large striated burrows from fluvial deposits of the neogene vinchina formation la rioja argentina a crab origin suggested by neoichnology and sedimentology abstract this study includes three aspects 1 the ichnotaxonomic treatment of large and dominantly vertical burrows ornamented with sharp bioglyphs from the fluvial neogene vinchina and toro negro formations northwest argentina 2 the description and interpretation of the sedimentary facies where these burrows occur and 3 neoichnologic observations on large ornamented burrows from seasonal wetlands of the rio pilcomayo national park argentina as possible modern analogues of the trace fossils and the sedimentary environment a new ichnogenus and ichnospecies capayanichnus vinchinensis is proposed to include the large striated burrows the new ichnotaxon is distinguished by a combination of a predominantly vertical orientation overall l shape when fully developed absence of lining and burrow bifurcation a distinct surface texture and lack of burrow enlargements the hosting sedimentary facies of the vinchina formation can be grouped into fluvial channel and splay floodplain facies associations the rivers of that unit were of two main types single channel rivers with frequent channel avulsion and overbank flow and multichannelised rivers with poorly defined margins at least some of these rivers were ephemeral or with intermittent discharge the climate was probably seasonal and semiarid as suggested by sedimentologic evidence c vinchinensis was dominantly recorded from the top of fluvial channels interpreted as abandoned channels and proximal intermediate and distal splay facies the large ornamented burrows found in an extant comparable example were constructed by freshwater crabs these burrows can be distinguished by the overall architecture the taxonomy and sex of its occupants and the environmental setting where they were found the neoichnologic signatures used in the interpretation of the fossil example include the common oval burrow cross section and the surface texture in particular the surface texture in the modern crab burrows includes abundant comma shaped marks sets of grooves oblique to burrow axis and long segmented grooves the predominantly oval cross section absence of lining and the strongly ornamented burrow surface suggest that c vinchinensis was produced by freshwater crabs the key features of the surface ornament are long sets of three four ridges whose width is in average one third of the burrow major axis other features that also point to a crab origin are a massive filling common burrow ends in a casing mudstone chevron pattern in sets of surface ridges and possible cheliped marks the new ichnotaxon is restricted in the vinchina and toro negro formations to fluvial facies and is absent in shallow lacustrine facies

the randeck maar palaeoenvironment and habitat differentiation of a miocene lacustrine system abstract the randeck maar in s germany is a well known fossil lagerstatte with exceptionally preserved fossils particularly insects and plants which thrived in and around the maar lake during the mid miocene climatic optimum late early early middle miocene mammal zone mn5 we provide the first critical and detailed overview of the fauna and flora with lists of 363 previously published partially revised and newly identified taxa plant remains are the most diverse group 168 taxa followed by insects 79 the flora points towards subhumid sclerophyllous forests and mixed mesophytic forests the former being an indication for the occurrence of seasonal drought three main sections can be differentiated for the habitats of the randeck maar lake system 1 deep and open water lake habitats with local and short termed mass occurrences of insect larvae amphibians and or gastropods while fish is particularly scarce the interpretation of the water chemistry is problematic because contradictive palaeoenvironmental indicators for both brackish and freshwater conditions exist 2 shallow parts of the lake comprise a narrow reed belt with insects and gastropods living on the exposed plant stems as well as turtles 3 crater slopes and surrounding plateaus were mainly covered by subhumid sclerophyllous to mixed mesophytic forests depending on sun exposition and soil conditions horses and other forest dwellers preferably lived in forested habitats while proboscideans and rhinoceratids occupied more open habitats our study also brings up contradictive results that cannot be untangled with the current state of knowledge and thus directions for future studies are discussed

shear margins in glaciers and ice sheets analytical and numerical techniques are used to examine the flow response of a sloped slab of power law fluid power n subjected to basal boundary conditions that vary spatially across the flow direction as for example near an ice stream margin with planar basal topography the primary assumption is that basal shear stress is proportional to the basal speed time a spatially variable slip resistance the ratio of mean basal speed to the speed originating from shearing through the thickness denoted as r gives a measure of how slippery the bed is the principal conclusion is that a localized disturbance in slip resistance affects the basal stress and speed in a zone spread over a greater width of the flow in units of ice thickness h the spatial scale of spreading is proportional to a single dimensionless number r n r n 1 1 n 1 derived from n and r the consequence for a shear zone above a sharp jump in slip resistance is that the shearing is spread out over a boundary layer with a width proportional to r n for an ice stream caused by a band of low slip resistance with a half width of wh the margins influence velocity and stress in the central part of the band depending on r n in comparison to w three regimes can be identified which for n 3 are quantified as follows low r defined as r 3 1w for which the boundary layers from both sides bridge across the full flow width and the driving stress in the center is supported almost entirely by side drag intermediate r for which the driving stress in the center is supported by a combination of basal and side drag shear zones that are narrower than predicted on the basis of this theory r 3 would require localized softening of the ice to explain the concentration of deformation at a shorter scale

