestive of an environment in which reworking and local transport were frequent events similar features are shown by concentrations near the tops of the hsts except that there shells were largely concentrated in lenses and in pavements rather than in beds as in the transgressive lags associated sedimentary structures indicate deposition above fair weather wave base in a high energy environment concentrations occurring in the mfz in contrast are autochthonous and highly time averaged having accumulated during times of low rates of sedimentation below storm wave base this is supported by their high preservation quality comparatively high percentage of articulated shells shells of infaunal organisms commonly preserved in life position biogenic alteration being the most important taphonomic agent the dominant elements of these shell concentrations i e seebachia megacuccullaea and indotrigonia in the upper jurassic and pisotrigonia in the lower cretaceous are endemic to the ethiopean faunal province and belong to lineages that rapidly evolved during this time period

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

the fugloy reef at 70 n acoustic signature geologic geomorphologic and oceanographic setting this is the first in depth study of a cluster of cold water coral reefs the fugloy reefs found at 70 n on the norwegian margin combining high resolution seismic reflection data side scan sonar video images and oceanographic measurements reveals the geologic geomorphologic and oceanographic setting in which the reefs occur the reefs consist mainly of the scleractinian ahermatypic lophelia pertusa and exist below the thermocline at water depths between 140 m and 190 m the reefs appear as cone shaped acoustically transparent features on seismic reflection data consistently located in places characterized by the availability of hard substrate high relief and periodical exposure to high tidal currents 30 cm s these currents transport water of the norwegian atlantic current to the reefs from an area with fluid expulsion related pockmarks the spatial relationship between reef pockmark locations and current directions suggests that seepage of biogenic gas might be a catalyst to reef growth with a height of more than 40 m some of the fugloy reefs are among the highest reported from the norwegian margin this indicates highly favourable growth conditions and conservative estimates indicate a net growth rate for the reefs of 5 mm year we expect that cold water reefs will be found further north along the barents sea margin as general awareness on the geophysical signature and appearance of the reefs increases because all known factors involved in reef establishment and growth are within the required intervals also further north

an enigmatic kilometer scale concentration of small mytilids late miocene guadalquivir basin s spain abstract upper miocene heterozoan carbonates crop out extensively in a ne sw trending belt 42 km long and 1 5 8 km wide along the so called el alcor topographic high from carmona to dos hermanas seville s spain these carbonates formed at the southern active margin of the guadalquivir basin the foreland basin of the betic cordillera they change to marls basinward ne and to sands landward se and sw therefore carbonate production was constrained to a limited area in an otherwise siliciclastic shelf the carbonates up to 40 m thick overlie a gradually coarsening upward succession of marls followed by silts and sandstones the carbonate sequence can be divided into three subunits corresponding from bottom to top to lowstand transgressive and highstand system tract deposits the lower subunit exhibiting extensive trough cross bedding is interpreted as a shallow water bar deposit the intermediate subunit onlaps underlying sediments and was deposited in deeper low turbulence conditions the upper subunit deposits accumulated in a well oxygenated outer platform based on benthic foraminiferal assemblages the presence of hummocky and swaley cross stratification in these latter deposits suggests that they were affected by storms pervasive fluid escape structures are also observed throughout the carbonates the three subunits consist of bioclastic packstones to rudstones made up of abundant fragments of small mytilids isotopic data from serpulid polychaete ditrupa tubes show 13c depleted values up to 16 1 whereas 18o yields normal marine values additional isotopic data on shells of scallops oysters and small mussels as well as bulk sediment show diagenetic alterations based on actualistic examples of massive concentrations of mussels the nearly monospecific composition of the el alcor deposits together with negative 13c values of ditrupa tubes indicates that cold seeps presumably promoted carbonate formation however the absence of typical features of cold seep deposits such as authigenic carbonates mediated by anaerobic bacterial activity and the typical chemosynthetic shelly organisms makes the large carbonate body of el alcor an unusual cold seep deposit

responses of benthic foraminifera to environmental variability a case from the middle jurassic of the kachchh basin western india abstract at the western margin of the indian plate the jurassic sedimentary succession of the kachchh basin provides well developed exposures for fauna based studies based on a quantitative analyses of 67 samples spanning middle bathonian late callovian interval the paleoenvironment of the jumara section the depocenter of the kachchh basin is inferred four benthic foraminiferal assemblages are recognized by both clustering and nmds ordination methods these assemblages vary in biotic traits such as life habit and diversity as well as in abiotic traits such as sediment type nutrient availability and oxygen level the bathonian spirillina polygyrata assemblage that dominates an outer neritic oligotrophic setting has a preference for calcareous substrates in the earliest callovian the epistomina mosquensis assemblage replaced the latter as oxic conditions decreased and terrigenous influx increased two successive and less diverse assemblages had a preference for non calcareous substrates and dominated the mid early late callovian landscape these are the oxic lenticulina subalata assemblage inner to middle neritic oligotrophic setting in the mid early to mid middle callovian and the dysoxic reophax metensis assemblage mesotrophic to eutrophic middle neritic setting in the late middle to late callovian linear regression models suggested that sea level oxygenation and sediment type are the main abiotic factors controlling the distribution of the fauna moreover taxa with specific biotic traits such as shell composition calcareous vs agglutinated and selection strategy r vs k strategy occupied different environmental settings furthermore diversity and epifaunal infaunal ratio had a cyclic pattern comparable to those of third order sea level fluctuations

climatically versus eustatically controlled sediment supply driven cycles carbonate siliciclastic high frequency sequences in the valanginian of the neuquen basin argentina carbonate siliciclastic high frequency sequences are formed by reciprocal sedimentation in siliciclastic dominated successions the carbonate rich interval is typically associated with transgressive conditions and relatively low terrigenous influx particularly in distal parts of the marine basin however key questions for each individual case are what sort of depositional system developed during transgressions and what controls sediment supply fluctuations this paper integrates outcrop and subsurface data to present a high resolution sequence stratigraphic study of small scale 2 18 m carbonate siliciclastic cycles deposited during the valanginian in a proximal distal transect of the neuquen basin western argentina and discusses those key issues carbonate hemicycles in this study are composed of cross bedded oolitic skeletal grainstones and packstones to massive skeletal floatstones which accumulated in carbonate ramps with high biogenic production in their distal sector bivalves serpulids echinoids and significant contribution of non biogenic ooids material in inner ramp settings siliciclastic material is present only at the base of the hemicycles but rapidly diminishes upwards these carbonate hemicycles have retrogradational staking patterns in proximal sectors and less obvious trends in distal areas the siliciclastic hemicycles comprise shallowing upward successions that include mudstones bioturbated muddy sandstones sandstones with hcs and scs and bioturbated sandstones these facies were collectively deposited in a storm and wave influenced offshore shoreface depositional system during normal regressions these shoreface systems were likely fed by littoral drift from riverine inputs located tens of kilometers to the south the duration of the investigated small scale transgressive regressive cycles can be estimated in 50 to 150 kyr and they are bounded by marine transgressive surfaces placed at the bases of carbonate hemicycles the bounding discontinuities together with the sequence architecture do not suggest periods of sea level falls between cycles nor high amplitude relative sea level changes during a cycle formation additionally the low proportion of mixed sediments suggests rapid changes in the rate between terrigenous supply and carbonate productivity the resulting sequence architecture cannot be reasonably explained by autocyclic controls or eustatic changes alone it is argued here that high frequency changes in sediment supply driven by orbitally induced climate fluctuations could be a better explanation for these sequences particularly in the context of a long term relative sea level rise in this scenario periods of low siliciclastic influx during extreme arid conditions would develop a negative balance with accommodation and prompt carbonate systems and transgression on the other hand during more humid conditions relatively high sediment flux would temporarily overcome long term accommodation producing the regressive siliciclastic hemicycles as this scenario does not require high frequency sea level falls it would satisfactorily explain the observed sequence architecture the distal mulichinco carbonate hemicycles would be hard to distinguish from transgressive fossiliferous rich deposits that characterize transgressive regressive cycles in clastic systems in the mulichinco case however these carbonate hemicycles are recording the onset of carbonate ramps not the trapping of siliciclastic sediments in transgressive coasts e g filling estuaries this alternative scenario ultimately controlled by reciprocal sedimentation could be common in epicontinental basins developed under arid to semiarid conditions and its identification could provide additional templates for basin scale correlations and hydrocarbon exploration within carbonate siliciclastic small scale cycles

faunal response to transgressive regressive cycles example from the jurassic of western india abstract upper callovian to oxfordian shelf sediments at ler in the kachchh basin western india are interpreted in terms of transgressive regressive cycles the transgressive phases are represented by thin layers of reworked and bored concretions sometimes in association with skeletal concentrations the regressive phases are documented by much thicker units of largely fine grained sediments the benthic fauna of transgressive and regressive phases differes markedly and thus mirrors the sedimentary cycles during transgressive phases non sedimentation produced hard substrates colonized mainly by byssate cemented or pedicle attached suspension feeding epifaunal species whilst sediment input during regressive phases lead to soft substrate conditions characterized by infaunal deposit and suspension feeders as well as by epifaunal opportunists whereas the composition of the regressive fauna remains fairly constant through time that of successive transgressive faunas often differs drastically this is possibly due to a greater environmental sensitivity of epifaunal taxa as compared to infaunal taxa

