stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

sedimentology stratigraphic occurrence and origin of linked debrites in the west crocker formation oligo miocene sabah nw borneo abstract the west crocker formation oligocene early miocene nw borneo consists of a large 20 000 km2 submarine fan deposited as part of an accretionary complex a range of gravity flow deposits are observed the most significant of which are mud poor massive sandstones interpreted as turbidites and clast rich muddy sandstones and sandy mudstones interpreted as debrites an upward transition from turbidite to debrite is commonly observed with the contact being either gradational and planar or sharp and highly erosive based on their repeated vertical relationship and the nature of the contact between them these intervals are interpreted as being deposited from one flow event which consisted of two distinct flow phases fully turbulent turbidity current and weakly turbulent to laminar debris flow the associated bed is called a co genetic turbidite debrite with the upper debrite interval termed a linked debrite linked debrites are best developed in the non channellised parts of the fan system and are absent to poorly developed in the proximal channel levee and distal basin floor environments due to outcrop limitations the genesis of linked debrites within the west crocker formation is unclear based on clast size and type it seems likely that a weakly turbulent to laminar debris flow flow phase was present when the flow event entered the basin a change in flow behaviour may have led to deposition of a sand rich unit with turbidite characteristics which was subsequently overlain by a mud rich unit with debrite characteristics flow transformation may have been enhanced by the disintegration and incorporation into the flow of muddy clasts derived from the upstream channel floor channel mouth or from channel levee collapse lack of preservation of this debrite in proximal areas may indicate either bypass of this flow phase or that the available outcrops fail to capture the debris flow entry point establishing robust sedimentological criteria from a variety of datasets may lead to the increasing recognition of co genetic turbidite debrite beds and an increased appreciation of the importance of bipartite flows in the transport and deposition of sediments in deepwater environments

ancient lacustrine hyperpycnites a depositional model from a case study in the rayoso formation cretaceous of west central argentina abstract hyperpycnal flows originate when sediment laden fluvial discharges enter standing lower density water because of their excess density the flows plunge near the river mouth and continue to travel basinward as a quasi steady and fully turbulent underflow the related deposits are hyperpycnites and constitute a particular type of turbidite with poorly known facies and facies tracts although hyperpycnal flows seem to be quite common in present times their occurrence in fossil strata is poorly documented this paper addresses the characteristics and depositional processes of shallow lacustrine sandy hyperpycnites on the basis of the field analysis of well exposed lower cretaceous strata rayoso formation in the neuquen basin of west central argentina the rayoso formation is composed of clastic and minor evaporitic red beds up to 1200 m thick deposited in a shallow perennial lake of variable salinity affected by long lived hyperpycnal flows main clastic facies are composed of fine grained sandstones with climbing ripples and plane beds other common sandstone facies include massive beds and low angle cross stratification most sandstone facies are related to traction plus fallout processes and often show a vertical fluctuation between sedimentary facies originated under different traction plus fallout conditions within single beds these fluctuations are interpreted to be evidence of deposition from flow fluctuations in sustained hyperpycnal flows most beds internally show the existence of three depositional phases acceleration ap erosion plus bypass ep and deceleration dp which record the complete evolution of a single long lived hyperpycnal flow at a fixed point additionally the depositional evolution of a single long lived hyperpycnal flow with distance records initially the progressive basinward migration of the ap and ep phases and finally an overall deposition under the dp phase both in proximal and distal areas this evolution provides an adequate explanation for the basinward extension of channelized features and for the occurrence of fine grained sandstones with climbing ripples both in proximal and distal positions within the same hyperpycnal system consequently facies analysis derived from application of the bouma sequence is not valid for deposits of quasi steady hyperpycnal flows

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

procedures used for luminescence dating of sediments abstract an account of the procedures for thermoluminescence tl and optically stimulated luminescence osl dating of sediments used at the nordic laboratory for luminescence dating is given the topics discussed include sampling sample preparation separation of quartz and feldspars using heavy liquids dose rate estimation and methods for estimating the equivalent dose special attention is paid to the partial bleach tl technique of mejdahl 1988 which appears to give reliable results for partially bleached sediments optically stimulated luminescence dating using stimulation by infra red ir and green light has been taken up and especially added dose methods using stimulation by ir or green light have been tried with some success some sources of error are discussed including the adverse effect of shallow traps

anatomy of a subaqueous ice contact fan and delta complex middle pleistocene north west germany this paper presents a detailed analysis of the high resolution facies architecture of the middle pleistocene porta subaqueous ice contact fan and delta complex deposited on the northern margin of glacial lake weser northwest germany a total of 10 sand and gravel pits and more than 100 wells were examined to document the complex facies architecture the field study was supplemented with a ground penetrating radar survey and a shear wave seismic survey all collected sedimentological and geophysical data were integrated into a high resolution three dimensional geological model for reconstructing the spatial distribution of facies associations the porta subaqueous fan and delta complex consist of three fan bodies deposited on a flat lake bottom surface at the margin of a retreating ice lobe the northernmost fan complex is up to 55 m thick 6ae2 km wide and 6ae5 km long the incipient fan deposition is characterized by high energy flows of a plane wall jet very coarse grained highly scoured jet efflux deposits with an elongate plan shape indicate a high froude number probably 5 these jet efflux sediments are deposited in front of a large 3ae2 km long up to 1ae2 km wide and up to 25 m deep flute like scour indicating the most proximal erosion and bypass area of the jet that widens and deepens with distance downstream to the region of maximum turbulence approximately five times the conduit diameter evidence for subsequent flow splitting is given by the presence of two marginal gravel fan lobes deposited in front of 1ae 3t o 2ae5 km long flute like scours that are 0ae8 to 1 km wide and 7 to 20 m deep in response to continued aggradation small jets developed at the periphery of these bar like deposits and filled in the low areas adjacent to the original superelevated regions locally raising the depositional surface and characterized by large scale trough cross stratified sand and pebbly sand the incision of an up to 1ae2 km wide and up to 35 m deep channel into the evolving fan is attributed to a catastrophic drainage event probably related to a lake outburst and lake level fall in the range of 40 to 60 m at the mouth of this channel highly scoured jet efflux deposits formed under hydraulic jump conditions during flow expansion subsequently gilbert type deltas formed on the truncated fan margin recording a second lake level drop in the range of 30 to 40 m these catastrophic lake level falls were probably caused by rapid ice lobe retreat controlled by the convex up bottom topography of the ice valley

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

deciphering the paleoceanographic significance of early oligocene braarudosphaera chalks in the south atlantic abstract the recurrence of braarudosphaera chalks in the lower oligocene sequences of the subtropical south atlantic has been a long standing conundrum with many hypotheses having been advanced to explain the genesis of these exotic nannofossil assemblages here we evaluate different paleoceanographic models within the context of stable isotope 18o 13c data measured from bulk sediment samples and well preserved foraminifera two closely spaced braarudosphaera layers from a lower oligocene foram subzone p21a 29 4 28 5 ma section drilled in the southeastern atlantic dsdp site 363 are investigated maximum durations for the blooms that deposited the lower and upper braarudosphaera layers are estimated to be 1 1 and 2 2 k y respectively bulk sediment samples enriched in braarudosphaerid carbonate exhibit pronounced 18o increases on the order of 0 6 1 0 which we attribute to isotopic disequilibria driven by braarudosphaerid vital effects the two braarudosphaera layers straddle a single peak in benthic foraminiferal 18o values suggesting that these blooms may recur on glacial interglacial timescales this same pair of braarudosphaerid layers also occurs as a couplet bundled with prolonged 6 7 k y thermocline cooling evidence that these stratigraphically distinct deposits may represent a split signal for a single paleoceanographic paleoclimatic event subsumed within this episode of subsurface cooling are two short lived negative excursions 0 5 in the 13c record of a thermocline dwelling planktonic foraminifer that coincide with the braarudosphaerid layers thus benthic to thermocline 18o and 13c gradients were reduced during the braarudosphaerid blooms a hallmark signature for strengthened upwelling both braarudosphaerid layers are marked by transient divergences in the stable isotopic signals of two shallow dwelling species of planktonic foraminifera these transient 18o offsets may reflect subtle differences in the depth ecologies of these two mixed layer species if so then braarudosphaerid depositional events may represent subsurface blooms that took place within the lower parts of the euphotic zone alternatively these transient 18o offsets may reflect periods of pronounced seasonality with braarudosphaerid blooms occurring during spring upwelling the recurrence of braarudosphaera blooms on both sides of the south atlantic is believed to reflect rhythmic changes in the vigor and configuration of gyre circulation we speculate that the termination of braarudosphaera blooms in the south atlantic near the end of the early oligocene may be related to paleoceanographic change caused by the crossing of a critical threshold in the tectonic opening of the drake passage and the development of the antarctic circum polar current

a major trough mouth fan on the continental margin of the bellingshausen sea west antarctica the belgica fan a 330 km length of the little known continental shelf edge and slope of the bellingshausen sea west antarctica is investigated using multibeam swath bathymetric and sub bottom profiler evidence the shelf break is at 650 700 m across the 150 km wide belgica trough and to either side is about 500 m when full glacial ice advanced across the shelf to reach the shelf break it was partitioned into fast and slow flowing elements with an ice stream filling the trough this had important consequences for the nature and rate of sediment delivery to the adjacent continental slope off belgica trough the upper continental slope has convex outward contours indicating a major sedimentary depocentre of gradient 1 2 degrees acoustic profiles and cores from the depocentre show a series of diamictic glacigenic debris flows the depocentre is interpreted as a trough mouth fan built largely by debris delivered from the ice stream the slope is steeper beyond the trough margins at up to 6 degrees the main morphological features on the bellingshausen sea slope are gully systems and channels major canyons and late quaternary slides are absent most gullies and channels are found on the fan gullies are about 15 25 m deep a few hundred metres wide and some are 25 km long the largest channel is over 60 km long about a kilometre wide and 10 to 15 m deep the channels provide pathways for sediment by passing of the upper slope and transfer to the continental rise and beyond by turbidity currents gullies on the bellingshausen sea margin cut through debris flows on the slope assuming the debris flows are linked mainly to downslope transport of diamictic debris when ice was at the shelf edge under full glacial conditions then those gullies cut into them formed during deglaciation belgica fan is 22 000 km 2 in area and about 60 000 km 3 in volume it is the largest depocentre identified to date on the continental margin of the west antarctic ice sheet fed by an interior ice sheet basin of approximately 200 000 km 2 c 2008 elsevier b v all rights reserved

behaviour of particle laden flows into the ocean experimental simulation and geological implications the behaviour of subaerial particle laden gravity currents e g pyroclastic flows lahars debris flows sediment bearing floods and jokulhlaups flowing into the sea has been simulated with analogue experiments flows of either saline solution simple suspensions of silicon carbide sic in water or complex suspensions of sic and plastic particles in methanol were released down a slope into a tank of water the excess momentum between subaerial and subaqueous flow is dissipated by a surface wave at relatively low density contrasts between the tank water and the saline or simple suspensions the flow mixture enters the water and forms a turbulent cloud involving extensive entrainment of water the cloud then collapses gravitationally to form an underwater gravity current which progresses along the tank floor at higher density contrasts the subaerial flow develops directly into a subaqueous flow the flow slows and thickens in response to the reduced density contrast which is driving motion and then continues in the typical gravity current manner complex suspensions become dense flows along the tank floor or buoyant flows along the water surface if the mixtures are sufficiently denser or lighter than water respectively flows of initially intermediate density are strongly influenced by the internal stratification of the subaerial flow material from the particulate depleted upper sections of the subaerial flow becomes a buoyant gravity current along the water surface whereas material from the particulate enriched lower sections forms a dense flow along the tank floor sedimentation from the dense flow results in a reduction in bulk density until the mixture attains buoyancy lifts off and becomes a secondary buoyant flow along the water surface jokulhlaups lahars and debris flows are typically much denser than seawater and thus will usually form dense flows along the seabed after sufficient sedimentation the freshwater particulate mixture can lift off to form a buoyant flow at the sea surface leading to a decoupling of the fine and coarse particles flood waters with low particulate concentrations 2 may form buoyant flows immediately upon entering the ocean subaerial pyroclastic flows develop a pronounced internal stratification during subaerial run out and thus a flow splitting behaviour is probable which agrees with evidence for sea surface and underwater flows from historic eruptions of krakatau and mont pelee a pyroclastic flow with a bulk density closer to that of sea water may form a turbulent cloud resulting in the deposition of much of the pyroclasts close to the shore dense subaqueous pyroclastic flows will eventually lift off and form secondary buoyant flows either before or after the transformation to a water supported nature

