quantitative comparisons of depositional architectures of unconfined and confined turbidite sheet systems abstract degree of confinement refers to the degree to which sediment gravity flows are influenced by the surrounding basin relief and interact with the basin margins and is a key controlling factor in determining the depositional architectures of turbidite sheet systems two well exposed late palaeozoic sandy turbidite sheet systems in the paganzo basin at cerro bola north west argentina termed stages ii and iv unconfined and highly confined respectively provide three dimensional constraints on facies associations stacking patterns depositional geometries and evolution of these turbidite sheet systems cluster analysis has been applied to define facies associations in these two systems at an appropriate hierarchical level depending on the overall nature of the system the overlap index oi oi a0 a1 where a0 is the overlap area and a1 is the area of underlying depositional element is adopted to quantitatively characterise the stacking patterns the two turbidite sheet systems show contrasts in that 1 stage ii is built up by four hierarchical elements each stacked in a shingled or compensational way with the majority of overlap index values of 0 7 and 0 8 to form higher hierarchical elements whereas in stage iv individual beds stack vertically with oi 1 together forming the stage and 2 four facies associations have been identified in stage ii by cluster analysis and they occur in a spatial sequence from axis to fringe one facies association has been identified in stage iv and it shows little variation spatially across the basin in unconfined systems depositional elements are self organized and autocyclic controls are dominant whereas in highly confined systems confinement has suppressed the autocyclic signal and systems are allocyclically controlled

distribution of soluble impurities in cold glacial ice understanding the microstructure of ice underpins the interpretation of ice core measurements and many ice sheet properties a detailed study of polar snow and ice using scanning electron microscope sem and x ray analysis revealed the microstructural distribution of soluble impurities sublimation under vacuum etching concentrated impurity from both the bulk and grain boundaries on to the specimen surfaces in detectable quantities sublimation in the cold room before examination preetching collected previously unobservable quantities of impurity at triple junctions a heterogeneous distribution of impurities was observed chloride was frequently found to originate from the lattice but not usually at triple junctions other impurities particularly sodium chloride were detected at grain boundaries and bubble surfaces sulphate was often found at triple junctions in specimens containing a high bulk concentration of the acid frequently in conjunction with cations this suggests the possibility that veins were only filled with significant amounts of impurity when the surrounding grain boundaries were saturated the model of impurity arrangement inferred from the results reconciles differences between previous sem studies additionally it is consistent with and explains recent electrical conduction observations the disconnected arrangement of impurity filled grain boundaries and veins limits opportunities for significant post depositional solute movement

the assessment of the hydrocarbon potential and maturity of silurian intervals from eastern part of moesian platform romanian sector abstract the aim of this paper is the assessment of the hydrocarbon potential and maturity of silurian intervals from the c l rasi bordei verde biruin a perimeter east moesian platform all the information gathered from the wells drilled in the mentioned perimeter is used for the evaluation of the shale gas potential too this major sedimentary basin has all geological conditions for hydrocarbons generation migration and accumulation the main conclusions of the all geo analyses are the following the xrd analyses show that the samples consist of clay minerals with organic material the organic matter contained in the samples of the wells shows widely distributed type of organoclasts in absence of true vitrinite originating from higher plants in these lower paleozoic series the various encountered organic remains consist of tasmanites microporous or homogeneous fragments structured fragments of graptolites oxidized or naturally rich in oxygen organoclasts inherited from the continent phytoclasts fungal remains the maturity of the silurian at nd rei borehole is established taking into account the fluorescence of the tasmanites and the reflectance of graptolites the maturity increases with depth between 0 70 and 1 eq vro the organic matter of biruin a and c l rasi boreholes is overmature with maturity of around 1 40 1 55 at 400 m in biruin a and a maturity increase with depth between 1 85 and 2 05 eq vro in c l rasi borehole those values are mainly deduced from vitrinite graptolite correlation according to the maturity trend deduced of c l rasi and nd rei boreholes the high maturity of biruin a for such a low burial around 400 m indicates a possible erosion around 3400 m due to uplift the silurian studied samples consist of carbonated claystones with an organic matter of type ii with relatively low residual toc content less than 1 2 weight for the overmature boreholes biruin a and c l rasi and less than 1 6 weight in nd rei borehole

stable carbon isotope systematics of methane ethane and propane from low permeability hydrocarbon reservoirs abstract we have reassessed the stable carbon isotope systematics of methane c1 ethane c2 and propane c3 in more than 500 natural gas samples from low permeability hydrocarbon reservoirs around the world with the purpose of providing new tools for thermal maturity assessment of natural gas that is increasingly produced from such reservoir types world wide a low permeability reservoir resembles a semi closed system and we found that the stable carbon isotope distribution in c1 c3 alkanes differs partially from what has been previously observed in natural gas from conventional hydrocarbon accumulations e g c isotope distributions dominated by rayleigh distillation and kinetic isotope effects in a low permeability reservoir isotope exchange may play a more prominant role in the carbon isotope distribution driving the system towards an even isotopic distribution eid of 6 between methane and ethane and ethane and propane at ro of 1 5 at higher maturity ethane and propane depleted in 13c are formed as a consequence of thermal cracking of wet gas components and possibly free radical decomposition polymerization reactions which leads to the occurrence of isotope reversals 13cc2

cyclic stacking pattern architecture and facies of the turbidite lobes in the macigno sandstones formation chattian aquitanian northern apennines italy abstract this study presents a detailed facies analysis of an 800 m thick stratigraphic succession in the basinal turbidites of the macigno sandstones formation msf recording the first foredeep in the northern apennines italy this stratigraphic succession shows an evident stacking pattern that besides the basal part 200 m thick dominated by fine grained and thin beds is characterized by seven magnificently exposed sandstone lobes from 90 to 19 m thick separated by well developed fine grained interlobe deposits thanks to the detailed facies analysis not only a well defined architectural hierarchy has been identified but a facies scheme has also been proposed whereby cyclic recurring of three facies associations has in turn been identified each facies association records a well determined evolutionary stage of lobe development where an early depositional stage of the lobe building phase is followed by a flow impact and bypass stage recording flow decelerations and hydraulic jumps induced by the morphology created by the underlying depositional lobe the latter phase promotes a switching and channel feeder avulsion that heralds the third phase of abandonment with the deposition of fine grained interlobes the facies stacking pattern and the evolutionary model of the msf also supported by other similar field and experimental works are intended as a contribution to the understanding of intrinsic autogenic mechanisms at the basis of sand rich depositional lobe development

the hydrochemistry of lake vostok and the potential for life in antarctic subglacial lakes our understanding of lake vostok the huge subglacial lake beneath the east antarctic ice sheet has improved recently through the identification of key physical and chemical interactions between the ice sheet and the lake the north of the lake where the overlying ice sheet is thickest is characterized by subglacial melting whereas freezing of lake water occurs in the south resulting in 210 m of ice accretion to the underside of the ice sheet the accreted ice contains lower concentrations of the impurities normally found in glacier ice suggesting a net transfer of material from meltwater into the lake the small numbers of microbes found so far within the accreted ice have dna profiles similar to those of contemporary surface microbes microbiologists expect however that lake vostok and other subglacial lakes will harbour unique species particularly within the deeper waters and associated sediments the extreme environments of subglacial lakes are characterized by high pressures low temperatures permanent darkness limited nutrient availability and oxygen concentrations that are derived from the ice that provides the meltwater copyright 2002 john wiley sons ltd

jurassic deep water fans in the neo tethys ocean the kashafrud formation of the kopet dagh basin iran abstract the middle jurassic kashafrud formation of northeast iran was deposited in the kopet dagh basin linked to the neo tethys ocean the 2 km thick succession commences with fluvio marine boulder conglomerates that occupy bedrock valleys but the bulk of the formation comprises a deep water succession of interbedded sandstone and mudstone packages with trace fossils and sparse ammonites neogene collisional events deformed the strata to create the kopet dagh mountains the deep water succession represents channel lobe systems and associated levees and overbank areas on slope to basin floor fans northward paleoflow suggests that rivers drained uplands along the paleo tethys suture zone forming fan deltas on a narrow shelf with associated sediment transport to deeper water coarse sands extrabasinal pebbles and plant fragments are present throughout the formation and a thick boulder conglomerate unit lies within the turbidite succession these observations suggest proximity to terrestrial sources throughout deposition sandstone packages are mainly less than 10 m thick maximum 84 m and numerous lensoid packages of thick bedded sandstone tens of meters thick and up to 200 m wide represent submarine channel fills thick bedded lenses and sheets show a relatively narrow range of paleoflow direction and represent major submarine conduits whereas the more varied paleoflow direction of thin bedded packages suggests that many were deposited on levees the presence in the kashafrud formation of potential source rocks in the form of organic rich mudstones and abundant plant fragments suggests that the formation may have contributed to hydrocarbon fields within overlying formations sandstone sheets and channel fills could form local reservoirs