ecostratigraphy and sequence stratigraphy in high frequency sea level fluctuations examples from jurassic macroinvertebrate assemblages abstract sequence stratigraphy is a method for stratigraphic analysis providing interpretative models with the aim of integrating the subsurface and surface information for correlations and therefore biostratigraphical data has become increasingly valuable in this context given the foregoing unsolved problems still arise out of the difficulty in obtaining local biostratigraphical data which can certainly be related to the fact that the linkages of contemporaneous depositional systems are facies independent and also because of the comparatively broad time span accepted for the cycles of high frequency sea level fluctuations 3rd order and lesser ones other restrictions have to do with the comparative complexity of ancient e g mesozoic platform systems whose extent and subdivision lead to deviations in the stratal patterns as regards those proposed by the existing synthetic models of sequence stratigraphy moreover at present the attempts at correlation of data obtained in ancient platforms with those from distal areas of continental margins which are normally characterized by low sedimentation rates are made indirectly oloriz et al 1991 and are still at a comparatively early stage of development we here propose an ecostratigraphical approach for correlation and characterization of system tracts in the context of high resolution stratigraphy the interpretation of the geological record must of course be undertaken with regard to recognizable local determining factors the observable trends in the record of benthic epibenthic marine macroinvertebrate assemblages are analyzed in this context examples of the upper jurassic ammonite record and especially bivalves among benthic faunas are analyzed on the south and west iberian margins using the sequence stratigraphy frame proposed for this margin by marques et al 1991 the data obtained are compatible with the contraction expansion of ecospaces which could presumably be related to the evolution of highstand transgressive and shelf margin wedge system tracts we also comment on published data by others authors concerning fluctuations in ammonite assemblages and ammonite phenotypes chronological aspects related with sequences stratigraphy analyses and the record of benthic assemblages within the framework of high frequency fluctuations in relative sea level the approach proposed here proves to be a useful complement in sequence stratigraphy analyses and will also be of use in more profound study of the ecostratigraphic characterization of system tracts and new interpretations of the fossil record

seafloor geomorphology of the sw barents sea and its glaci dynamic implications abstract three dimensional 3d reflection seismic imaging techniques provide a unique means of identifying large scale submarine geomorphic features produced by former ice sheets we have used such techniques to image the geomorphology of the sw barents sea but using a dense grid of 2d seismic covering a 240 000 2 km large study area supplemented with 3d seismic from selected areas the study area is located at the convergence of ice flow from the former fennoscandian barents sea and svalbard ice sheets the morphology of the major cross shelf troughs is characterized by elongated ridge groove features interpreted to be glacial bedforms produced by fast flowing grounded glaciers mega scale glacial lineations have been grouped into distinct flow sets related to three specific ice flow events these events document the last glacial maximum lgm and two readvances during deglaciation of specific interest is a detailed and well preserved set of seafloor imprints in the bjornoyrenna trough which acted as the main pathway for ice streams draining the surrounding ice sheets the geomorphic features indicate that bjornoyrenna hosted six separate ice stream lobes that diverged fan like at their margins but were not all active simultaneously an end moraine zone 68 km wide up to 85 m high and 300 km long filled the whole width of this major glacial trough as a result of high sediment flux within sub ice stream deformable beds the imprint of this ice stream system can be followed on our seabed images for 500 km however detailed geomorphologic elements demonstrate that these imprints reflect time transgressive behaviour and do not indicate the length or width of single ice streams the seismic derived seafloor geomorphology demonstrates that the barents sea ice behaved in a much more dynamic way during the last glaciation than previously assumed with major shifts between ice originating from the fennoscandian spitsbergen and barents sea ice sheets

palaeoclimate reconstructions of the middle jurassic of kachchh western india an integrated approach based on palaeoecological oxygen isotopic and clay mineralogical data abstract the middle jurassic sedimentary succession of the kachchh basin shows significant changes in lithology faunal content and diversity across the bathonian callovian boundary the change in lithology from predominantly carbonates in the middle and late bathonian to siliciclastics in the callovian is accompanied by a drop in species diversity from high to moderate characteristic faunal elements of the bathonian corals sponges the bivalves eligmus and members of the opinae are absent or rare in the callovian in contrast callovian sediments contain comparatively high proportions of nuculid bivalves the clay mineral assemblage reveals prominent variations in the smectite vs kaolinite abundance especially during the bathonian to callovian transition from the bajocian to the middle bathonian smectite becomes the dominant clay mineral and is nearly exclusively present in the late bathonian towards the middle callovian its content gradually decreases and kaolinite becomes the dominant clay mineral illite generally is only a minor component throughout the middle jurassic based on these results the bajocian to middle bathonian time interval is interpreted to represent subtropical climatic conditions with seasonal droughts and a moderate supply of terrigenous clastics to the basin the late bathonian was a period with a semi arid climate hot seasonal droughts and a minor input of terrigenous clastics the increase in kaolinite contents in the callovian suggests a subtropical humid climate with less prominent seasonal droughts and a higher input of siliclastics into the basin accompanied by a higher nutrient influx oxygen isotope ratios measured on bathonian to early callovian brachiopod shells give palaeotemperatures of 19 24 c callovian to oxfordian paleotemperatures calculated from oxygen isotopes measured on belemnite rostra range from 11 to 21 c the lower palaeotemperatures estimated from the oxygen isotopic composition of belemnite calcite are explained by assuming that the belemnites spent most of their life span in colder regions of the malagassy gulf and migrated into the warmer subtropical waters of the kachchh basin combining these various lines of evidence the changes in lithology and faunal composition taking place in the kachchh basin during the middle jurassic appear to reflect largely a change towards increasing humidity rather than a distinct decrease in water temperature

time specific aspects of facies state of the art examples and possible causes abstract the term time specific facies tsf was introduced to the scientific community by the late otto h walliser to refer to unique facies typical of particular narrow intervals some of which were related to bioevents in some senses however the concept was recognized much earlier and is even engrained in the very names of some geologic periods the concept of time specific facies is expanded slightly herein to include distinctive or unique regional to global characteristics of the sedimentary record that characterize particular intervals of geologic time the recognition of time specific and widespread processes in the sedimentary record is a critical step in unraveling the interplay between processes of differing scale these range from very short term but widespread facies that overlap with event deposits to general facies types that may persist for intervals up to 10s of millions of years in duration this paper briefly summarizes the history of development of the tsf concept provides examples to illustrate a few of the key aspects of time specific facies and offers a few tentative explanations for this phenomenon among the factors that control tsfs abrupt changes in redox conditions and early diagenetic mineralization sedimentary condensation often associated with abrupt sea level change altered climate and paleoceanography and biotic evolution and extinction seem to be most critical and permit a preliminary genetic classification of tsfs inevitably however many tsfs reflect multiple effects and some remain largely unexplained

sedimentary imprints of former ice sheet margins insights from an end ordovician archive sw libya fromthe proterozoic to the quaternary the evolution of the earthwas characterised by recurrent periods of glaciation however the margins of many ancient ice sheets are poorly defined on palaeogeographic reconstructions the extent and outlines of ancient ice sheets can be better understood through careful documentation of sediments deposited at the ice sheet margin an outstanding example is provided herein based on an end ordovician archive in libya tihemboka area murzuq basin the four sets of structures include i subglacial glaciotectonic structures and soft sediment deformations from flowing glacier ice such as intraformational glacial striae intraformational deformation shear planes sheath folds normal microfaults and large scale glaciotectonic folds and thrusts ii structures resulting from overpressured subglacial meltwater flows such as clastic dykes and tunnel valleys iii proglacial depositional structures and facies related to highmagnitude meltwater floods such as sandstone intraclasts large scale bedforms resulting from supercritical flows climbing dune cross stratification and kettle holes and iv deformation structures resulting from free floating and nonglacier ice such as ice keel scours and ice crystal marks such a set of structures points to an ice marginal essentially continental depositional setting and provides an excellent suite of criteria to identify margins of ancient ice sheets in the stratigraphic record at a regional scale a reconstruction through time and space of the related depositional wedge is proposed this corresponded to a seismic scale n120 m in thickness 40 km in length ice marginal wedge in front of an essentially warm based ice sheet inducing concomitant large scale glaciotectonic deformation glacial basin and tunnel valley downcuttings the related ice front was associated with high energy meltwater flows feeding a network of deeply incised proglacial channels downstream and beyond them a fluvioglacial deltaic system shallow ice marginal permafrost most likely affected the depositional wedge at a larger scale the tihemboka ice marginal wedge is interpreted as related to a stillstand period over the gondwana platform developed over an estimated interval of a few thousands of years based on these data the conditions that arose in a particularly favourable context for the development the preservation and the identification of ice marginal wedges in the geological record are reviewed significant meltwater derived sediment deposition and aggradation in an accommodation space resulting either from preglacial inheritance glacial downcuttings and or glacio isostatic lithospheric flexure or active tectonic subsidence 1 myr are required for their formation and subsequent preservation

cenozoic erosion and sedimentation in the western barents sea abstract seismic reflection data and well logs are used to interpret cenozoic sedimentary environments in the south western barents sea using volumetric calculations and compaction trend analysis the cenozoic erosion and sedimentation rates have been quantified marine environments ranging from neritic to bathyal water depths dominated the southern barents sea during the late palaeocene at the palaeocene eocene boundary a southwards progradation commenced along the uplifted and eroded loppa and stappen highs during the early eocene to mid miocene sedimentation continued in the intracratonic basins as well as along the newly established continent ocean boundary in the embryonic northern norwegian greenland sea substantial erosion occurred on the westernmost margin particularly on the stappen high during this time interval in the mid miocene during a period of relative lowstand of sea level a system of lowstand fans was deposited west of the stappen high later a pronounced progradation of the shelf edge commenced during the mid miocene to late pliocene the shelf edge prograded between 20 and 40 km during the mid pliocene to early pleistocene the barents sea and adjacent land areas were uplifted a fluvial glaciofluvial drainage system developed on the continental shelf resulting in pronounced erosion there and very high sedimentation rates on the continental margin during the last 0 8 ma several large glaciations on the barents sea shelf proper have resulted in overdeepened troughs and high sedimentation rates at the continental shelfbreak and on the continental slope the overall cenozoic erosion varies spatially as well as temporally in the svalbard area close to 3 km of rocks have been eroded since the oligocene the same amount or more was eroded from the stappen high during the palaeocene and early neogene in the south western areas during the eocene mid miocene erosion occurred along the margin in addition the loppa high and adjacent areas served as sediment source areas during the late pliocene and pleistoncene the average erosion in the south western barents sea amounted to about 600 m erosion was greater in the south east than to the west and north and was more extensive where the former glacial ice streams had flowed