model for how microbial methane generation can preserve early porosity in dolomite and limestone reservoirs in some dolomite and limestone hydrocarbon reservoirs protection from cementation is a primary factor in porosity preservation we present a model in which methanogens methane producing microorganisms produce methane gas ch4 g that outgasses from solution in pore space creating a two phase system that reduces effective hydraulic conductivity k protecting pore space from cementation methanogens have been implicated in dolomite formation and can generate methane to fill pore space of a model near surface carbonate sediment 37 5 primary porosity with ch4 g in 180 to 4650 yr depending on nutrient levels gas generation results in occlusion of the aqueous phase from pore spaces and throats creating a two phase flow regime reducing the effective hydraulic conductivity of model marine carbonate sand by about 50 from 2 8 to 1 2 cm day in as little as 55 yr therefore reducing aqueous fluid flow necessary for cementation despite rapid burial and complete cessation of methanogenesis effective hydraulic conductivity could take more than 100 000 yr to return to its original value if methanogenesis continues with burial the effective hydraulic conductivity is reduced to zero after 250 yr dolomites can preserve more primary porosity with depth than other carbonates we propose that in addition to increased structural resistance a biogenic model exists for porosity preservation in dolomites that is linked to the activity of methanogens this model represents specific end member cases and illustrates the effect of methane buildup in relationship to the extent of reservoir diagenesis

arabia eurasia collision and the forcing of mid cenozoic global cooling the end of the eocene greenhouse world was the most dramatic phase in the long term cooling trend of the cenozoic era here we show that the arabia eurasia collision and the closure of the tethys ocean gateway began in the late eocene at 35 ma up to 25 million years earlier than in many reconstructions we suggest that global cooling was forced by processes associated with the initial collision that reduced atmospheric co2 these are 1 waning volcanism across southwest asia 2 increased organic carbon storage in paratethyan basins e g black sea and south caspian 3 increased silicate weathering in the collision zone and 4 a shift towards modern patterns of ocean currents associated with increased vigour in circulation and organic productivity

subglacial floods beneath ice sheets subglacial floods jokulhlaups are well documented as occurring beneath present day glaciers and ice caps in addition it is known that massive floods have occurred from ice dammed lakes proximal to the laurentide ice sheet during the last ice age and it has been suggested that at least one such flood below the waning ice sheet was responsible for a dramatic cooling event some 8000 years ago we propose that drainage of lakes from beneath ice sheets will generally occur in a time periodic fashion and that such floods can be of severe magnitude such hydraulic eruptions are likely to have caused severe climatic disturbances in the past and may well do so in the future

saalian to weichselian stratigraphy and sedimentation along the lagjaeren hogjaeren escarpment southwest norway quaternary sediments along a profile crossing the southern part of the jaeren escarpment southwestern norway have been investigated with regard to their glacial history and sea level variations deposits from at least three glaciations and two ice free periods between oxygen isotope stage 6 and the late weichselian have been identified subglacial till directly overlain by a glaciomarine regressional succession indicates a deglaciation and amino acid ratios in elphidium excavatum between 0 083 and 0 118 date this event to oxygen isotope stage 6 sea level dropped from 130 to below 110 m a s l subsequently a short lived ice advance deposited a marginal moraine and a sandur locally on the escarpment stratigraphical position and luminescence dates around 148 ka bp suggest deposition during the final stage 6 deglaciation a late weichselian till covers most of the surface of jaeren in addition to a well documented westerly ice flow glaciotectonic indications of ice flow towards the north have been found ice flow directions and a hiatus between oxygen isotope stage 6 and the weichselian indicate enhanced erosion along the escarpment and the influence of a norwegian channel ice stream copyright 1999 john wiley sons ltd

shallow water methane seep faunas in the cenomanian western interior seaway no evidence for onshore offshore adaptations to deep sea vents sulfi de rich environments in shallow water were considered as sites where animals acquired preadaptations enabling them to colonize deep sea hydrothermal vents and seeps or where they survived extinction events in their deep sea habitats here we document late cenomanian shallow water seep communities from the tropic shale in the western interior seaway united states as a possible refutation of these hypotheses the late cenomanian was a time of extremely warm deep water temperatures which supposedly facilitated adaptations to the deep sea and of widespread oceanic anoxia oceanic anoxic event 2 that supposedly extinguished deep water vent and seep faunas contrary to the expectations the taxa of the tropic shale seeps were not found at coeval or younger deep water seep or vent deposits furthermore a cluster analysis of faunal similarity among cretaceous vent and seep faunas revealed no distinction between pre and post cenomanian seep faunas but instead strong similarities among aptian to late cretaceous seep faunas this suggests that a low temperature gradient from shallow to deep water did not facilitate invasions of deep sea vents and seeps from shallow water and that preadaptation for living at deep sea vents and seeps did not evolve at shallow water methane seeps the vast majority of adaptations to successfully colonize deepsea vents and seeps were most likely acquired below the photic zone

architectural analysis of a volcaniclastic jokulhlaup deposit southern iceland sedimentary evidence for supercritical flow the 1918 eruption of the glacially capped katla volcano southern iceland generated a violent jokulhlaup or glacial outburst flood inundating a large area of m rdalssandur the proglacial outwash plain where it deposited ca 1 km3 of volcaniclastic sediment the character of the 1918 jokulhlaup is contentious having been variously categorized as a turbulent water flow a hyperconcentrated flow or as a debris flow based on localized outcrop analysis in this study outcrop based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi stationary antidunes and down current migrating antidunes and from regular based bedsets associated with transient chute and pool bedforms all of which are associated with turbulent transcritical to supercritical water flow conditions antidune wavelengths range from 24 to 96 m corresponding to flow velocities of 6 to 12 m sec 1 and average flow depths of 5 to 19 m this range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts architectural analysis of the 1918 jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jokulhlaup that could not have been achieved through localized outcrop analysis the observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions the physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations regarding modes of deposition and formative flow hydraulics are to be made

forms at the base of till units indicating deposition by lodgement and melt out with examples from the wartanian tills near belchatow central poland abstract observations from a 2 to 4 km long till section in the belchatow quarry central poland show that the contact between till and sub till deposits is generally sharp and undeformed the tills contain a range of features typical of melt out processes however in laterally equivalent till bodies features typical of lodgement and subglacial shearing e g sub till deformation structures clast ploughing are common recognition of melt out and lodgement tills as separate subglacial facies indicating different subglacial conditions may prove rather simplistic in palaeoenvironmental reconstruction so called melt out and lodgement till facies probably represent only extreme end members of a range of basal till facies types till sections described here show features suggesting that both basal melt out and lodgement processes operated during one episode of subglacial deposition

anatomy of shelf deltas at the edge of a prograding eocene shelf margin spitsbergen although shelf edge deltas are well imaged seismic features of holocene and pleistocene shelf margins documented outcrop analogues of these important sand prone reservoirs are rare the facies and stratigraphic architecture of an outcropping shelf edge delta system in the eocene battfjellet formation spitsbergen is presented here as well as the implications of this delta system for the generation of sand prone shelf margin clinoforms the shelf edge deltas of the battfjellet formation on litledalsfjellet and hogsnyta produced a 3 5 15 km shelf edge attached slope apron 70 m of sandstones proximally tapering to zero on the lower slope the slope apron consists of distributary channel and mouth bar deposits in its shelf edge reaches passing downslope to slope channels chutes that fed turbiditic lobes and spillover sheets in the transgressive phase of the slope apron estuaries developed at the shelf edge and these also produced minor lobes on the slope the short headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf and the shelf edge position of the discharging deltas made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin the abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane parallel laminae within turbidite beds in the slope channels and thick spillover lobes with repetitive alternations of massive and flatlaminated intervals the examined shelf edge to slope system now preserved mainly below the shelf break and dominated by sediment gravity flow deposits has a threefold stratigraphic architecture a lower progradational part in which the clinoforms have a slight downward directed trajectory a thin aggradational zone and an upper part in which clinoforms backstep up onto the shelf edge a greatly increased density of erosional channels and chutes marks the regressive to transgressive turnaround within the slope apron and this zone becomes an angular unconformity up near the shelf edge this unconformity with both subaerial and subaqueous components is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level the studied shelf margin clinoforms accreted mostly during falling stage sea level below the shelf edge but the outer shelf later became estuarine as sea level became re established above the shelf edge

alluvial responses to the changing earth system alluvial systems are complex self organizing and hierarchical in structure they represent stored and transitory sediment bodies transported by rivers that have eroded their catchments and created multiscalar landforms and sedimentary architectures over a range of time scales the central question we address in this paper is how environmental signals are autogenically processed and recorded by the fluvial sediment system we compare databases of alluvial units that are well constrained in terms of dating control with direct or proxy records of environmental change river system responses to environmental change are evaluated over three nested time periods spanning the past 200 000 years first focusing on mediterranean european and african catchments river responses to relatively abrupt and short term late pleistocene dansgaard oeschger and heinrich climate events are examined second the effects of rapid and globally significant episodes of holocene climate change on european rivers together with anthropogenic land use impacts are assessed last little ice age flooding and alluvial responses to modern climate warming are reviewed with particular reference to upland britain these studies are shown to have significant implications for modelling local regional and global scale alluvial responses to future environmental change they highlight the necessity for numerical simulation models to be fully informed by field based knowledge and understanding of the memory effects of whole fluvial sediment systems particularly those that have experienced repeated phases of environmental change copyright 2008 john wiley sons ltd

late ordovician glaciogenic reservoir heterogeneity an example from the murzuq basin libya in north africa late ordovician glaciogenic reservoirs contain large volume of recoverable hydrocarbon reserves but their heterogeneity and internal complexity means they are poorly understood to improve this understanding this paper presents the case study of the murzuq basin sw libya and a synthesis of the stratigraphic architecture of upper ordovician glaciogenic reservoirs the mamuniyat formation within it particular attention is paid to regionally extensive stratigraphic boundaries and the geometry of sandstone units of potential reservoir quality four disconformity bound units are recognised the bounding surfaces of which are flat or of high relief unit 1 the oldest and unit 3 are mud dominated and tend towards non reservoir in contrast units 2 and 4 the youngest are sand dominated have poor to excellent reservoir quality but distinctly different sedimentological architectures across the basin unit 2 comprises transitions from glaciofluvial intertidal sandstones to offshore turbidites and formed exclusively during glacial retreat the occurrence of a significant palaeotopography affected sandbody geometry with glaciofluvial intertidal deposits concentrating in the lee of these palaeohighs or infilling the bottom of tunnel valleys unit 4 is a compound stratigraphic unit recording the effects of glacial retreat and isostatic rebound in deep marine settings turbidite fans were deposited during retreat but in shallow water settings structural reactivation and sediment reworking had a more profound effect on sedimentation sedimentological architectures are variable at this level and include prograding coarse clastic wedges away from a palaeohigh or the infill of half graben basins during isostatic rebound