bed thickness distributions on mars an orbital perspective studies on earth show that sedimentary bed thickness and bed thickness distributions record information about the processes controlling sediment deposition high resolution digital terrain models dtms such as those derived from the high resolution imaging science experiment hirise now provide the opportunity to quantify bed thickness properties on mars over several orders of magnitude down to the submeter scale this study uses hirise dtms and visible images to measure bed thickness distributions at 10 deposits on mars with the aim of determining whether statistical techniques can provide useful criteria for distinguishing sedimentary depositional processes basic statistics including mean thickness and range are examined as are histograms cumulative frequency plots and log log plots statistical tests interrogate these deposits for thinning or thickening upward trends and the presence of normal lognormal and exponential distributions although there are challenges associated with these methods the statistical analysis of bed thickness coupled with morphological and mineralogical interpretations has the potential to be a powerful tool for characterizing and classifying sedimentary rocks on mars in particular bed thickness statistics are particularly well suited for examining changes in sediment supply and accommodation within martian sedimentary sequences

the role of subglacial water in ice sheet mass balance subglacial water can significantly affect the velocity of ice streams and outlet glaciers of ice sheets depending on the geometry and capacity of the subglacial hydrologic system increased surface melting in greenland over the coming decades may influence the ice sheet s mass balance furthermore subglacial lakes in antarctica can modulate ice velocities and act as nucleation points for new fast flowing ice streams in the coming decades significant changes in the polar regions will increase the contribution of ice sheets to global sea level rise under the ice streams and outlet glaciers that deliver ice to the oceans water and deformable wet sediments lubricate the base facilitating fast ice flow the influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system water moving rapidly through a well connected system of conduits or channels will have little impact on ice sheet velocities but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet and thereby trigger increased ice sheet velocities in greenland the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice sheet mass balance in antarctica subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice flow tributaries climate models of ice sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics

subglacial methanogenesis a potential climatic amplifier 1 subglacial environments are a previously neglected component of the earth s global carbon cycle a reflection of the view held until recently that they are dominated by abiotic and oxic conditions here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over north america and europe during glaciations were host to significant populations of anaerobic microorganisms including methanogens able to metabolize organic carbon sequestered during interglacials and overridden during quaternary glacials in doing so we review the current evidence for subglacial methane release during deglaciation estimate the size of the subglacial reservoir of organic carbon soc and assess the amount of soc available to subglacial microbes and the likely pathways and rates of carbon turnover we then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations we calculate that the soc equates to 418 610 pg c and includes carbon from terrestrial soils vegetation peatlands lake and marine sediments the soc that is potentially available for microbial conversion to methane is smaller than this estimate due to 1 glacial erosion 2 accumulation of recalcitrant organic carbon compounds over time 3 conversion to carbon dioxide by aerobic anaerobic respiration and 4 incomplete conversion of labile organic matter to methane we estimate that the total soc available for conversion to methane is 63 pg c our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates we believe however that there is a strong likelihood that subglacial microbes could convert 63 pg of soc to methane during a glacial cycle if this were the case release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations our findings suggest that it may well be important to consider subglacial environments as active components of the earth s carbon cycle conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation however awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions

hydrochemical characteristics of bulk meltwater from an entire ablation season longyearbreen svalbard the ionic and isotopic characteristics of bulk waters emanating from the cold based longyearbreen central svalbard in 2004 are examined to determine lithological hydrological and glaciological controls on water composition solute provenance and chemical denudation the geology consisted of reactive coal seams and associated sedimentary rocks acidity caused by microbial mediated oxidation of sulfides and to a lesser extent nitrogen bearing minerals was neutralized by congruent dissolution of dolomite and incongruent weathering of silicates in open system subglacial drainage channels the ablation season was divided into an early melt season a peak flow period and a late melt season the runoff distribution during these periods was 1 7 89 7 and 8 6 respectively whereas the solute flux distribution was 1 9 82 1 and 16 0 respectively comparisons between different annual solute flux estimation methods indicated that extrapolation of peak flow period data significantly underestimated both the early and late melt season solute fluxes about 3 8 of the solutes derived from sea salt spray 0 7 from acid aerosol deposition and 95 5 from crustal organic sources the physical and chemical conditions resulted in diffusion of co 2 rather than atmospheric drawdown the cation equivalent weathering rate and the crustal solute yield were 322 meq m 2 a 1 and 22 tkm 2 a 1 respectively which are within the regional range of svalbard however the chemical weathering intensity was as high as 940 meq m 3 owing to the relatively low specific discharge of 0 34 ma 1

strontium isotope composition of runoff from a glaciated carbonate terrain abstract the relationship between subglacial chemical weathering processes and the sr isotope composition of runoff from robertson glacier alberta canada is investigated this glacier rests on predominantly carbonate bedrock of upper devonian age but silicate minerals are also present the provenance of solute in meltwaters is found to vary systematically with solute concentration and by inference subglacial water residence time in dilute waters the principal process of solute acquisition is calcite dissolution fueled by protons derived from the dissolution of co 2 and subsequent dissociation of carbonic acid at higher solute concentrations dolomite dissolution coupled to sulfide oxidation is more important sr concentration is found to increase with total solute concentration in two separate meltwater streams draining from the glacier but 87 sr 86 sr only increases in the eastern melt stream carbonate and k feldspar sources are shown to dominate the sr content of the western stream irrespective of concentration they also dominate the sr content of the eastern stream at low and intermediate concentrations but at higher concentrations muscovite with high 87 sr 86 sr is also an important sr source this reflects the outcrop of muscovite bearing lithologies in the catchment of the eastern stream and an increase in the rate of weathering of k silicates relative to that of carbonates as more concentrated solutions approach saturation with respect to carbonates nonstoichiometric release of 87 sr 86 sr and preferential release of sr over k from freshly ground k silicate surfaces may also occur this may help to explain the radiogenic nature of runoff from distributed subglacial drainage systems which are characterized by long water rock contact times and water flow through environments in which crushing and grinding of bedrock are active processes although the exchangeable sr in tills has higher 87 sr 86 sr than local carbonate bedrock only the more concentrated meltwaters from the eastern stream display similarly high values the most dilute waters which probably transport the bulk of the dissolved sr flux from the glacier have 87 sr 86 sr characteristic of local carbonate bedrock thus the results suggest that although enhanced weathering of silicate minerals containing radiogenic sr such as muscovite does occur in glaciated carbonate terrains it is unlikely to contribute to any enhanced flux of radiogenic sr from glaciated continental surfaces to the oceans

seasonal speedup along the western flank of the greenland ice sheet it has been widely hypothesized that a warmer climate in greenland would increase the volume of lubricating surface meltwater reaching the ice bedrock interface accelerating ice flow and increasing mass loss we have assembled a data set that provides a synoptic scale view spanning ice sheet to outlet glacier flow with which to evaluate this hypothesis on the ice sheet these data reveal summer speedups 50 to 100 consistent with but somewhat larger than earlier observations the relative speedup of outlet glaciers however is far smaller 15 furthermore the dominant seasonal influence on jakobshavn isbrae s flow is the calving front s annual advance and retreat with other effects producing outlet glacier speedups an order of magnitude larger seasonal melt s influence on ice flow is likely confined to those regions dominated by ice sheet flow