model experiments on the evolution and stability of ice streams this is the publisher s version also available electronically from http www igsoc org annals 23

seasonal acceleration of inland ice via longitudinal coupling to marginal ice we use an ice flow model to demonstrate how flow variations initiated in the marginal zone of an ice sheet affect flow farther inland through longitudinal along flow coupling our findings allow for an alternate interpretation of seasonal accelerations observed near the equilibrium line of the greenland ice sheet zwally and others 2002 we demonstrate that these observations can be explained by accelerations initiated up to 12 km closer to the margin where the ice is 40 thinner is heavily crevassed experiences a seasonal doubling of velocity and where the ablation rate surface meltwater flux and ice temperature are likely higher our modeling and observations suggest that conditions and processes normally found near ice sheet margins are adequate for explaining the observations of zwally and others 2002 this and considerations of the likely subglacial hydrology in the marginal zone lead us to suggest that seasonal accelerations may have limited impact on ice sheet mass balance even in the face of climate warming

on the relationship between surface and basal properties on glaciers ice sheets and ice streams the influence of basal disturbances on the steady state surface topography and on surface velocities of glaciers and ice sheets is investigated numerically this is done for finite amplitude basal perturbations in both bed topography and basal slipperiness using a nonlinear ice rheology and a nonlinear sliding law the effects of varying the exponent n in glen s flow law on transfer characteristics are mainly quantitative and do not affect qualitative aspects of the transfer amplitudes and phase shifts such as the number of maxima and inflection points when plotted as functions of wavelength in particular the well known maximum in bed to surface transfer amplitude for a newtonian medium at sufficiently high slip ratios ratio between mean sliding velocity and mean ice deformational velocity also forms for n 1 transfer amplitudes generally become smaller with increasing n for wavelengths less than about 3 times the mean ice thickness h for larger wavelengths the situation is reversed and transfer amplitudes increase with n for active ice streams characterized by high basal slipperiness low surface slopes 0 5 and fairly constant for all wavelengths longer than about 3 5h with increasing n and decreasing surface slope the lower limit of wavelengths over which horizontal stress gradients can be ignored increases markedly perturbation solutions for newtonian medium are found to give an accurate description of the transfer characteristics for bedrock amplitudes up to 50 ice thickness and for fractional amplitudes of slipperiness perturbations up to 0 5

links between acceleration melting and supraglacial lake drainage of the western greenland ice sheet 1 the impact of increasing summer melt on the dynamics and stability of the greenland ice sheet is not fully understood mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding here we compare subdaily ice velocity and uplift derived from nine global positioning system stations in the upper ablation zone in west greenland to surface melt and supraglacial lake drainage during summer 2007 starting around day 173 we observe speedups of 6 41 above spring velocity lasting 40 days accompanied by sustained surface uplift at most stations followed by a late summer slowdown after initial speedup we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting most lake drainages were undetectable in the velocity record and those that were detected only perturbed velocities for 1 day suggesting preexisting drainage systems could efficiently drain large volumes of water the dynamic response to melt forcing appears to 1 be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses and 2 decrease over the course of the summer presumably as the subglacial drainage system evolves to greater efficiency the relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here thus increases in summer melting may not guarantee faster seasonal ice flow

transient glacier response with a higher order numerical ice flow model in this paper a higher order numerical flowline model is presented which is numerically stable and fast and can cope with very small horizontal grid sizes 10 m the model is compared with the results from blatter and others 1998 on haut glacier d arolla switzerland and with the european ice sheet modelling initiative benchmarks huybrechts and others 1996 results demonstrate that the significant difference between calculated basal drag and driving stress profiles in a fixed geometry disappears when the glacier profile is allowed to react to the surface mass balance conditions and reaches a steady state dynamic experiments show that the mass transfer in higher order models occurs at a different speed in the accumulation and ablation areas and that the front position is more sensitive to migration compared to the shallow ice approximation

the basal stress distribution of ice stream e antarctica inferred by control methods the irregular spatial distribution and velocity independence of basal friction derived from landsat measured surface velocity suggests that ice stream flow is not controlled by the properties of a deformable basal till alone rigid bedrock substrata may contact the base of the ice stream in small 100 km2 areas where the velocity field displays strong vorticity and where the ice stream surface appears rumpled in landsat images

