dune recovery after storm erosion on a high energy beach vougot beach brittany france abstract on 10th march 2008 the high energy storm johanna hit the french atlantic coast generating severe dune erosion on vougot beach brittany france in this paper the recovery of the dune of vougot beach is analysed through a survey of morphological changes and hydrodynamic conditions data collection focused on the period immediately following storm johanna until july 2010 i e over two and a half years results showed that the dune retreated by a maximum of almost 6 m where storm surge and wave attack were the most energetic dune retreat led to the creation of accommodation space for the storage of sediment by widening and elevating space between the pre and post storm dune toe and reducing impacts of the storm surge dune recovery started in the month following the storm event and is still ongoing it is characterised by the construction of secondary embryo dunes which recovered at an average rate of 4 4 5 cm per month although average monthly volume changes varied from 1 to 2 m 3 m 1 these embryo dunes accreted due to a large aeolian sand supply from the upper tidal beach to the existing foredune these dune construction processes were facilitated by growth of vegetation on low profile embryo dunes promoting backshore accretion after more than two years of survey the sediment budget of the beach dune system showed that more than 10 000 m 3 has been lost by the upper tidal beach we suggest that seaward return currents generated during the storm of 10th march 2008 are responsible for offshore sediment transport reconstitution of the equilibrium beach profile following the storm event may therefore have generated cross shore sediment redistribution inducing net erosion in the tidal zone

continuity and facies heterogeneities of shallow carbonate ramp cycles sinemurian lower jurassic north east spain the lateral continuity and facies heterogeneities of metre scale cycles in a greenhouse lower jurassic sinemurian carbonate ramp from the northern iberian basin spain was evaluated from extensive field analysis carried out on a well exposed 12 km long outcrop eleven high frequency continuous cycles and their bounding surfaces are traceable laterally through the entire outcrop however three of these cycles are found to split laterally into discontinuous cycles of more limited distribution up to 3 to 5 km of lateral extent the continuous and discontinuous cycles have a similar field expression in one dimensional logs as a consequence the number of cycles that can be differentiated is variable along the logged sections i e from 11 to 16 cycles have variable facies heterogeneities and sedimentary trends depending on the environment of formation shallowing upward and symmetrical cycles occur in protected lagoon tidal flat areas and in the open marine high energy domain these cycles show significant facies heterogeneities which were controlled mainly by lateral migration of a mosaic of facies over an irregular topography deepening upward and aggradational cycles are generated in low energy sub wave base open marine areas facies are laterally homogeneous reflecting low potential for carbonate accumulation and inability to fill the created accommodation space in this low relief and relatively deep area cycle boundaries are generated by stages of rapid accommodation gain involving the flooding of the carbonate ramp they are more likely to originate from regional tectonic pulses related to the extensional tectonics operating in the northern iberian basin rather than greenhouse low amplitude eustacy discontinuous cycles tend to occur in thickened areas and are interpreted as originating from the infill of wedge shaped accommodation space resulting from differential subsidence i e local tectonic pulses in conclusion where thickness variations occur in extensional settings lateral continuity of cycles should not be expected in less well exposed or in one dimensional sections and in wells it would not be possible to distinguish continuous from discontinuous cycles or to understand such two dimensional heterogeneities identification of unique cycle forming mechanisms or attempting cyclostratigraphic long distance correlation of cycles is unrealistic without a detailed analysis of the architecture of cycles in laterally continuous outcrops

assessing aeolian beach surface dynamics using a remote sensing approach a remote sensing technique for assessing beach surface moisture was used to provide insight into beach surface evolution during an aeolian event an experiment was carried out on october 21 2007 at greenwich dunes prince edward island national park canada during which cameras were mounted on a mast on the foredune crest at a height of about 14 m above the beach maps of beach surface moisture were created based on a calibrated relationship between surface brightness from the photographs and surface moisture content measured in situ at points spaced every 2 5 metres along a transect using a delta t moisture probe a time sequence of maps of surface moisture content captured beach surface evolution through the transport event at a spatial and temporal resolution that would be difficult to achieve with other sampling techniques such as impedance probes erosion of the foreshore and berm crest resulted in an increase in surface moisture content in these areas as the wetter underlying sediments were exposed flow expansion downwind of the berm crest led to sand deposition and a consequent decrease in surface moisture content remote sensing systems such as the one presented here allow observations of the combined evolution of beach surface moisture shoreline position and fetch distances during short term experiments and hence provide a comprehensive rendering of sediment erosion and transport processes

geomorphometry and landform mapping what is a landform abstract starting from a concept of the land surface its definition and subdivision from digital elevation models dems is considered high resolution dems from active remote sensing form a new basis for geomorphological work which is moving on from consideration of whether data are accurate enough to how the surface of interest can be defined from an overabundance of data discussion of the operational definition and delimitation of specific landforms of varying degrees of difficulty from craters to mountains is followed by the applicability of fuzzy boundaries scaling usually allometric is shown to be compatible with the scale specificity of many landforms this is exemplified by glacial cirques and drumlins classification of a whole land surface is more difficult than extraction of specific landforms from it well dissected fluvial landscapes pose great challenges for areal analyses these are tackled by the delimitation of homogeneous elementary forms and or land elements in which slope position is considered the boundaries are mainly breaks in gradient or aspect but may also be in some type of curvature breaks in altitude are rare elementary forms or land elements are grouped together into functional regions landforms such as hill sheds it may often be useful to recognise fuzziness of membership or core and periphery of a surface object plains and etched or scoured surfaces defy most of these approaches and general geomorphometry remains the most widely applicable technique it has been applied mainly within arbitrary areas and to some extent to drainage basins but more experimentation with mountain ranges and other landforms or landform regions is needed geomorphological mapping is becoming more specialised and its legends are being simplified its incorporation into geographical information systems gis has required greater precision with definitions and the separation of thematic layers so that it is converging with specific geomorphometry and becoming more flexible and more applicable with a broader range of visualisation techniques

controls and predictability of carbonate facies architecture in a lower jurassic three dimensional barrier shoal complex djebel bou dahar high atlas morocco spatial information on lithofacies from outcrops is paramount for understanding the internal dynamics external controls and degree of predictability of the facies architecture of shallow water carbonate platform tops to quantify the spatial distribution and vertical stacking of lithofacies within an outer platform shoal barrier complex integrated facies analysis and digital field technologies have been applied to a high relief carbonate platform exposed in the djebel bou dahar lower jurassic high atlas morocco the outer platform is characterized by subtidal cross bedded coarse grainstone to rudstone grading into supratidal pisoidal packstone rudstone with tepees that together formed a 350 to 420 m wide shoal barrier belt parallel to the margin this belt acted as a topographic high separating a restricted lagoon from the subtidal open marine region low energy tidal flats developed on the protected flank of the barrier facing the lagoon lithofacies patterns were captured quantitatively from outcrop and integrated into a digital outcrop model the outcrop model enabled rapid visualization of field data and efficient extraction of quantitative data such as widths of facies belts in addition the spatial heterogeneity was captured in multiple time slices i e during different phases of cyclic base level fluctuations in general the lateral continuity of lithofacies is highest when relative water depth increased during flooding of the platform top establishing low energy subtidal conditions across the whole platform and when the accommodation space was filled with tidal flat facies heterogeneity increased during deposition of the relief building bar facies that promoted spatial diversification of depositional environments during the initial phases of accommodation space creation cycles commonly are composed of a thin transgressive tidal flat unit followed by coated grain rudstone bar facies lateral to the bar facies pisoidal grainstone beach deposits accumulated these bar and beach deposits were overlain by subtidal lagoonal facies or would grow through the maximum flooding and highstand there the bars either graded into supratidal pisoidal facies with tepees when accommodation space was filled or were capped by subaerial exposure due to a sea level fall modified embedded markov analysis was used to test the presence of common ordering in vertical lithofacies stacking in a stationary interval constant depositional mode analysis of individual sections did not reveal any ordering which may be related to the limited thickness of these sections composite sections however rejected the null hypothesis of randomness the addition of stratigraphically significant information to the markov analysis such as exposure surfaces and lateral dimensions of facies bodies strengthens the verdict of unambiguous preferential ordering through careful quantitative reconstruction of stratal geometry and facies relationships in fully integrated digital outcrop models accurate depositional models could be established that enhanced the predictability of carbonate sediment accumulation 2009 the authors journal compilation 2009 international association of sedimentologists