the cretaceous tertiary transition the fossil sequences from cores across the cretaceous tertiary boundary show a range of transition times and transition time intervals depending on the fossil indicators and the location of the site these variations together with the pattern of iridium distribution with depth at some sites differences in total amounts of iridium variations in noble metal abundances normalized to extraterrestrial concentrations the depositional effects that might be expected in a reducing environment and the clay mineralogy of the boundary layer clays put into question the interpretation that an extraterrestrial event was the cause of the faunal changes and the iridium anomaly in the vicinity of the cretaceous tertiary transition it seems more likely that an explanation for the changes during the transition will come from continued examination of the great variety of terrestrial events that took place at that time including extensive volcanism major regression of the sea from the land geochemical changes and paleoclimatic and paleoceanographic changes

sediment laden gravity currents with reversing buoyancy there are many natural occurrences of sediment laden gravity currents in which the density of the interstitial fluid is less than that of the ambient fluid although the bulk density of the current is greater such currents are driven by the excess density of suspended particles however after sufficient particles have sedimented the current will become buoyant cease its lateral motion and ascend to form a plume examples of such currents include brackish underflows in deltas turbidity currents and pyroclastic flows experimental studies are described which show that due to sedimentation sediment laden gravity currents decelerate more rapidly than saline currents of the same density there is little difference in the experiments between a sediment laden current with neutrally buoyant interstitial fluid and one with buoyant interstial fluid until sufficient sediment has been lost to cause the latter kind of current to lift off a marked deceleration is then observed and a plume is generated with lift off occurring along the length of the current the resulting buoyant plume then generates a gravity current below the upper surface of the fluid in the tank the deposit from a current with buoyant fluid shows a fairly abrupt decrease in thickness beyond the lift off distance and has a flatter profile than that from a simple sediment current a theoretical model is presented which is based on the two layer shallow water equations and incorporates a model of the sedimentation in which particles are assumed to be uniformly suspended by the turbulence of the current the model shows good agreement with the observed lengths of the experimental currents as a function of time and predicts the lift off distance reasonably well these processes have implications for the behaviour of turbidity currents the interpretation of turbidites mixing processes in the oceans and the lift off of pyroclastic flows

glaciation and deglaciation of the libyan desert the late ordovician record detailed outcrop studies at the flanks of al kufrah basin libya reveal the nature of glacially related sedimentation and post depositional deformation styles produced in association with the late ordovician glaciation during which ice sheets expanded northward over north africa to deposit the mamuniyat formation at the se basin flank jabal azbah the mamuniyat formation is sand dominated and incises interfingering braidplain and shallow marine deposits of the hawaz formation the glacially related sediments include intercalations of mud chip bearing tabular sandstones and intraformational conglomerates which are interpreted as turbidite and debrite facies respectively these record aggradation of an extensive sediment wedge in front of a stable former ice margin an increase in mudstone content northward is accompanied by the occurrence of more evolved turbidites a widespread surface bearing streamlined nw se striking ridges and grooves punctuates this succession the structures on the surface are interpreted to have formed during a regional north westward ice advance above siltstones bearing arthrophycus burrows and orthocone bearing sandstones beneath tidal bars testify to glaciomarine conditions for deposition of the underflow deposits beneath by contrast the northern basin margin jabal az zalmah is appreciably different in recording shallower water paralic sedimentation styles and major glaciotectonic deformation features although facies analysis also reveals northward deepening here a siltstone wedging from 8 to 50 m toward the north was deposited lower delta plain succeeded by climbing ripple cross laminated sandstones up to 60 m in thickness distal through proximal delta mouth bar deposits with occasional diamictite interbeds these rocks are deformed by thrusts and 50 m amplitude fault propagation folds the deformation locally sealed by a diamictite then overlain by conglomeratic lag during ultimate deglaciation integrating observations from both basin margins a model of fluvial dominated delta systems feeding a pulsed debrite and turbidite fan system in a shallow proglacial shelf is proposed

a quaternary aminostratigraphy constraining chronology of depositional environments in the north sea basin abstract the aminostratigraphy of up to 1000 m of glacial and interglacial sediments in the north sea basin nsb is compiled from multiple boreholes sites and dated using strontium isotope sr analysis to provide a chronological framework extending throughout the quaternary the quaternary aminostratigraphy within the nsb can be divided into five amino zones az az1 youngest to az5 based on alle ile ratios which are used to correlate depositional events recorded in sedimentary facies from multiple borehole sites the new relative and absolute chronology also ties to seismostratigraphy and multi generational tunnel valley fill early pleistocene sediments produce az5 ratios with sr ages around 1 4 1 5 ma deposited in marine to glacimarine conditions sediments with az4 ratios are constrained by sr ages and magnetic polarity to 1 3 0 9 ma spanning the eccentricity to axial tilt insolation periodicity change of the mid pleistocene transition mpt some coarse grained sedimentary units with az4 ratios may be linked to ice proximal deposition during the mpt sediments with az3 ratios are poorly chronologically constrained to between 1 1 and 0 26 ma at least one episode of diminished coarse clasts and increased foraminiferal diversity during this mid pleistocene time suggests a progression from ice proximal to warmer possibly interglacial conditions furthermore the stratigraphically deepest generation of tunnel valleys cut strata with az3 ratios indicating subglacial conditions at least once during the mid pleistocene sediments with az2 ratios corresponding to mis7 5 are tied to seismic units including a thick up to 40 m deformation till suggesting glacial incursion into the nsb during mis6 followed by tunnel valley cutting of the this till thought to be an mis6 event also the geometry and cross cutting complexities of such tunnel valleys precludes further correlation of this ice extent the youngest aminostratigraphic zone az1 is recognised in all boreholes and well constrained to mis4 2 and the youngest set of tunnel valleys attributed to a single or multiple glacial advances at this time

reversing buoyancy in turbidity currents developing a hypothesis for flow transformation and for deposit facies and architecture a turbidity current that contains fresher or otherwise less dense water than its surroundings may initially be denser than the ambient and propagate as a bottom hugging flow but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient seawater it is proposed that this reversal in buoyancy may be a significant mechanism controlling the structure and facies of turbiditic deposits buoyancy reversal followed by lofting may directly affect the relative distribution of fine and coarse material in the deposit while buoyancy reversal itself may mediate the transformation between dilute and highly concentrated suspension flows particularly in distal regions and thus lead to the formation of complex turbiditic beds in particular the generation of distal co genetic debrites may be expected similar transformations occur within dilute pyroclastic density currents where a mobile basal concentrated flow termed a surge derived pyroclastic flow develops through rapid sedimentation from the suspended load of the overlying surge the physical mechanisms involved in these processes are discussed leading to the proposal of some associated facies models these are compared with field data from the northern apennines with some striking similarities being noted as well as some differences on the basis of this discussion some directions are suggested for future experimental and modelling work on the topic

significance of fine grained sediment lofting from melt water generated turbidity currents for the timing of glaciomarine sediment transport into the deep sea abstract sediment lofting from turbidity currents is a process that occurs in density currents generated from fresh water discharges into the sea and other gravity currents that can produce reversed buoyancy settling of suspended sediment from the top or deposition from the bottom of the flows may lower the density below that of ambient seawater causing the currents to lift up from their substrate either in part or as a whole through buoyancy reversal as is well known from experiments fine grained sediment lofting on a large scale during times of heinrich events has been inferred for ice proximal regions of the northwest labrador sea adjacent to the margin of the late pleistocene laurentide ice sheet lis the evidence comes from a distinct depositional facies of stacked graded mud layers containing ice rafted debris ird the significance of the lofted fine grained depositional facies arises from its genetic link to large sand and gravel transporting turbidity currents that were generated by melt water discharges from the hudson strait outlet of the lis and are the likely source of the lofted sediment the observed lofted depositional facies is exclusively found in heinrich layers through this stratigraphic relationship the lofted facies ties the main pulses of sediment supply in the labrador basin to heinrich events heinrich events thus appear to be the times of the main depositional activity in the labrador sea a hitherto unknown aspect of these phenomenal events besides their known role as intense iceberg discharges

ostracods crustacea through permian triassic events abstract through geological times the main turnover of marine ostracod group occurred at the permian triassic boundary ptb when the palaeozoic world gave way to meso cenozoic world as quite all the groups ostracods intensively suffered of the end palaeozoic events but they have the particularity to pass the ptb and to be present in quite all marine environments we have studied the ostracod assemblages from the best preserved marine permian triassic sections through the world these sections are for most of them located along the palaeo tethys margins south china block and tibet r p china bukk mountains hungary dolomites italy taurus mountains turkey and elbourz mountains iran these areas present different environmental settings from very shallow water to deep shelf the biostratigraphy is well constrained by the presence of conodont index in deep environment from external shelf to slope all the permian ostracods disappear slightly before the ptb and are absent from the early triassic the last representatives of palaeopsychrospheric forms occur in the early anisian on the platforms during the late permian the ostracods are abundant and highly diversified everywhere along peri tethyan margins the typical palaeozoic forms are mixed with the very first meso cenozoic representatives the specific extinction rates in the latest permian vary from 74 to 100 during the earliest triassic two different settings have to be considered with or without microbialitic deposits the development of microbialites gives favorable ecological conditions to ostracods during the griesbachian the fauna is composed of both new comers and surviving palaeozoic forms the reduction of size is frequently observed this interval is called survival stage during the dienerian and the smithian the fauna are very scarce and poor these two substages represent the maximum of poverty for the ostracod fauna may be due to the development of anoxia on the platforms during the spathian occurs the beginning of the true recovery the very last palaeozoic representatives are found in the earliest anisian which is the radiation stage of ostracod fauna with typical new comers the interval of palaeozoic meso cenozoic ostracod turnover is quite long about 15 my

late ordovician climbing dune cross stratification a signature of outburst floods in proglacial outwash environments climbing dune scale cross statification is described from late ordovician paraglacial successions of the murzuq basin sw libya this depositional facies is comprised of medium grained to coarse grained sandstones that typically involve 0 3 to 1 m high 3 to 5 m in wavelength asymmetrical laminations most often stoss depositional structures have been generated with preservation of the topographies of formative bedforms climbing dune cross stratification related to the migration of lower flow regime dune trains is thus identified related architecture and facies sequences are described from two case studies i erosion based sandstone sheets and ii a deeply incised channel the former characterized the distal outwash plain and the fluvial subaqueous transition of related deltaic wedges while the latter formed in an ice proximal segment of the outwash plain in erosion based sand sheets climbing dune cross stratification results from unconfined mouth bar deposition related to expanding sediment laden flows entering a water body within incised channels climbing dune cross stratification formed over eddy related side bars reflecting deposition under recirculating flow conditions generated at channel bends associated facies sequences record glacier outburst floods that occurred during early stages of deglaciation and were temporally and spatially linked with subglacial drainage events involving tunnel valleys the primary control on the formation of climbing dune cross stratification is a combination between high magnitude flows and sediment supply limitations which lead to the generation of sediment charged stream flows characterized by a significant relatively coarse grained sand sized suspension load concentration with a virtual absence of very coarse to gravelly bedload the high rate of coarse grained sand fallout in sediment laden flows following flow expansion throughout mouth bars or in eddy related side bars resulted in high rates of transfer of sands from suspension to the bed net deposition on bedform stoss sides and generation of widespread climbing dune cross stratification the later structure has no equivalent in the glacial record either in the ancient or in the quaternary literature but analogues are recognized in some flood dominated depositional systems of foreland basins