maturation thermique des roches meres dans les bassins des basses terres du saint laurent et dans quelques buttes temoins au sud est du bouclier canadien caradocian source rocks belonging to the utica group occur around and overlay the southeastern part of the canadian shield from the ottawa embayment in the southwestern part of st lawrence lowlands to the anticosti island basin the kerogen of the source rocks is mainly made up of amorphous organic matter transmitted light resembling a solid bitumen framework in reflected light and contains a small portion of zooclasts graptolites and chitinozoans the kerogen is often too mature to have preserved the structure of the original constituents except those of graptolites and chitinozoans otherwise uv fluorescent colonial alga and tasmanites are observed in the eastern half of the st lawrence lowlands stratigraphic and tectonic burial is the main control of source rock thermal maturation from an area located 50 km west of quebec city the estimated vitrinite reflectance ro std of the source rock increases in both northeastern montmorency falls and southwestern st maurice river directions from ro std of 1 2 to 1 5 and 1 7 respectively the source rocks of the ottawa embayment and montreal area western half of the basin are overmature due to hydrothermal and igneous activities 2 3 ro std 2 8 in chicoutimi and lac saint jean outliers the source rocks show reflectances between 0 9 and 1 2 slightly less than reflectance values in the quebec city area ro std between 1 2 and 1 5 on anticosti island the thermal maturation is related to burial only and increases downdip of the inclined platform from the northeast toward the southwest ro std between 0 9 and 2 1 these observations suggest that the st lawrence platform and the southeastern canadian shield were buried by at least 3 5 km of paleozoic strata prior to erosion to grenville basement this implies that most potential hydrocarbon fields are presumably also lost by erosion

tracking low temperature tectonism of the st lawrence platform and humber zone southern quebec appalachians through apatite and zircon u th he thermochronology the st lawrence platform slp and humber zone hz of the southern quebec appalachians have been the subject of extensive studies to resolve the degree of thermal maturation yet the timing of the thermal maximum is not well understood we have employed apatite ahe and zircon zhe u th he thermochronometry across a network of late cambrian to late ordovician siliciclastic and grenvillian basement outcrops to resolve the thermal history below 200 c single crystal dates from individual samples exhibit age dispersion by as much as 300 million years with a strong positive to negative correlation with increasing effective uranium eu concentration the data in the southwestern portion of the basin allow for thermal maxima of up to 200 c during the late ordovician or early devonian regional burial trends combined with local estimates of paleogeothermal gradients indicate that if sedimentation continued after the late ordovician there was no significant increase in burial in southwestern portions

late neoproterozoic to permian tectonic evolution of the quebec appalachians canada abstract due to the unique location of the quebec appalachians in a re entrant of the paleo north american margin and to the fact that the area largely escaped late paleozoic deformation this segment of the orogen preserves evidence of the early orogenic stages that are partly obscured elsewhere despite diachronicity both along and across strike of the orogen five tectonic events of regional significance are recognized 1 the earliest event is mainly recorded by neoproterozoic to early ordovician normal faults associated with extension of the laurentian craton and the establishment of a passive continental margin 2 the second event the ordovician taconian orogeny is marked by foreland directed deformation and corresponds to the principal deformational and metamorphic events recorded by the laurentian margin 3 the third event early salinic is early silurian it is restricted to the southern part of the quebec appalachians and consists of hinterland se directed thrusts folds and retrograde metamorphism 4 the fourth event late salinic is recorded by regional scale late silurian to early devonian normal or transtensional faults and is associated with the formation of the connecticut valley gaspe trough and 5 the last event the devonian acadian orogeny affects with variable intensity all the pre carboniferous lithologies this tectonic synthesis implies that the subdivision of the peri laurentian oceanic tracts proposed in other segments of the appalachians should be applied with caution in quebec and that the structural style the number of oceanic domains and possibly the vergence of subduction change along the strike of the orogen in particular the similarities of the thetford mines and boil mountain ophiolitic complexes and sedimentary covers and the lack of evidence for a major intervening suture are consistent with the maximum allochtony hypothesis i e the assumption that the southern quebec ophiolites are rooted east of the chain lake massif a geodynamic model involving the taconian obduction of a large ophiolitic nappe s the docking of a peri gondwanan gander medial new england terrane in early salinic the formation of large sedimentary basins connecticut valley gaspe and merrimack troughs due to trench rollback and or delamination during the late salinic event and collision at the outer margin of composite laurentia during the acadian orogeny can account for the protracted structural and metamorphic history of the quebec appalachians

sedimentation in deep sea lobe elements implications for the origin of thickening upward sequences the frequency and origin of thickening upward packages in the sediments of deep sea environments has been a topic of much recent debate excellent bed scale exposures in the carboniferous ross formation western ireland allow single surfaces to be traced laterally and the detailed architecture of whole packages to be evaluated using multiple vertical logs the deposits comprise architectural elements including bed sets lobe elements and composite lobes with the lobe elements being arranged in thickening upward depositional packages results show that these packages are the result of the progradation of each lobe element whereby each package records a vertical trend from distal to proximal deposits accompanied by an increasing frequency of megaflutes and ultimately the development of broad erosional surfaces we propose a six stage model for lobe element evolution that documents successive phases of deposition sediment bypass erosion and lobe abandonment this new model provides a mechanism for lobe element switching and explains the development of thickening upward successions this allows the re examination of existing process models for these sedimentary packages in deep sea sediments

mesozoic fault reactivation along the st lawrence rift system eastern canada thermochronologic evidence from apatite fission track dating the st lawrence rift system is an active fault zone where reactivation of late proterozoic iapetus related faults is believed to occur it forms both a ne sw trending half graben and nw se trending grabens that link and include the ottawa bonnechere and saguenay river grabens both interpreted as aulacogens the rift faults locally preserve kinematic evidence for normal sense displacement the lack of isotopic chronological constraints and the absence of strata younger than the ordovician make it difficult to determine the timing of fault increments field relations in the quebec city charlevoix and saguenay river regions suggest faulting event s younger than the devonian age charlevoix crater we determined apatite fission track aft ages for grenvillian basement rocks from the hanging wall and footwall of typical rift faults at different locations of the st lawrence and saguenay river fault systems along the st lawrence rift system the footwall rocks of major faults yielded late triassic early jurassic aft ages ranging from 235 28 ma to 184 22 ma the hanging wall samples yielded older ages between 443 44 ma and 279 28 ma along the nw trending saguenay river fault system that are consistent with triassic early jurassic normal faulting at ca 250 200 ma based on hefty inverse models of fission track length distributions younger late jurassic aft ages ranging from 152 17 ma to 149 14 ma in the hanging wall of the ne sw trending st lawrence fault system suggest the occurrence of localized faulting increments during the late jurassic the latter aft age discontinuities are interpreted as the result of normal faulting at ca 250 200 ma followed by tectonic inversion evidence for the reactivation and inversion of preexisting normal faults during or after jurassic time is also found in the mesozoic rift related basins of the atlantic coast the nw se trending compressive stress field currently documented along the st lawrence river is consistent with tectonic inversion along the st lawrence rift system this study provides geochronological support for atlantic rift related extensional deformation followed by compressional deformation in the interior of the canadian shield more than 500 km west of the axis of the mesozoic atlantic rift basins

revisiting the appalachian structural front and offshore anticosti basin northern gulf of st lawrence canada by integrating old and new geophysical datasets abstract the anticosti basin is a large predominantly marine sedimentary basin centered within the northern gulf of st lawrence poor quality vintage seismic reflection data collected more than 25 years ago in the offshore part of the basin failed to depict its geometry however recently acquired multibeam bathymetry and magnetic data can be used in combination with high resolution seismic lines to map the paleozoic succession within the honguedo strait the upper part of the offshore sedimentary succession consists of approximately 1140 m of sediments younger than those exposed on anticosti island the offshore part of the basin includes a 40 km wide fold and fault belt sub parallel to the coastline of the gaspe peninsula the structural style is characterized by broad open synclines narrow anticlines and nw striking faults with dextral strike separations which bears similarities to that of the gaspe belt that formed mainly during the middle devonian acadian orogeny this study indicates that the appalachian deformation front is located to the north of its classically inferred location moreover it suggests that the curvature of the early paleozoic assemblages in the gulf of st lawrence is partly a late devonian feature an improved understanding of the offshore architecture of the basin may help to develop new paleogeographic reconstructions and hydrocarbon exploration models in this under explored frontier basin