simulation and measurement of surface shear stress over isolated and closely spaced transverse dunes in a wind tunnel topographic interactions generate multidirectional and unsteady air ow that limits the application of velocity pro le approaches for estimating sediment transport over dunes results are presented from a series of wind tunnel simulations using irwin type surface mounted pressure sensors to measure shear stress variability directly at the surface over both isolated and closely spaced sharp crested model dunes findings complement existing theories on secondary air ow effects on stoss transport dynamics and provide new information on the in uence of lee side air ow patterns on dune morphodynamics for all speeds investigated turbulent unsteadiness at the dune toe indicates a greater more variable surface shear despite a signi cant drop in time averaged measurements of streamwise shear stress at this location this effect is believed suf cient to inhibit sediment deposition at the toe and may be responsible for documented intermittency in sand transport in the toe region on the stoss slope streamline compression and ow acceleration cause an increase in ow steadiness and shear stress to a maximum at the crest that is double that at the toe of the isolated dune and 60 70 per cent greater than at ow reattachment on the lower stoss of closely spaced dunes streamwise ow accelerations rather than turbulence have greater in uence on stress generation on the stoss and this effect increases with stoss slope distance and with incident wind speed reversed ow within the separation cell generates signi cant surface shear 30 40 per cent of maximum values for both spacings this supports eld studies that suggest reversed ow is competent enough to return sediment to the dune directly or in a de ected direction high variability in shear at reattachment indicates impact of a turbulent shear layer that despite low values of time averaged streamwise stress in this region would inhibit sediment accumulation downwind of reattachment shear stress and ow steadiness increase within 6 h h dune height of reattachment and approach upwind values by 25 h a distance of at least 30 h is suggested for full boundary layer recovery which is comparable to uvial estimates the irwin sensor used in this study provides a reliable means to measure skin friction force responsible for sand transport and its robust simple and cost effective design shows promise for validating these ndings in natural dune settings copyright 2003 john wiley sons ltd

wave beach and dune interactions in southeastern australia abstract a morphodynamic classification of surfzones beaches and dunes of the microtidal low to high energy southeast australian coast is presented the first section a waves and beaches briefly deals with the transformation of deep water wave energy as it crosses the shelf nearshore and surfzone depending on the deep water wave characteristics and shelf and inshore morphology resultant breaker wave energy may be high moderate or low and the accompanying beach surfzone morphodynamic state in fine to medium sand beaches either dissipative intermediate or reflective dissipative beaches have wide surfzones with shore parallel bar s and channel s and predominantly shore normal circulation intermediate beaches are characterised by rip circulation crescentic transverse bars and megacusps and reflective beaches by a barless surfzone and steep cusped or bermed beach each beach form has a characteristic level of beach stability zone of sediment storage and mode of beach and dune erosion landward aeolian sediment transport of swash deposited sand section b is dependent on the subaerial beach topography and the aerodynamic flow regime across that topography characteristic profile shapes are ascribed to each beach type dissipative intermediate and reflective aeolian sand transport rates are potentially highest on dissipative beaches moderate on intermediate beaches and lowest on reflective beaches these rates determine the potential size of foredunes which are correspondingly largest on dissipative beaches and smallest on reflective beaches the combination of mode and frequency of beach dune erosion rates of aeolian sand transport and foredune volume and morphology provide an explanation of the nature and morphology of landward occurring large scale dune systems dissipative beaches are frequently characterised by large scale transgressive dune sheets intermediate by a trend from large scale parabolic dune systems high wave energy to small scale blowouts low wave energy and reflective beaches by minimal dune development

post storm beach and dune recovery implications for barrier island resilience abstract the ability of beaches and dunes to recover following an extreme storm is a primary control of barrier island response to sea level rise and changes in the frequency and or magnitude of storm surges whereas erosion of the beach and dune occurs over hours and days it can be years to decades before the beach and dune are able to recover to their pre storm state as a consequence there are numerous descriptions of near instantaneous beach and dune erosion due to storms the immediate onshore transport of sand and the initial phases of beach and dune recovery following a storm but a paucity of data on long term beach and dune recovery a combination of previously published data from galveston island texas and new remotely sensed data from santa rosa island florida is used in the present study to quantify the rate of dune recovery for dissipative and intermediate beach types respectively recovery of the dune height and volume on galveston island was observed within two years following hurricane alicia 1983 and was largely complete within six years of the storm despite extensive washover in contrast the dunes on santa rosa island in northwest florida began to recover four years after hurricane ivan 2004 and only after the profile approached its pre storm level and the rate of vegetation recovery regrowth was at a maximum results show that complete recovery of the largest dunes in height and volume will take approximately 10 years on santa rosa island which suggests that these sections of the island are particularly vulnerable to significant change in island morphology if there is also a change in the frequency and magnitude of storm events in contrast the areas of the island with the smallest dunes before hurricane ivan exhibited a rapid recovery but no further growth in profile volume and dune height beyond the pre storm volume and height despite continued recovery of the largest dunes to their pre storm height a change in storm magnitude and or frequency is a potential threat to barrier island resilience particularly for those sections of the island where dune recovery has historically taken the longest time further study is required to determine how and why dune recovery varies for the dissipative and intermediate beaches of galveston island and santa rosa island respectively

dunefoot dynamics along the dutch coast the dynamics of the dunefoot along a 160 km portion of the dutch coast has been investigated based on a data set of annual surveys dating back to as early as 1850 the linearly detrended or residual dunefoot positions comprise an alongshore uniform and an alongshore non uniform component the former is expressed as 10 to 15 m of landward retreat along extensive 10 km stretches of coast during years with severe storm surges and as up to 5 m of seaward advance during years without significant storm activity the latter alongshore non uniform component is organized in sandwave like patterns which may have a longevity of decades to up to the duration of the entire data set 150 years their wavelengths vary along the coast from 3 5 to 10 km migration rates are 0 200 m a 1 dunefoot sandwaves are shown to be the shoreward extensions of similar sandwave patterns in the beach position the non uniform dunefoot behaviour constitutes at least 80 per cent of the total residual dunefoot dynamics implying that along the dutch coast residual dunefoot variability is controlled by temporal and spatial variability in beach characteristics and not by storm induced uniform erosion various potential mechanisms causing beach sandwaves are discussed copyright 2002 john wiley sons ltd

aeolian sand strip mobility and protodune development on a drying beach examining surface moisture and surface roughness patterns measured by terrestrial laser scanning ephemeral aeolian sand strips are commonplace on beaches their formation during high energy sand transport events often precedes the development of protodunes and their dynamics present interesting feedback mechanisms with surface moisture patterns however due to their temporary nature little is known of their formation mobility or the specifics of their interaction with beach surface characteristics similarly surface moisture has an important influence on sediment availability and transport in aeolian beach systems yet it is difficult to quantify accurately due to its inherent variability over both short spatial and temporal scales whilst soil moisture probes and remote sensing imagery techniques can quantify large changes well their resolution over mainly dry sand close to the aeolian transport threshold is not ideal particularly where moisture gradients close to the surface are large in this study we employed a terrestrial laser scanner to monitor beach surface moisture variability during a three and a half hour period after a rain event and investigated relationships between bedform development surface roughness and surface moisture our results demonstrate that as the beach surface dries sand transport increases with sediment erosion occurring at the wet dry surface boundary and deposition further downwind this dynamic structure dependent upon changing surface moisture characteristics results in the formation of a rippled sand strip and ultimately a protodune our findings highlight dynamic mobility relationships and confirm the need to consider transient bedforms and surface moisture across a variety of scales when measuring aeolian transport in beach settings the terrestrial laser scanner provides a suitable apparatus with which to accomplish this