birth and demise of a middle jurassic isolated shallow marine carbonate platform on a tilted fault block example from the southern iberian continental palaeomargin abstract subbetic middle jurassic oolitic limestones of the jabalcuz formation crop out in san cristobal hill near jaen city andalucia spain between hemipelagic limestone and marl successions the jabalcuz limestones range in facies from calcareous breccias and micritic limestones to white cross bedded oolitic limestones recent erosion has exhumed a jurassic isolated shallow water carbonate platform on the san cristobal hill this shallow platform developed on a tilted fault block an almost continuous laterally extensive outcrop reveals tectono sedimentary features distinctive of block tilting in the different margins of the fault block the studied sections represent various palaeogeographic positions in the ancient shallow water carbonate platform and basin transition this exceptional outcrop allows to decipher the triggering mechanisms of the birth evolution and drowning of this jurassic isolated shallow water carbonate platform two shallowing upward depositional sequences separated by flooding surfaces can be distinguished on two different sides of the fault block in the southeastern part of the outcrop proximal sections grade vertically from distal talus fault breccias with bivalve and serpulid buildup intercalations to white cross bedded oolitic limestones defining the lowermost depositional sequence upwards overlying a flooding surface the second sequence with oolitic limestones prograding over micritic deposits is recorded in the southwest oolitic peloidal and more distal micritic facies alternate with notable southeastern progradation of oolitic facies in the upper part of the section which represents the upper depositional sequence the top of this second depositional sequence is another flooding surface recorded by the sedimentation of marls with radiolarians from the overlying formation in the northwestern outcrops the two depositional sequences are also almost completely preserved and can be differentiated a 100 m thick succession composed of a basal slumped unit of micritic and peloidal limestones overlain by cross bedded oolitic limestones represents the lowermost sequence the superposition of a newer slumped unit of micritic and peloidal limestones on the cross bedded oolitic limestones defines the lower part of the uppermost depositional sequence finally the central sections are less thick and comprise a facies succession consisting almost entirely of oolitic limestones locally oolitic limestones often show cross bedding and prograding clinoforms the cross bedding has centrifugal directions around the perimeter outcrops of san cristobal hill whereas in the centre palaeocurrents are highly variable the sense of the palaeoslopes as deduced from slumps also fits with a centrifugal pattern finally in the southwestern outcrops the demise of the carbonate platform is marked by backstepping oolitic facies the presence of lumachelle facies and onlapping hemipelagic facies all the data point to the birth evolution and drowning of an isolated shallow water carbonate platform that developed on a tilted fault block the fault block tilting controlled the development of talus breccias in the southeastern part and of slumps in the northwest dipping hangingwall ramp in the shallowest environments produced by the tilting uppermost part of the fault block a shallow marine carbonate platform developed carbonate production mainly oolitic kept up with relative sea level fluctuations and extended the platform at least to the northwest southeast and southwest based on observable data finally tectonics and sea level fluctuations drowned this carbonate platform

cenozoic margin development and erosion of the barents sea core evidence from southwest of bjornoya abstract five stratigraphic boreholes at the western barents sea margin reveal an evolution from a palaeocene normal shelf setting to a complex late cenozoic offshore marginal marine system influenced by mass flows and finally a glacially influenced shelf environment palaeocene epeiric sea sedimentation was sourced by erosion at the stappen high earliest eocene extension associated with volcanism was followed by rapid subsidence of the vestbakken volcanic province which became filled by sediments from an uplifted stappen high by the middle eocene siliciclastic shelf sediments were deposited and the infill had reached a balance with subsidence tectonic movements at this time may have caused local uplift which restricted the ventilation of local basins west of the stappen high but marine conditions existed in the area until early oligocene times when subaerial exposure was caused by tectonic uplift and probably also a fall in eustatic sea level pronounced oligocene and pliocene unconformities reflect major events of uplift and erosion at the margin and abundant fossil reworking indicates erosion of the uplifted cretaceous and tertiary strata the oligocene erosion had its associated depocentre to the south and west of the study area and was less important regionally than the pliocene pleistocene phase the pliocene uplift first led to local erosion along the margin subsequent subsidence may initially have had a thermal component this was followed by extensive downwarping under the load of largescale deposition sourced by regional erosion in the barents shelf region an eocene volcanic phase was probably related to the initiation of seafloor spreading isotopically dated volcaniclastic intervals in one of the cores give evidence of a late pliocene volcanic phase this event was associated with local tectonic movements which may be part of a regional uplift in the western northwestern part of the barents sea glaciations caused by the neogene climatic deterioration became enhanced by uplift and this led to extensive regional glacial erosion the main depocentre was offset to the south by ice flow curving around the uplifted area

late wisconsin subglacial megaflood paths in alberta evidence of late wisconsin subglacial megafloods includes fields of giant flutings drumlins tunnel channels and scoured bedrock tracts scoured tracts are marked by channeled scabland water eroded depressions s forms and postglacial development of solonetzic saline clay pan soils on cretaceous bedrock belts of hummocky terrain and small zones of moraine plateaus are remnants left by incomplete sheet flood erosion of initial subglacial sediment later modified by ice pressing among multiple subglacial discharges the largest was the livingstone lake event which transmitted laurentide water from the northwest territories and northern saskatchewan through alberta to montana and the mississippi drainage this flood was augmented by cordilleran water relayed under valley glacier piedmonts coalescent with south western laurentide ice the short duration megaflood probably occurred within the longer time interval of 18 15 ka

faunal replacement in the early jurassic of northern chile implications for the evolution in mesozoic benthic shelf ecosystems abstract long term within habitat species replacement is either evolutionary or ecological in nature ecological replacement of dominant species by unrelated species which share essentially the same niche requirements is a very characteristic feature of early jurassic benthic shelf faunas from northern chile more than that an examination of the relevant literature reveals that the process was significant in mesozoic benthic shelf ecosystems on the whole it occurred among all important guilds and in a broad range of environmental subdivisions salinity controlled environments coarse grained and fine grained shallow shelf mid to outer shelf and oxygen controlled environments in contrast evolutionary replacement of dominant faunal elements appears to have been limited to restricted basins faunal replacement was the underlying process of several distinctive patterns in the temporal distribution of mesozoic benthic shelf faunas that is the evolutionary stability of dominant morphoptypes the widespread occurrence of parallel associations and the persistence of guild assemblages through time fluctuations of relative sea level are regarded as a substantial controlling factor of within habitat species replacement

ice sheets viewed from the ocean the contribution of marine science to understanding modern and past ice sheets over the last two decades marine science aided by technological advances in sediment coring geophysical imaging and remotely operated submersibles has played a major role in the investigation o

chronology of tertiary fan deposits off the western barents sea implications for the uplift and erosion history of the barents shelf abstract a combined biostratigraphic and seismic study was performed on three holes drilled in the western barents sea two holes penetrate the thick sedimentary wedge which forms a large fan located off a trough on the barents sea shelf the bjornoyrenna fan the study shows that the fan was built over a short time span in the late pliocene pleistocene mainly due to glacial erosion of the barents shelf region this contrasts earlier age assignments which concluded that fan deposition started in the oligocene the results have a major impact on the understanding of trough mouth fan formation and has important bearing on the history of the sedimentary basins of the barents shelf

new palaeontological investigations in the jurassic of western thailand abstract the paleontological investigations of the jurassic of western thailand districts of mae sot tak mae sot highway padaeng tak and ban mae kut luang zinc mines and umphang klo tho provide age constraints for the late indosinian orogeny the paleotethys closure and the timing of the marine jurassic inundation of sundaland the basal conglomerate of the jurassic is derived from the pelagic triassic mae sariang substratum stratigraphy microfacies and paleontology of the jurassic marine strata focus especially on ammonites bivalves large benthic foraminifera and algae among ammonites the tethyan catulloceras perisphinctoides gemmellaro marks the upper toarcian aalensis zone along the tak mae sot highway and riccardiceras longalvum vacek malladaites pertinax vacek abbasites sp and vacekia sp indicate middle aalenian to lowermost bajocian in the padaeng mine se of mae sot and klo tho umphang vacekia sp spinammatoceras schindewolfi linares and sandoval and malladaites vaceki linares and sandoval indicate middle aalenian to lowermost upper aalenian at ban mae kut luang ne of mae sot among foraminifers the large benthic foraminifer timidonella sarda bassoullet chabrier and fourcade in the western tethys is indicative for aalenian bajocian times as characterized in the section at the tak padaeng zinc mine and the klo tho formation near umphang the endemic foraminifer gutnicella kaempferi characterizes the pu khloe khi formation near umphang among bivalves shallow marine dominantly endemic fauna includes parvamussium donaiense mansuy and bositra ornate quenstedt from the toarcian to the early bajocian a consideration of the faunal affinity shows that the fauna is partly endemic with northern tethyan eurasian affinity