magnitude and frequency in proglacial rivers a geomorphological and sedimentological perspective abstract proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments this paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective the nature of the meltwater inputs can be characterised as low magnitude high frequency primarily controlled by ablation inputs from the source glacier or high magnitude low frequency primarily controlled by exceptional inputs the most important high magnitude low frequency inputs are catastrophic outburst floods often referred to by the term jokulhlaup icelandic for glacier burst glacier surges are an additional form of cyclical variation impacting the proglacial environment which briefly alter the volumes and patterns of meltwater input the sedimentary consequences of low magnitude high frequency discharges are related to frequent variations in stage the greater directional variability that sediment will record and the increased significance of channel confluence sedimentation in contrast the most significant characteristics of high magnitude low frequency flooding include the presence of large flood bars and mid channel jokulhlaup bars hyperconcentrated flows large gravel dunes and the formation of ice block kettle hole structures and rip up clasts glacier surges result in a redistribution of low magnitude high frequency processes and products across the glacier margin and small floods may occur at the surge termination criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics studies of quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime sediment supply the pattern of glacier advance or retreat and proglacial topography a model of sandur development is suggested which shows how discharge magnitude and frequency in combination with sandur incision and aggradation controlled by glacier advance and retreat can control sandur stratigraphy

subglacial deformation and water pressure cycles as a key for understanding ice stream dynamics evidence from the late ordovician succession of the djado basin niger subglacial deformation is crucial to reconstructing glacier dynamics sediments associated with the late ordovician ice sheet in the djado basin niger exhibit detailed structures of the subglacial shear zone three main types of subglacial shear zones ssz are discriminated the lowermost ssz developed on sandstones displays riedel macrostructures and cataclastic microstructures these resulted from brittle deformation associated with strong glacier bed coupling and low pore water pressure where they developed on a clay rich bed the overlying ssz display s c to s c fabrics sheath folds and dewatering structures these features indicate high ductile shear strain and water overpressure on fine grained sand beds the ssz exhibit homogenized sand units with sand stringers interpreted as fluidized sliding beds the succession of subglacial deformation processes depends on fluid pressure behavior in relation to subglacial sediment permeability fluid overpressure allows subglacial sediment shear strength and ice bed coupling to be lowered leading to ice streaming

weichselian land sea interactions western norway norwegian sea abstract six major weichselian glacier expansions including the younger dryas are recorded in western norway three of the advances reached the continental shelf while the others were restricted to the coastal areas during the upper weichselian glacial maximum 18 20 ka there was an ice free corridor between the british and the scandinavian ice sheets in the northern north sea more or less complete deglaciation of southern norway seems to have happened some time around 90 and 70 ka large parts of the norwegian sea were at least seasonally open with influx of atlantic surface water in periods through isotope substage 5d to stage 4 possibly also during a short time interval close to the 2 3 boundary a small area in the southeastern norwegian sea was ice free all these influxes of atlantic water seem to correlate to periods with interstadial conditions in western norway during times with the most extensive continental glaciations there are no traces of any influx of atlantic surface water the western norwegian glacial record and the norwegian sea surface circulation record seem to vary with a ca 20 ka cycle during the weichselian this indicates a dominance of the precessional orbital forcing between the ca 100 ka interglacial glacial interglacial cycle

regional geology and petroleum systems of the illizi berkine area of the algerian saharan platform an overview abstract the berkine and illizi basins are palaeozoic mesozoic intraplate depressions that preserve an over 7000 m thick sedimentary rock record and contain world class petroleum systems with over 39 bboe eur hydrocarbon reserves regional seismic transects and a wealth of well data are used to review the tectonostratigraphic evolution of the area the gondwana palaeozoic and tethys mesozoic supercycles make up the bulk of the phanerozoic succession these 1st order cycles record extensional basin formation followed by a protracted period of overall net subsidence and conclude with basin inversion and regional uplift during the hercynian and alpine orogenies respectively structural styles were dictated by transpressional or transtensional reactivation of mostly nne oriented basement structural grain of late proterozoic ea cambrian pan african age and vertical movement of long wavelength regional highs and lows local tectonism is considered to be the far field effect of plate tectonic processes that affected the north african plate boundaries such as the caledonian and hercynian orogenies the opening of the tethys and atlantic oceans and the alpine orogeny these were accompanied by localised thermal mantle processes regional unconformities subdivide the gondwana and tethys supercycles into eight and seven megasequences respectively these regional units often record 2nd order transgressive regressive cycles that constrain the mapping of reservoir seal pairs and of main source rock intervals the lower palaeozoic megasequences are characterised by sand rich laterally extensive coarse grained fluvial and shallow marine reservoirs interbedded with thin and widespread marine shales they were mostly deposited in shorelines of shallow epeiric seas and continental braided river systems or during the late ordovician in a short lived continental glacial system third order sequences display ramp style geometries with largely parallel to low angle sigmoidal stratal patterns early mesozoic sedimentation followed the late palaeozoic uplift and peneplanation in the form of hinterland sequences containing fluvial and alluvial sandstones and playa lake mudstones and evaporites interbedded with thin lacustrine or shallow marine shales and dolomites the prolific petroleum systems that evolved within these series are associated with the early silurian and late devonian world class source rocks and numerous paleozoic and triassic reservoirs this regional review provides a renewed comprehensive insight into the geological evolution of the area that can help guide local exploration efforts but also serves as a model for exploration in other intracratonic basins of the world

jokulhlaups a reassessment of floodwater flow through glaciers 1 in glaciated catchments glacier generated floods jokulhlaups put human activity at risk with large sporadic jokulhlaups accounting for most flood related fatalities and damage to infrastructure in studies of jokulhlaup hydrodynamics the view predominates that floodwater travels within a distinct conduit eroded into the underside of a glacier however some jokulhlaups produce subglacial responses wholly inconsistent with the conventional theory of drainage by focusing on icelandic jokulhlaups this article reassesses how floodwater flows through glaciers it is argued that two physically separable classes of jokulhlaup exist and that not all jokulhlaups are an upward extrapolation of processes inherent in events of lesser magnitude and smaller scale the hydraulic coupling of multiple nonlinear components to the flood circuit of a glacier can induce extreme responses including pressure impulses in subglacial drainage representing such complexity in mathematical form should be the basis for upcoming research as future modeling results may help to determine the glaciological processes behind heinrich events moreover such an approach would lead to more accurate predictive models of jokulhlaup timing and intensity

recognition and significance of sharp based mouth bar deposits in the eocene green river formation uinta basin utah sandstone bodies in the sunnyside delta interval of the eocene green river formation uinta basin previously considered as point bars formed in meandering rivers and other types of fluvial bars are herein interpreted as delta mouth bar deposits the sandstone bodies have been examined in a 2300 m long cliff section along the argyle and nine mile canyons at the southern margin of the uinta lake basin the sandstone bodies occur in three stratigraphic intervals separated by lacustrine mudstone and limestone together these stratigraphic intervals form a regressive transgressive sequence individual sandstone bodies are texturally sharp based towards mudstone substratum in proximal parts the mouth bar deposits only contain sandstone whereas in frontal and lateral positions mudstone drapes separate mouth bar clinothems the clinothems pass gradually into greenish grey lacustrine mudstone at their toes horizontally bedded or laminated lacustrine mudstone onlaps the convex upward sandstone bars the mouth bar deposits are connected to terminal distributary channel deposits together these mouth bar channel sandstone bodies accumulated from unidirectional jet flow during three stages of delta advance separated by lacustrine flooding intervals key criteria to distinguish the mouth bar deposits from fluvial point bar deposits are i geometry ii bounding contacts iii internal structure iv palaeocurrent orientations and v the genetic association of the deposits with lacustrine mudstone and limestone

cycles steps and co2 paleoceanography in the united states from 1983 1986 the field of paleoceanography experienced continued growth during the last three years the first international conference on paleoceanography was held in zurich switzerland in july 1983 and a new journal devoted to the topic paleoceanography american geophysical union washington d c began publication in spring 1986 edited by dr james kennett of the university of rhode island nine legs of the r v glomar challenger concentrated upon paleoceanographic topics legs 71 75 in the south atlantic leg 81 in the north atlantic leg 85 in the equatorial pacific leg 86 in the northwest pacific and leg 90 in the southwest pacific several special symposia and conferences resulted in volumes of collected papers dealing with topics such as climate variability hansen and takahashi 1984 the global carbon cycle sundquist and broecker 1985 catastrophes and earth history berggren and van couvering 1984 orbital insolation and periodicity berger et al 1984 and coastal upwelling suess and thiede 1983 some very useful books have been published which summarize existing information on radiolaria anderson 1983 neogene planktonic foraminifera kennett and srinivasan 1983 calcareous nannofossils haq 1983 1984 and biostratigraphy bolli et al 1983

the temporal distribution of evolutionary and migrational events in pelagic systems episodic or continuous the evolutionary and ecological dynamics of origination immigration and extinction emigration patterns of two pelagic groups planktic foraminifera and calcareous nannofossils within two paleoceanographic regions over the past 40 m y are compared with predictions of the turnover pulse hypothesis that speciation extinction and migration are pulsed or episodic and synchronous with change in the physical environment the specific species dynamics examined of the records of 918 species include expected time to extinction origination immigration as a function of geologic time extinction emigration as a function of biologic age and geologic time and the interactive effects of time of origination immigration and geologic time on the probability of extinction emigration overall there is little empirical support for times of evolutionary quiescence or ecological stability rather the dominant pattern is one of continuous rather than episodic evolutionary and ecological activity there is little evidence of synchroneity of response among cohorts or with major change in the physical environment coeval species experience the same time periods differently in terms of the probability of speciation immigration and extinction emigration the empirical patterns support the hypothesis that at this taxonomic and temporal resolution the controlling factors on evolutionary and ecological turnover are more omnipresent than pulsed or episodic

the subglacial origin of the lake agassiz ojibway final outburst flood arc shaped scours sandwaves and channels on the hudson bay seafloor suggest that the catastrophic drainage of lake agassiz ojibway occurred as a subglacial flood beneath the laurentide ice sheet which covered northern north america

facies characteristics of a proglacial turbiditic sand lobe at svalbard abstract a shallow marine turbiditic lobe inferred to be associated with an ice contact delta was deposited during the last glaciation weichselian at svalbard the norwegian arctic the postglacially raised sandy lobe is exposed in a 200 m long river section and exhibits six units that reflect an early phase of glaciomarine mud deposition followed by three episodes dominated by deposition from sandy turbidity currents the lobe is characterized by a complex pattern of turbidite filled erosional features from thin scour fills reflecting a highly mobile flow pattern to stacked chute fill deposits showing confined flow the sandy turbidites show rhythmic deposition of massive to graded laminae deposited from suspension alternating with faint laminae or ripple cross lamination deposited from tractional transport semi continuous turbidity currents are thought to have been generated by retrogressive slumping of ice proximal well sorted sandy deposits on the delta front and slope the lateral and vertical changes of lithofacies within the sandy lobe are mainly attributed to normal mechanisms of turbiditic lobe growth with only minor effect from synsedimentary glacier terminus movement and minor changes in the meltwater outflow position this detailed mapping of facies changes allows a fairly accurate reconstruction of the axis of the former discharge outlet