integrated ichnofacies models for deserts recurrent patterns and megatrends abstract although it is commonly assumed that the trace fossil record of eolian dunes and associated environments is invariably poor a systematic review of the available information indicates that this is not necessarily the case a model involving five main phases of colonization of desert environments through the phanerozoic is proposed in this paper the first phase cambrian silurian involved animal incursions into coastal dune fields directly from the sea although it is unlikely that these animals would have remained for long periods of time in coastal deserts the second phase devonian reflects the activities of dune pioneers that left their fluvial habitat to enter temporary or permanently into inland deserts the third phase carboniferous permian involved the colonization of deserts by tetrapods the fourth phase triassic cretaceous involved a major exploitation of the infaunal ecospace as reflected by the appearance of more varied behavioral patterns in sub superficial structures the fifth phase paleogene recent reflects the appearance of the ecological dynamic that characterizes modern desert communities the invertebrate ichnofacies for eolian dunes is re named herein as the octopodichnus entradichnus ichnofacies honoring the seminal work of previous workers who simultaneously tackled the issue of eolian dune ichnofacies the chelichnus ichnofacies is retained for vertebrate trace fossil assemblages in eolian settings both ichnofacies occur in mobile and temporary stabilized sandy substrates subject to frequent erosion and deposition and to strong seasonality desert settings consist of complex mosaics of habitats or physical units associated with organism activity trace fossil distribution can be understood as reflecting the partitioning of desert settings in a mosaic of landscape units characterized by water content and its temporal fluctuations nutrient availability nature of the substrate and the dominant organisms present in turn desert systems are dynamic entities that change as a response to regional climate landscape units such as eolian sand seas salt flat and playa lake systems ephemeral rivers and alluvial fans interact in response to regional scale climate variations in hyper arid arid and semiarid climatic settings ancient deserts completely developed under hyper arid climatic conditions rarely preserve trace fossils due to the absence of moisture near the surface however the alternation of wet periods may represent windows for life development and thus preservation of biogenic structures arid deserts display complex patterns of dunes combined with dry wet and flooded interdunes dry desert elements e g dunes interdunes sand sheets typically record the entradichnus octopodichnus and chelichnus ichnofacies slight rises in regional precipitation produce elevation of the water table and increase of fluvial discharges that provide water and sediment to the system these processes may result in the local concentration of trace fossils in wet interdunes and ephemeral fluvial systems illustrating the scoyenia and chelichnus ichnofacies in semiarid systems playa lakes expand by the addition of freshwater evolving into freshwater lakes and fluvial systems may become more common lake margins and fluvial overbanks typically contain trace fossil assemblages that may be ascribed to the scoyenia ichnofacies

messinian event in the black sea evidence of a messinian erosional surface in 1975 sediment cores from leg dsdp 42b sites 380a and 381 revealed a thin sediment layer in the black sea basin which points to a shallow water environment at the miocene pliocene boundary with these facts and in the wake of hypothesis of the messinian salinity crisis msc it was proposed that the black sea like the mediterranean sea suffered a desiccation period at the end of the messinian hsu k j and giovanoli f 1979 messinian event in the black sea palaeogeography palaeoclimatology palaeoecology 29 75 93 whereas the main topics of the msc in the mediterranean sea is now widely accepted the lack of evidence for a messinian erosional surface in the black sea left the debate about the messinian desiccation of this basin open until today the analysis of high resolution multi channel seismic data acquired during the blason surveys brings important new elements for this scientific debate 1 down the slope offshore the bosporus we show a clear erosional surface correlated to the top of the upper miocene shallow water environment unit of site dsdp 381 the overlying lower zanclean unit inevitably dates this erosional surface of the messinian event 2 a wide intra pontian erosional surface ipu is evidenced on the romanian shelf the ipu is characterized by a sharp decrease in the incision rate from outer deep canyons to inner shelf superficial incisions network according to the most recent paratethyan and mediterranean stratigraphic scale correlations the ipu erosional surface is considered as the analogue to the messinian erosional surface described down the slope offshore the bosporus in addition to recently discovered inland erosional signature the wide regional erosional surface we underline on the western black sea margins validates the black sea messinian desiccation hypothesis we also demonstrate that evaporative draw down of the black sea implied the installation in the basin of a negative hydrologic budget during the messinian the lack of a major messinian danube canyon on the romanian shelf supports the hypothesis of a messinian danube trapped in the dacic basin however the presence of a messinian superficial incision network connecting the location of the modern danube delta to deeply incised messinian canyons on the outer shelf ipu makes the hypothesis of a danube reaching the partially desiccated black sea still possible

hamilton type principles applied to ice sheet dynamics new approximations for large scale ice sheet flow ice sheet modelers tend to be more familiar with the newtonian vectorial formulation of continuum mechanics in which the motion of an ice sheet or glacier is determined by the balance of stresses acting on the ice at any instant in time however there is also an equivalent and alternative formulation of mechanics where the equations of motion are instead found by invoking a variational principle often called hamilton s principle in this study we show that a slightly modified version of hamilton s principle can be used to derive the equations of ice sheet motion moreover hamilton s principle provides a pathway in which analytic and numeric approximations can be made directly to the variational principle using the rayleigh ritz method to this end we use the rayleigh ritz method to derive a variational principle describing the large scale flow of ice sheets that stitches the shallow ice and shallow shelf approximations together numerical examples show that the approximation yields realistic steady state ice sheet configurations for a variety of basal tractions and sliding laws small parameter expansions show that the approximation reduces to the appropriate asymptotic limits of shallow ice and shallow stream for large and small values of the basal traction number