lateral continuity of facies and parasequences in middle cambrian platform carbonates carrara formation southeastern california u s a abstract lateral and vertical changes within a 40 m thick interval of peritidal carbonates middle cambrian jangle limestone member carrara formation se california produce a mosaic pattern of laterally continuous and discontinuous facies shallowing upward cycles 2 20 m thick parasequences and surfaces bounding parasequences this mosaic pattern was traced bed by bed across 1 8 km of continuously exposed outcrop and then correlated to sections in nearby ranges within parasequences contacts between successive subtidal facies tend to be sharp but may pass laterally into gradational contacts most subtidal facies extend laterally for less than 300 m passing gradationally over tens of centimeters to meters into other laterally adjacent subtidal facies lateral facies contacts between subtidal nodular ribbon rock and intertidal fenestral limestone are gradual over a few meters whereas contacts between vertically juxtaposed facies generally are sharp parasequence boundaries generally are sharp and locally show several tens of centimeters of erosional relief over lateral distances of several meters most parasequences and their bounding surfaces extend for the 1 8 km of outcrop studied and correlate to nearby ranges with varying degrees of confidence several parasequences however do not extend laterally for more than a few hundred meters and are not distinguishable in a vertical profile from those that extend laterally for tens of kilometers the stratigraphic relationships at eagle mountain southeastern california support a model in which the lateral continuity of parasequence surfaces is principally determined by accommodation variations and the lateral continuity of facies is most strongly influenced by the intrinsic dynamics of spatially and temporally heterogeneous sediment production the presence of parasequence boundaries of highly variable lateral extent suggests that the magnitude of accommodation variations was comparatively small consistent with the independent evidence for passive margin subsidence and transitional greenhouse conditions for the middle cambrian

numerical forward modeling of carbonate platform dynamics an evaluation of complexity and completeness in carbonate strata abstract it is clear that carbonate strata are complex and incomplete but the nature and origins of the complexity and the origin and distribution of hiatuses remain poorly understood a three dimensional numerical forward model of carbonate platform systems has been used to investigate how variations in complexity and completeness arise in carbonate strata the model includes depth dependent carbonate production occurring as a stochastic mosaic of producing elements across a topographic surface it also includes depth dependent sediment erosion transport and deposition governed by a regional transport direction that can vary stochastically through time and by wave refraction that causes local variations in transport direction combined mosaic production and variable sediment transport create a complex distribution of prograding islands generating self organizing shallowing upward parasequences of variable thickness and variable lateral extent hiatuses occur throughout the parasequences not just at the base and top generated by nondeposition due to mosaic production and by erosional scour this erosion is triggered by variations in water depth and fetch distance created by complex island morphologies preserved strata represent between 15 and 60 of total elapsed time measured at a 2 ky resolution and much of the preserved thickness represents punctuated deposition with depositional events spanning only a few thousand years stratigraphic completeness depends on subsidence rate and sediment transport rate so that completeness generally increases with increasing subsidence rate and decreasing transport rate but shows a nonlinear relationship with subsidence rate this suggests that reliable estimates of completeness of ancient carbonate strata require more than knowledge of subsidence rate and sea level change particularly because the real situation is likely to be considerably more complex than represented in this model the stochastic production mosaic and stochastic variations in regional transport direction create complex strata whereas the self organizing island progradation process creates simpler ordered strata a combination of the two processes creates an intermediate level of complexity producing strata consisting of laterally impersistent parasequences with numerous erosion surfaces and complex stacking patterns and complex thickness distributions this has important implications for parasequence correlation in outcrop and the subsurface

spatial patterns of sediment accumulation on a holocene carbonate tidal flat northwest andros island bahamas abstract to characterize spatial patterns of sedimentation and analyze the morphology of part of the modern tidal flats of northwest andros island in the bahamas this study integrated remote sensing geographic information systems gis and carbonate sedimentology the fundamental data are a landsat tm image that has been classified to create a thematic map of eight subfacies interpreted to represent a distinct tidal flat subenvironment such as adjacent marine exposed levee beach ridge pond and algal marsh spatial statistics of the thematic map characterize the patterns of sediment accumulation quantitative analysis highlights several interesting results concerning subfacies character and distribution 1 of the eight mapped subfacies low algal marsh is most widespread representing 27 5 of the total area whereas exposed levee beach ridge is the least widespread accounting for 10 of the area 2 the patches of different subfacies have different shape complexities with low algal marsh high algal marsh and mangrove ponds being the least complex and exposed levee beach ridge being the most complex 3 markov chain analysis suggests that lateral transitions between different subfacies are highly ordered and 4 frequency distribution of subfacies patch area and lacunarity gap size distribution data exhibit power law relationships over several orders of magnitude consistent with fractal characteristics the fractal nature of patch size and gaps between facies illustrate that on this tidal flat neither the size nor the spatial distribution of subfacies has a characteristic scale this statistical behavior is consistent with the presence of self organization or emergence of pattern in the absence of a template or external forcing the statistical self organization on the tidal flat is the cumulative expression of local processes but it becomes apparent only through analysis of the whole system these results are inconsistent with models suggesting that tidal flats include a migrating complex of randomly distributed randomly sized subenvironments ancient successions that include random patterns may reflect the more pronounced influence of forces external to the sedimentary system instead of an absence of those forces

meso scale aeolian sediment input to coastal dunes the nature of aeolian transport events abstract observations of aeolian transport in coastal areas have focused on short term experiments because of limitations imposed by instrumentation this paper uses a case study at greenwich dunes prince edward island national park canada to analyze how sediment transport takes place at the beach over periods of weeks to months a monitoring station provided hourly time series of vegetation cover shoreline position fetch distances surficial moisture content presence of ice and snow wind speed and direction and transport processes over nine months analysis shows that high wind speeds may not generate any net transport into the dunes because of the limitations imposed by snow ice cover moisture and short fetch distances despite extreme winds during intense storms such events often lead to wave scarping rather than aeolian sediment input to the foredunes when sediment was transported on the beach the magnitude was regulated by a combination of factors including angle of wind approach fetch distance moisture content and duration of the wind event in particular angle of wind approach and therefore fetch distance may demote a high magnitude wind event with strong transport potential to one with no transport at all which poses challenges for predicting the effects of individual storms over the course of several months a significant proportion of sediment delivery to the foredunes was associated with wind events of low to medium magnitude it is suggested here that large magnitude wind events have low probabilities of resulting in transport towards the foredune because factors such as wave inundation play an increasing role in preventing sediment movement across the beach this has implications for modelling and management and highlights differences between the magnitude and frequency of aeolian transport events in the coastal environment compared to those in deserts and to fluvial sediment transport

mechanisms associated with the erosion of sand dune cliffs magilligan northern ireland a fifteen year history of coastal dune recession at magilligan northern ireland has revealed both time and space contrasts in processes and morphology since 1968 storm frequency has increased while dune retreat reached a peak 5 4 m in 1978 1979 three types of dune eroding events are noted resulting from particular wave wind tide combinations the spatial variability in dune scarping is associated with vegetation and soil development and slope failures range from granular avalanches to retrogressive rotational slumps

bedrock channel incision along piccaninny creek australia piccaninny creek in northwestern australia drains approximately 60 km 2 of high relief sandstone and conglomerate terrain the drainage basin lies within the seasonal tropics and is characterized by ephemeral high magnitude flows flood flows of 50 to 100 m 3 s 1 are probably primarily responsible for the spectacular erosional features along the bedrock channel segments of the creek these erosional features occur in two basic forms as parallel longitudinal grooves and as a downstream sequence that begins with shallow linear depressions parallel to flow and ends in a deep narrow inner channel the longitudinal grooves are assumed to result from longitudinal vortices while the erosional sequences which closely resemble von karman vortex streets are interpreted to result from turbulent vortices shed off irregularities of the channel bed the longitudinal grooves and the inner channel sequence alternate with each other and with gravel floored depositional reaches downstream along the channe

fluvially sculpted rock bedforms in twenty mile creek niagara peninsula ontario sculpted rock bedforms s forms on whirlpool sandstone are described from the bed of twenty mile creek the morphologies identified undulating surfaces rises furrows comma forms spindles potholes and transverse troughs are those described for sculpted bedrock forms p forms s forms developed in subglacial environments additional morphologies identified are undercut downsteps and quarried surfaces in the lee of bedrock rises morphological differences between the subglacial and fluvial forms are attributed to the difference between confined conduit flow in the subglacial case and open channel flow in the fluvial examples in fluvial systems the descending bedrock surface presents rock differently to oncoming flows and favours certain s forms quarried lee faces and undulating surfaces in a strong flow fluvial environment s forms develop by wear dominant sediment transport modes are large clasts up to metre dimensions and suspended silt clay with a small 7 hard or heavy mineral compone