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

440 ma ice stream in north africa landsat images aster digital elevation models aerial photographs and field investigations in the western murzuq basin libya and the adjacent tassili n ajjers algeria provide paleogeomorphological evidence for the existence of a late ordovician ice stream at least 200 km long and 80 km wide this includes mega scale glacial lineations an associated subglacial meltwater drainage system and ice front features this first comprehensive description of a pre cenozoic ice stream may help to identify other examples in the proterozoic to paleozoic glacial record reconstruction of the extent and behavior of former ice sheets and reservoir prospect analysis in glacially related successions have to take into account the potential occurrence of ice streams

sedimentation beneath ice shelves the view from ice stream b abstract ice shelf development is favored by rapid flow of cold ice from outlet glaciers or ice streams into protected embayments with localized high spots basal melting of ice shelves is rapid near the ice front and may occur near the grounding line ice from outlet glaciers may contain significant englacial debris that is deposited as a dropstone diamicton in regions of basal melting englacial debris is sparse or absent in ice streams evidence from ice stream b draining into the ross ice shelf of west antarctica suggests that the rapid ice velocity arises from deformation of a several meter thick water saturated basal till layer that is eroding an unconformity on sediments beneath and that has deposited a till delta tens of meters thick and tens of kilometers long at the grounding line sea level fall would cause conveyor belt recycling of this till delta and grounding line advance across the ross sea to the edge of the continental shelf forming an ice sheet with a low ice stream profile resting on a several meter thick deforming till layer eroding an unconformity the modern ross sea is characterized by a regional unconformity overlain by a diamicton of probable latest pliocene pleistocene age measuring several meters to tens of meters thick we hypothesize that this diamicton is a deformed glacial till and that the ross sea sediments record one or more expansions of the till lubricated west antarctic ice sheet to the edge of the continental shelf

linked debrites in sand rich turbidite systems origin and significance abstract the outer parts of a number of small late jurassic sandy deep water fans in the northern north sea are dominated by the stacked deposits of co genetic sandy and muddy gravity flows sharp based structureless and dewatered sandstone beds are directly overlain by mudclast breccias that are often rich in terrestrial plant fragments and capped by thin laminated sandstones pseudonodular siltstones and mudstones the contacts between the clast rich breccias and the underlying sandstones are typically highly irregular with evidence for liquefaction and upward sand injection the breccias contain fragments up to metre scale of exotic lithologies surrounded by a matrix that is extremely heterogeneous and strewn with multiphase and variably sheared sand injections and scattered coarse and very coarse sand grains often coarser than in the immediately underlying sand bed markov chain analysis establishes that the breccias consistently overlie sandstones and the character of the breccias and their external contacts rule out a post depositional origin via in situ liquefaction intrastratal flowage or bed amalgamation and disruption the breccias are interpreted as debrites that rode on a water rich sand bed just deposited by a co genetic concentrated gravity current as such they are referred to as linked debrites to distinguish them from debrites emplaced in the absence of a precursor sand bed the distinction is important because these linked debris flows can achieve significant mobility through entrainment of both water and sediment from beneath and they ride on a low friction carpet of liquefied sand this explains the paradox presented by fan fringes in which there are common debrites when conventional thinking might predict that deposits of low concentration gravity currents should be more important here in fact evidence for transport by low concentration turbidity currents is rare in these systems several possible mechanisms might explain the formation of linked flows but the ultimate source of both sandy and clast rich flow components must be in shallower water on the basin margin the debrites are not triggered from distal slopes flow partitioning may have occurred by upslope erosion and retardation of the mudclast charged portion of an erosional sandy density current partial flow transformation of a precursor debris flow and or hydraulic segregation and reconcentration of the flaky clasts and carbonaceous matter during transport linked debrites are not restricted to small sand rich fans and similar mechanisms may be responsible for the long runout of debris flows in other systems the recognition of a distinct class of linked debrites is of wider importance for facies prediction reservoir heterogeneity and even carbon fluxes and sequestration on continental margins

the eocene oligocene boundary and the psychrospheric event in the tethys as recorded by deep sea ostracods from the massignano global boundary stratotype section and point central italy abstract latest eocene earliest oligocene deep water ostracods from the massignano global boundary stratotype section and point gssp central italy were studied from a palaeoecological perspective to investigate the psychrospheric event in the tethys although quantitative analyses were hampered by the low incidence of fauna the high resolution sampling used in this study 148 samples distributed over a 23 m thick succession spanning 3 m y allowed the following inferences 1 overall features e g abundance diversity composition of the assemblages suggest a middle lower bathyal environment with no significant palaeobathymetrical changes 2 today a similar fauna notably characterised by the common occurrence of the genus agrenocythere would likely be encountered in upper psychrospheric conditions water masses beneath the permanent thermocline with a temperature range of 4 10 c 3 although no noticeable faunal turnover has been recognised throughout the succession minor faunal changes seem to occur in the first part of the section probable appearance of legitimocythere presequenta and to a lesser extent also across the eocene oligocene boundary the presumed appearance of l presequenta latest eocene correlates quite well in timing and possible significance with the faunal changes observed in other microfossil groups foraminifers and dinocysts this event is possibly linked to a cooling pulse which might have been caused by the arrival or increasing advection of cold bottom waters in the study area faunal evolution across the eocene oligocene boundary is thought to be consistent with an intensification of the cooling trend and an increase of primary productivity which fits fairly well with the 13c record relationships between the subtle ostracod faunal changes observed in the massignano gssp and the main late eocene early oligocene psychrospheric event can be only speculative nevertheless we found no evidence that precludes the possibility of interpreting the massignano ostracod pattern as a subdued local expression of this major event although speculative this is a reasonable hypothesis because the investigated area is situated in western tethys far from the main circulation of deep ocean waters

the response of nw iberian vegetation to north atlantic climate oscillations during the last 65 kyr pollen and oceanographic data from deep ocean core md95 2039 provide a centennial to millennial scale record of conditions offshore and of the vegetation of north west iberia for the period 10 65 ka the planktonic oxygen isotope record of this core reflecting predominantly sea surface temperature sst shows a pattern of millennial scale oscillations that is very similar to climatic changes recorded by the greenland ice core records over the same interval in turn tree populations show a pattern of rapid expansions and contractions that follow the pronounced and abrupt isotopic shifts recorded offshore through marine isotope stage mis 3 this millennial scale pattern of vegetation change alternating between steppe and open woodland is superimposed on a longer term pattern of shrinking ericaceous heathland and decreasing size of successive interstadial tree populations trees persisted during the last glacial maximum lgm at greater abundance than during many of the coldest episodes of mis 3 this agrees with the marine data which indicate that lgm sea surface temperatures here were significantly warmer than the minima recorded in mis 3 our combined marine terrestrial record together with data from nearby sequences provides a stepping stone between terrestrial sequences and the greenland ice core and north atlantic marine records this will permit a better understanding of the behaviour of vegetation across different regions at several scales of climatic forcing

biotic response of tethyan bathyal ostracodes through the eocene oligocene transition the composite faunal record from the massicore and massignano global stratotype section and point east central italy abstract the eocene oligocene transition eot is marked by a double stepped positive 18 o excursion of 1 3 and a deepening of the calcium compensation depth ccd interpreted to represent marked antarctic glaciation and global ocean atmosphere cooling i e oi 1 event a 0 5 m 55 70 kyr resolution ostracode faunal study of the massicore drilled up section from the italian massignano quarry containing the eocene oligocene global stratotype section and point gssp revealed a relative increase in krithe and decreases in faunal evenness and shannon index correlative to the oi 1 event these transient faunal changes may reflect local water column changes e g export production or intensified thermohaline flow of cooler deep waters through the paleotethyan seaway comparison of these massicore ostracode faunal data to previously published massignano quarry ostracode faunal data reveals similar relative abundances among common taxa where the study intervals overlap and thereby provide a more complete tethyan ostracode record spanning all of c13n and the broader eot at the gssp locality

source and dispersal of jokulhlaup sediments discharged to the sea following the 1996 vatnajokull eruption the october 1996 gjalp eruption beneath vatnajokull glacier led to one of the largest jokulhlaups glacial floods in iceland in the twentieth century a catastrophic discharge of meltwater and sediment swept across the skeidararsandur flood plain to the sea tephra from the eruption consists of vesicular sideromelane shards with a basaltic andesite composition 53 sio 2 3 mgo 0 8 k 2 o after the flood sediment samples were collected from the flood plain and off the southeast coast of iceland where a major sediment plume had been created by the discharge compositions of glass shards from flood plain and seafloor deposits do not match those of the gjalp magma flood plain samples consist primarily of blocky to poorly vesicular sideromelane clasts with compositions that are characteristic of grimsvotn volcanic products 50 sio 2 5 5 mgo 0 4 k 2 o marine samples collected near the jokulhlaup outflow into the sea also consist primarily of blocky to poorly vesicular sideromelane clasts with compositions that are for the most part similar to products of the grimsvotn volcanic center distal marine samples have more vesicular sideromelane clasts with compositions that are similar to products of the katla volcanic center e g 48 sio 2 4 5 mgo 0 8 k 2 o significant deposition to the seafloor was apparently limited to an area just offshore of the skeidararsandur there is no indication that juvenile volcanic material from the gjalp eruption was carried by the 1996 jokulhlaup onto the flood plain or into the ocean instead the jokulhlaup carried primarily older volcaniclastic material eroded by the flood

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

palaeotectonic implications of increased late eocene early oligocene volcanism from south pacific dsdp sites late eocene early oligocene 42 35 myr sediments cored at two dsdp sites in the south west pacific contain evidence of a pronounced increase in local volcanic activity particularly in close association with the eocene oligocene boundary this pulse of volcanism is coeval with that in new zealand and resulted from the development of an indo australian pacific plate boundary through the region during the late eocene the late eocene earliest oligocene was marked by widespread volcanism and tectonism throughout the pacific and elsewhere and by one of the most important episodes of cenozoic climatic cooling

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

delta slope processes and turbidity currents in prodeltaic submarine channels queen inlet glacier bay alaska large submarine channels lead away from the coarse grained fjord head delta in queen inlet glacier bay alaska coarse sediment loads from carroll glacier are transported down the delta foreslope and through the submarine channels and finer material is dispersed throughout the fjord from overflow plumes slides and slumps occur intermittently on the delta foreslope a recording current meter positioned in a submarine channel 1 m above the bottom and 2 7 km seaward from the delta brink indicated during july 1989 predominantly quasi continuous downfjord currents although several small surges were also observed flows occurred throughout the daily tidal cycle in both neap and spring periods for intervals of up to several hours often beginning and ending rapidly current velocities ranged from 0 to 120 cm s 1 averaging 12 cm s 1 over one 56 h period and 16 cm s 1 over a 13 h period suspended sediment concentrations 1 m above bottom commonly exceeded 2 g l 1 and attained 8 2 g l 1 the density added to

initiation of turbidity currents outcrop evidence for eocene hyperpycnal flow turbidites abstract the most widely used although not as widely documented explanation for initiation of turbidites is the conversion of catastrophic sediment failures into turbidites such instantaneous sediment failures generate short lived surge type flows that deposit turbidite beds described as bouma sequences in this communication we present data from the eocene central basin of spitsbergen that shows turbidite systems that are volumetrically dominated by thick ungraded and laminated sandy turbidite beds deposited by gradual aggradation from sustained flows sustained flows are long lived and more or less continuous they can be generated by a variety of mechanisms e g 1 instability during volcanic eruptions and the consequent remobilisation of unconsolidated material 2 seismically triggered subaerial sliding within the drainage 3 storm surges 4 retrogressive slope failure 5 breaching and 6 hyperpycnal flows our database shows that in the eocene central basin the sustained flows were generated by hyperpycnal flows i e by direct river effluent the hyperpycnal flow turbidites have been recognized on the basis of 1 physical connection between fluvial and turbidite channels at the shelf edge 2 abundance of thick turbidite sandstone beds 3 sand prone nature of the turbidite systems 4 downslope changes of individual thick sandy turbidite beds and their collapsed pinch out segments 5 great abundance of continental material leaves coal fragments in turbidite beds 6 low abundance of associated slumped or debris flow beds and 7 the occurrence of turbidites in systematically accreted shelf margins these features strongly suggest that hyperpycnal flow generated by direct river effluent deposited significant number of turbidite beds in the documented slope and basin floor turbidite successions we also argue that the hyperpycnal flows are preferentially fed into the deepwater slopes beyond the shelf edge during the falling stage and lowstand of relative sea level the turbidite beds were studied in the context of seismic scale 1 15 km dip oriented outcrops by measuring detailed vertical sections following individual beds and packages of beds downslope for distances over 5 km lateral mapping and helicopter taken photomosaics