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

hardgrounds reworked concretion levels and condensed horizons in the jurassic of western india their significance for basin analysis jurassic sediments in the shallow pericratonic basins of kachchh and rajasthan western india exhibit numerous signs of reduced sedimentation omission erosion and in situ reworking in combination with synsedimentary cementation hardgrounds developed on carbonate shoals in the bathonian of rajasthan whilst reworked concretion levels are characteristic of offshore siliciclastic sediments of the callovian of kachchh a prominent marker horizon the oxfordian dhosa oolite member occurs throughout much of the kachchh sub basin and is a highly condensed unit characterized by hardgrounds intraformational cobbles reworked concretions stromatolitic iron crusts iron oncoids and shell lags hardgrounds reworked concretion levels and condensation horizons are interpreted as the preserved relicts of transgressive pulses such pulses were possibly controlled by eustatic rise of sea level of at least equal importance however was a tectonic control which is demonstrated by the presence of small neptunian dykes boulder beds derived from small submarine cliffs and rapid lateral facies and thickness changes in the dhosa oolite member these indications of extensional tectonics are thought to be connected to rifting and initial sea floor spreading between africa and india

iceberg deformation and erosion in soft sediments southeast norway abstract trenches in soft glaciomarine sediments have been excavated through two relict iceberg scours one upslope and the other horizontal and through one iceberg gravity crater the scours are 70 and 30 m wide respectively and are 1 m deep the grounding features were formed by current driven icebergs during flooding of previously emergent sea bottom 9200 yrs b p the clay beneath the scours and craters is deformed and small and larger scale folding small faults and thrusts joints fissures and collapsed lamination are found different scouring mechanisms apply for initial phases of upslope scouring and horizontal scouring at the start of upslope scouring the sediment mass is removed by thrusting and the depth of deformation within the subsoil is shallow in horizontal scouring two thirds of the scour depression is due to erosion and one third to deformation of the subsoil the deformation can in this case be detected down to four times the scour depth the current velocities are critical for survival of the plough ridges along the horizontal scour the plough ridges are missing because of current erosion during and after scouring

the significance of hiatus beds in shallow water mudstones an example from the middle jurassic of switzerland abstract limestone beds formed in nearly carbonate free shallow water mudstones by discontinuous sedimentation and erosion are called hiatus beds anaerobic oxidation of organic matter by microbes provided excess alkalinity inducing carbonate precipitation a multiphase history of such beds is documented from the swiss jurassic by several cementation and dissolution phases four cement types occur micrite as earliest cement 13c 10 to 20o oo stellate calcite between micrite cemented parts 13c 5 to 10o oo fibrous calcite cement in dissolution cavities 13c 30o oo and blocky calcite in remaining pores 13c 5o oo except for the late blocky cement all cements contain pyrite indicating carbonate precipitation within the sulfate reduction zone after early cementation by micrite the beds moved relatively upwards into a shallower geochemical zone and some even to the seafloor because of erosion cavities formed during reburial by dissolution in the upper part of the sulfate reduction zone and in the upper part of the methanogenic zone strongly reduced sedimentation rates provided the requisite stable geochemical conditions for at least several thousands of years which permitted precipitation and dissolution of carbonate by biochemical processes and diffusion this happened on short lived swells caused by differential subsidence and rotation along listric faults when basement structures became reactivated during the extensional stress regime from opening of the tethys during the jurassic and cretaceous breakup of pangea the shelf area increased and differential subsidence on these newly formed shelves was the main factor responsible for the observed post paleozoic maximum in hiatus beds and hiatus concretions

postrift deltaic sedimentation in western kachchh basin insights from ichnology and sedimentology abstract the postrift stage in the pericratonic kachchh rift basin of western india is represented by a thick sequence of a diachronous megadelta system the deposition of this deltaic sequence was initiated during the mid kimmeridgian and ended in the albian the sedimentation was interrupted by two transgressive events demarcating three subcycles within the megadelta system the present study addresses the older mid kimmeridgian to tithonian jhuran delta an attempt is made here to delineate the nature of the jhuran delta using the ichnological and sedimentological parameters the jhuran delta which consists of 14 lithofacies is grouped into seven lithofacies associations corresponding to the prodelta subaqueous gravity flow delta front distributary channel distributary mouth bar and shoreface depositional environments along with a transgressive unit overlapping the lower delta of the megadelta system three distinct stages of deltaic evolution are delineated along with the fourth stage of transgression and delta destruction the prodelta environment of stage i is characterized by moderate ichnodiversity represented by nine recurring ichnotaxa suggesting alternating brackish and fully saline water conditions which indicate river dominated deltaic sedimentation stage ii shows a marked increase in the influence of river fresh water water as indicated by a submarine mass failure that includes debris flow chaotic and contorted structures sediment gravity failure and water escape structures and suggesting a higher rate of sedimentation ichnologically this phase indicates low ichnodiversity with sporadic occurrences of ophiomorpha and palaeophycus stage iii indicates the mixed dominance of river and wave processes sediments deposited in the delta front environment show moderate ichnodiversity with nine ichnotaxa the distributary mouth bar environment comprises 6 recurring ichnotaxa including the ichnoassemblages of both river and marine wave environments integrated ichnological data suggest deposition in a mixed environment the jhuran delta stage ended with a marine transgressive event and reworking of the deltaic sands which were overlain by a thick shoreface deposit thus the upper jurassic jhuran delta represents a river dominated wave influenced delta

sinking slabs below fossil subduction zones abstract the fate of sinking lithospheric slabs following the cessation of subduction is examined using a two dimensional numerical model of mantle convection the model incorporates rigidly moving oceanic plates which recycle through the underlying viscous mantle and rigid continental plates which cannot be subducted due to their inherent buoyancy the model is used to study the effects of the cessation of subduction due to the accretion of a 4000 km wide block of continental crust to the margin of a large stationary continent e g the india asia collision we model a continental block representative of greater india that is carried along with an oceanic plate towards a subduction zone at the leading edge of a much larger stationary continent which represents asia prior to continental collision subducted oceanic plate material under rides the margin of the larger continent for several hundred kilometres before peeling away from the surface boundary layer and descending into the mantle as a cold narrow slab consequently once a moving continental block arrives at the continental margin and closes over the original subduction zone the surface location of the continental suture lies several hundred kilometres seaward of the location of the cold remnant of the sinking slab the ongoing convective flow in the subcontinental mantle adjusts to accommodate the change in mechanical boundary condition at the upper surface a step increase in viscosity at 660 km depth slows the rate of slab descent substantially but cannot account for mid mantle thermal anomalies attributed to subduction zones that became extinct more than 140 my ago the horizontal displacement of the slab remnants relative to the continental crustal suture depends on the relative motion of the fossil plate boundary at the surface and the underlying mantle over riding of an intra oceanic subduction zone or the indenting of a smaller subcontinent into a larger continental mass can cause the tomographically observed cold anomalies to be displaced laterally by thousands of kilometers from the location of the former converging plate boundary

the subglacial geomorphology of southeast alberta evidence for subglacial meltwater erosion a coherent pattern of landforms in southeast alberta forms a subglacial landform continuum scoured bedrock tracts flutes transverse bed forms and tunnel channels in this continuum are inferred to be products of erosion by turbulent subglacial meltwater flows beneath the laurentide ice sheet bedrock and glacigenic sediment are truncated by an erosional surface flutes and extensive boulder lags across the truncation surface strongly suggest erosion by high velocity turbulent flows tunnel channels dissect the erosion surface and record channelization of earlier sheet flows convex longitudinal profiles of channels indicate subglacial meltwater flow northeast southwest trending transverse bed forms are superimposed on the preglacial divide and may be either glaciotectonic ridges or fluvial bed forms landforms reflect the dominance of erosion in the subglacial environment likely by catastrophic meltwater flows of the livingstone lake megaflood event the subglacial meltwater hypothesis accounts for e

erosion of bedrock by subglacial meltwater georgian bay ontario a regional view a spectacular series of sculpted erosional forms s forms is mapped and described from a 70 km wide area along the shore of georgian bay ontario which except for a scattered boulder lag has been swept clean of sediment a great variety of sculpted forms is described and illustrated and grouped into three classes transverse longitudinal and nondirectional forms transverse forms comprise transverse troughs muschelbruche sichelwannen and comma forms longitudinal forms comprise spindle flutes cavettos and furrows and nondirectional forms consist of undulating surfaces and potholes transverse forms are preferentially located on stoss slopes and longitudinal forms on lee slopes of rock rises undulating nondirectional forms are found on distal slopes and potholes at major breaks in slope this correlation of form and bed topography suggests that relief exerts considerable control on both form and location form geometry is also inferred to be related to coherent flow structures and their int

ice sheet numerical modeling and marine geophysical measurements of glacier derived sedimentation on the eurasian arctic continental margins long range side scan sonar images of the barents sea continental margin have been analyzed in conjunction with results from previous geophysical investigations to determine a qualitative model for sedimentation over the bear island and storfjorden trough mouth fans these data indicate that gravity driven debris flows are major processes in the downslope transport of glacial material delivered to the shelf break when ice sheets advanced across the continental shelf during late weichselian time 4000 km 3 of sediments were deposited over the bear island fan 280 000 km 2 while 700 km 3 of sediments were deposited over the storfjorden fan 40 000 km 2 a numerical ice sheet model including sediment deformation and transport beneath ice streams reconstructs the glacial conditions required to transport large volumes of sediment to the late weichselian eurasian continental margin model results indicate that glaciation of the eurasian high arctic occurred after 28 ka and that ice streams within bathymetric troughs were active by ca 25 ka the maximum ice sheet thickness over the barents sea was about 1400 m there was a secondary dome 1 0 13 cm yr 1 averaged over the fan the rate was 6 cm yr 1 equivalent to 0 6 cm yr 1 over the fan over the storfjorden trough mouth the modeled sediment volume at the continental margin of the bear island and storfjorden troughs agrees well with the volumes of late weichselian sediment inferred from seismic records from these large prograding submarine fans sensitivity experiments show that adjustments to model environmental inputs do not significantly affect the results