thin film channelized drainage or sheetfloods beneath a portion of the laurentide ice sheet an examination of glacial erosion forms northern new york state usa abstract morphologic analyses of characteristic bedrock erosion forms found in northern new york state usa were used to reconstruct the subglacial conditions under which they may have been produced observations from sites on wellesley island n y at point salubrious n y and at an open pit mine near balmat n y were combined with regional mapping of a diverse suite of glacial erosion forms in order to establish the areal extent and significance of subglacial drainage in northern new york results of these site specific and regional studies are the basis for discussion of the probable role of subglacial meltwater in the region bedrock erosion forms preserved at various locations in northern new york are interpreted as products of flow separation of localized subglacial meltwater during ice bed decoupling the regional distribution of these forms indicates that they are largely restricted to pre existing subglacially modified bedrock valleys that served as subglacial tunnel channels regionally extensive deep subglacial meltwater flow characterized as sheetfloods is not required to account for the erosional features described from specific sites in northern new york state

poisson processes of carbonate accumulation on paleozoic and holocene platforms abstract cambro ordovician carbonate lithofacies units in the elbrook and conococheague formations exposed at wytheville virginia as well as those in many other phanerozoic peritidal sequences exhibit exponential thickness frequency distributions that is occurrence frequency decreases exponentially with linear increase in unit thickness such distributions are characteristic of waiting times between independent poisson events this relative frequency of spaces of different size between horizons of lithologic change is what one would expect if the horizons were distributed randomly throughout carbonate successions abundances of different lithologies both as net stratigraphic thickness and as number of occurrences also decreases exponentially among successively rare sediment types with each lithology being about 60 as plentiful as the next more abundant rock type relations between net thickness and number of occurrences for each facies define a linear trend coincident with a mean thickness for all wytheville units of 0 48 m a relation indicating that thickness distribution is independent of facies type similar relations are apparent for the horizontal extent of carbonate sediment bodies from the holocene florida bahama platform areal extents of individual facies units lithotopes are described by a frequency distribution in agreement with that anticipated for a population of equidimensional facies elements whose diameter distribution follows an exponential frequency distribution although regional gradients in sediment texture and composition are also apparent along most transects from platform margin to interior such frequency distributions indicate that lateral extents of individual sediment reflect a largely stochastic distribution of facies boundaries across this holocene surface lithotope abundances also yield trends of exponentially decreasing dominance among successively subordinate facies with each being about 70 as extensive the next more abundant sediment type relations between areas and abundances for all lithotopes define a covariant trend corresponding to a mean area of 2 2 103 km2 for all florida bahamas lithotopes we consider several numerical models of stochastic carbonate accumulation although not demonstrably unique scenarios incorporating the sequential superposition of randomly placed coniform lithotopes result in thickness and area frequency distributions that are the same as those observed in ancient and modern platform deposits such simulations of poisson processes of sediment accumulation are in general agreement with stochastic models of lithologic heterogeneity that have been more widely applied to petroleum reservoirs and groundwater aquifers to the as yet unknown degree that peritidal lithofacies area and thickness are correlated data from paleozoic and holocene platforms suggest that carbonate units should exhibit length height ratios of approximately 105 given the decimeter scale over which facies are designated in most paleozoic peritidal successions these relations predict mean lateral extents on the order of several tens of kilometers a value in general agreement with the few data that exist on spatial continuities of peritidal lithotopes in paleozoic carbonate sequences

sequence stratigraphy of the red river formation williston basin usa stratigraphic signature of the ordovician katian greenhouse to icehouse transition abstract the upper katian upper ordovician red river formation is a carbonate evaporite supersequence that formed in the epicratonic williston basin of western north america this study focuses on the upper part of the formation in the southern us part of the basin the studied succession is made up of three transgressive regressive sequences rr1 rr2 and rr3 each 0 5 1 m y in duration and composed of relatively few meter scale high frequency cycles parasequences sequence boundaries are characterized by intraclastic breccia laminated dolomite successions that have been truncated and capped by evaporite deposits subaqueous anhydrites within each sequence represent evaporite lowstand systems tracts lsts that formed during relative sea level lows that lead to the precipitation of gypsum later recrystallized into anhydrite in a quiet salina type environment transgressive tst and early highstand systems tracts hst are composed of subtidal facies of predominantly skeletal mudstone to wackestone packstone with abundant burrow mottling late hsts are predominantly composed of peritidal porous laminated dolomite the study illustrates how the sequence stratigraphic framework of carbonate evaporite deposits from the williston basin relates to the late ordovician glacio eustasy transitional climates and low basin subsidence in an arid setting

remote sensing of geomorphology and facies patterns on a modern carbonate ramp arabian gulf dubai u a e abstract the occurrence of power law relationships in the spatial distribution of sedimentary lithotopes has been identified in both modern and ancient carbonate depositional bodies in this study facies patterns and their spatial relationships are investigated quantitatively in an arabian gulf shallow subtidal carbonate ramp setting using a synergy of ikonos satellite imagery and vessel based acoustic bathymetry survey three dimensional reconstruction of the facies distribution on the seabed enabled quantification of relationships between eight dominant facies classes and the association of particular lithotopes to water depth fractal behavior was investigated using a combination of boundary and patch based metrics and the spatial distribution of early diagenetically cemented hardgrounds and unconsolidated carbonate sand were shown to display strong fractal properties in contrast we show that landscape scale processes can be treated as essentially deterministic and facies neighborhood patterns are strongly probabilistic identifying that the heterogeneity of shallow subtidal carbonate facies scales with a power law within certain thresholds has the potential to serve as a tool in environmental reconstruction in the ancient where information on the lateral persistence of facies units is difficult to obtain the findings are relevant to the interpretation of stratigraphic sequences and paleo depth analysis

3d mapping efficacy of a drone and terrestrial laser scanner over a temperate beach dune zone abstract understanding dynamic earth surface processes requires various spatial and temporal information to help produce patterns of landform change recent developments in sensor technology such as structure from motion sfm camera mounted airborne unmanned aerial vehicles uavs and terrestrial laser scanning tls have provided a means of acquiring high resolution spatial data on land surface topography through repeat surveys these techniques enable much better understanding of what is termed geomorphometry where we can examine a geomorphic surface for change over space and time in coastal environments change can involve significant alteration and generation of landforms over relatively short periods and therefore we require a means of measuring surface morphology quickly and over large areas here we examine a section of a beach dune system in nw ireland using sfm uav and tls plus baseline dgps data points to assess the value of these techniques and to understand their effectiveness and limitations issues such as accuracy resolution and differences of digital elevation models dems are assessed for their efficiency associated challenges and relative performance over variations in terrain types and analytical approaches we also examine the implications for differences in areal and volume calculations of the coastal landforms using both approaches we find that sensor performance is highly dependent on the terrain being measured with undulations slope vegetation cover acquisition resolution point density and interpolation issues all having pronounced impacts on effectiveness and data quality in general the tls performed better over flatter low angled topography containing sparse non vegetated areas than in areas with complex landforms where survey shadows appear to compromise final dems the sfm uav shows good performance over different terrains with the exception of relatively flat featureless areas such as sandy beaches and densely vegetated surfaces where differences between techniques are 1 m data acquisition however is much 30 faster using a sfm uav with more extensive survey areas covered than using a tls

environmental covariation of metazoans and microbialites in the lower ordovician boat harbour formation newfoundland abstract an antagonistic view of the relationship between microbialites and metazoans has long been inferred in part because of the large scale anticorrelation of these two groups through geologic time the nexus of this relationship occurs in the early paleozoic era stromatolites declined in abundance as complex animals and algae diversified but thrombolites a type of microbialite little known before the proterozoic cambrian boundary proliferated for the first time well preserved parasequences in the basal portion of the lower ordovician boat harbour formation western newfoundland contain a succession of stromatolites and thrombolites that permit an investigation into the role metazoans played in shaping the nature and abundance of microbialites in early paleozoic carbonate seas sessile benthic animals colonized thrombolite surfaces but are nearly absent from stromatolites bioturbation rarely co occurred with microbialites but is widespread in clastic carbonates that lack microbialites our results thus support the hypothesis of ecological antagonism between microbial communities and motile benthic animals but also demonstrate biological facilitation between thrombolites and both sessile benthic animals and nekton