trough mouth fans palaeoclimate and ice sheet monitors abstract trough mouth fans are fans at the mouth of transverse troughs channels on glaciated continental shelves on the northwest european glaciated continental margin eight trough mouth fans varying in size between 2700 and 215 000 km 2 have been identified the trough mouth fans are depocentres dominated by debris flows accumulated in front of ice streams draining the former large northwest european ice sheets the debris flow units are separated by hemmipelagic interglacial interstadial sediments it is inferred that the number of debris flow units record the number of shelfbreak positions of the ice sheet margins the number found varies between three in the south and eight in the north typical trough mouth fans and related debris flow units seem to have been formed later than the early mid pleistocene thus the north european ice sheets did not form ice streams extending to the shelfbreak in any appreciable length before the mid pleistocene besides being loci for sediment deposition the trough mouth fans were also the main sites of fresh water supply to the ocean in the form of icebergs during the mid late pleistocene ice ages

incorporation of ca isotopes in carapaxes of marine ostracods abstract we studied mg ca sr ca and ca isotope ratios of ostracod carapaxes from surface sediments retrieved during research cruises to the southern and equatorial eastern atlantic collected specimens originate from water depth between 30 and about 5000 mbsl and cover bottom water temperatures between 0 and 23 c analysed taxa include buntonia sp cytherella sp henryhowella sp krithe sp poseidonamicus sp and ruggieria sp calcium isotope ratios of the studied specimens are in the overall range of other marine calcifiers and show a variability of about 0 75 over a temperature range of 20 c there is no overall linear relation between temperature and ca isotope fractionation but some species show a maximum 44 40ca at intermediate temperatures mg ca and sr ca agree well with values of previously published carapaxes demonstrating large inter and intra species variability and different responses to bottom water temperatures magnesium is highly variably distributed within the carapax with mg enrichment in the inner part of the shell of most taxa this enrichment is independent from the incorporation of sr which shows less variability within the carapax the ca isotope vs sr ca systematic in the ostracods deviates from inorganic calcite and foraminifers the ostracod array is most likely controlled by either mixing of material originating from a precursor phase and newly grown calcite or rayleigh type fractionation during precipitation from a restricted fluid reservoir indicating varying degrees of ca and sr consumption during calcite precipitation the different slope of the ca isotope vs sr ca relation shown by the ostracods compared to those of inorganic calcite and foraminifers opens a new approach for the determination of ca isotope and sr ca ratios of past ocean water

downfan transformation from turbidity currents to debris flows at a channel to lobe transitional zone the lower pleistocene otadai formation boso peninsula japan transformation of turbidity currents into debris flows across a channel to lobe transition zone was recognized on the basis of lateral mapping of a falling stage systems tract deposit in the lower pleistocene otadai formation submarine fan sequence on the boso peninsula japan the most proximal outcrops comprise 1 to 4 m thick turbidites which are laterally equivalent to debrites encased in turbidites in outcrops farther down flow such turbidites and encased debrites were deposited from single flow events the most distal outcrops comprise only thinner 2 to 40 cm thick turbidites debrites contain many siltstone clasts and finer grained sediments which are characterized by deep water faunas and clay mineral composition similar to those of interbedded hemipelagites therefore the transformation of turbidity currents into debris flows is interpreted to have occurred in response to the incorporation of many siltstone clasts and finer grained sediment particles into the precursor turbidity currents through erosion of muddy substrates subsequently turbulence in the precursor turbidity currents was suppressed and near bed flow with higher sediment concentration developed intense erosion of muddy substrates is interpreted to have occurred in response to the increase in intensity of turbulence in the precursor turbidity currents at the mouths of middle fan channels the precursor turbidity currents or turbidity currents generated by dilution of debris flows produced a turbidite deposit which was subsequently overrun by the debris flow in a proximal lobe environment the debris flows are interpreted to have subsequently been transformed into turbidity currents which are recorded by turbidite deposition in the more distal lobe environment debrites can characterize the proximal portion of an attached lobe deposit in a channel to lobe transition zone such debrites can be significant heterogeneities for fluid flows in sand prone successions from middle fan channel to attached lobe deposits

macroevolutionary history of the planktic foraminifera planktic foraminifera are an abundant component of deep sea sediment and are critical to geohistorical research primarily because as a biological and geochemical system they are sensitive to coupled bio hydro lithosphere interactions they are also well sampled and studied throughout their evolutionary history here we combine a synoptic global compilation of planktic foraminifera with a stochastic null model of taxonomic turnover to identify statistically significant increases in macroevolutionary rates there are three taxonomic diversifications and two distinct extinctions in the history of the group the well known cretaceous paleogene extinction is of unprecedented magnitude and abruptness and is linked to rapid environmental perturbations associated with bolide impact the eocene oligocene boundary extinction occurs due to a combination of factors related to a major reorganization of the global climate system changes in ocean stratification seawater chemistry and global climate recur as primary

jokulhlaup deposits in proglacial areas abstract this paper discusses the main causes and characteristics of jokulhlaup glacier burst floods and explores the extent to which they generate depositional landform and sediment assemblages that are distinct from those of normal braided river outwash type i outwash two main jokulhlaup outwash environments are identified type ii outwash produced by sudden drainage of ice dammed lakes and type iii associated with drainage during subglacial geothermal activity and distinguished by deposits resulting from high sediment concentrations and hyperconcentrated flows in fluid flows especially ones yielding type ii outwash the most common deposits are large scale expansion bars and locally eddy and pendant bars and mega ripples or dunes both forms normally composed of large scale gravel cobble cross bedding often capped by an imbricated boulder lag a type b2 lithofacies sequence the armour is absent only where runoff decreased too rapidly to allow surface winnowing other jokulhlaup facies include extensive boulder beds type c inverse normally graded cobble beds type ds ice proximal debris flow deposits and deformed bedding containing diamicton clasts types g and h and slack water sediments type a type iii outwash is dominated by massive homogeneous flood surge granules underlain by pre surge gravels and capped by post surge fluid bedforms reflecting deposition during both the rising and falling limbs of the flood hydrograph type e4 the paper demonstrates that jokulhlaups do generate distinctive assemblages of depositional landforms and sediments and concludes with a model of the dominant lithofacies sequences and associated landforms in proglacial environments subject to jokulhlaup drainage

high energy ephemeral stream deltas an example from the upper silurian holmestrand formation of the oslo region norway abstract the late orogenic deposits of the upper silurian holmestrand formation of the oslo region norway comprises sharply alternating ephemeral stream and sandy beach face deposits the formation is divided into three units reflecting the down slope change on an extensive ephemeral stream delta system the lower unit of the formation comprises ephemeral stream sediments as stacked sheet sandstone bodies deposited on a broad coastal floodplain each sheet is bounded by a lower intraclast strewn scoured surface overlain by massive horizontally stratified low angle and trough cross bedded sandstones in the medial and upper units of the formation the ephemeral stream sediments alternate with beach face deposits forming ephemeral stream deltas the ephemeral stream deltas are marked by intraclast strewn scoured surfaces and dominated by trough cross bedded sandstones they may contain escapement burrows marine bioturbation and wave working of the delta surfaces the beach face deposits are composed of alternating irregular horizontally stratified sandstones with current and wave ripple cross lamination and tabular cross bedded sandstones deposition took place in a coastal non to micro tidal shallow water environment influenced by longshore currents and low palaeo wave energy seven ichnotaxa are recognized and support the sedimentary record of a transitional environment between a broad coastal floodplain and a shallow marine environment the presence of calcretes indicate an arid to semi arid palaeo climate

distribution and origin of hybrid beds in sand rich submarine fans of the tanqua depocentre karoo basin south africa abstract this study documents the stratigraphic and palaeogeographic distribution of hybrid event beds that comprise both debris flow cohesive and turbidity current non cohesive deposits this is the first study of such beds in a submarine fan system to combine outcrop and research borehole control and uses a dataset from the skoorsteenberg formation of the tanqua depocentre in the karoo basin south africa three types of 0 1 1 0 m thick hybrid beds are observed which have a basal weakly graded fine grained sandstone turbidite division overlain by a division of variable composition that can comprise 1 poorly sorted carbonaceous rich material supported by a mud rich and micaceous sand matrix 2 poorly sorted mudstone clasts in a mud rich sand silt matrix or 3 gravel grade rounded mudstone clasts in a well sorted mud poor sandstone matrix these upper divisions are interpreted respectively as 1 the deposit of a debris flow most likely derived from shelf edge collapse 2 the deposit of a debris flow most likely developed through flow transformation from turbidity current that eroded a muddy substrate and 3 from a turbidity current with mudstone clasts transported towards the rear of the flow all three hybrid bed types are found concentrated at the fringes of lobes that were deposited during fan initiation and growth the basinward stepping of successive lobes means that the hybrid beds are concentrated at the base of stratigraphic successions in medial and distal fan settings hybrid beds are absent in proximal fan positions and rare and thin in landward stepping lobes deposited during fan retreat this distribution is interpreted to reflect the enhanced amounts of erosion and availability of mud along the transport route during early lowstands of sea level therefore hybrid beds can be used to indicate a fan fringe setting infer lobe stacking patterns and have a sequence stratigraphic significance

late ordovician glacial pavements revisited a reappraisal of the origin of striated surfaces the recognition of ice related unconformities is of prime importance when dealing with the sequential architecture of pre pleistocene glacial successions late ordovician striated surfaces strikingly preserved in north gondwana were long considered as abrasion surfaces at the sole of a grounded glacier overriding unlithified sediments or having resulted from the scouring action of drifting icebergs field observations from mauritania and libya show that these striated surfaces require an alternative interpretation which can be applied to similar surfaces described elsewhere such as in permo carboniferous or neoproterozoic glacial sequences a new model is proposed that involves superimposed concurrent decollement planes within a subglacial brittle shear zone in unlithified sand beds shear zones in subglacial sediments are well known in quaternary deposits but to date it has not been demonstrated that they may form striated surfaces occurring at continent scale with orientations consistent with palaeo ice flow reconstructions based on larger scale indicators

vegetation dynamics in southern france during the last 30 ky bp in the light of marine palynology the composition of the glacial vegetation of southern french plains has been a matter of debate for several decades vegetation is considered as steppic according to french and spanish lacustrine pollen records whereas cave deposits suggest the presence of mesothermophilous trees through the last glacial maximum in our paper we display new palynological records from marine sediments of the gulf of lions they indicate the presence of abies picea and deciduous quercus in the gulf of lions certainly located in the drainage basins of the pyreneo languedocian rivers these populations that were sensitive to short climatic events during marine isotopic stage 2 could have been linked to northeastern spanish and southeastern french relicts already evidenced by phylogenetic data these trees were absent from the rhone drainage basin during the deglaciation and certainly also disappeared from the pyreneo languedocian drainage basins from ca 17 to 15 ky cal bp finally the last glacial maximum does not appear as stable cold and dry as previously thought