application of vertebrate trace fossils to palaeoenvironmental analysis abstract this is a review of the main uses of vertebrate trace fossils ichnofabrics and ichnofacies in the palaeoenvironmental analysis of sedimentary sequences the article accounts for the significant developments produced in the last three decades including the application of the ichnofacies concept to vertebrate trace fossils recognition of footprints in cross sectional view and their distinction from inorganic structures and burrow fills is first discussed the response of different substrates showing contrasting water content and imprinted by different animals or devices is compared in terms of the morphology of the resultant footprint trackways with sand crescents are typical of aeolian cross strata and are absent in associated flat lying to low angle deposits thick packages of highly bioturbated sandy dune and interdune sediments have been interpreted as reflecting periods of increased rainfall neoichnological observations in modern lake basins suggest that distinct zones can be recognized in the margins of fossil ponds and lakes including onshore shoreline and shallow subaqueous zones abundant flamingo like footprints and flamingo nest mounds are good indicators of alkaline and or saline lake waters hippopotamus trails are found closely associated with modern and fossil freshwater wetlands dinosaur and pterosaur swim traces from lacustrine and fluvial deposits can be used to estimate water depth turtle crocodile amphibian hippopotamus and fish swim traces allow one to infer a subaqueous substrate certain modern intertidal fish feeding traces are oriented with the predominant tidal current and can be used as palaeocurrent indicators the preferential orientation of tetrapod trackways in lacustrine and fluvial deposits is analyzed vertebrate trace fossils can help to infer discharge variability in fluvial channels the descriptions of vertebrate ichnofabrics are commonly limited to heavily bioturbated beds due to trampling by vertebrates and to a few examples of ichnofabrics with discrete trace fossils the nature and implications of the recognized vertebrate ichnofacies are still being debated and have a limited utility in palaeoenvironmental analysis the distinction of a potential vertebrate burrow ichnofacies in carbonate bearing palaeosols is proposed to represent well drained soils developed under arid or semiarid climate

stratigraphic and structural characteristics of the romanian black sea shelf abstract the western black sea basin opened during cretaceous times by back arc rifting in association with a north dipping subduction at the rear of the cretaceous early tertiary pontide volcanic arc the sedimentary wedge developed on the shelf of the romanian black sea sector reflects a complex interplay between large scale rifting uplift of the orogenic flanks large scale post rift subsidence and sea level changes we examine the detailed structural configuration of this sector for a regional correlation with the adjacent offshore in ukraine and bulgaria the evolution of the western black sea basin started in the albian cenomanian times when two extensional phases with significantly different directions n s and subsequently e w lead to the formation of a complex interplay between isolated blocks organised in horsts and grabens generally deepening eastwards superposition of normal faults footwall blocks from the two extensional episodes generated a deeply subsided area with enhanced accommodation space i e the histria depression and consequently recorded a larger thickness of paleogene sediments in the post rift stage re activation of faults and associated folding reflects repeated inversion during the late cretaceous oligocene times associated with subsequent periods of non deposition and or erosion during moments of basin fill exposure these periods of inversion recorded in the black sea are controlled by coeval orogenic deformations taking place in the balkans pontides and the crimean thrust belt sea level fluctuations during the neogene and late alpine tectonics in the neighbouring orogens caused massive sedimentation followed by sediment starvation and or significant erosion large thicknesses of sediments accumulated during the pontian presumably associated with an extensional episode deepening the distal parts of the basin and with differential compaction structures the interpretation of a high quality seismic dataset combined with published data allowed the correlation of major structural units and lineaments defined onshore towards the carpathians with the ones deeply buried below the western black sea basin sediments unit correlations are furthermore used to derive an integrated tectonic image of the western black sea area

the effects of transverse bed topography variations in ice flow models 1 a suite of ice flow models is subject to a performance test designed to investigate treatment of flow over variable basal topography using transfer functions developed by gudmundsson 2003 and numerical models of various complexity this study demonstrates that a widely used flowband model has strong limitations associated with its underlying assumptions and thus should be applied only in specific geometrical settings its performance can be significantly improved by using the laterally averaged basal topography instead of centerline topography in applications where spatial variability of flow fields is important hybrid ice flow models can be a viable alternative to flowband models in addition analysis of horizontal distributions of the various ice flow characteristics e g surface elevation velocity and horizontal stress components shows that field observations that focus on assessing these parameters only along the centerline of ice flow could be misleading these results also suggest that such spatial variability needs to be taken into account when designing field surveys of ice flow