foredunes and blowouts initiation geomorphology and dynamics this paper reviews the initiation dynamics geomorphology and evolution of incipient foredunes established foredunes and blowouts incipient foredunes may be initiated in a variety of ways leading to the formation of ramps terraces or ridges depending on progradation rates vegetation type and cover sediment transport rates and scale of erosional processes vegetation cover morphology growth rates and types combine with aerodynamic processes to determine dune and swale morphology established foredunes are classified into five morpho ecological types and the flow behaviour over two types is detailed a new model of foredune evolutionary paths at various possible time scales is presented blowout initiation dynamics and sediment transport and evolution is examined throughout the review the gaps in present understanding of dune processes and a range of ideas for new research possibilities are provided

spatial characterization resolution and volumetric change of coastal dunes using airborne lidar cape hatteras north carolina the technological advancement in topographic mapping known as airborne light detection and ranging lidar allows researchers to gather highly accurate and densely sampled coastal elevation data at a rapid rate the problem is to determine the optimal resolutions at which to represent coastal dunes for volumetric change analysis this study uses digital elevation models dem generated from lidar data and spatial statistics to better understand dune characterization at a series of spatial resolutions the lidar data were collected jointly by the national aeronautics and space administration nasa the national oceanic and atmospheric administration noaa and the u s geological survey usgs dems of two study sites 100 200 m located in cape hatteras national seashore north carolina were generated using a raster based geographic information system gis changes in the dune volume were calculated for a 1 year period of time fall 1996 1997 at grid cell resolutions ranging from 1 1 to 20 20 m directional statistics algorithms were used to calculate local variance and characterize topographic complexity data processing was described in detail in order to provide an introduction to working with lidar data in a gis results from these study sites indicated that a 1 2 m resolution provided the most reliable representation of coastal dunes on cape hatteras and most accurate volumetric change measurements results may vary at other sites and at different spatial extents but the methods developed here can be applied to other locations to determine the optimum resolutions at which to represent and characterize topography using common gis and database software

carbonate platform dominated by peloidal sands lower ordovician la silla formation of the eastern precordillera san juan argentina the lower ordovician la silla formation of the precordillera of west central argentina is part of the west facing early palaeozoic tropical carbonate platform succession that comprises the core of the cuyania terrane up to 360 m thick it is exposed in several thrust sheets over a distance of some 250 km along and across depositional strike over a palinspastically unrestored distance of about 35 km la silla formation is a strikingly pure limestone with subordinate finely crystalline dolomite and rare chert it accumulated on a more or less uniformly subsiding passive margin copious precipitation of microcrystalline calcite probably influenced by microbial activity to varying degrees led to the generation of peloids ooids and aggregates of these grains as well as small amounts of lime mud intraclasts stromatolites and thrombolites rare bioclasts are limited mostly to scattered gastropods and trilobite sclerites bioturbation is present locally the array of carbonate rock types is grouped into eight recurring lithofacies in order of decreasing abundance i peloidal grainstone ii laminated dolostone iii intraclastic rudstone iv microbial laminite v peloidal packstone vi ooidal grainstone vii thrombolite boundstone and viii mudstone these facies represent sediments that formed solely in a shallow subtidal marine environment with no evidence of restricted conditions hypersalinity or subaerial exposure no events of eustatic sea level change are recorded by far the dominant facies is grainstone composed of well sorted fine sand sized peloids and peloidal aggregates in homogeneous tabular to gently undulating medium to thick beds cross lamination is scarce clusters of sub metre sized microbial patch reefs developed sporadically the shallow platform is envisaged to have been covered by extensive peloidal sand flats and low relief banks and little lime mud was generated the setting was probably microtidal and may not have been affected by strong trade winds it was washed by frequent relatively gentle wave action but without experiencing powerful storms in the middle member anomalous lenses of intraclastic rudstone and laminated dolostone occur as graded beds overlying sharply downcut scoured surfaces up to 20 cm deep these are interpreted to indicate a phase when accretion was punctuated occasionally by tsunamis generated from rift faulting seaward of the platform margin the remarkably uniform peloidal grainstone composition over a broad area shows that given the appropriate combination of climate environmental and ecological factors large portions of some early palaeozoic platforms were dominated by grainy sediment and remained under well agitated conditions within fair weather wave base without distinct lateral facies differentiation or tidal flat aggradation

subglacial erosional marks wilton creek ontario a variety of p forms are discussed in terms of the agent producing them a general conclusion based on form and the location of striations relative to p forms is that they are produced by meltwater rather than ice erosional marks in the wilton creek valley ontario are different from earlier described p forms their relationship to striations establishes them as being of subglacial origin and their form similarity with flutes together with the partial or total absence of striations on them suggests a fluvial origin large scale forms are interpreted as spindle shaped flutes associated with flow separation small scale forms are subdivided into straight spindle forms curved spindle forms braided forms and scallops they appear not to have followed the inverse relationship between size and flow velocity reported for some other erosional marks potential but speculative explanations for these small scale forms are that they are related to taylor gortler vortices vortices on mixing layers or trailing

formation of ephemeral bedform turrets in coastal foredunes abstract rare erosional turret bedforms are described in a coastal foredune environment these ephemeral structures are formed as a result of moist columns of sand being sculpted by aeolian action of saltating particles mature formation of these features appears to be facilitated by the action of an advancing foredune ridge first preserving and then isolating the turrets for further enhanced erosion within a dune environment it is envisaged that these structures may be preserved in dune stratigraphy

anatomy of a cyclically packaged mesoproterozoic carbonate ramp in northern canada abstract carbonates in the upper member of the mesoproterozoic victor bay formation are dominated by lime mud and packaged in cycles of 20 50 m these thicknesses exceed those of classic shallowing upward cycles by almost a factor of 10 stratigraphic and sedimentological evidence suggests high amplitude high frequency glacio eustatic cyclicity and thus a cool global climate ca 1 2 ga the victor bay ramp is one of several late proterozoic carbonate platforms where the proportions of lime mud carbonate grains and microbialites are more typical of younger phanerozoic successions which followed the global waning of stromatolites facies distribution in the study area is compatible with deposition on a low energy microtidal distally steepened ramp outer ramp facies are hemipelagic lime mudstone shale carbonaceous rhythmite and debrites mid ramp facies are molar tooth limestone tempestite with microspar intraclast lags in a marine environment where stromatolitic and oolitic facies were otherwise rare large stromatolitic reefs developed at the mid ramp coeval with inner ramp facies of microspar grainstone intertidal dolomitic microbial laminite and supratidal evaporitic red shale deep subtidal outer ramp cycles occur in the southwestern part of the study area black dolomitic shale at the base is overlain by ribbon nodular and carbonaceous carbonate facies all of which exhibit signs of synsedimentary disruption cycles in the northeast are shallow subtidal and peritidal in character shallow subtidal cycles consist of basal deep water facies and an upper layer of subtidal molar tooth limestone tempestite interbedded with microspar calcarenite facies peritidal cycles are identical to shallow subtidal cycles except that they contain a cap of dolomitic tidal flat microbial laminite and rarely of red shale sabkha facies or of sandy polymictic conglomerate a transect along the wall of a valley extending 8 5 km perpendicular to depositional strike reveals progradation of inner ramp tidal flats over outer and mid ramp facies during shoaling the maximum basinward progradation of peritidal facies coincides with a zone of slope failure that may have promoted the development of the stromatolitic reefs the sea level history of the victor bay formation is represented by three hectometre scale sequences an initial flooding event resulted in deposition of the lower victor bay shale member upper member carbonate cycles were then deposited during highstand mid ramp slumping was followed by late highstand reef development the second sequence began with development of an inner ramp lowstand unconformity and a thick mid ramp lowstand wedge a second transgression promoted a more modest phase of reef development at the mid ramp and shallow water deposition continued inboard a third and final transgressive episode eventually led to flooding of the backstepping ramp overall consistent cycle thickness and absence of truncated cycles as well as the high rate and amount of creation of accommodation space suggest that the periodicity and amplitude of sea level fluctuation were relatively uniform and point to a eustatic rather than tectonic mechanism of relative sea level change high amplitude high frequency eustatic sea level change is characteristic of icehouse worlds in which short term large scale sea level fluctuations accompany rapidly changing ice volumes affected by milankovitch orbital forcing packaging of cyclic upper victor bay carbonates therefore supports the hypothesis of a late mesoproterozoic glacial period as proposed by previous workers