trace fossils in the mesozoic sediments of kachchh western india abstract the mesozoic succession of kachchh western india is a classic example of the value of trace fossils in the interpretaion of depositional sequences because this sequence has traditionally been referred to as gondwana and because the previous emphasis has been on body fossils a misconception has been established concerning this fascinating nearshore sequence preliminary investigations of generally well preserved physical and biogenic structures in the mesozoic rocks of kachchh reveal that the entire succession represents deposition in a shallow marine coastal setting i e lagoons embayments tidal flats estuarine channels shoals and shallow shelf the patcham formation shows poor preservation of trace fossils due to lack of appropriate lithologies the chari formation contains a rich ichnofauna of special interest are horizons of bioconglomerates showing reworked fillings of thalassinoides burrows and pholad borings the katrol formation exhibits a diversified and well preserved assemblage of burrows including an unusual feeding burrow here recorded for the first time the umia formation though devoid of body fossils contains a rich and varied assemblage of ichnofossils the uppermost part of this unit the bhuj member contains several thick horizons of densely rhizocorallium bioturbated sand which supports a marine setting contrary to the general belief of its fluvial origin

depositional environments and diagenesis of the kuldhar and keera dome carbonates late bathonian early callovian of western india abstract this paper describes 11 microfacies types in late bathonian early callovian carbonates of the kuldhar member of the jaisalmer formation rajasthan and the keera golden oolite member of the chari formation kachchh mainland western india the different microfacies associations reported in this study reflect an ideal shallowing upward sequence representing a system of bioclastic bars developed on the lower ramp evolving into an oolitic bar to bank system separating restricted lagoonal from lower ramp environment four main types of cements i e bladed fibrous syntaxial overgrowth and blocky cement characterized in a few cases by ferroan calcite and anhydrite ii occur in these carbonates the study also reveals that chemical compaction followed the two phases of early mechanical compaction that largely governed porosity of these limestones however micritization and neomorphism also contributed significantly in this respect diagenetic signatures in these carbonates suggest that marine phreatic and fresh water phreatic environments dominated but deep burial diagenesis also played its role in shaping these rocks the early and late diagenetic changes have been controlled by the depositional facies evolving in a basin riddled with rifting in an extensional tectonic regime forcing regional scale sea level fluctuations

jurassic sedimentary cycles and eustatic sea level changes in southern tibet abstract the marine jurassic sequence in southern tibet is well exposed has an abundant fossil record and provides a good basis for the study of paleoeustasy from measured sections nine lhtho facies representing four broad sedimentary environments inner and outer shelves slope and bathyal can be recognised their vertical ranges show that shelf deposits are mainly present in the lower and middle jurassic whilst outer shelf slope and bathyal environments dominate in the middle and upper jurassic on the basis of these after comparison of the two main approaches used in analysing sea level movements i e the exxon eustatic curve and eustatic cycles jurassic eustatic sea level changes in southern tibet are described the resulting curve is seen to correspond closely with earlier published global curves the cause of these sea level changes is thought to lie in the breakup of gondawanaland and the northwards drift of the indian subcontinent and associated microplates

ichnology of an eocene shallow marine passive margin condensed section eastern gulf coastal plain alabama u s a abstract exposures of the eocene tallahatta formation in southern alabama u s a provided the opportunity to document the ichnologic character of a highly condensed passive margin transgressive systems tract and its two component parasequences the studied succession is dominated by variably glauconitic fossiliferous muddy sands deposited in shallow marine shelf settings thorough bioturbation and abundance of mud indicate quiet background conditions whereas admixed sand and localized scour features indicate periodic influence by bottom currents parasequences delineated based on vertical trends in glauconite abundance are bounded at their bases by flooding surfaces marked by thalassinoides dominated firmground ichnofabrics but internally host moderately diverse cruziana ichnofacies assemblages recurring softground ichnofossils include asterosoma chondrites diopatrichnus ophiomorpha planolites rosselia teichichnus thalassinoides and enigmatic composite structures the distributions and abundances of which vary within and between parasequences increasing prominence of diopatrichnus and rosselia towards parasequence tops reflects organismal responses to environmental changes associated with shallowing and or enhanced preservation potential of shallow tier structures in response to increased sedimentation rates maximum sediment starvation during deposition of the uppermost parasequence is reflected by peaks in burrow density softground ichnofossil diversity and concentrations of entobia bored shells and teredolites bored logs enigmatic composite burrows and common thalassinoides with linings and or meniscate backfills are ubiquitous and may be diagnostic of sediment starvation and prolonged habitation of slowly accreting substrates

signature of ice streaming in bjornoyrenna polar north atlantic through the pleistocene and implications for ice stream dynamics the geomorphology of palaeo ice stream beds and the internal structure of underlying tills can provide important information about the subglacial conditions during periods of fast flow and quiescence this paper presents observations from three dimensional seismic data revealing the geomorphology of buried beds of the bjornoyrenna bear island trough ice stream the main drainage outlet of the former barents sea ice sheet repeated changes in ice dynamics are inferred from the observed successions of geomorphic features megablocks aligned in long chains parallel to inferred ice stream flowlines and forming dipping plates that are thrust one on top of another are taken as evidence for conditions of compressive ice flow mega scale glacial lineations msgl and pull apart of underlying sediment blocks suggest extensional flow the observed pattern of megablocks and rafts overprinted by msgl indicates a change in ice dynamics from a compressional to an extensional flow regime till stiffening due to subglacial freezing is the favoured mechanism for creating switches in sub ice stream conditions the observed pattern of geomorphic features indicates that periods of slowdown or quiescence were commonly followed by reactivation and fast flow during several glaciations suggesting that this may be a common behaviour of marine ice streams

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

the last glacial maximum of svalbard and the barents sea area ice sheet extent and configuration abstract the timing extent and configuration of the late weichselian barents ice sheet has been debated for several decades this debate has arisen largely because of the limited or conflicting field evidence on which most models have been based in particular reconstruction of the marine parts of the former barents ice sheet has been controversial this paper aims to review the geological observations and interpretations regarding the size and timing of the late weichselian ice sheet combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour sub glacial till with overlying glacimarine deposits dated to the late weichselian is found over most of the barents sea floor and the continental shelf west of svalbard glacially induced debris flow deposits on the large bjonoya and isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation isobase maps show a centre of post glacial uplift in the north central barents sea and glaciological and isostatic modelling suggest that the ice sheet was 2000 3000 m thick in this area the ice sheet was confluent with ice over the kara sea but the interaction between the barents and kara ice sheets is not yet fully understood the deglaciation of the barents ice sheet started ca 15 ka probably by calving within the deeper troughs by 12 ka most of the central barents sea was ice free and ice remained over the svalbard franz josef land and novaja zemlya archipelagos and adjacent shallow shelf areas the coasts and fjords of these islands were ice free by 10 ka

hydrocarbon plumbing systems above the snohvit gas field structural control and implications for thermogenic methane leakage in the hammerfest basin sw barents sea abstract based on the analysis of the high resolution 3d seismic data from the sw barents sea we study the hydrocarbon plumbing system above the snohvit and albatross gas field to investigate the geo morphological manifestation and the dynamics of leakage from the reservoir fluid and gas escape to the seafloor is manifested in this area as mega pockmarks 1 2 km wide large pockmarks

interpretation of late ordovician glaciogenic reservoirs from 3 d seismic data an example from the murzuq basin libya understanding the recessional behaviour of ancient pre cenozoic ice sheets based on seismic reflection studies is generally difficult through scarcity of data in north africa however hydrocarbon exploration has produced high quality seismic reflection datasets that permit an analysis of the morphology and internal sedimentary architecture of incisions of late ordovician age related to the hirnantian glaciation analysis of a high resolution 3 d seismic dataset covering a small area in western libya the n murzuq basin reveals a sharply defined wnw ese oriented palaeo escarpment with a higher cliff forming western margin and a lower basin forming eastern margin the palaeo escarpment defines the western flank of a sub basin extending up to 60 km in width known as the awbari trough the escarpment and the trough are interpreted as the morphological expression of a major unconformity dividing pre glacial sediments below from late ordovician hirnantian glacially related sediments above two hypotheses are considered for the origins of both the escarpment and the awbari trough 1 as a tectonic feature such as a half graben that was active during sedimentation and 2 a glacially related palaeotopography with the latter interpretation preferred owing to the lack of evidence for syn sedimentary fault activity the width of the awbari trough compares to the large scale cross shelf troughs in modern high latitude settings such as the barents shelf produced by ice streams the awbari trough was progressively filled in by gravity flow deposits throughout the course of the glaciation until the initial incision became filled in with sediments during an overall glacial retreat phase and ceased to influence sedimentation patterns glacial re advance across the basin produced a second unconformity observed in seismic data above this unconformity meltwater processes incised a shallow 20 m and wide 5 km subglacial tunnel valley stabilization of the ice front prior to its ultimate retreat resulted in the deposition of a delta complex prior to the early silurian transgression

fluted moraine formation and till genesis below a temperate valley glacier slettmarkbreen jotunheimen southern norway clast fabric and morphological data have been used to determine the origin of fluted subglacial tills exposed by recent retreat of the slettmarkbreen glacier norway a new method for the interpretation of clast fabric data allows aspects of the strain and depositional history of the till to be reconstructed the till formed by a combination of lodgement and subsole deformation by slip along discrete shear planes lodgement was dominant for the larger size fractions 125 mm while the smaller material was more susceptible to deformation the fluted till surface reflects the tendency for the till matrix to deform into regions of low confining pressure in the lee of lodged boulders downglacier components of till flow are thought to have resulted in significant sediment transfer towards the margin