airborne surface profiling of glaciers a case study in alaska a relatively lightweight and simple airborne system for surface elevation profiling of glaciers in narrow mountain valleys has been developed and tested the aircraft position is determined by kinematic global positioning system gps methods the distance to the glacier surface is determined with a laser ranger the accuracy is about 0 3 m sufficient to permit future changes to be observed over short time intervals long term changes can be estimated by comparison of profiles with existing maps elevation profiles obtained in 1993 94 from three glaciers in central and south central alaska are compared with maps made about 1950 the resulting area averaged seasonally corrected thickness changes during the interval are gulkana glacier central alaska range 11 m worthington glacier central chugach mountains 7 m and bear lake glacier kenai mountains 12 m all three glaciers retreated during the interval of comparison the estimated uncertainty in the average thickness change is 5 m which is mainly due to errors in the existing maps constraints on the accuracy of the maps are obtained by profiling in proglacial areas

transmission of basal variability to a glacier surface 1 transmission of basal variability to a glacier surface is investigated using analytical models for a linearly viscous medium the three dimensional transient response of the surface to both bedrock undulations and spatial variations in basal slipperiness for perturbations of arbitrary wavelengths is determined using perturbation methods both information transfer toward the surface and lateral transmission of horizontal stresses are strongly affected by the slip ratio that is the ratio of basal sliding to deformational velocity for any mean bedrock slope and above a minimum value of slip ratio the amplitude transfer of bedrock undulations toward the surface has a local maximum at undulation span corresponding to about 3 8 times the mean ice thickness the transmission of basal variability to a glacier surface increases quite significantly with increasing slip ratio this explains why the surfaces of fast flowing ice streams are more undulating than the slower moving bordering areas at slip ratios higher than about 100 the flow of glaciers and ice sheets becomes nonlocal in the sense that surface velocities and buildup and propagation of surface undulations cannot be calculated accurately on the basis of local thickness and slope using linearized long wave theories at these slip ratios instead of the more accurate arbitrary wavelength theory gives estimates of decay times that are an order of magnitude too small and phase velocities several times too large the problem of the propagation and decay of small amplitude surface undulations on glaciers in three dimensions is solved small amplitude surface waves on glaciers are strongly diffusive and dispersive redistribution of mass on ice sheets and glaciers is a diffusion process and it is misleading albeit not mathematically incorrect to describe the reaction of glaciers to surface perturbations in terms of a wave propagation

the geological history of the istria depression romanian black sea shelf tectonic controls on second third order sequence architecture the istria depression or sub basin of offshore romania lies at the intersection of the trans european tornquist teisseyre zone and the black sea back arc basin just outboard of the east carpathian orogenic welt its late mesozoic cenozoic succession records an extraordinary cpolyphase history of subsidence and sedimentation interrupted by several quite spectacular 2nd 3rd order erosional unconformities reflecting the interplay between these teetonic domains the unconformities divide the succession into a number of stratigraphic sequences the sub basin first developed as a transtensional rift in the triassic early jurassic evolving into a narrow oceanized trough in later jurassic this was tilted west during the early cretaceous by uplift and rifting in the western black sea and the residual late jurassic topography was filled and buried by a west facing clastic evaporite wedge late aptian albian post rift subsidence and spreading in the western black sea imposed a strong easterly tilt encouraging the partial evacuation of its early cretaceous sedimentary fill by gravity driven mass wastage the incised valley topography was subsequently buried in the later cretaceous and early cenozoic during the mid late cenozoic the black sea basin experienced intermittent periods of partial to complete isolation from the world ocean and significant base level drawdown the first major sea level fall occurred in the eocene when the istria depression was deeply incised to be healed by oligocene shales during the subsequent rise yet another period of drawdown and exposure occurred in mid miocene with extensive shelf margin mass wastage and erosion followed by reflooding and deposition of a transgressive backstepping sequence in mid late miocene messinian drawdown in the mediterranean caused a further period of isolation and falling base level the shelf margin was again exposed and experienced widespread mass wastage and slumping a marine connection was re established in late messinian rising sea level eroded the earlier slumped sequence and the margin was healed by a lowstand prograding wedge in late miocene early pliocene this was followed by shelf sedimentation in the plio pleistocene periodically interrupted by canyon incision events testifying to continued climatically or tectonically imposed base level fluctuations several direct and indirect tectonic factors were responsible for valley canyon incision within the istria depression and erosion of the romanian black sea shelf margin these include 1 the local structural framework 2 direct tectonic uplift and tilting and 3 more indirect tectonically imposed isolation encouraging significant base level falls