lithofacies character and architecture across a pennsylvanian inner platform transect sierra de cuera asturias spain abstract seismic scale outcrops of lower pennsylvanian steep margined carbonate platforms in northern spain sierra de cuera cantabrian mountains provide the opportunity to link depositional facies to platform interior architecture lithofacies character vertical stacking patterns and spatial distribution of depositional facies and shallowing upward cycles were investigated to provide a semiquantitative depositional model for inner platform strata a 70 m thick succession of eight shallowing upward cycles 2 5 15 m thick was studied across a 2 km wide transect cycles consist of algal bioherms and skeletal packstone lithofacies association b deposited in an open marine and sub wave base environment which are locally lateral to crinoid dominated packstone lithofacies association d lithofacies association b developed on a transgressive one meter thick high energy coated grain grainstone lithofacies association a and is overlain by open marine to restricted lagoonal deposits lithofacies association c indicative of decreased paleo water depth cycle boundaries are marine flooding surfaces occurring at the base of lithofacies a and the top of lithofacies c petrographic and outcrop evidence of subaerial exposure is conspicuously lacking cycle and lithofacies thickness varies laterally and all the lithofacies can be either continuous for the 2 km width of investigation or discontinuous terminating within tens to hundreds of meters in most of the cycles the lithofacies succession changes laterally because of lateral facies transitions between lithofacies b and d and pinching out of lithofacies a and c meter scale variations in depositional topography are related to the stacked lens shaped bioherms assigned to lithofacies b and appear to control the thickness and lateral continuity of the overlying facies sierra de cuera strata do not resemble other pennsylvanian cycles driven by high frequency high amplitude glacio eustasy which are commonly characterized by subaerial exposure surfaces developed on subtidal deposits except for the absence of peritidal facies and the presence of low relief algal bioherms on the platform top the necessary accommodation to enhance the growth of bioherms on the platform top was probably due to high frequency 100 240 ky moderate amplitude nearly 40 m sea level fluctuations combined with subsidence rates of 70 140 m my tectonic subsidence might have been responsible for the lack of evidence of subaerial exposure surfaces in the examined moscovian strata the studied inner platform lithofacies character and architecture were controlled by the interplay of high frequency changes in accommodation and the presence of meter scale depositional topography attributed to lateral variations of carbonate accumulation

an extensive erosion surface of a strongly deformed limestone bed in the gushan and chaomidian formations late middle cambrian to furongian shandong province china sequence stratigraphic implications abstract in order to understand sequence development and sea level fluctuations during the late middle cambrian to early furongian on the north china epeiric platform the present study focuses on a unique subtle erosion surface of an extensive approx 100 km strongly deformed limestone bed in the uppermost part of the gushan formation shandong province china the gushan formation and the overlying chaomidian formation consist mainly of shales and a variety of carbonates that were deposited in subtidal environments e g deep subtidal shallow subtidal shoreface shoal subtidal microbial flat and restricted platform interior three third order depositional sequences s1 3 are identified each of which comprises a thin transgressive systems tract tst and a relatively thick highstand systems tract hst each sequence is bounded by a drowning unconformity sb1 a subaerial unconformity sb2 or a surface of submarine erosion sb3 the upper sequence boundary sb2 of sequence 1 s1 is represented by a subtle erosion surface of an extensive deformed limestone bed with a wide variety of soft sediment deformation structures e g lime mudstone breccias chaotic wacke packstone laminae and fragments homogenized oolites and clastic dykes and is overlain by small sporadic microbial buildups and an extensive bioclastic grainstone bed the deformed limestone was formed during early diagenesis by differential deformation processes brecciation liquefaction fluidization and injection which were most likely induced by pore water overpressure during the period of rapid sea level fall despite the lack of subaerial exposure features e g paleokarst paleosol etc the characteristics of the erosion surface cutting well lithified sediment below the missing of a significant geological record the prochuangia biozone and the worldwide correlatable positive carbon isotope excursion collectively indicate that the erosion surface developed under conditions of subaerial exposure after contemporaneous marine cementation of the deformed sediment the missing of the prochuangia biozone is most likely due to non deposition at a subaerial hiatal surface the erosion surface was submerged as a result of subsequent rise in sea level where sporadic microbial buildups formed under suitable conditions freshly deposited winnowed shell dominated transgressive lag deposits containing chuangia trilobite fragments brachiopod shells and abundant glauconite grains formed with continued rise in sea level which became in turn overlain by shale dominated facies the unique combination of the subtle erosion surface sensu stricto a subaerial unconformity and the underlying deformed limestone bed provides an important criterion for recognizing the subtle changes in relative sea level on shallow epeiric platforms

discussion inferred subglacial meltwater origin of lakes on the southern border of the canadian shield in their paper the authors r gilbert and j shaw add small finger lakes in narrow valleys incised through an up icefacing cuesta to the lengthening list of landforms large and small that they and their like minded colleagues ascribe to erosion or deposition by high discharge subglacial drainage this list has included previously drumlins erosion marks subglacial erosion s forms rogen moraine fluvial dunes tunnel channels a moraine and regional landform assemblages often in these works the glaciofluvial flooding argument is so convincingly based on the field evidence and counters the glacial argument so effectively that one feels the conceptual ground shift and one s stance upon it changed occasionally however as in shaw and gilbert 1990 and the present paper the argument seems to be based on little more than that other features have been explained by this process so why not this feature too in the present paper the authors give an excellent detailed description of the distribution and form of long narrow lake basins incised into a limestone cuesta facing up ice over the precambrian shield of southeastern ontario they liken them to the new york finger lake valleys and those in the niagara cuesta of ontario which have been viewed previously as of glacial origin thus preferential erosion by fast flowing ice and the presumed absence of subglacial tributaries convincingly account for the valley forms of the finger lakes and other reentrant or through valleys p 1634 however they caution any agent that might have preferentially eroded through valleys could take the place of glaciers in the above discussion p 1634 any agent that is except subaerial fluvial erosion which they discount on grounds going back to playfair s law if large volumes of subglacial meltwater were to be channelized across escarpments p 1634 original emphasis valleys would be cut similar in many respects to glacial troughs thus is the subglacial meltwater hypothesis introduced not solely from evidence but with much supposition tributaries would cut by the same floods anastomose shaw 1988 brennand and shaw 1994 and esker ridges with dendritic patterns and accordant junctions recordonly the most powerful flood events brennand 1994 p 9 the argument continues both through valley and reentrant valley regions finger lakes and niagara cuesta lie astride major flood routes proposed by shaw and gilbert 1990 this would be fine if the latter reconstruction met with wide independent acceptance but it seems unfair to seek such support from it when that paper so summarily dismisses the widely accepted glacial history of for example the western borderlands of lake ontario the present argument has nevertheless gained momentum albeit cheaply leading to we suggest that meltwater floods may well explain the prominent valleys we describe here p 1635 emphasis added this seems strangely shy but may recognize the thinness of the logical ice at this point furthermore flow was across a wide area upstream of the escarpment p 1635 yet tunnel channels and an esker in one of them lie upstream as well as downstream of the escarpment brennand and shaw 1994 p 507 indicating channelled not sheet flow nearly equal spacing p 1635 of the valleys in question suggests to the authors that linearly concentrated escape of sheetfloods over the escarpment was hydrodynamically rather than morphologically or structurally controlled as was the origin of fluting on the tops of escarpment promontories noses p 1635 we are left in the dark however as to how this control works rather we leap ahead to as the flow streamed around the escarpment and noses into the valleys p 1635 given the valleys we can follow the argument into counterrotating vortices a residual medial ridge in one valley and the localization of valley floor basins but it is exasperating to miss how a high discharge high velocity sheetflood becomes patterned into longitudinal counterrotating vortices when it meets an escarpment this is not to say that the phenomenon is incredible but be unlikely p 1635 yettunnel channels said to have been we are entitled t o more by way of explanation than the van dyke reference more accessible than this and charac