eocene and early oligocene micropaleontology and paleoenvironments in se umbria italy a detailed study based on calcareous nannofossils and planktonic and benthic foraminifera has been carried out on five sections in the scaglia group of the umbrian region visso and cascia areas central italy these sections are characterized by continuous pelagic sedimentation and are constituted mainly of marls marly limestones and limestones of early eocene to early oligocene age calcareous turbidites with shallow water skeletal debris discharged from the latium abruzzi carbonate platform are interbedded within the pelagic sequences the biostratigraphic study based on calcareous nannofossils and planktonic foraminifera confirmed the continuous succession of standard events and revealed some new ones these results allow us to refine the biostratigraphic resolution with a very good correlation between calcareous nannofossil and planktonic foraminiferal zonations the major features and events recognized are the early middle eocene boundary zones p9 p10 is characterized by the first occurrence fo of hantkeninids by abundant thick walled globigerinatheka g senni and by spinose acarininids a decrease has been noted in planoconvex morozovellids and an increase of low spired subbotinids the benthic assemblage shows a great variability with an increase in the zone p11 of the large heterolepa and cibicidoides this is an event of worldwide significance in the calcareous nannofossils the fo of nannotetrina sp was used to define the lower boundary of zone cp13 instead of n fulgens because poor preservation prevented identification at the specific level the fo of reticulofenestra umbilica marking the lower boundary of zone cp14 occurs in the upper part of zone p11 the zone p13 was recognized indirectly because of the absence of the index species orbulinoides beckmanni the base of the zone is close to the fo of turborotalia cerroazulensis and is defined by an increase of catapsydrax sp and by the last occurrence lo of acarinina bullbrooki the top of the zone is defined by an increase of the high spired subbotinids of the s corpulenta group and the disappearance of morozovella spinulosa the middle late eocene boundary zones p14 p15 is characterized by the extinction of the spinose acarininids and of the smooth walled planorotalites from zone p13 to zone p15 there is a replacement in the benthic assemblages in fact pleurostomella heterolepa and anomalinoides capitata characterize these zones bolivinids become abundant and uvigerinids appear around the p14 p15 boundary the late eocene is characterized by an increase of subbotinids with abortive chambers and of the turborotalia cerroazulensis lineage hantkeninids and cribohantkeninids are rare particularly c inflata the fo of istmolithus recurvus has been noted at the base of zone p16 within this zone globigerinatheka index and turborotalia cunialensis coexist the lo of g index is associated with a strong decrease of representatives of the genus globigerinatheka at the same level of the lo of g index the coeval extinctions of discoaster barbadiensis and discoaster saipanensis are noted just above this level within zone p17 the lo of t cerroazulensis lineage t cocoaensis and t cunialensis has been recognized the eocene oligocene boundary is defined by planktonic foraminifera at the extinction level of hantkeninids and cribrohantkeninids shortly following that of the t cerroazulensis group

the origins of glacially related soft sediment deformation structures in upper ordovician glaciogenic rocks implication for ice sheet dynamics in the upper ordovician glaciogenic rocks of west gondwana many soft sediment deformation structures are attributed to glaciotectonic processes however little is known about the subglacial and ice marginal processes associated with this ice sheet a systematic description and interpretation of these soft sediment deformation structures is supplemented by a comparison with late quaternary and modern glacial settings to provide qualitative constraints on the character of ancient subglacial thermal regimes soft sediment striations were formed by discontinuous shear induced deformation beneath an ice sheet that oscillated between warm and cold based thermal regimes beneath warm based ice coupling across the ice bed interface was poor with sliding and loading occurring at this surface loading of soft waterlogged sediments allowed the development of fluted surfaces which are also associated with the formation of truncated folded zones during times of cold thermal regimes coupling across the ice bed interface was enhanced by freezing which caused changes in the position of the freezing front these discontinuous changes coupled with sustained subglacial shearing resulted in the development of stacked soft sediment striated surfaces in areas where the subglacial substrate had an irregular topography complex shear zones formed that comprised stacked duplex systems interlayered with highly strained units preserving pervasive folded lineations at the ice front large glaciotectonic deformation structures comparable with push moraines developed during sustained periods of re advance that created composite thrust and fold systems deformation was transmitted for up to 1 km from the ice front and reduced in intensity with distance other deformation structures include dome like folds that consist of central anticlines 30 to 70 m in width with tight rim synclines that formed by the load induced diapiric intrusion of muds an ice sheet surging mechanism is inferred for the development of composite thrust and fold systems and the coeval sediment diapirs these surges potentially caused the widespread reorganisation of a glacial load resulting in the pro to subglacial extrusion of soft sediments

depositional environments and sequence stratigraphy of paralic glacial paraglacial and postglacial upper ordovician siliciclastic deposits in the murzuq basin sw libya abstract the application of sequence stratigraphy methods to glaciogenic deposits is more problematic than in normal paralic deposits because changes in the relative sea level are strongly influenced by an interplay between glacial advance and retreat and concomitant isostatic loading and rebound of the continental shelf the study of outcrop and subsurface sections of the upper ordovician glaciogenic melaz shuqran and the mamuniyat formations murzuq basin sw libya yielded important information on understanding changes in the relative sea level related to glacier movements three depositional sequences were recognized depositional sequence one ds 1 corresponds to the entire melaz shuqran formation that was bounded below by subglacial erosion surface i e sequence boundary sb formed during glacier advance into shallow water areas this surface correlates with a transgressive surface ts in deep water areas and records an initial rise in the relative sea level owing to glacier advance and loading of the continental shelf transgression occurred due to the slower rate of eustatic sea level fall than the isostatic loading the transgressive systems tract tst comprises shoreface sandstones and offshore mudstones diamictites with ice rafted debris further rise in relative sea level was associated with glacial retreat which resulted in sediment starvation in deep water areas and the formation of a condensed section these deposits represent glacial depositional systems the highstand systems tract hst comprises prograding deltaic deposits which was formed when the rate of sediment supply exceeds the rate of relative sea level rise the hst deposits represent paraglacial depositional systems depositional sequence two ds 2 corresponds to the lower and middle part of the mamuniyat formation and is bounded below by deep erosional surface sb that cuts into ds 1 as an incised valley which was formed during glacial advance across the continental shelf incision occurred due to the faster rate of eustatic sea level fall than the rate of isostatic loading glacier retreat and the concomitant rise in relative sea level resulted in the deposition of braided fluvial sediments in a lowstand systems tract lst and tide dominated estuarine sediments in a tst these deposits represent glacial depositional systems the hst sediments represent prograding foreshore to shoreface deposits which were formed when the rate of sediment supply exceeded the rate of relative sea level rise these deposits represent paraglacial depositional systems depositional sequence three ds 3 corresponds to the upper part of the mamuniyat formation and is bounded below by an erosional surface sb that was formed as a result of isostatic rebound associated with relative sea level fall ds 3 lst comprises gilbert type deltaic conglomeratic sandstones grading upwards into sandstones subsequent relative sea level rise during the late ordovician resulted in deposition of shoreface tst sandstone further rise in the relative sea level resulted in sediment starvation in deep water areas and the formation of thin hardground layer i e condensed section that marks the upper boundary of late ordovician deposits this study provides predictive model for the spatial and temporal distribution of ancient glaciogenic depositional facies that may have important implications in hydrocarbon explorations

constraining the efficiency of turbidity current generation from submarine debris flows and slides using laboratory experiments abstract results from a small set of laboratory experiments are presented here that help further constrain the processes governing the production of turbidity currents from impulsive failures of continental shelf and slope deposits three mechanisms by which sediment can be transferred from a parent debris flow to a less dense turbidity current were observed and quantified these mechanisms are grain by grain erosion of sediment from the leading edge of the parent flow detachment of thin layers of shearing material from the head of the parent flow and turbulent mixing at the head of the parent flow which transfer process dominates an experimental run depends on whether the large dynamic stresses focused on the head of the debris flow are sufficient to overcome a effective yield strength for the parent sediment water mixture and on whether the dynamic stresses are sufficient to induce the turbulent flow of the parent mixture analysis of data from marr et al geol soc am bull 113 2001 1377 and mohrig et al geol soc am bull 110 1998 387 support the use of a shear strength to dynamic stress ratio in constraining necessary critical values for occurrence of the different production mechanisms direct sampling of turbidity currents using racks of vertically stacked siphons was used to measure both the quantity of sediment eroded from the heads of non mixing parent flows and the distribution of particle sizes transported by the developing turbidity currents acoustic backscatter imaging was used to better resolve the internal boundary separating any turbulent mixing zone near the front of a flow from unmodified parent material

occurrence of hyperpycnal flows and hybrid event beds related to glacial outburst events in a late ordovician proglacial delta murzuq basin sw libya abstract a late ordovician glacially related delta is documented based on architecture and facies from outcrops in the western murzuq basin libya sandstone megabeds highlight clinoform geometries of a proglacial low angle shallow water delta the progradational wedge extends over 25 km from the sse to the nnw and is about 100 m thick two types of clinothems have been distinguished and eleven facies sequences are characterized in relation with their along slope positions sand prone facies sequences in type 1 clinothems relate to high magnitude low frequency glacial outburst floods generating a freshwater highly concentrated plunging hyperpycnal flow at the river mouth during the waxing stage the slope adjustment of an out of grade profile causes significant erosion the resulting additional sediment charge involves along foresets a downslope flow transformation into a co genetic sandy debris flow and high density turbidity flow hybrid event beds including linked debrites and turbidites are the resulting deposits in the lower slope decreasing sediment concentration of the high density turbidity flow leads to sediment lofting and to a second flow transformation resulting in a lower density turbidity flow and a concomitant rising sediment plume deposition results in crude ripple cross stratification debrite deposition is temporally restricted to an early segment of the rising limb of the flood hydrograph during the ensuing waxing stage uninterrupted sustained flow conditions maintain up to the peak flow permitting the aggradation of thick sandstone successions with crude ripple cross stratification during the waning stage backstepping of the whole depositional system leads to prevailing sedimentation in the delta plain setting mouth bar development and channel plugs are characterized by climbing dune cross stratification cdcs shale prone sedimentation in type 2 clinothems essentially corresponds to background ablation related sedimentation but also includes minor debrite bearing outburst related event beds this study documents the links between glacial outbursts hyperpycnal flows and hybrid beds in low angle delta settings and illustrates a type of proximal sand dominated hyperpycnite dam failure of subglacial lakes is inferred for the outburst generation comparison with modern and pleistocene examples may suggest that outburst events were days to several years in duration type 1 clinothem with a 1 40 ky recurrence period type 2 clinothem

linking river flood dynamics to hyperpycnal plume deposits experiments theory and geological implications turbid river plumes entering ocean or lake water of lesser density i e hyperpycnal plumes can plunge to form turbidity currents providing an important link between terrestrial sediment sources and marine depositional sinks a leading hypothesis suggests that hyperpycnal plume deposits accurately record the rising and falling discharge of a flooding river in terms of sediment size grading bedform sequence and deposit thickness which if correct has significant implications for unraveling river dynamics reservoir potential and earth history from marine event beds herein we present one of the first experimental flume studies aimed at testing this hypothesis results indicate that depth averaged hyperpycnal plume velocities can be uncorrelated or even anti correlated with river discharge at certain seabed locations because of translation of the plunge point resulting from temporal variations in discharge and sediment concentration through the duration of a river flood an advection length scale of settling sediment is found to be an important control on hyperpycnal plume deposits where coarse sediment sand is most likely to record multiple flow accelerations and decelerations related to plunge point translation even for a river flood with a single peaked hydrograph in contrast fine sediment mud is relatively insensitive to local plunge point dynamics and is most likely to preserve directly rising and falling river discharge finally it was found that the necessary fluvial sediment concentration to form a plunging plume can be much larger than the concentration typically used assuming density equivalence because of deposition upstream of the plunge point