evidence for subglacial water transport in the west antarctic ice sheet through three dimensional satellite radar interferometry 1 radarsat data from the 1997 antarctic mapping mission are used interferometrically to solve for the 3 dimensional surface ice motion in the interior of the west antarctic ice sheet wais an area of 125 km2 in a tributary of the kamb ice stream slumped vertically downwards by up to 50 cm between september 26 and october 18 1997 areas in the bindschadler ice stream also exhibited comparable upward and downward surface displacements as the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well we suggest transient movement of pockets of subglacial water as the most likely cause for the vertical surface displacements these results and related lidar observations imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult to observe subglacial environment and its important influence on ice dynamics

ice temperature and high geothermal flux at siple dome west antarctica from borehole measurements a verlical temperature profile through the west antarctic ice sheet wais at the summit of siple dome reveals an elevated geothermal flux this could be the root cause for the existence of a dynamic ice stream system in the wais siple dome is still frozen on its bed but adjacent ice streams have bed temperatures at the pressure melting point of ice although present day temperature increases due to climatic change do not have an immediate effect on the basal conditions that control the velocity of the ice indirect ellbcts like a rapid disintegration of the floating ice shelves or additional melt water input at the surface could give rise to speed up of the ice streams with an ensuing rise in sea level ongoing melt at the base of the ice and changes at the margins will allow continued rapid flow of the ice streams with a possibility of disintegration within a relatively short period of time of at least part of the wais

stable isotope evidence for microbial sulphate reduction at the bed of a polythermal high arctic glacier glacier beds may be host to a range of microbial communities which drive oxic waters towards anoxia along certain hydrological flowpaths chemical and isotopic signatures in meltwaters from finsterwalderbreen a polythermal glacier on sedimentary bedrock in svalbard show clear evidence for anoxia at the glacier bed increases in 34s and 18o of sulphate indicate that microbial sulphate reduction has resulted in significant decreases in sulphate concentration the 13c of the dissolved inorganic carbon dic is isotopically light 13c 8 which is consistent with the use of bedrock kerogen and or the necromass of sulphide oxidising bacteria as organic substrates for the sulphate reducing bacteria calculated rates of organic carbon mineralisation correspond to 10 of the total annual dic flux of the glacial meltwaters this microbial ecosystem is chemoautotrophically based ultimately being sustained by the kerogen and or bacterial necromass and sulphides in the bedrock this work suggests that glacier beds can be refugia for life when climatic and or atmospheric conditions are otherwise inclement and also supports the contention that microbial life is present in subglacial lake vostok

basal mechanics of ice stream b west antarctica 2 undrained plastic bed model based on the results of our studies of the physical conditions beneath ice stream b we formulate a new analytical ice stream model the undrained plastic bed model henceforth the upb model mathematically the upb model is represented by a non linear system of four coupled equations which express the relationships among ice sliding velocity till strength water storage in till and basal melt rate we examine this system of equations for conditions of ice stream stability over short timescales that permit holding ice stream geometry constant less than hundreds of years temporal variability is introduced into the upb model only by the direct dependence of till void ratio changes e t on the basal melting rate m r since till strength b e and ice stream velocity u b b change as long as till void ratio varies the first condition for ice stream stability is that of constant till water storage 0 the second condition for ice stream stability arises from the feedback between ice stream velocity till strength and the basal melting rate which depends on shear heating m r u b b this is the weak till condition which requires that in a steady state till strength is a small fraction of the gravitational driving stress b n 1 1 d the salient feature of the upb model is its ability to produce two thermo mechanically controlled equilibrium states one with a strong bed and slow ice velocities ice sheet mode and one with a weak bed and fast ice velocities ice stream mode this bimodality of basal conditions is consistent with the available observations of subglacial conditions beneath slow and fast moving ice in west antarctica basal conditions that do not correspond to these two steady states may occur transiently during switches between the two stable modes the upb model demonstrates that ice streams may be prone to thermally triggered instabilities during which small perturbations in the basal thermal energy balance grow leading to generation or elimination of the basal conditions which cause ice streaming

an inventory of active subglacial lakes in antarctica detected by icesat 2003 2008 through the detection of surface deformation in response to water movement recent satellite studies have demonstrated the existence of subglacial lakes in antarctica that fill and drain on timescales of months to years these studies however were confined to specific regions of the ice sheet here we present the first comprehensive study of these active lakes for the antarctic ice sheet north of 868 s based on 4 5 years 2003 08 of nasa s ice cloud and land elevation satellite icesat laser altimeter data our analysis has detected 124 lakes that were active during this period and we estimate volume changes for each lake the icesat detected lakes are prevalent in coastal antarctica and are present under most of the largest ice stream catchments lakes sometimes appear to transfer water from one to another but also often exchange water with distributed sources undetectable by icesat suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow thus these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds but also may withdraw water at other times to slow flow

supracrustal faults of the st lawrence rift system quebec kinematics and geometry as revealed by field mapping and marine seismic reflection data abstract the st lawrence rift system from the laurentian craton core to the offshore st lawrence river system is a seismically active zone in which fault reactivation is believed to occur along late proterozoic to early paleozoic normal faults related to the opening of the iapetus ocean the rift related faults fringe the contact between the grenvillian basement to the nw and cambrian ordovician rocks of the st lawrence lowlands to the se and occur also within the grenvillian basement the st lawrence rift system trends ne sw and represents a se dipping half graben that links the nw se trending ottawa bonnechere and saguenay river grabens both interpreted as iapetan failed arms coastal sections of the st lawrence river that expose fault rocks related to the st lawrence rift system have been studied between quebec city and the saguenay river brittle faults marking the st lawrence rift system consist of ne and nw trending structures that show mutual crosscutting relationships fault rocks consist of fault breccias cataclasites and pseudotachylytes field relationships suggest that the various types of fault rocks are associated with the same tectonic event high resolution marine seismic reflection data acquired in the st lawrence river estuary between rimouski the saguenay river and forestville identify submarine topographic relief attributed to the st lawrence rift system northeast trending seismic reflection profiles show a basement geometry that agrees with onshore structural features northwest trending seismic profiles suggest that normal faults fringing the st lawrence river are associated with a major topographic depression in the estuary the laurentian channel trough with up to 700 m of basement relief a two way travel time to bedrock map based on seismic data from the st lawrence estuary and comparison with the onshore rift segment suggest that the laurentian channel trough varies from a half graben to a graben structure from sw to ne it is speculated that natural gas occurrences within both the onshore and offshore sequences of unconsolidated quaternary deposits are possibly related to degassing processes of basement rocks and that hydrocarbons were drained upward by the rift faults

glacier meltwater hydrochemistry abstract glacierised areas present an ideal environment in which to study water rock interaction since chemical weathering rates are high and anthropogenic impacts are often minimal detailed investigations of meltwater quality variations have suggested the importance of these environments in estimates of terrestrial chemical erosion and global biogeochemical cycles most notably the role of meltwaters in co2 sequestration during episodes of deglaciation has attracted considerable attention since this may impact on climate at glacial interglacial timescales however there is still considerable uncertainty surrounding estimates of co2 drawdown by meltwaters which remains to be resolved water flow through glaciers exerts an important control on ice mass dynamics and influences the quantity and quality of water delivered to environments downstream of glacierised basins thus the study of the configuration and dynamics of subglacial drainage systems is important not only to enhance scientific understanding but also to allow effective water resource utilisation in glacierised headwater catchments bulk meltwater quality characteristics draining terrestrial ice masses also offer the potential to provide unique information on hydrological and hydrochemical processes operating in the inaccessible subglacial environment here significant advances have been made in understanding the controls on chemical weathering reactions based on the identification of key dissolved indicator species this has allowed water quality variations to be exploited as a tool for both subglacial hydrochemical and hydrological investigations as a result this area of glaciology has received considerable attention in recent years utilising an increasing range of dissolved ions and integrating field and laboratory studies however uncertainty still surrounds certain areas of meltwater quality science including the role of microorganisms in a system which to date has largely been viewed as abiotic a better understanding of the processes and rates of chemical weathering in glacierised environments has the potential to enhance our understanding of the environment and to facilitate the exploitation of water quality variations for both scientific and applied objectives in this paper the development and current state of meltwater quality science as a tool for investigating subglacial hydrology and geochemistry is detailed and problems and future directions identified this will hopefully stimulate wider interest in an important area of aquatic chemistry with significant applied implications