macroforms large bedforms and rhythmic sedimentary sequences in subglacial eskers south central ontario implications for esker genesis and meltwater regime abstract eskers of south central ontario were deposited in closed subglacial conduits which were continuous main conduits this interpretation is supported by the intimate association of eskers with an anastomosing network of tunnel channels relatively continuous esker ridges minimal post formational disturbance of esker sediments intercalation of till and stratified sand and gravel diapiric folding at an esker core low variability in palaeocurrent direction and upslope flow paths down esker trends in clast lithology roundness and sphericity indicate continuous conduits with sediment supply by subglacial deformation of adjacent material into the conduits melt out of sediment from the conduit walls and fluvial resedimentation esker ridge morphology is attributed to synchronous erosion transportation and deposition along the main conduits such that ridge discontinuities are primarily explained as zones of non deposition during esker formation composite pseudoanticlinal and oblique accretion avalanche bed macroforms are identified gravel facies within these macroforms were deposited from fluidal flows or hyperconcentrated dispersions progradation of macroforms or migration of constituent large bedforms through the main conduits may have temporarily blocked constricted portions of those conduits and acted as possible internal autogenic controls on sediment availability and flow resistance the location of macroforms within conduits was primarily controlled by conduit geometry and sediment availability and later by feedback between macroform and conduit geometries sand and gravel units alternate rhythmically in vertical section rhythmicity is interpreted as a response to episodic flood flows controlled by seasonal changes in water supply but not necessarily representing annual events fans beads anabranched reaches and extended hummocky deposits are intimately associated with the main esker ridges they are interpreted in terms of subglacial cavities and localized flotation zones connected to the main conduits during flood events in phase wave structures are the products of hydraulic jumps in hyperconcentrated flood flows at flow expansions into swells within the main conduits into cavities connected to the main conduits or at a grounding line esker ridges record only the most powerful flood events whereas fans and beads record flow events in finer detail being primarily depositional reservoirs laterally fining deposits record the waning stages of conduit operation

crowd sourced identification of the beach dune interface abstract the dune toe is the boundary at the beach dune interface that is important to our understanding of foredune development storm impact assessments and management decisions although there are several morphometric based estimates of the dune toe there is no consensus on an operational definition and whether those metrics match field observations this study uses a crowd source approach to compare dune toe selections and definitions among members of the geomorphology listserv respondent selections of the dune toe varied depending on the type of imagery used the complexity of the backshore and the self identified expertise of the respondent the variation by method and research background raises important questions about how landform boundaries are identified in coastal geomorphology and possibly within other areas of geomorphology

trilobite extinctions facies changes and the roece carbon isotope excursion at the cambrian series 2 3 boundary great basin western usa the mass extinction of the olenellid trilobites occurred around the cambrian series 2 series 3 boundary like many other crises it coincided with a negative carbon isotope excursion but the associated palaeoenvironmental changes remain unclear to investigate the causal mechanism for this event we report facies changes pyrite framboid petrography and carbon isotope values from cambrian series 2 series 3 traditionally early middle cambrian boundary strata of the carrara formation death valley region california and pioche formation nevada these data reveal regionally changing water depths from high energy nearshore facies oolitic grainstone to more offshore silty marl and finer grained carbonate mudstone in the carrara formation the series boundary occurs within a deepening succession transitioning from high energy nearshore facies oolitic grainstone and oncolitic packstone to offshore marl the latter of which contains pyrite framboid populations indicative of low oxygen dysoxic depositional conditions intermittent dysoxia persisted below sub wave base settings throughout the early and middle cambrian but did not intensify at the time of extinction arguing against anoxia as a primary cause in the olenellid trilobite extinction within both field areas the extinction interval coincided with a minimum in 13ccarb values which we interpret as the regional manifestation of the redlichiid olenellid extinction carbon isotope excursion roece the series 2 series 3 boundary is reported to closely coincide with a large amplitude sea level fall that produced the sauk i ii sequence boundary but the placement of the series 2 series 3 boundary within a transgressive interval of the carrara formation shows that this is not the case the main sequence boundary in the succession occurs much lower in the succession at the top of the zabriskie quartzite and therefore precedes the extinction of the olenellids and roece

carbon isotope stratigraphy of cenomanian turonian platform carbonates from the southern apennines italy a chemostratigraphic approach to the problem of correlation between shallow water and deep water successions the carbon isotope record of three sections of shallow water carbonates from the upper cretaceous sequences of the southern apennines italy shows a pronounced positive excursion of about 4 5 using the upper cenomanian cisalveolina fraasi level as a biostratigraphic tie point we correlate this excursion to the oae 2 isotopic event comparison with the standard reference 13 c curve of eastbourne england shows that the overall character of the excursion is clearly reproduced in the shallow water curves chemostratigraphic correlation allows definition of the age of some important shallow water biostratigraphic events to the precision of an ammonite zone using the well established bio chronostratigraphic framework defined in the eastbourne section the onset of the cenomanian turonian isotopic excursion coincides with a transgressive trend recorded by the occurrence of more open marine facies and culminating with an incipient drowning in one of the sections studied our data suggest that the open ocean isotopic signal is most faithfully recorded and preserved in shallow water platform carbonates during transgressive periods when the effects of meteoric diagenesis and seawater ageing are less severe

thrombolite fabrics and origins influences of diverse microbial and metazoan processes on cambrian thrombolite variability in the great basin california and nevada thrombolites are a common component of carbonate buildups throughout the phanerozoic that are usually described as microbialites with an internally clotted texture a wide range of thrombolite textures have been observed and attributed to diverse processes leading to difficulty interpreting thrombolites as a group interpreting thrombolitic textures in terms of ancient microbial and metazoan ecosystems requires understanding diverse processes specifically those due to microbial growth and metazoan activity many of these processes are reflected in thrombolites in the cambrian carrara bonanza king highland peak and nopah formations great basin california usa they comprise eight thrombolite classes based on variable arrangements and combinations of depositional and diagenetic components four thrombolite classes hemispherical microdigitate bushy coalescent columnar and massive fenestrated contain distinct mesoscale microbial growth structures that can be distinguished from surrounding detrital sediments and diagenetic features by contrast mottled thrombolites have mesostructures that dominantly reflect post depositional processes including bioturbation mottled thrombolites are not bioturbated stromatolites but rather formed from disruption of an originally clotted growth structure three thrombolite classes arborescent digitate amoeboid and massive contain more cryptic textures all eight of the thrombolite classes in this study formed in similar cambrian depositional environments marine passive margin overall this suite of thrombolites demonstrates that thrombolites are diverse in both internal fabrics and origin and that clotted and patchy microbialite fabrics form from a range of processes the diversity of textures and their origins demonstrate that thrombolites should not be used to interpret a particular ecological evolutionary or environmental shift without first identifying the microbial growth structure and distinguishing it from other depositional post depositional and diagenetic components furthermore thrombolites by definition are fundamentally different from stromatolites and dendrolites in which the laminae and dendroids reflect a primary growth structure because clotted textures in thrombolites do not always reflect a primary microbial growth structure this article is protected by copyright all rights reserved

drivers of alongshore variable dune erosion during a storm event observations and modelling abstract the ability to understand and predict alongshore variable sand dune erosion is key to better coastal management this study utilizes detailed observations immediately pre during and post storm topography waves and water levels collected over a 6 day period at the 3 6 km long narrabeen collaroy beach in south east australia to identify and explore drivers of the highly variable alongshore dune erosion caused by an east coast low storm in june 2011 key characteristics of the immediately pre storm subaerial morphology obtained by airborne lidar beach slope dune toe elevation dune height varied considerably alongshore daily airborne lidar surveys conducted at low tide indicated considerable temporal variability in the evolution of the subaerial beach profile despite considerable alongshore variability in the magnitude of modelled inshore wave heights during the storm it was instead observed that the predominant determinant of maximum dune erosion was the pre storm dune toe elevation a simple dune impact model forced with local alongshore variable inshore wave modelling was found to successfully predict up to 85 of the observed alongshore variability in dune erosion at this site with this erosion tidally modulated over the 6 days to time periods when the waves were directly impacting the dune importantly alongshore variation in wave height is shown to account for just 10 of the alongshore variability in dune erosion during this storm these results reconfirm that knowledge of the pre storm subaerial morphology in particular the elevation of the dune toe with respect to time varying water levels during a storm is a key driver of alongshore variability in the erosion response along dune backed sandy coastlines