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

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

sediment distribution and sea floor morphology of storbanken implications for the glacial history of the northern barents sea acoustical sparker 3 5 khz and side scan sonar and sedimentological data from a local study on storbanken in the northern barents sea support the concept of a late weichselian ice sheet covering most of the barents sea during a major halt in the retreat of the ice sheet locally thicker 38 m accumulations of ice proximal glaciomarine sediments were deposited after which rapid retreat took place sea floor morphology indicates that the retreat across storbanken most likely took place without surging or climatically controlled oscillations intense iceberg ploughing characterizes the sea floor down to water depths of 210 220 m most of this is relict but occasional gouges in the shallowest regions may have had a more recent origin the apparent lower limit of ploughing interpreted in terms of relative sea level indicates a rather moderate isostatic depression this probably resulted from a thin ice sheet fed from several ice source areas depth of the plough marks is largely dependent on thicknes

petrofacies provenance and diagenesis of the dhosa sandstone member chari formation at ler kachchh sub basin western india abstract the sandstones of the dhosa sandstone member of late callovian and early oxfordian age exposed at ler have been analyzed for their petrofacies provenance tectonic setting and diagenetic history these sandstones are fine to medium grained and poorly to well sorted the constituent mineral grains are subangular to subrounded these sandstones were derived from a mixed provenance including granites granite gneisses low and high grade metamorphic and some basic rocks of the aravalli range and nagarparkar massif the petrofacies analysis reveals that these sandstones belong to the continental block recycled orogen and rifted continental margin tectonic regime the imprints of early and deep burial diagenesis of these sandstones include different stages of compaction cementation change in crystal boundaries cement cement boundaries chertification and neomorphism the sequence of cementation includes precipitation of calcite and its subsequent replacement by fe calcite and silica cements the typical intermediate burial 2 3 km depth diagenetic signatures of these sandstones are reflected in the formation of suture and straight line boundaries and triple junctions with straight line boundaries the depositional environment relatively low energy environment that was below storm wave base but subjected to gentle currents of the dhosa sandstone member controlled the early diagenesis which in turn influenced the burial diagenesis of these sandstones

postmortem transport and resedimentation of foraminiferal tests relations to cyclical changes of foraminiferal assemblages abstract cyclical changes in microfossil mainly foraminiferal assemblages were analysed for sixteen boreholes from three stratigraphical levels in the lower and middle miocene of the central paratethys the following characteristics of assemblages were quantified and used for interpretation of cyclical changes in assemblages 1 abundance of foraminifers calcareous nannoplankton sponge spicules and diatoms 2 similarity diversity and epifauna infauna ratio of benthonic foraminiferal assemblages 3 planktic benthic ratio of foraminiferal assemblages the palaeoecology mainly palaeobathymetry fluctuations were interpreted from the species composition of assemblages values of the mentioned quantitative characteristics as well as palaeoecological interpretations may be influenced by postmortem transport and resedimentation of foraminiferal tests therefore prior to the interpretation of cyclical changes of quantitative characteristics the studied sections were classified on the basis of the intensity of taphonomical changes in foraminiferal assemblages three different categories of sections were obtained for every category those quantitative characteristics of foraminiferal assemblages were chosen which reflect cyclical changes most efficiently 1 cyclical changes of abundance of foraminifers calcareous nannoplankton and sponge spicules as well as the fluctuations in palaeobathymetry for sections dominated by indigenous foraminifers 2 percentage of indigenous suspension transported bedload transported and reworked foraminiferal tests and changes in the abundance of indigenous tests for sections dominated by transported tests 3 different modes of test preservation used for the identification of a cycle boundary for sections with only transported or reworked tests the distinguished cycles were interpreted predominantly as manifestations of relative sea level changes if comparable data exist from other paratethys regions the determined cycles can be correlated with the other basins

lower palaeozoic unconformities in an intracratonic platform setting glacial erosion versus tectonics in the eastern murzuq basin southern libya the stratigraphic record of the eastern murzuq basin has been importantly influenced by deformation resulting in angular and or deeply erosional unconformities though the overall context is intracratonic major transgressive events and the ordovician glaciation are nevertheless documented allowing the delineation of tectonic eustasy or climate driven unconformities lower palaeozoic key events and related unconformities that characterize the north gondwana platform have therefore a signature in the eastern murzuq basin the basement cover unconformity also known as the infra tassilian surface truncates all the deformed and metamorphosed lower cambrian and older rocks above is a middle cambrian to lower ordovician megasequence murizidie and hasawnah fms which is in turn truncated by an intra ordovician angular unconformity this megasequence is unconformably overlain by a middle ordovician hawaz fm to silurian tanzzuft and akakus fms megasequence which includes the upper ordovician glaciogenic unit mamuniyat fm bounded at the base by a polygenic glacial erosion surface showing corrugated glacial lineations tillites and glaciotectonic structures the middle ordovician to silurian megasequence is finally truncated by a base devonian angular unconformity overlain by fluvial sandstones regarding the possibility that those fluvial deposits may be as younger as late devonian in the eastern murzuq basin based on palaeoflora the so called caledonian unconformity might be here a much younger mid eifelian surface and the occurrence of the lower devonian tadrart fm is questioned the upper ordovician glacial erosion surface which is sometimes referred to as the taconic unconformity usually truncates middle ordovician strata in the murzuq basin but reaches significantly deeper stratigraphic levels in places that have been previously involved in the intra ordovician deformation event in the murizidie southeastern murzuq basin the infra tassilian surface the intra ordovician unconformity and the upper ordovician glacial erosion surface amalgamate together here an estimate of the glacial erosion depth cannot be derived from the stratigraphic hiatus beneath the glacial incision the main part of which relate to the intra ordovician tectonic event the upper ordovician climate related glacial erosion surface is not a valid unconformity for a sequence hierarchy framework of the lower palaeozoic although it presents most of the physical attributes of tectonic driven unconformities

trypanites ichnofacies palaeoenvironmental and tectonic implications a case study from the miocene disconformity at foz da fonte lower tagus basin portugal abstract a well preserved bioeroded surface occurs at the unconformity separating cretaceous limestones and lower miocene sediments outcropping on the western coast of the peninsula of setubal central west portugal the ichnoassemblage present in this bioeroded surface is herein assigned to the trypanites ichnofacies the preservation characteristics of the borings reflect several episodes of encrustation boring and physical erosion the erosional truncation of bioerosive structures and the predominant preservation of the largest borings gastrochaenolites isp in the ichnocoenoses are herein related with repeated phases of bioerosion and physical abrasion occurred during an early miocene transgressive pulse the recognition of this bioeroded transgressive surface also allowed confirming the presence at that time of an emergent topographic relief related to salt domes formed earlier probably already during palaeogene times

glacial geology of outer bjornoyrenna southwestern barents sea the upper cenozoic glacigenic succession in outer bjornoyrenna bear island trough southwestern barents sea is investigated utilizing data from six shallow boreholes 143 m below sea bed and seismic profiling overdeepened troughs in the lowermost part of a large plio pleistocene wedge at the shelf margin are interpreted as glacial erosion forms this suggests that the overlying succession which basinward attains a thickness of several km was deposited during a period with glaciations large scale possible sand ridges in the stratigraphic lower part of this succession are confined to two north south trending zones parallel to the present shelf break they probably formed in a continental shelf coastal environment with exceptionally high sediment supply and fluctuating relative sea level related to glaciations a core from a channel fill in the lower part of the succession consists of possibly glaciofluvial gravelly sand intercalated with till most of the other cores are dominated by middle and upper pleistocene muddy massive partly fissile diamictons interpreted to be mainly tills undrained shear strength of these cores ranges from about 20 kn m 2 to more than 300 kn m 2 and both underconsolidated intervals compared to the present burial depth are found an underconsolidated interval comprising eemian interglacial biourbated marine sediments overlain by laminated weichselian glaciomarine sediments on the outher shelf is covered by 50 100 m of muddy diamicton this diamicton is suggested to be mainly till deposited by a late weichselian ice sheet which was grounded to more than 500 m below present sea level earlier weichselian ice expansions did not reach the outer shelf based on the stratigraphy in the shallow cores and seismic interpretation we suggest that there have been five major expansions of grounded ice to the shelf break since ca 440 ka the present study suggests that glacial erosion was a major process in the late cenozoic denudation of the barents sea and in large areas perhaps as much as 200 250 m of preexisting strata could have been eroded by glaciers since about 440 ka

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

a highly mobile laurentide ice sheet revealed by satellite images of glacial lineations satellite images of the north american continent reveal previously unrecognized patterns of crossing drift lineations reflecting unexpected shifts of centres of mass of the laurentide ice sheet throughout the last glacial cycle such shifts must must have been associated with major global atmospheric circulation changes