surface and subsurface signatures of gas seepage in the st lawrence estuary canada significance to hydrocarbon exploration abstract the seabed of the st lawrence estuary is characterized by many fluid releasing features on multibeam bathymetric images these features correspond to crater like depression pockmarks predominantly found on the northwestern shoulder of the 300 m deep laurentian channel as well as on the channel floor aligned pockmarks which define segments up to 12 km long are frequent in the laurentian channel whereas they are preferentially associated with submarine landslides on the northwestern shoulder of the channel on high resolution seismic profiles pockmarks found in the laurentian channel are characterized by seismic chimneys that may be traced down to the autochthonous paleozoic rocks st lawrence platform suggesting a thermogenic origin for the gas on the northwest shoulder of the laurentian channel the seismic signature of pockmarks does not extend downward to the reflector that corresponds to bedrock st lawrence platform and or grenvillian province suggesting together with high sedimentation rate a biogenic origin for the gas these results are discussed in the light of the data collected in the onshore parts of the st lawrence platform and suggest the presence of a mature hydrocarbon source the conclusions are supportive arguments for the hydrocarbon prospectivity of both the onshore and offshore segments of the paleozoic autochthonous domain st lawrence platform

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

enhancement of glacial solute fluxes in the proglacial zone of a polythermal glacier annual proglacial solute fluxes and chemical weathering rates at a polythermal high arctic glacier are presented bulk meltwater chemistry and discharge were monitored continuously at gauging stations located at the eastern and western margins of the glacier terminus and at the outlet 2 5 km downstream where meltwaters discharge into the fjord fluxes of non snowpack hco 3 so 4 2 ca 2 and mg 2 increase by 30 47 between the glacier terminus and the outlet indicating that meltwaters are able to access and chemically weather efflorescent sulphates carbonates and sulphides in the proglacial zone smaller increases in the fluxes of non snowpack derived na k and si indicate that proglacial chemical weathering of silicates is less significant en3hanced solute fluxes in the proglacial zone are mainly due to the chemical weathering of active layer sediments the pco 2 of active layer ground waters is above atmospheric pressure this implies that solute acquisition in the active layer involves no drawdown of co 2 the annual proglacial chemical weathering rate in 1999 is calculated to be 2600 meq m 2 this exceeds the chemical weathering rate for the glaciated part of the catchment 790 meq m 2 by a factor of 3 3 hence the proglacial zone at finster walderbreen is identified as an area of high geochemical reactivity and a source of co 2

statistical appraisal of bed thickness patterns in turbidite successions andaman flysch group andaman islands india abstract the bed thickness distribution of two turbidite successions in the oligocene andaman flysch group india which differ in terms of their paleogeography and sediment supply has been assessed statistically the purpose was to evaluate depositional cyclicity using the non parametric waldron test and also to assess possible environmental control on the bed thickness magnitude distribution both sections reveal a positively skewed distribution in bed thickness patterns the z value obtained through waldron s test failed to reject the null hypothesis of randomness and thus discards a cyclic pattern juxtaposition of sediments of different proximalities in an elongated forearc fan complex is the possible cause for this absence of cyclicity the studied sections however differ in their bed thickness magnitude distribution slope turbidite successions with sediment supply solely from the outer arc reveals a scaling behavior while the outer fan succession with mixing of sediments from different sources show a negative exponential distribution this highlights the possible control of the depositional system and sediment supply on the bed thickness magnitude distribution of turbidite successions irrespective of the triggering mechanism unequivocal application of the power law distribution in turbidite successions demands reconsideration

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

borehole drainage and its implications for the investigation of glacier hydrology experiences from haut glacier d arolla switzerland studies of glacier hydrology rely increasingly on measurements made in boreholes as a basis for reconstructing the character and behaviour of subglacial drainage systems in temperate glaciers in which boreholes remain open to the atmosphere following drilling the interpretation of such data may be complicated by supraglacial or englacial water flows to and from boreholes we report on a suite of techniques used to identify borehole water sources and to reconstruct patterns of water circulation within boreholes at haut glacier d arolla switzerland results are used to define a number of borehole drainage types examples of each drainage type are presented along with the manner in which they influence interpretations of borehole water levels borehole water quality data and borehole dye traces the analysis indicates that a full understanding of possible borehole drainage modes is required for the correct interpretation of many borehole observations and that those observations provide an accurate indication of subglacial conditions only under relatively restricted circumstances copyright 2001 john wiley sons ltd

fossil brines preserved in the st lawrence lowlands quebec canada as revealed by their chemistry and noble gas isotopes abstract brines in cambrian sandstones and ordovician dolostones of the st lawrence lowlands at becancour quebec canada were sampled for analysis of all stable noble gases in order to trace their origin and migration path in addition to quantifying their residence time major ion chemistry indicates that the brines are of na ca cl type possibly derived from halite dissolution 87 sr 86 sr ratios and ca excess indicate prolonged interactions with silicate rocks of the proterozoic grenville basement or the cambrian potsdam sandstone the brines constrain a 2 3 contribution of mantle 3 he and large amounts of nucleogenic 21 ne and 38 ar and radiogenic 4 he and 40 ar 4 he 40 ar and 21 ne 40 ar ratios corrected for mass fractionation during incomplete brine degassing are identical to their production ratios in rocks the source of salinity halite dissolution plus the occurrence of large amounts of 40 ar in brines constrain the residence time of becancour brines as being older than the cretaceous evaporites in the st lawrence lowlands likely existed only during devonian silurian time brines might result from infiltration of devonian water leaching halite penetrating into or below the deeper cambrian ordovician aquifers during the devonian the basin reached temperatures higher than 250 c allowing for thermal maturation of local gas prone source rocks utica shales and possibly facilitating the release of radiogenic 40 ar into the brines the last thermal event that could have facilitated the liberation of 40 ar into fluids and contributed to mantle 3 he is the cretaceous monteregian hills magmatic episode for residence times younger than the cretaceous it is difficult to find an appropriate source of salinity and of nucleogenic radiogenic gases to the becancour brines

high geothermal heat flow basal melt and the origin of rapid ice flow in central greenland age depth relations from internal layering reveal a large region of rapid basal melting in greenland melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet locally high melt rates indicate geothermal fluxes 15 to 30 times continental background the southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin

pre syn and post imbrication deformation of carbonate slices along the southern quebec appalachian front implications for hydrocarbon exploration thrust imbricated shelf carbonate slices form a wide but poorly understood part of the southernmost quebec appalachian structural front comprehensive structural analysis of two slices exposed at surface the saint dominique and philipsburg slices shows that pre and post imbrication structures are important in defining the final architecture of the slices the dominant structural style is characterized by thrusts and associated asymmetrical folds tear faults oblique ramps and incipient backthrusts developed during wnw ese shortening a forward breaking piggy back sequence of thrusting is recognised as well as minor out of sequence thrusting the complexity and diversity of contractional structures is directly influenced by lithology bed thickness and shale content bedding parallel slip planes are important in the concentration activation and reactivation of deformation in that there are the loci for veining faulting and folding recognition of lithostructural units provides guidelines for t

diagenesis and anchimetamorphism in an overthrust belt external domain of the taconian orogen southern canadian applachians ii paleogeothermal gradients derived from maturation of different types of organic matter abstract 3hermal maturation patterns have been established for the external domain of taconian orogen of the southern quebec appalachians between quebec city and the u s border reflectance of three types of organic matter om measured in the same sample shows that graptolite reflectance r g is higher than pyrobitumen reflectance r b which in turn is higher than reflectance of amorphous organic matter r a r g r b and r a are converted to vitrinite equivalent reflectance from which maximum paleotemperatures were calculated inverted diagenesis is preserved in northwest part of the chaudiere nappe to the southeast original burial diagenetic grade was upgraded by later synorogenic heating in the st lawrence lowlands paleogeothermal gradients at maximum burial were 33 37 c km a gradual southwestward increase in maturation level suggests increasing post taconian burial depth from 4 6 to 6 7 km indicating an increasing thickness of eroded rocks from northeast to southwest along logan s line one of the most important contributions of this study is the proof that the acadian orogeny has affected the successor basin of the taconian orogeny in the st lawrence lowlands the thermal effect of the mid cretaceous intrusion of the monteregian hills on their country rocks is limited to one diameter or less of the intrusive body as shown by the narrow