is the impact of the messinian salinity crisis in the black sea comparable to that of the mediterranean abstract erosional features have been observed along the black sea shelf in wells and on seismic reflection profiles that are broadly similar to the seismic stratigraphic signature of the messinian salinity crisis msc in the mediterranean in particular the intra or middle pontian unconformity has been suggested by some as the manifestation of the msc in the black sea basin missing strata and prominent lithological changes associated with the inferred msc unconformity indicate erosional removal of parts of the underlying cenozoic deposits in the shelf areas of the entire black sea the magnitude of the relative sea level drop associated with this unconformity has been much debated and ranges from tens of meters to thousands of meters the suggestion of a very large 1600 m sea level drop in the black sea during the msc is primarily based on the findings of shallow water clastics and carbonates in deep sea drilling project dsdp wells 380 and 381 however recently acquired long offset seismic data clearly show that both of these wells penetrated gravity driven mega slumps and mass transport complexes therefore the interpreted shallow water msc units in these deepwater wells do not represent in situ rock formations but rather allochthonous strata derived from the basin margin moreover compared to the typical seismic expression of the msc in the mediterranean detailed interpretation of 2d 3d seismic data sets in the bulgarian and turkish black sea revealed considerably more complexity this marked difference is tentatively attributed to the extent of erosion associated with the msc in the black sea i e the multiple msc incisions occurred in a submarine setting not on a subaerially exposed palaeoslope therefore the magnitude of the sea level drop and the overall impact of the msc in the black sea appear to be significantly less than in the mediterranean

palaeonvironmental and palaeoecological significance of flamingo like footprints in shallow lacustrine rocks an example from the oligocene miocene vinchina formation argentina abstract this article describes the lacustrine trace fossil assemblage of the late oligocene early miocene vinchina formation of northwest argentina the thick 5000 m continental succession of the formation is essentially fluvial with thin aeolian and lacustrine intervals the trace fossil assemblage from the lacustrine facies is dominated by bird footprints notably flamingo like palmate bird footprints and also contains invertebrate traces the assemblage is of contrasting composition with those of the ubiquitous fluvial facies of the vinchina formation we identify the possible trace maker of the web footed bird footprints and infer the palaeoenvironmental and palaeoecological meaning of the lacustrine trace fossil assemblage of the vinchina formation the lacustrine succession is mainly composed of wave rippled fine grained sandstones and siltstones and wave rippled heterolithic facies with subordinate laminated mudstone and medium grained sandstone with parallel lamination or cross bedding metre scale shallowing upward cycles are typical and desiccation cracks were observed in a single bedding plane the analysed interval was deposited in a wave dominated littoral zone of a shallow permanent lake basin ichnofossils were found mostly in three trampled horizons of the upper part of the analysed succession the trace fossil assemblage is dominated by phoenicopterichnum isp flamingo like footprints slender bird tracks without web traces and triangular and fusiform hypichnial ridges interpreted as bird undertracks the remaining trace fossils are lockeia siliquaria bivalve resting trace rusophycus isp shallow arthropod burrow taenidium barretti endostratal meniscate burrow and small hypichnial double knobs possible beak probing marks neoichnological observations on modern chilean flamingo footprints phoenicopterus chilensis suggest that phoenicopterichnum isp is morphologically akin to modern flamingo footprints although its average size is slightly smaller the likely producers of the fossil footprints are members of the palaelodidae and phoenicopteridae which are recorded in south america since the late oligocene phoenicopterichnum isp appears in cuasi parallel trackways with short pace length and forming a low angle with ripple crests by comparison with observations of modern flamingo behaviour during this study and of shorebird studies from the literature these tracks and trackways likely reflect flock feeding behaviour probably filter feeding in a subaqueous belt parallel to the waterline invertebrate ichnofossils that appear on the same slabs from trampled horizons are mainly triangular and fusiform hypichnial ridges while phoenicopterichnum isp and sparse small hypichnial double knobs also occur in consequence it is possible that these birds were foraging on small invertebrates represented by lockeia siliquaria rusophycus isp and probably taenidium barretti in the coast of the vinchina lake the only fossil evidence for these invertebrates is the impression of articulated valves probably belonging to a small mollusc potential producer of lockeia trace fossil assemblages dominated by flamingo like footprints including ichnogenera phoenicopterichnum culcitapeda and similar unnamed tracks are indicative of alkaline and or saline waters as suggested by the specialised filter feeding mechanism of late oligocene to modern phoenicopteriformes these particular assemblages are distinguished as a subset within the shorebird ichnofacies with a definite palaeoenvironmental and palaeoecological meaning the phoenicopterichnum ichnosubfacies

sedimentary basin tectonics from the black sea and caucasus to the arabian platform introduction the palaeozoic to recent evolution of the tethys system gave way to the largest mountain chain of the world extending from the atlantic to pacific oceans the alpine himalayan mountain chain which is still developing as a result of collision and northwards con vergence of continental blocks including apulia in the west the afro arabian plate in the middle and the indian plate in the east this special publication addresses the main problems of the middle part of this system incorporating the balkans black sea and greater caucasus in the north and the afro arabian plate in the south since the early mesozoic a number of small to large scale oceanic basins opened and closed as the intervening continental fragments drifted northwards and diachro nously collided with and accreted to the southern margin of the eurasian plate despite the remark able consequences of this in terms of subduction obduction and orogenic processes little is known about the timing and palaeogeographic evolution of the region this includes the amounts of short ening and interplay between synconvergent extension and compression development of magmatic arc and arc related basins and the timing and mechanism of their deformation the chapters pre sented in this special publication present new information that help to fill some of the gaps of the puzzle