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

crinoid biofacies in upper carboniferous cyclothems midcontinent north america faunal tracking and the role of regional processes in biofacies recurrence abstract coordinated stasis is a pattern of long term multispecies evolutionary and ecological stability bounded by rapid turnover events one class of models proposed to explain the paleoecological pattern of biofacies stability typified by ecological locking states that biotas within habitats become integrated into ecological units that through population and community level processes rebound and persist through short term disturbances this high frequency community resilience allows the units to persist through geologic time tracking their preferred habitats during transgressions and regressions because species are tightly woven into the fabric of the ecosystem there is little opportunity for speciation this also buffers them against extinction this ecological locking by ecosystem homeostatic processes produces long intervals of regionally stable biofacies in the fossil record in these models the primary structuring mechanisms are at the local community level controlled by species autecology species interactions and local disturbance regime an opposing class of models states that species are fundamentally independent and that species interactions are not strong nor spatio temporally persistent enough to forge communities into integrated units with long term persistence community recurrence would be expected as long as the various habitat types recur in time and space species autecologies remain stable the pool of available species remains intact and the recruitment of species into local habitats is not interrupted the focus of these models is dominantly at the regional level controlled by biogeographic history and dispersal among as well as within communities the results of this study of crinoids from the upper carboniferous lansing group of midcontinent north america show that they are distributed among five recurrent paleocommunity types or biofacies which are generally arrayed along an onshore offshore gradient two of these biofacies are restricted to the offshore dysaerobic horizons of the most extensive cyclothem in the group the other three biofacies recur consistently among the cycles however this repeated pattern includes a regionally distributed offshore biofacies unique to late transgressive deposits that is not found in analogous regressive deposits while the distribution of the two shoreward biofacies is consistent with faunal tracking the recurrence of a biofacies unique to late transgressive horizons is not consistent with an integrated paleocommunity that tracks shifting habitats through transgression and regression these results favor the alternative models namely that biofacies develop in place via dispersal from a persistent species pool in response to prevailing environmental conditions the recurrence of apparently ephemeral biofacies through time underscores the importance of regional processes in controlling local paleocommunity composition the establishment of refuges or source populations during environmental bottlenecks i e lowstands is critical to maintaining the regional species pool through time for continued recruitment into local sink paleocommunities during more amenable times i e highstands metapopulation dynamics among habitats are equally important in maintaining species within a region through time conflicting observations of stochastic individualistic and deterministic integrated behaviors of the same ecological systems probably result from differences in the scales of analyses and therefore the processes being studied

large scale effects of subglacial meltwater flow in the southern slave province northwest territories canada broad corridors in the southern slave province of the northwest territories are marked by meltwater scoured bedrock irregular and transverse gravel ridges gravel bars crag and tail features tails formed of gravel drumlins boulder lags potholes plunge pools meltwater sculpted slopes in some cases defining till plateaus and eskers most of the above features can either be attributed to the subglacial erosion of till by high velocity turbulent meltwater under high pressures and or meltwater transport and deposition of the eroded material potholes plunge pools and meltwater sculpted slopes developed in unconsolidated deposits have received little attention in the literature although they are the equivalent of similar features in bedrock that have had their origin attributed to subglacial meltwater erosion in the case of inverted plunge pools eroded materials including boulders have been transported upwards by meltwater some tens of metres during their formation features and deposits o

regional correlations across the internides externides front northwestern rif belt morocco during the late cretaceous early burdigalian times palaeogeographical and palaeotectonic implications

glacigenic sediments on a passive continental margin as exemplified by the barents sea abstract reflection seismics data borehole data and gravity cores have been used to map the sedimentary facies of the epicontinental southwestern barents sea its continental margin and adjacent coastal areas an upper unconformity with a glacially eroded morphology extends over most of the continental shelf up to 300 m of stratiform glacigenic sediments overlie this unconformity these sediments can be grouped into seismic units which are separated by smooth or irregular erosional surfaces each sequence may be up to 150 m thick normally with a lateral extent of 100 300 km three dominant seismic signatures may be discerned semi transparent stratified and chaotic reflection patterns these sediments are partly glacifluvial in origin but on the whole they represent more or less tectonized glacimarine deposits the deeper troughs on the continental shelf contain an undeformed postglacial glacimarine marine trough fill the greatest thickness up to 1000 m of glacigenic sediments occurs at the shelf break and below the upper slope the depocentres are situated at trough mouth fans the sediments comprise several prograding sequences with a complex sigmoid oblique character indicating alternating upbuilding and depositional bypass erosion in the topset segment small and large scale slide scars are observed on the upper slope and debris lobes on the lower slope a marked progradation seems to have occurred during the plio pleistocene glacial periods this progradation also resulted in an unstable slope with various types of sediment gravity flows currents flowing along the slope were established during interglacials and gullying by cold dense shelf water and downslope transport occurred maximum net sedimentation rates are 0 2 m ka continental slope 0 4 m ka shelf break 0 1 m ka shelf stratiform diamictons 1 m ka shelf trough fills and 60 m ka fjord trough fills

subglacial processes of the scandinavian ice sheet in fennoscandia inferred from flow parallel features and lithostratigraphy abstract subglacial processes of the last scandinavian ice sheet in fennoscandia were investigated on two different scales a detailed case study in southwestern finland and a generalized study in the central parts of the ice sheet previously reconstructed time transgressive glacial flow patterns were correlated with different types of glacial flow parallel features and lithostratigraphic units the comparison of orientations of each flow parallel feature with relative ages of different flow patterns enabled estimations of relative distances of the orientation generating processes in relation to the receding ice margin this method was also used to infer sedimentary environments of each lithostratigraphic facies identified generalized lithostratigraphic sequences were compiled in fennoscandia using sections described previously in areas of ice streams a sandy till showing mature deformation structures forms till sheets drumlins and some ribbed moraines the facies is overlain by occasional glaciofluvial deposits and partly washed deformation till both indicating abundant excess water at the ice bed interface in interlobate areas glaciofluvial material is under and overlain by a silty till showing ductile deformation structures in places uppermost thin clayey till interpreted to be a subglacial melt out till mantles underlying till and subglacial glaciofluvial deposits the characteristics of different units are controlled by ice flow velocities subglacial hydrology and deformation type of the substratum the time transgressive origin of till beds and intervening washed sediment as well as divergent ice flow patterns is emphasized ice flow was concentrated in streams which generated marginal fan shaped lobes interstream areas of low basal velocities and melting rates were left between adjacent ice streams in areas of ice streams fast basal ice flow velocities continuously generated heat and meltwater which flowed at first in the sediment and closer to the margin also in thin discontinuous sheets at the ice bed interface excess water may have subsequently formed a linked cavity system and channelized to a tunnel network initiating esker deposition or incision of tunnel channels most processes operated continuously during deglaciation with spatial and temporal differences in their activity the mode of subglacial drainage changed periodically during deglaciation and was probably controlled by the volume of subglacial meltwater available in some periods sheet flow of basal water deposited major marginal complexes and subsequently tunnel networks were re established esker pattern and sedimentation rates of proglacial varved clays indicate that tunnel drainage of subglacial water was partly episodic

late cenozoic environments in the barents sea we examine the paleoceanography and paleogeography of the barents sea during the late cenozoic glacial regime by seismostratigraphy and core analysis during the smaller glaciations which probably dominated the first period of the glaciogenic regime approximately 2 5 0 8 ma glaciomarine processes with sediment influx from the adjacent mainland prevailed the barents sea has been covered by grounded ice sheets several five to 10 times during the late cenozoic we speculate that these glaciations occurred during the last 0 8 ma during these larger glaciations the margin of the ice sheet expanded to the shelf edge and the continental shelf break and slope acted as a depocenter and prograded rapidly frequent sediment gravity flows accumulated on the lower continental slope during interglacials the barents sea was converted to a starved continental margin most of the barents sea was glaciated during the maximum of the last glaciation 19 16 ka a two stepped deglaciation 16 to 13 ka and 13 to 10 ka occurred incipient atlantic water reached the western areas about 13 ka and totally replaced the arctic water by 10 ka these paleoceanographic events were delayed in the eastern barents sea

preservation of autochthonous shell beds by positive feedback between increased hardpart input rates and increased sedimentation rates abstract the preservation of nonrapidly buried autochthonous shell concentrations with noncementing epifaunal animals in life position presents a taphonomic dilemma if in fact an increase in shelliness is driven by a decrease in sedimentation rate a 150 cm thick densely packed shell bed with brachiopods from the lower jurassic of morocco shows lower levels of postmortem alteration than shell poor beds indicating that its formation is primarily governed by variations in hardpart input rates varying dominance and size structure of the main shell producer brachiopod zeilleria rehmanni indicate that its increased population density was the main trigger in the shell bed formation thinner and less common microbial crusts in the shell bed than in shell poor beds indicate that higher shelliness is not due to lack of sediment on the basis of actualistic data from modern mussel and oyster shell beds the suspension feeding of a high density population leads to high biodeposition rates through production of

approaching trophic structure in late jurassic neritic shelves a western tethys example from southern iberia the palaeoenvironmental conditions and trophic structure of a mid outer neritic biota microfossils mainly forams and macroinvertebrate assemblages have been approached in middle oxfordian lowermost kimmeridgian deposits from the prebetic zone betic cordillera in south eastern spain according to relationships between fossil assemblages and lithofacies a general seaward trend is identified which displays decreasing sedimentation rates and nutrient inputs but increasing substrate consistency and presumably depth midshelf terrigenous rich deposits in the external prebetic relate to the highest sedimentation rates and nutrient availability these two parameters correlate with the highest content in vagile benthic calcareous perforate epifaunal forams as well as with potentially deep infaunal forams and infaunal macroinvertebrates outer shelf lumpy deposits in the internal prebetic show the lowest sedimentation rates and nutrient availability and the highest records for macro micro nektonics and planktics in contrast vagile benthic calcareous perforate epifaunal and potentially deep infaunal forams are scarcer in the midshelf environments colonial encrusting forams benthic microbial communities and sessile benthic macro invertebrates increase from the middle to outer shelf trophic analysis structuring through the integration of benthic microbial communities foraminiferal and macroinvertebrate fossil assemblages makes it possible to interpret a a trophic level frame composed of producers and primary and secondary consumers b a main trophic group differentiation in suspension feeders detritus feeders browsers grazers carnivores and scavengers c a preliminary approach to food chain structure supported by suspension feeders deposit feeders and predators active prey selection carnivores and d a food pyramid model which takes into account both recorded fossils and envisaged i e ecologically inferred organisms