statistical analysis of turbidite cycles in submarine fan successions tests for short term persistence abstract to statistically test and evaluate the significance of asymmetric upward thickening and thinning trends and other cyclic patterns in turbidite successions 28 bed by bed sections with a wide coverage in geological time tectonic settings facies characteristics and depositional environments were measured and described first 286 sandstone packets were selected from the 28 turbidite sections through statistically based segmentation then these packets were examined by three powerful correlation tests kendall s spearman s and pearson s correlation tests and four tests for randomness only 34 11 9 of the sandstone packets pass tests designed to identify asymmetry at the 10 significance level monte carlo simulation and calculation of cumulative binomial probabilities indicate that the number of asymmetric cycles identified in the original set of sandstone packets is indistinguishable from the number expected to result from random processes eighty six sandstone packets from five sections were tested for upward coarsening and fining trends forty two of these packets were from channel deposits and the rest from lobes and basin plain deposits only 25 29 of the 86 packets coarsen or fine upward however 33 50 of packets from coarse grained channel fills show asymmetric grain size trends mostly as upward fining cycles 15 of the 42 tested packets from channel deposits these upward fining trends in channel deposits are interpreted as the result of channel filling or the stacking of onlapping deposits at a channel mouth results from this study strongly suggest that asymmetric bed thickness cycles have essentially no statistical significance in turbidite successions and therefore cannot provide a key criterion for identification of sub environments in submarine fan systems it follows that models for submarine fans based on the widely publicized hypothesis of common asymmetric cycles should be reconsidered instead other criteria such as specific facies characteristics large scale geometry and degree of sand bed clustering may provide the best tools for discrimination of submarine fan sub environments in natural systems the disordered vertical arrangement of thicker and thinner beds likely results from irregular variations in flow volumes concentrations and precise pathways of turbidity currents over the short time scales represented by tens of meters of section most submarine fans are built by aggradation not progradation so that facies shifts are controlled mostly by channel switching and avulsion and not by progressive basinward or landward advance or retreat of one sub environment over another aggradation does not tend to generate asymmetric trends in bed thickness the same arguments are believed to hold for grain size trends in submarine fan packets except in the case of coarse grained channel deposits where upward fining is conspicuous

statistical analysis of turbidite bed thickness patterns from the alpine fold and thrust belt of western and southeastern greece abstract a statistical evaluation of turbidite bed thickness was performed for 11 turbidite successions which constitute part of foreland basins formed along the alpine fold and thrust belt of western and southeastern greece the purpose was to compare the results from this study with previously published investigations and discuss if and how statistical approaches could contribute to the environmental analysis of turbidite deposits in tectonically complex areas bed thickness datasets exhibit a clear non normal signal in their distribution behavior statistical analysis was focused on i fitting of widely used non normal theoretical distribution models using robust non parametric goodness of fit statistical tests and ii detecting the possible presence of asymmetric bed thickness cycles and or non random bed thickness clustering results indicate that the studied bed thickness datasets are well characterized by a bimodal lognormal distribution model probably reflecting deposition from both high and low density turbidity currents several datasets exhibit distributions characterized by power law tails exponential distribution types were not observed all datasets exhibit non random thinning upward bed thickness trends probably due to tectonically induced gravity flows proposed methods for identifying depositional sub environments using turbidite bed thickness statistics were found to have limited applicability observations of the present study may prove useful for the environmental analysis of turbidite deposits in fold and thrust belt areas characterized by limited outcrop exposures

dynamic distributed drainage implied by the flow evolution of the 1996 1998 adventure trench subglacial lake discharge abstract the transport of subglacial water beneath the east antarctic ice sheet is an enigmatic and difficult to observe process which may affect the flow of the overlying ice and mixing of the oceans in the sub ice shelf cavities and ultimately global climate periodic outbursts are a critical mechanism in this process recent analysis of satellite data has inferred a subglacial hydraulic discharge totaling 2 km 3 traveling some 260 km along the ice bed interface of the adventure subglacial trench between 1996 and 1998 wingham et al 2006 rapid discharge connects antarctic subglacial lakes nature 440 1033 1036 using radar echo sounding data from the adventure subglacial trench region in conjunction with the previously reported satellite observations along with some basic modeling we calculate a mass budget and infer a flow mechanism for the 1996 1998 event the volume released from the source lake exceeded the volume received by the destination lakes by 1 1 km 3 this discrepancy indicates that some water must have escaped downstream from the lowest destination lake from 1997 onward the downstream release of water from the destination lakes continued until at least 2003 several years after the 1998 cessation of surface subsidence at the source lake by 2003 a total of 1 5 km 3 or nearly 75 of the water released by the source lake had traveled downstream from the destination lakes the temporal evolution of discharge from the outlet can be simulated with the classic ice walled semicircular channel model if and only if the retreat of the source lake shoreline is taken into account further downstream the ice bedrock geometry along the inferred flow path downstream includes many sections where thermal erosion of the overlying ice would not be sustainable along these reaches mechanical lifting of the ice roof and or erosion of a sedimentary substrate by a broad shallow water system would be most effective means of sustaining the discharge a distributed system is also consistent with the 3 month delay between water release at the source lake and water arrival at the destination lake observations of intermittent flat bright bed reflections in radar data acquired along the flow path are consistent with the presence of a broad shallow water system ultimately the presence of large subglacial lakes along the flow path of the 1996 1998 adventure subglacial trench flow path delayed the arrival of water to points downstream by approximately 12 months

multiple origin and regional significance of bedding parallel veins in a fold and thrust belt the example of a carbonate slice along the appalachian structural front abstract the development and evolution of bedding parallel veins bpv are investigated in the saint dominique carbonate slice southern quebec appalachian structural front in order to emphasize the regional significance of bpv in a fold and thrust belt and their importance in establishing its structural and diagenetic evolution structural and microstructural analyses reveal that most bpv display a laminated structure locally crosscut by a massive one both structures show mutual crosscutting relationships with bedding parallel or bedding perpendicular stylolites and with bedding perpendicular veinlets indicating that bpv cementation and deformation are continuous processes opening both sub parallel and sub perpendicular to the bpv walls are documented early bpv are planes of weakness that focus later reactivation and evidence of successive and sometimes opposite senses of opening are locally preserved within a single bpv the bedding parallel orientation of these veins proved particularly helpful in establishing the structural evolution of an area mostly characterized by front parallel structures with little crosscutting relationships otherwise petrographic and geochemical 18 o vpdb and 13 c analyses of structural cements suggest a common locally derived source for the fluids that percolated through bpv non bedding parallel veins and faults the isotopic ratios also reveal a significant enrichment in 18 o and 13 c through time this evolution is tentatively correlated with tectonic syn convergence exhumation of the saint dominique slice during its imbrication along the appalachian structural front after its burial under taconian thrust sheets

aseismic controls on in situ soft sediment deformation processes and products in submarine slope deposits of the karoo basin south africa intervals of soft sediment deformation features including vertical fluid escape and load structures are common and well exposed in permian lower slope deposits of the tanqua depocentre karoo basin the structures mainly comprise elongated flames and load structures associated with ruptured sandstones and structureless siltstones observed over a range of scales the presence of an upper structureless siltstone layer linked to the flames interpreted as a product of the debouching of fine grained material transported through the flame onto the palaeo seabed together with the drag and upward folding of lower sandstone layers is evidence that the flames were formed in situ by upward movement of sediment rich fluids flames are oriented parallel to the deep water palaeoslope in lateral splay deposits between two major slope channel complexes statistical correlation and regression analyses of 180 flame structures from seven stratigraphic intervals suggest a common mechanism for the deformation and indicate the importance of fluidization as a deformation mechanism importantly deformation occurred in an instantaneous and synchronous manner liquefaction and fluidization were triggered by incremental movement of sediment over steeper local gradients that were generated by deposition of a lateral splay on an inherited local north west facing slope seismic activity is not invoked as a trigger mechanism because of the restricted spatial occurrence of these features and the lack of indications of earthquakes during the time of deposition of the deep water succession the driving mechanisms that resulted in the final configuration of the soft sediment deformation structures involved a combination of vertical shear stress caused by fluidization development of an inverse density gradient and a downslope component of force associated with the local slope ground penetrating radar profiles confirm the overall north east orientation of the flame structures and provide a basis for recognition of potential larger scale examples of flames in seismic reflection data sets