high frequency depositional cycles in the muschelkalk middle triassic of southern poland origin and implications for germanic basin astrochronological scales abstract high frequency depositional cycles are often used for long distance correlations within sedimentary basins and constructing high resolution chronostratigraphic scales calibrated to the orbital clock such an approach has been used for the tropical epicontinental muschelkalk sea covering most of europe in the middle triassic this paper aims at establishing the spatial extent and internal architecture of shallow marine muschelkalk cycles within a small 120 by 50 km area of the germanic basin to identify their local vs regional distribution and cycle forming mechanisms three groups of cycles are distinguished 1 peritidal cycles representing a tidal flat lagoon system which experienced longer periods of emersion 2 shallow subtidal cycles formed around the fair weather wave base and 3 deep subtidal cycles developed around the storm wave base the three cycle types differ markedly in the composition facies homogeneity sedimentary trends hierarchical organization continuity and degree of lateral changeability and complexity which collectively translates into the ease of cycle recognition despite the differences the defined cycles do not extend laterally beyond the studied area and have laterally variable facies heterogeneities sedimentary trends and thicknesses this variability resulted from more or less mosaic infilling of accommodation space reflecting local bathymetry physicochemical conditions and carbonate production and accumulation rates on the platform accommodation space evolved by the interplay of eustatic sea level fluctuations regional subsidence and synsedimentary tectonic block movements but the contribution of these factors changed over time and was to varying degrees masked for each of the three cycle types by intrinsic sedimentary processes the study shows that middle triassic cycles of the germanic basin have a local to sub regional distribution and thereby are inappropriate for basin wide correlations and chronostratigraphic inferences it also strengthens the opinion of several workers that correlation of idealized cycles is unrealistic without checking the horizontal continuity of facies and key surfaces directly in the field

flow dynamics over a foredune at prince edward island canada time averaged windspeed profiles at eight locations over a relatively high 8 m vegetated topographically simple foredune were measured using cup and ultrasonic anemometry during an onshore wind event in may 2002 the experiment was part of a largerstudyonthesedimentarydynamicsofabeach dunecomplexinthegreenwichdunes princeedwardisland pei canada the foredune is vegetated with ammophila breviligulata and vegetation density ranged from 0 on the foredune ramp to upward of 70 at the dune crest topographic forcing and resulting flow acceleration was observed distinctly in windspeed profiles and linear speedup occurred for all elevations above the vegetation canopy a distinct inflection point is evident in normalized windspeed profiles over the dune indicating a net momentum sink below the vegetation canopy top and systematic speed down within the vegetation was observed up the foredune stoss slope wind speed profile structure was consistent for the range of incident wind speeds measured a comparison of normal and slightly oblique incident winds indicated that for similar approach winds wind speeds are consistently higher during oblique flow conditions the implications for foredune morphodynamics and sedimentation are discussed d 2004 elsevier b v all rights reserved

tunnel channels and associated landforms south central ontario their implications for ice sheet hydrology the peterborough trenton drumlin field and associated meltwater erosion marks s forms were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet the algonquin event recent theoretical modelling of ice sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet inductive testing of this hypothesis using observations in south central ontario forms the crux of this paper a geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns such a rough interactive geometry is suggested as the bed is drumlinized and flows responsible for drumlins may be expected to have eroded similar forms into the ice base three landforms in south central ontario namely tunnel channels megachannels and late stage sheet flow scours are described and interpreted as evidence of progressive channelization and flow diversion processes governed by the geometri

a simple model for the spatially variable coastal response to hurricanes abstract the vulnerability of a beach to extreme coastal change during a hurricane can be estimated by comparing the relative elevations of storm induced water levels to those of the dune or berm a simple model that defines the coastal response based on these elevations was used to hindcast the potential impact regime along a 50 km stretch of the north carolina coast to the landfalls of hurricane bonnie on august 27 1998 and hurricane floyd on september 16 1999 maximum total water levels at the shoreline were calculated as the sum of modeled storm surge astronomical tide and wave runup estimated from offshore wave conditions and the local beach slope using an empirical parameterization storm surge and wave runup each accounted for 48 of the signal the remaining 4 is attributed to astronomical tides indicating that wave driven process are a significant contributor to hurricane induced water levels expected water levels and lidar derived measures of pre storm dune and berm elevation were used to predict the spatially varying storm impact regime swash collision or overwash predictions were compared to the observed response quantified using a lidar topography survey collected following hurricane landfall the storm averaged mean accuracy of the model in predicting the observed impact regime was 55 4 a significant improvement over the 33 3 accuracy associated with random chance model sensitivity varied between regimes and was highest within the overwash regime where the accuracies were 84 2 and 89 7 for hurricanes bonnie and floyd respectively the model not only allows for prediction of the general coastal response to storms but also provides a framework for examining the longshore variable magnitudes of observed coastal change for hurricane bonnie shoreline and beach volume changes within locations that experienced overwash or dune erosion were two times greater than locations where wave runup was confined to the foreshore swash regime during hurricane floyd this pattern became more pronounced as magnitudes of change were four times greater within the overwash regime than in the swash regime comparisons of pre storm topography to a calm weather survey collected one year after hurricane floyd s landfall show long term beach volume loss at overwash locations here the volume of sand eroded from the beach was balanced by the volume of overwash deposits indicating that the majority of the sand removed from the beach was transported landward across the island rather than being transported offshore in overwash locations sand was removed from the nearshore system and unavailable for later beach recovery resulting in a more permanent response than observed within the other regimes these results support the predictive capabilities of the storm scaling model and illustrate that the impact regimes provide a framework for explaining the longshore variable coastal response to hurricanes

interplay of autogenic and allogenic processes on the formation of shallow carbonate cycles in a synrift setting lower pliensbachian traras mountains nw algeria

patterns of sand transport on vegetated foredunes the aeolian development of coastal foredunes is studied at two sites along the dutch coast amounts of sand transport are measured in cross sections over the foredunes and changes in surface height are monitored sand transport decreases rapidly landward of the vegetation boundary near the dunefoot changes in surface roughness and topography generate turbulence and upward flow causing a small part of the sand to be transported in suspension patterns of transport are found to be closely related to air flow which in turn is related to topography and vegetation density with steeper topography the amounts of sand transported landward from the dunefoot increase if vegetation density is low during oblique onshore winds most of the sand accumulates at the dune front during perpendicular onshore winds a large proportion of the sand is deposited landward of the slope when deflection of flow occurs landward transport of sand is interrupted

evidence for large scale subglacial meltwater flood events in southern ontario and northern new york state flow line patterns constructed from the orientation of drumlin long axes are used to infer two major subglacial meltwater floods in southern ontario and northern new york state in this interpretation the flood waters of the first event the algonquin surged southward in the later ontarian event powerful floods streamed southwestward along the basins of lakes ontario and erie bedrock fluting upstream pointing noses on escarpments and tunnel channels give supporting evidence for the regional flood hypothesis regional distributions of drift thickness may be explained by this hypothesis

an automated approach for extracting barrier island morphology from digital elevation models abstract the response and recovery of a barrier island to extreme storms depends on the elevation of the dune base and crest both of which can vary considerably alongshore and through time quantifying the response to and recovery from storms requires that we can first identify and differentiate the dune s from the beach and back barrier which in turn depends on accurate identification and delineation of the dune toe crest and heel the purpose of this paper is to introduce a multi scale automated approach for extracting beach dune dune toe dune crest and dune heel and barrier island morphology the automated approach introduced here extracts the shoreline and back barrier shoreline based on elevation thresholds and extracts the dune toe dune crest and dune heel based on the average relative relief rr across multiple spatial scales of analysis the multi scale automated rr approach to extracting dune toe dune crest and dune heel based upon relative relief is more objective than traditional approaches because every pixel is analyzed across multiple computational scales and the identification of features is based on the calculated rr values the rr approach out performed contemporary approaches and represents a fast objective means to define important beach and dune features for predicting barrier island response to storms the rr method also does not require that the dune toe crest or heel are spatially continuous which is important because dune morphology is likely naturally variable alongshore