sandwaves and sand transport on the barents sea continental slope offshore northern norway we integrate morphological geological and geophysical observations with oceanographic measurements and modelling results to interpret the processes behind the origin and evolution of sandwaves on the upper continental slope of the southwestern barents sea seven sandwave fields covering c 130 km2 and with a volume of c 72 106 m3 occur in water depths of c 475 800 m individual sandwaves reach heights up to 6 m the sandwaves are sinusoidal with asymmetric stoss lee side relationships and time lapse multibeam bathymetry analysis indicates that some sandwaves have migrated up to 10 m towards the nnw over a 4 year time period this contour current parallel migration is counteracted by currents in several other directions and the sand unit is thus not a simple contourite measurements show prominent diurnal period oscillations and clear spring neap variations of current direction and speed with along slope and cross slope current velocities up to 75 cm s 1 and 65 cm s 1 respectively numerical ocean modelling results produce eddies travelling along the slope positionally stable daily recurring vortices and bottom current velocity up to 100 cm s 1 in the sandwave fields sandwave migration towards the se is also observed and the cross slope currents are capable of transporting sand up and down the slope as evidenced by ripples migrating normal to the sandwaves eroded sand accumulates in the sandwave fields along the boundary between north atlantic water and norwegian sea arctic intermediate water this is a consequence of the combined effect of the nnw directed along slope norwegian atlantic current and tidally induced topographic waves the sandwave fields started to form 11 000 13 000 14c yrs bp or possibly later by current erosion of glacial sediments on the continental shelf and slope

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

evolution of the cenozoic sedimentary wedge during rifting and seafloor spreading west of the stappen high western barents sea abstract the cenozoic sedimentary wedge west of the stappen high is divided into five main stratigraphic units from oldest to youngest these are unit r unit b unit tec unit ted and unit tee unit r was deposited in a faulted relatively deep marine basin prior to the onset of seafloor spreading in the northernmost part of the norwegian greenland sea the unit was probably deposited from early eocene to early oligocene time with the stappen high as a major source area the base of unit b represents the onset of a second episode of faulting erosion and subsidence west of the stappen high the unconformity is probably related to the early oligocene anomaly 13 change in relative plate movements to a more west northwest trend causing rifting and later seafloor spreading in the northern norwegian greenland sea a period of heavy erosion on the paleocontinental slope and shelf break occurred in mid miocene time 15 5 ma the base of unit tec the relatively deep erosion west of the stappen high was probably related to compression and uplift along northeast southwest oriented faults combined with a period of low eustatic sea level the mid miocene to intra pleistocene parts of the cenozoic sedimentary wedge units tec and ted are dominated by complex lowstand fan deposits and prograding sequences deposited during gradual thermal subsidence of the margin several unconformities related to relative sea level changes are identified within this part of the wedge the most important sequence boundaries are the 5 5 ma base of unit ted boundary and the intra pleistocene 0 8 ma base of unit tee boundary which probably represent the onset of extensive ice sheet formation on the barents shelf

post variscan to early alpine sedimentary basins in the tauern window eastern alps the crystalline basement of the tauern window is locally covered by palaeozoic to mesozoic sediments that experienced alpine tectonometamorphism the sedimentary cover has been subdivided into mappable lithological units the correlation of these units the use of some dated marker intervals and independent palinspastic restoration provide evidence that the depositional area was differentiated into basins and swells at the end of the variscan orogeny during the carboniferous and permian intermontane basins formed in basement rocks and mainly continental clastics accumulated in elongate troughs later probably during the triassic there was levelling of the previous relief and subsidence of the basins but continental sedimen tation still prevailed although interrupted by some marine transgressions thereafter probably during the jurassic the area was progressively flooded and the sedimentation became increasingly calcareous the upper jurassic carbonates document complete submergence in some areas the upper jurassic carbonates directly rest on crystalline basement indicating renewed tectonic stretching the sedimentary cover shows striking similarities with coeval deposits within the germanic basin and the study area is therefore considered to have been part of the southern european continental margin of the tethys the so called vindelician land

pliocene pleistocene sequences bounded by subaerial unconformities within foramol ramp calcarenites and mixed deposits salento se italy nine discrete metre scale sequences of early pliocene to middle pleistocene age were deposited in the small novoli graben salento peninsula puglia s italy they consist of carbonate and mixed carbonate siliciclastic sediments deposited on a slowly subsiding foreland ramp skeletal concentrations and intervening less fossiliferous intervals have been examined to provide information on major environmental parameters and infer the dynamics of their changes taphonomic and palaeoecological analyses indicate that storm induced waves and currents reduced sediment input and settling behaviour of components were the main factors controlling the features of the various shellbed types the concentrations were formed below fair weather wave base in low stress inner to outer shelf environments and are often associated with surfaces or intervals that are characterized by sedimentary condensation vertical change in the fossil content within individual cycles indicates water depth changes that were parallel to climatic fluctuations hence may result from glacio eustatic sea level changes most sequences are bounded by subaerial karstic unconformities because of the regional setting of low subsidence rate the record of the relative sea level fluctuations is incomplete episodes of subaerial exposure and concomitant effects of vadose diagenesis are documented by i diagenetic changes leading to hardening of unconformity horizons ii local subvertical solution pits developed in the vadose zone below unconformity surfaces iii networks of polygonal cracks below unconformities and iv infilling of solution pits and polygonal cracks with vadose silt and marine sediment inwashed during transgressions following the subaerial stages lower sequences are characterized by tighter cementation and significant increase in moldic and vuggy porosity due to superimposition of the diagenetic effects of repeated high amplitude sea level fluctuations

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

shell beds as tools in basin analysis the jurassic of kachchh western india skeletal concentrations are ubiquitous in bathonian oxfordian shallow water sediments of the pericratonic basins of kachchh and rajasthan western india by analysing the biofabric of the concentrations and the taphonomic signatures of individual components it is possible to distinguish between the final concentration process recorded by the biofabric and events taking place prior to final deposition recorded by taphonomic signatures the skeletal concentrations are grouped in nine genetic types ranging from fair weather wave concentrations to storm concentrations and condensed concentrations they mainly reflect biological and hydraulic processes and in some instances permit estimates of their duration and show a rough zonation along a bathymetric gradient plotted against the stratigraphic sections the skeletal concentrations show in accordance with other sedimentological data three orders of bathymetric trends the first two orders are shallowing deepening cycles which possibly correspond to eustatic changes in sea level the third order represents parasequences with a strongly asymmetric sedimentary record skeletal concentrations are a useful additional tool in basin analysis but are best used in combination with other data

late cenozoic prograding wedges on the nw european continental margin their formation and relationship to tectonics and climate abstract during late pliocene to pleistocene times prominent prograding wedges were deposited along the continental margin of nw europe resulting in seaward shelf break migration of up to 150 km much of the sediment accumulation occurred marginal to the former mid to high latitude ice sheets the geographical distribution and stratigraphical and chronological data may suggest that the instigation of the wedges was variously related to tectonic uplift as well as a response to the late pliocene to pleistocene climate deterioration and onset of major northern hemisphere glaciations the onset of wedge growth on the nw uk and irish margins was initiated at about 4 ma in response to tectonic tilting of the margin in that region however glacially derived sediments here comprise a significant proportion of the wedges especially since 0 44 ma for the faroe margin no detailed chronology is available however it may be inferred that onset of glacigenic wedge growth here did not post date that observed on the nw uk and irish margins offshore norway wedge growth has largely occurred since ca 2 7 ma in response to northern hemisphere glaciations also recording a major change in sediments transport routes at 0 8 1 1 ma reflecting larger fennoscandian ice sheets presently it is uncertain whether the glacigenic wedge growth was preceded by a fluvial phase in response to uplift in this area in the western barents sea an early phase of wedge growth was glacio fluvial in character off western spitsbergen the development was similar to that of the barents sea although the glacigenic wedge growth phase may have started somewhat earlier the wedges commonly display gently inclined seaward prograding clinoforms and transparent to chaotic internal acoustic facies sampling of their sediments reveals that they are mainly composed of glacigenic diamicton interbedded with marine and glaciomarine sediments that to various extents have been affected by bottom current action the clinoforms of these wedges vary in geometry from oblique to sigmoidal and they also show varying degrees of aggradation throughout their development the resulting stratal stacking pattern can be attributed to a combination of variations in sediment supply sedimentary processes and accommodation space the latter being a function of tectonic movements and or loading induced subsidence as well as eustatic sea level fluctuations

corrugated megathrust revealed offshore from costa rica exhumed faults are rough often exhibiting topographic corrugations oriented in the direction of slip such features are fundamental to mechanical processes that drive earthquakes and fault evolution however our understanding of corrugation genesis remains limited due to a lack of in situ observations at depth especially at subducting plate boundaries here we present three dimensional seismic reflection data of the costa rica subduction zone that image a shallow megathrust fault characterized by corrugated and chaotic and weakly corrugated topographies the corrugated surfaces extend from near the trench to several kilometres down dip exhibit high reflection amplitudes consistent with high fluid content pressure and trend 11 18 oblique to subduction suggesting 15 to 25 mm yr 1 of trench parallel slip partitioning across the plate boundary the corrugations form along portions of the megathrust with greater cumulative slip and may act as fluid conduits in contrast weakly corrugated areas occur adjacent to active plate bending faults where the megathrust has migrated up section forming a nascent fault surface the variations in megathrust roughness imaged here suggest that abandonment and then reestablishment of the megathrust up section transiently increases fault roughness analogous corrugations may exist along significant portions of subduction megathrusts globally mature parts of the shallow megathrust beneath costa rica are characterized by striking corrugations that may channel fluids according to seismic images nascent sections of the subduction zone plate boundary appear only weakly corrugated