bed thickness characteristics of inner shelf storm deposits associated with a transgressive to regressive holocene wave dominated shelf sendai coastal plain japan holocene inner shelf storm deposits preserved beneath the sendai coastal plain facing the pacific coast of north eastern japan were formed during a transgressive regressive cycle the evolution of the holocene wave dominated depositional system along the sendai coast is reconstructed using 76 ams accelerator mass spectrometers 14c ages and the origin of bed thickness variations in the inner shelf storm deposits is explored the holocene succession is 30 m thick and overlies latest pleistocene to early holocene non marine deposits above a transgressive ravinement surface it comprises transgressive ravinement and inner shelf deposits and regressive inner shelf shoreface and coastal plain deposits the inner shelf deposits comprise alternating sand and mud layers interpreted as stacked storm beds the average preservation interval of a single storm bed is shortest during the transgression 5 7 20 6 years and then increases to a maximum during the early regression 83 3 250 0 years decreasing to 7 7 31 3 years with shoreline progradation average accumulation rates decreased during the transgression and then increased during the regression but the sand mud ratio varies little reflecting inefficient sediment segregation downdip on the inner shelf the vertical pattern of sand layer thicknesses also shows no relationship to position within the cycle although small scale intervals of upward thickening and thinning probably relate to lateral switching of river mouths and or random storm processes the average thickness of storm beds is the highest in the interval deposited during the period from maximum flooding to early regression this is probably because of the low preservation potential of thin beds associated with frequent low magnitude storms during this period of low accumulation rates and extensive reworking this preservation bias and the nature of the sendai inner shelf resulted in an absence of characteristic bed thickness trends in the preserved storm deposits

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

eustatic signals in deep marine sedimentary sequences recovered at odp site 978 alboran basin western mediterranean sea abstract a continuous section of pliocene marine sediments was recovered at ocean drilling program site 978 located in the alboran sea between spain and morocco three pliocene subunits have been defined at site 978 the lowermost subunit ic 129 2 m thick is characterized by alternating beds of lighter more calcareous and darker less calcareous claystone with bioturbated upper and lower contacts type 1 cycles the middle subunit ib 67 1 m thick is composed of relatively homogeneous nannofossil claystone and the uppermost subunit ia 211 6 m thick contains abrupt based darker terrigenous layers interpreted as turbidites that are interstratified with lighter nannofossil claystone type 2 cycles the rhythmically bedded light and dark layers in subunit ic correlate with those in the rosello composite section of sicily a global reference standard for the pliocene time scale these sedimentary cycles are products of variations in precession and resulting continental runoff missing cycles occur during eustatic highstands the shift to more homogeneous sedimentation in subunit ib is represented in similar aged sequences throughout the mediterranean which display evidence of submarine mass wasting mediterranean wide slope degradation was likely a response to rapid sea level change at approximately 3 ma this change in sedimentation style was accompanied by an upsection increase in sediment accumulation rates associated with turbidite influx in subunit ia turbidite frequency throughout the pliocene section can be linked to eustatic changes in sea level with turbidite maxima corresponding with mid sequence downlap surfaces and their associated condensed sections

taconian melanges in the parautochthonous zone of the quebec appalachians revisited implications for foreland basin and thrust belt evolution in the quebec appalachians disruption imbrication and thrusting of the taconian foreland basin sequence are responsible for the development of chaotic units within the turbiditic sequence of the caradocian sainte rosalie group the main lithologic assemblage of the parautochthonous zone these chaotic units have been termed olistostromes or tectonosomes on the basis of field criteria and following pini s 1999 classification olistostromal units containing blocks of the middle mudstone utica shale and upper turbidite units ste rosalie group of the foreland basin and spanning the caradocian n gracilis c americanus o ruedemanni and c spiniferus graptolite zones were deposited and incorporated into the sainte rosalie group disruption of more competent beds of the flyschic sequence and fault stacking and slicing of older rock units occurred along major thrust faults and now form structurally aligned corridors or tectonosomes graptolites and new chitinozoan data from both olistostromes and tec

facies clustering in turbidite successions case study from andaman flysch group andaman islands india abstract bed thickness data of two turbidite sections viz corbyn s cove section south andaman and kalipur section north andaman those belong to oligocene andaman flysch group a forearc submarine fan system were assessed for facies clustering employing hurst statistics both the sections show hurst phenomenon and reveal clustering in terms of thick and thin beds forcing behind event bed depositions in either of the studied sections was assessed statistically and inferred to be non random and with cyclicities of irregular physical length the inferred paleogeography through hurst criteria though worked well for distal fan setting i e basin floor sheet sandstones of corbyn s cove section its unequivocal application in proximal fan deposits remains to be tested the mismatch in paleogeographic interpretation between hurst test result lobe interlobe and field observation channel levee for the inner fan deposit is explained through differential facies stacking between fans grow in sea level lowstand and highstand lower bed amalgamation poor sand to mud ratio and subordinately present thick event deposits may be the result of active growth of andaman flysch fan in sea level highstand and expressed in lower hurst k value for inner fan channel levee association kalipur section compared to many of the channel levee deposits of lowstand fan systems observed world over

the full range of turbidite bed thickness patterns in submarine lobes controls and implications a widely misused criterion to interpret lobe deposits in submarine fan systems at outcrop and in core and well logs is a thickening and or coarsening upward profile lobe deposits from the laingsburg depocentre sw karoo basin demonstrate that a full range of bed thickness patterns exists within lobes when lobes are defined by their laterally extensive bounding surfaces that are marked by abrupt facies changes five types of bed stacking patterns are identified thickening upward thinning upward thickening then thinning upward thinning then thickening upward and constant the abrupt bounding surfaces are interpreted to record avulsion of feeder distributive channels the stratigraphic bed thickness pattern preserved in a lobe reflects the internal organization of smaller scale lobe elements rather than lobe wide initiation and progradation as implied by a thickening upward only pattern the full range of bed thickness patterns in lobes can be used to understand the stacking of lobe elements the evolution of sediment deposition through time and space and the relative movement of depocentres

maturation thermique de la matiere organique dans un bassin du paleozoique inferieur basses terres du saint laurent quebec canada the organic matter om sampled in 15 oil exploration wells and 102 outcrops of cambrian ordovician rocks in the st lawrence lowlands consists of zooclasts chitinozoans graptolites and scolecodonts and solid bitumen mainly pyrobitumen the reflectance of pyrobitumen transformed in vitrinite equivalent ro std b indicates that the upper part of the platform sequence is mature condensate zone in the quebec area but overmature in the montreal area the platform is divided into three domains based on optical texture of om and types of bitumen domain 1 south of montreal contains a highly reflecting and coked pyrobitumen showing alteration rims domain 3 east of trois rivieres contains low reflecting late solid bitumen commonly associated with oil impregnations domain 2 located midway contains a pyrobitumen with moderate reflectance and locally fine mosaic texture the thermal maturation in the autochthonous sequences of the st lawrence lowlands and in the appalachian allochthons increas

widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling bacterial populations found in subglacial meltwaters and basal ice are comparable to those in the active layer of permafrost and orders of magnitude larger than those found in ice cores from large ice sheets populations increase with sediment concentration and 5 24 of the bacteria are dividing or have just divided suggesting that the populations are active these findings 1 support inferences from recent studies of basal ice and meltwater chemistry that microbially mediated redox reactions may be important at glacier beds 2 challenge the view that chemical weathering in glacial environments arises from purely inorganic reactions and 3 raise the possibilities that redox reactions are a major source of protons consumed in subglacial weathering and that these reactions may be the dominant proton source beneath ice sheets where meltwaters are isolated from an atmospheric source of co 2 microbial mediation may increase the rate of sulfide oxidation under subglacial conditions a suggestion supported by the results of simple weathering experiments if subglacial bacterial populations can oxidize and ferment organic carbon it is important to reconsider the fate of soil organic carbon accumulated under interglacial conditions in areas subsequently overridden by pleistocene ice sheets