ice sheet velocity mapping a combined interferometric and speckle tracking approach the first and second radarsat antarctic mapping missions amm 1 and 2 have now acquired interferometric synthetic aperture radar sar overmuch of the ice sheet the radarsat 24 day repeat cycle is nearly ideal for measuring slow ice motion e g 1 but application of sar interferometry is limited in faster moving areas with a 1day repeat period ers 1 2 tandem sar data are much better matched to fast motion but are not always available fortunately several authors have demonstrated the ability to measure velocity in fast moving areas by tracking sar speckle from image to image which works well even in the absence of visible features while these estimates have intrinsically lower resolution and poorer accuracy than direct phase measurements they serve well in areas where there are no data suitable for conventional interferometry this paper describes algorithms i have developed for merging interferometric and speckle tracking data from multiple swaths to form a single seamless mosaic of velocity at each point in the mosaic all the available data are combined to produce estimates of the velocity and the associated error this technique is demonstrated using radarsat data collected over lambert glacier antarctica during amm 1 and 2

application of neoichnological studies to behavioural and taphonomic interpretation of fossil bird like tracks from lacustrine settings the late triassic early jurassic santo domingo formation argentina abstract the purpose of this study is to apply neoichnological observations to the behavioural and taphonomic interpretation of a late triassic early jurassic track surface from the santo domingo formation argentina containing hundreds of bird like tracks and trackways in addition the factors affecting the formation and preservation of bird tracks in lacustrine settings are particularly addressed the 5 5 m2 fossil track surface contains different types of trace fossils the avian ichnotaxa gruipeda dominguensis the most abundant bird like tracks with elongated hallux impressions small epichnial rounded pits and invertebrate traces skolithos taenidium the modern environmental analogue chosen for the neoichnological studies was a coastal freshwater pond the bajo de los huesos chubut argentina seasonally occupied by sandpipers calidris bairdii and calidris fuscicollis charadriiformes the comparison between the fossil succession and the modern example suggests that they share lithology and sedimentary structures and that sedimentary processes and local palaeoenvironment were fairly similar and do not bias ichnological comparisons field observations allowed to distinguish twenty one behaviours that produced distinct traces and four modern footprint types 1 to 4 related to specific substrate conditions in particular the preferential formation of bird tracks parallel to the waterline also confirmed by studies on droppings and invertebrate fauna of the pond and other associated sedimentary features ripple marks wrinkle marks mud drape thickness and trace fossils were important for recognition of the shoreline in the fossil example these observations also allowed us to distinguish the adjacent deeper and shallower parts of the fossil pond and can be applicable to other similar case studies contrasting sediment properties and footprint types some relationships and constraints on the formation and preservation of modern footprints are proposed although these are very complex processes that will require further studies five of the behaviours recognised in the modern pond were inferred from the sixteen trackways distinguished on the fossil track surface including walking walking with a zig zag path short runs probing and landing with legs directed forward possible trace of flight the recognition of traces of flight volichnia probing marks and tracks showing morphology similar to modern shorebirds g dominguensis strongly suggest an avian affinity for the producers of the fossil tracks and in consequence the santo domingo track site would be younger than supposed

biogenic structures in exhumed surfaces around saline lakes an example from lake bogoria kenya rift valley abstract five overprinted suites of animal and plant traces around saline alkaline lake bogoria kenya are described from a set of interfingering late pleistocene and holocene exhumed surfaces that reveal a complex story of changes in lake level and environmental controls on trace assemblages through time these stratigraphic surfaces are amalgamated and form a co planar surface the sediments were first deposited during intermediate lake levels then reworked and cemented during low lake levels and were subsequently overlain by transgressive lacustrine sediments during higher lake levels ongoing exhumation of the surface near the present shoreline has reactivated the sediments as a substrate for the activities of epifaunal and infaunal animals as well as plant growth the modern environmental setting at lake bogoria is very similar to that of the preserved exhumed surfaces which allows comparisons between observed sets of environmental factors affecting animal behaviour and their representation in the fossilized examples pronounced lateral environmental heterogeneity around saline and hypersaline lakes may lead to concentrations of life around sites with vital resources such as freshwater at lake bogoria groups of fault controlled hot springs represent these oases and have been a relatively consistent feature in and around the lake during the development of the exhumed surfaces together the diverse assemblage of animal trace suites from lake bogoria represent the mermia and scoyenia ichnofacies but can be divided into five suites that reveal details of laterally heterogeneous sets of environmental factors and are useful indicators of lake level substrate moisture content substrate cohesion etc suite 1 comprises the traces of chironomid larvae diptera chironomidae formed in subaqueous lacustrine settings suite 2 includes the traces of flamingos phoeniconaias minor and phoenicopterus ruber formed at the shoreline suite 3 compares well with the mermia ichnofacies and comprises trails and burrow systems associated with relatively fresh saturated to extremely shallow subaqueous substrates suite 4 is comparable to both the pre and post desiccation suites of the scoyenia ichnofacies is the most diverse suite at lake bogoria and mainly comprises the burrows of beetles earwigs and their larvae as well as a diverse set of rhizoliths and vertebrate tracks suite 5 contains a moderately diverse set of traces attributed to termites and ants