mid and late devonian arenites deposited by sheet flood braided streams and rivers in the northern barrier ranges far western new south wales australia abstract extensive and well exposed fine grained fluvial sandstone and less common pebbly coarse grained fluvial sandstone of devonian age crop out in the northern barrier ranges of far west new south wales australia these strata were deposited largely on low gradient alluvial fans in a basin and range landscape and contain common sedimentary structures especially streaming lineations and tabular cross beds around 400 of these sedimentary structures were measured to determine the palaeoflow trends of the sheet floods streams or rivers which deposited the sandstone the strata are mapped as the mid devonian coco range sandstone and the late devonian nundooka sandstone which together are around 2 7 km thick they were deposited at the western margin of the large emsian to early carboniferous darling basin the coco range sandstone is emsian to eifelian in age based on fragments of fossil fish and it is separated from the frasnian famennian late devonian nundooka sandstone by the north trending nundooka creek fault the eastern boundary of the nundooka sandstone is formed by the western boundary fault eastward of this fault is the north trending and 40 km wide bancannia trough which contains gently folded late silurian to early carboniferous strata up to 7 5 km thick most of the coco range sandstone and all of the nundooka sandstone are non graded fine and very fine grained light brown sub litharenites which are considered to have been deposited mainly on low gradient alluvial fans sedimentary successions of 1 75 to 5 25 m thickness in the fine grained arenite usually commence with sm massive or slumped sh laminated arenite or st trough cross beds sp tabular cross bedded sandstone an erosional surface commonly underlies the sedimentary successions and they are interpreted to be the result of deposition from decelerating sheet floods units composed of tabular cross bedded strata several metres thick are rarely channelised and are interpreted to represent deposition within braided streams flowing upon the fans or deposited at the margin of sheet floods in the coco range sandstone there are two sheet like coarse pebbly arenite units the valley tank and copi dam members which together total 200 m in thickness unimodal palaeocurrent trends and heavy mineral suites from within the coarse grained arenite indicate a derivation from the south near broken hill sedimentary structures within the coarse grained arenite indicate a platte river style of deposition upon distal braid plains whereas local interdigitation of coarse grained arenite with fine arenite strata shows that deposition was essentially continuous i e the coarse arenite do not overlie unconformities and the two lithotypes represent interdigitation of alluvial fans and braid plain deposition the northward progradation of the coarse arenite units was probably due to a sudden retardation of basement downwarping

weichselian sediments at foss eikeland jaeren southwest norway sea level changes and glaciation history the jaeren area in southwestern norway has experienced great changes in sea levels and sedimentary environments during the weichselian and some of these changes are recorded at foss eikeland four diamictons interbedded with glaciomarine and glaciofluvial sediments are exposed in a large gravel pit situated above the post glacial marine limit the interpretation of these sediments has implications for the history of both the inland ice and the norwegian channel ice stream during a middle weichselian interstadial a large glaciofluvial delta prograded into a shallow marine environment along the coast of jaeren a minor glacial advance deposited a gravelly diamicton and a glaciomarine diamicton was deposited during a following marine transgression this subsequently was reworked by grounded ice forming a well defined boulder pavement the boulder pavement is followed by glaciomarine clay with a lower laminated part and an upper part of sandy clay the laminated clay probably was deposited under sea ice whereas more open glaciomarine conditions prevailed during deposition of the upper part the clay is intersected by clastic dykes protruding from the overlying late weichselian till preconsolidation values from the marine clay suggest an ice thickness of at least 500 m during the last glacial phase the large variations in sea level probably are a combined effect of eustasy and glacio isostatic changes caused by an inland ice sheet and an ice stream in the norwegian channel copyright 2002 john wiley sons ltd

beds comprising debrite sandwiched within co genetic turbidite origin and widespread occurrence in distal depositional environments co genetic debrite turbidite beds occur in a variety of modern and ancient turbidite systems their basic character is distinctive an ungraded muddy sandstone interval is encased within mud poor graded sandstone siltstone and mudstone the muddy sandstone interval preserves evidence of en masse deposition and is thus termed a debrite the mud poor sandstone siltstone and mudstone show features indicating progressive layer by layer deposition and are thus called a turbidite palaeocurrent indicators ubiquitous stratigraphic association and the position of hemipelagic intervals demonstrate that debrite and enclosing turbidite originate in the same event detailed field observations are presented for co genetic debrite turbidite beds in three widespread sequences of variable age the miocene marnoso arenacea formation in the italian apennines the silurian aberystwyth grits in wales and quaternary deposits of the agadir basin offshore morocco deposition of these sequences occurred in similar unchannellized basin plain settings co genetic debrite turbidite beds were deposited from longitudinally segregated flow events comprising both debris flow and forerunning turbidity current it is most likely that the debris flow was generated by relatively shallow few tens of centimetres erosion of mud rich sea floor sediment changes in the settling behaviour of sand grains from a muddy fluid as flows decelerated may also have contributed to debrite deposition the association with distal settings results from the ubiquitous presence of muddy deposits in such locations which may be eroded and disaggregated to form a cohesive debris flow debrite intervals may be extensive 26 x 10 km in the marnoso arenacea formation and are not restricted to basin margins such long debris flow run out on low gradient sea floor 0 1 may simply be due to low yield strength 50 pa of the debris water mixture this study emphasizes that multiple flow types and transformations between flow types can occur within the distal parts of submarine flow events

deep sea benthonic foraminiferal faunal turnover near the eocene oligocene boundary abstract eocene oligocene deep sea benthonic foraminifera in d s d p site 277 in the southwest pacific have been analyzed to determine the benthonic foraminiferal response to the development of the psychrosphere near the eocene oligocene boundary biostratigraphic ranges of 41 taxa show that 23 taxa are found throughout the late eocene to early oligocene sequence while 18 taxa exhibit first or last occurrences comparison of the faunal changes in site 277 with a benthonic foraminiferal oxygen isotope record shows that the development of the psychrosphere did not have a profound effect upon the benthonic foraminifera and the overall faunal change preceding and subsequent to the bottom water circulation event occurred gradually the inferred water mass event affected the relative abundance of one species epistominella umbonifera the lack of major faunal changes at the eocene oligocene boundary in site 277 probably reflects either wide environmental tolerances of the benthonic foraminifera or a bottom water temperature change less than 3 c examination of previously published benthonic foraminiferal biostratigraphic data from d s d p sites 167 171 357 360 363 and 400a and deep sea ostracode data from d s d p leg 3 show faunal changes occurred during discrete intervals in the middle eocene early oligocene the faunal patterns from these data and from site 277 show that the eocene oligocene cooling event did not cause rapid catastrophic changes of the benthonic faunas of the open ocean although significant faunal changes are associated with the water mass event in sites 167 171 and 400a the benthonic faunal changes in middle eocene early oligocene time are consistent with the gradual decrease of inferred bottom water temperatures based on previously published oxygen isotopic data the 18 o eocene oligocene enrichment of 0 76 is a major event in the southern ocean oxygen isotopic record but is considerably less in magnitude than the 1 75 2 00 change that occurred gradually from mid early eocene to the eocene oligocene boundary the benthonic foraminiferal and isotopic data indicate that bottom water circulation may have developed during the middle eocene to early oligocene interval with the 3 c bottom water cooling near the eocene oligocene boundary representing part of this development

deposits related to the failure of the malpasset dam in 1959 an analogue for hyperpycnal deposits from jokulhlaups abstract sediment cores collected in the gulf of frejus se france contain submarine deposits related to the failure of the malpasset dam in 1959 these deposits constitute a dark sandy terrigeneous layer of 10 40 cm thickness lying above an erosion surface the deposits are composed of ungraded non bioturbated sands and silts displaying no apparent sedimentary structure but rich in organic matter and rock or shell fragments during the event this layer prograded onto the inner continental shelf and froze rapidly these hyperconcentrated flow deposits are related to an unsteady inertia flow generated by a surge like flood and bedload dominated hyperpycnal flow rapid freezing on flow sides generated lateral coarse grained levee shape deposits the deposits related to the failure of the malpasset dam are drastically different from classical suspended load dominated hyperpycnites deposited by a steady flood generated hyperpycnal flow however they are comparable with present day deposits on a volcanic ice covered margin icelandic jokulhlaups with ancient deposits resulting from the pulsating output of subglacial lakes during a deglaciation or with martian landforms resulting from sporadic ice melt events during early martian times

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

neritic southern extratropical foraminifera and the terminal eocene event abstract if the terminal eocene event tee records a major bolide impact or other extraterrestrial happening then there ought to be disruption of benthonic foraminiferal communities especially in rather shallow neritic environments we record the arrivals and departures of 180 species in a composite succession through the later middle eocene late eocene and earliest oligocene in southern australia the rate of new arrivals increases at each of several transgressions each of which also marks a climatic amelioration the sharpest increase in rate of departure is found at a regional regression within the latest eocene there is no evidence of major disruption of the fauna at the end of the eocene the tee on this data was not extraterrestrial in origin and was hardly cataclysmic the study suggests instead that the origins of late eocene biotic change should be sought through earthly configurations of climate and sea level

paleoceanographic events and deep sea ostracodes eight recognized or theorized paleoceanographic events during the past 70 million years were tested against changes in the global deep sea benthic ostracode fauna two events the sudden cretaceous tertiary boundary event at 66 million years ago and the more gradual 40 million year event formation of the psychrosphere show up most dramatically before the 40 million year event ostracodes freely radiated into the deeper water regions but were provincial the development of thermal stratification isolated these deep water taxa mostly the survivors of the cretaceous tertiary boundary event which adapted to a new free flowing but more frigid ecosystem and spread rapidly throughout the world

quaternary erosion and depositional processes western norwegian fjords norwegian channel and north sea fan abstract the southern norwegian fjords the northern north sea and north sea margin represent major pathways of sediment flux from the southern part of fennoscandia to the deep sea basin volumes genesis and chronology of the temporary and semi permanent quaternary sediment repositories are reviewed the fjord infill is dominated by sediments from the last deglaciation 150 km 3 the norwegian channel is occupied by tills and glaciomarine marine sediments 5000 km 3 the north sea fan comprises glacially fed debris flow fingers lobes constituting 80 of deposits in the mid to late pleistocene together with hemipelagic and mass transport slide sediments totalling 15 000 km 3 the norwegian channel represents a dynamic transport conduit whereby during peak glaciation a fast flowing ice stream has drained large parts of the southern fennoscandian ice sheet several times the sediment flux to the deep sea is temporarily interrupted between glacials when stored in the channel but under glacial maxima the channel is probably largely bypassed with material transported as subglacial load and deposited as debris flows on the north sea fan sediments on the fan have a much longer storage time numerous glaciation cycles but are further transported to the deep sea in large slide events the volume of quaternary sediments found along this sediment pathway plus that which slid to the deep sea total at least 25 000 km 3 corresponding to an averaged 120 m of erosion across southern norway

sandstone body structures and ephemeral stream processes in the dinosaur canyon member moenave formation lower jurassic utah u s a abstract studies of fluvial sandstone body structures in the lower jurassic dinosaur canyon member suggest a threefold subdivision of the ephemeral stream deposits sandstone sheets with interbedded siltstones are less than 1 m thick and laterally extensive for hundreds of metres they are interpreted as sheetflood deposits simple channel sandstone bodies are a few metres thick and a few tens of metres wide they reflect solitary channel incision episodic migration and plugging multistorey channel sandstone bodies are a few metres thick and laterally extensive for hundreds of metres they are composed of several channel shaped storeys and exhibit only local incision the multistorey sandstone bodies are interpreted as braided ephemeral stream deposits two sandstone sheet subtypes with grooves and mounds respectively are interpreted as intermediate between the sheetflood deposits and solitary incised channel deposits on one hand and between sheetflood deposits and braided stream deposits on the other hand the solitary channels and braided streams are accordingly interpreted to be initiated from sheetfloods through differential erosion and differential deposition respectively this model of channel evolution from sheetfloods is probably applicable to other semiarid and arid fluvial environments dominated by surface runoff