large and rapid melt induced velocity changes in the ablation zone of the greenland ice sheet continuous global positioning system observations reveal rapid and large ice velocity fluctuations in the western ablation zone of the greenland ice sheet within days ice velocity reacts to increased meltwater production and increases by a factor of 4 such a response is much stronger and much faster than previously reported over a longer period of 17 years annual ice velocities have decreased slightly which suggests that the englacial hydraulic system adjusts constantly to the variable meltwater input which results in a more or less constant ice flux over the years the positive feedback mechanism between melt rate and ice velocity appears to be a seasonal process that may have only a limited effect on the response of the ice sheet to climate warming over the next decades

influence of subglacial geology on the position of a west antarctic ice stream from seismic observations ice streams drain much of the interior west antarctic ice sheet and buffer the main ice reservoir from oceanic influences1 2 the slow flowing interior feeds the floating ross ice shelf with ice via fast flowing ice streams3 that are believed to modulate sea level change through their control of inland ice storage understanding ice stream behaviour and predicting the response to climate change4 requires a better knowledge of the subglacial geology5 6 it is known that a thawed ice bed and high pressure basal water are necessary but not sufficient conditions to cause ice streaming7 8 moreover it has been hypothesized that a soft sedimentary bed is also required because of its intrinsic low frictional resistance to flow9 and owing to its high erodibility so as to generate till that can deform and lubricate ice motion10 11 or to bury rough features and smooth the bed for sliding here we use seismic observations to provide evidence that one margin of the upglacier part of an ice stream is directly above the boundary of a basin with such sedimentary fill the ice stream is within the basin and the ice outside the basin is slow flowing the basin fill presents an order of magnitude lower frictional resistance to ice flow than the subglacial material outside the basin we conclude that the ice stream position is dependent on subglacial geology

textural trends in turbidites and slurry beds from the oligocene flysch of the east carpathians romania deep water sandstone beds of the oligocene fusaru sandstone and lower dysodilic shale exposed in the buza uu valley area of the east carpathian flysch belt romania can be described in terms of the standard turbidite divisions in addition mud rich sand layers are common both as parts of otherwise normal sequences of turbidite divisions and as individual event beds eleven units interpreted as the deposits of individual flows were densely sampled and 87 thin sections were point counted for grain size and mud content s3 ta divisions which form the bulk of most sedimentation units have low internal textural variability but show subtle vertical trends in grain size most commonly coarse tail normal grading is associated with finetail inverse grading the mean grain size can show inverse grading normal grading or a lack of grading but sorting tends to improve upward in most beds fine tail inverse grading is interpreted as resulting from a decreasing effectiveness of trapping of fines during rapid deposition from a turbidity current as the initially high suspended load fallout rate declines if this effect is strong enough the mean grain size can show subtle inverse grading as well thus thick inversely graded intervals in deep water sands lacking traction structures do not necessarily imply waxing flow velocities if the suspendedload fallout rate drops to zero after the deposition of the coarse grain size populations the remaining finer grained flow bypasses and may rework the top of the s3 division forming well sorted coarser grained current structured tt units alternatively the suspended load fallout rate may remain high enough to prevent segregation of fines leading to the deposition of significant amounts of mud along with the sand mud content of the sandstones is bimodal either 3 13 or more than 20 two types of mud rich sandstones were observed coarser grained mud rich sandstones occur towards the upper parts of s3 ta divisions these units were deposited as a result of enhanced trapping of mud particles in the rapidly deposited sediment finer grained mud rich units are interbedded with ripple laminated very fine grained sandy tc divisions during deposition of these units mud floccules were hydraulically equivalent to the very fine sand and silt sized sediment the mud rich sandstones were probably deposited by flows that became transitional between turbidity currents and debris flows during their late stage evolution

meltwater discharge through the subglacial bed and its land forming consequences from numerical experiments in the polish lowland during the last glaciation numerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in nw poland primarily its flow pattern velocities and fluxes we have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady state and transient conditions the results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin all model runs show water discharge at the ice forefield driven by ice sheet thickness modulated down ice decreasing hydraulic heads in relation to non glacial times the transient 3d model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca 90 m below the ice bed interface and up to 40 km in front of the glacier comparison with empirical data suggests that depending on the model run only between 5 and 24 of the meltwater formed at the ice sole drained through the bed as groundwater this is consistent with field observations documenting abundant occurrence of tunnel valleys indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely in these areas the relief shows distinct palaeo ice lobes indicating fast ice flow possibly triggered by the undrained water at the ice bed interface owing to the abundance of low permeability strata in the bed the simulated groundwater flow depth is less than ca 200 m copyright 2009 john wiley sons ltd

melting and freezing beneath the ross ice streams antarctica we have estimated temperature gradients and melt rates at the bottom of the ice streams in west antarctica measured velocities were used to include the effects of horizontal advection and strain heating in the temperature model and to determine shear heating at the bed our modeled temperatures agree well with measured temperatures from boreholes in regions of steady flow we find that ice stream tributaries and the inland ice account for about 87 of the total melt generated beneath the ross ice streams and their catchments our estimates indicate that the ice plains of whillans ice stream and ice stream c even when active have large areas subject to basal freezing confirming earlier estimates that import of water from upstream is necessary to sustain motion the relatively low melt rates on whillans ice stream are consistent with observations of deceleration over the last few decades and suggest a shutdown may take place in the future possibly within this century while there are pockets of basal freezing beneath ice streams d and e there are larger areas of basal melt that produce enough melt to more than offset the freezing which is consistent with inferences of relatively steady flow for these ice streams over the last millennium

sedimentary processes at the base of a west antarctic ice stream constraints from textural and compositional properties of subglacial debris samples of sediments from beneath ice stream b at camp upb west antarctica provide the first opportunity to study the relationship between sediment properties and physical conditions in a sub ice stream environment piston coring in holes bored by hot water drilling yielded five 1 3 m long undisturbed subglacial sediment cores we analyzed granulometry composition and particle morphology in these cores the upb cores are composed of a clay rich unsorted diamicton containing rare marine diatoms sedimentary particles in these cores bear no evidence of the recent crushing or abrasion that is common in other subglacial sedimentary environments the presence of reworked diatoms and their state of preservation as well as the relative spatial homogeneity of this diamicton suggest that the upb cores sampled a several meter thick till layer and not in situ glacimarine sediments the till does incorporate material recycled from the subjacent poorly indurated tertiary glacimarine sediments of the ross sea sedimentary basin which extends beneath this part of the west antarctic ice sheet we propose that the lack of significant comminution in the upb till is ultimately due to its setting over these easily erodible clay rich source sediments the resulting fine grained till matrix inhibits glacial comminution because it facilitates buildup of high pore water pressures and hinders interparticle stress concentrations our observations are consistent with the conjecture that subglacial deformation of weak fine grained tills does not produce significant comminution of till debris elson 1988 based on our findings we hypothesize that extensive layers of weak till may develop preferentially where ice overrides preexisting poorly indurated fine grained sediments since such weak till layers create a permissive condition for ice streaming sub glacial geology may have an indirect but strong control over the location extent and basal mechanics of ice streams

hydrochemistry of ice stream beds evaporitic or microbial effects recently new data have been acquired on the chemical composition of waters within the glacial till beneath the kamb ice stream kis formerly ice stream c and the bindschadler ice stream bis formerly ice stream d two of the arteries of ice loss from the antarctic ice sheet ais we compare this water chemistry with basally stored subglacial waters from arctic and alpine glaciers and the only other measurements of sub ice sheet chemistry to date that emerging from beneath law dome near casey station sw antarctica during a jokulhlaup we find that the chemistries pose significant questions about the hydrology and biogeochemistry of ice sheet beds copyright 2010 john wiley sons ltd