petroleum geology of the black sea abstract the black sea comprises two extensional basins formed in a back arc setting above the northward subducting tethys ocean close to the southern margin of eurasia the two basins coalesced late in their post rift phases in the pliocene forming the present single depocentre the western black sea was initiated in the aptian when a part of the moesian platform now the western pontides of turkey began to rift and move away to the south east the eastern black sea probably formed by separation of the mid black sea high from the shatsky ridge during the palaeocene to eocene subsequent to rifting the basins were the sites of mainly deep water deposition only during the late miocene was there a major sea level fall leading to the development of a relatively shallow lake most of the margins of the black sea have been extensively modified by late eocene to recent compression associated with closure of the tethys ocean gas chromatography mass spectrometry and carbon isotope analysis of petroleum and rock extracts suggest that most petroleum occurrences around the black sea can be explained by generation from an oil prone source rock of most probably late eocene age although a wider age range is possible in the basin centres burial history modelling and source kitchen mapping indicate that this unit is currently generating both oil and gas in the post rift basin a palaeozoic source rock may have generated gas condensate in the gulf of odessa in bulgarian waters the main plays are associated with the development of an eocene foreland basin kamchia trough and in extensional structures related to western black sea rifting the latter continue into the romanian shelf where there is also potential in rollover anticlines due to gravity sliding of neogene sediments in the gulf of odessa gas condensate has been discovered in several compressional anticlines and there is potential in older extensional structures small gas and oil discoveries around the sea of azov point to further potential offshore around the central azov high in offshore russia and georgia there are large culminations on the shatsky ridge but these are mainly in deep water and may have poor reservoirs there are small compressional structures off the northern turkish coast related to the pontide deformation these may include eocene turbidite reservoirs the extensional fault blocks of the andrusov ridge mid black sea high are seen as having the best potential for large hydrocarbon volumes but in 2200 m of water

impacts of flamingos on saline lake margin and shallow lacustrine sediments in the kenya rift valley abstract studies of modern holocene and pleistocene sediments around saline to hypersaline alkaline lake bogoria and lake magadi show that evidence of flamingo activity in marginal areas of these lakes is nearly ubiquitous flamingos produce discrete structures such as webbed footprints 9 cm long 11 cm wide and nest mounds 30 cm wide 20 cm high and they also extensively rework sediments in delta front delta plain and shoreline areas large 0 5 2 cm in diameter pinched bubble pores and ped like mud clumps are formed by the trampling and churning of wet clay rich sediments in these settings flamingo nest mounds although superficially similar to some thrombolite mounds are typically internally structureless unless formed on pre existing sediments that preserve internal structures the flamingo mounds consist of a dense packed oval shaped core a surrounding body of packed sediment and an external layer with a ped like texture of clumped mud the nests may contain open holes from roots or feather shafts incorporated into the nest and or burrows produced once the nests are abandoned in areas with high densities of flamingos lake margin sediments may be preferentially compacted particularly at breeding sites and become resistant to subaerial erosion and the effects of transgressive ravinement on time scales ranging from seasons to tens of thousands of years the relatively well compacted nest mounds and associated sediments also contribute to the stability of delta distributary channels during regressive transgressive cycles and can lead to the minor channelization of unconfined flows where currents are diverted around nest mounds pleistocene exhumed surfaces of relatively well indurated lake margin sediments at lake bogoria and lake magadi that are interpreted as combined regressive and transgressive surfaces flooding surface sequence boundary preserve evidence of flamingo activities and are overlain by younger porous lacustrine silts that preserve large bubble pores produced by flamingos

simulations of the greenland ice sheet 100 years into the future with the full stokes model elmer ice it is likely that climate change will have a significant impact on the mass balance of the greenland ice sheet contributing to future sea level rise here we present the implementation of the full stokes model elmer ice for the greenland ice sheet which includes a mesh refinement technique in order to resolve fast flowing ice streams and outlet glaciers we discuss simulations 100 years into the future forced by scenarios defined by the searise sea level response to ice sheet evolution community effort for comparison the same experiments are also run with the shallow ice model sicopolis simulation code for polythermal ice sheets we find that elmer ice is 43 more sensitive exhibits a larger loss of ice sheet volume relative to the control run than sicopolis for the ice dynamic scenario doubled basal sliding but 61 less sensitive for the direct global warming scenario based on the a1 b moderate emission scenario for greenhouse gases the scenario with combined a1b global warming and doubled basal sliding forcing produces a greenland contribution to sea level rise of 15cm for elmer ice and 12cm for sicopolis over the next 100 years