observed parameters for turbidity current flow in channels reserve fan lake superior abstract fine grained tailings discharged from a taconite ore processing operation near the shore of lake superior produced turbidity currents that transported the sediment from a small delta into deep water at silver bay minnesota deposition over nearly 20 years produced a sublacustrine fan with two prominent channels during 1972 and 1973 a current meter anchored 5 m above the lake floor adjacent to one of the channels recorded episodic turbidity current flow events lasting as long as two weeks to understand flow parameters for turbidity currents better a short term experiment within a channel on reserve fan in 1975 measured those variables not previously directly observed for channelized turbidity currents flow thickness flow density and concurrent velocity the observed flow thickn ss approximately 16 m is nearly four times the channel depth calculations using the average flow speeds 8 to 12 cm sec and the dilute concentration of the flow as measured during the experiment yield a value for the drag coefficient that is in remarkable agreement with estimated values commonly used for deriving speeds of turbidity currents using dimensions of submarine channels and properties of the sediments

into the deep a coarse grained carbonate turbidite valley and canyon in ultra deep carbonate setting abstract new high resolution multibeam mapping images detail the southern part of exuma sound southeastern bahamas and its unchartered transition area to the deep abyssal plain of the western north atlantic bounded by the bahama escarpment extending between san salvador island and samana cay the transition area is locally referred to as exuma plateau the newly established map reveals the detailed and complex morphology of a giant valley draining a long lived carbonate platform from its upper slope down to the abyssal plain this giant valley extends parallel to the slope of long island conception island and rum cay it starts with a perched system flowing on top of a lower cretaceous drowned main carbonate platform the valley shows low sinuosity and is characterized by several bends and flow constrictions related to the presence of the small relict isolated platforms that kept alive longer than the main platform before drowning and merging tributaries turbidite levees on either side of the valley witness the pathway of multiple gravity flows generated by upper slope over steepening around exuma sound through carbonate offbank transport some of them locally 15 and resulting slumping in addition additional periplatform sediments are transported to the main valley through numerous secondary slope gullies and several kilometre long tributaries draining the upper slopes of cays and islands surrounding exuma plateau some of them form knickpoints indicating surincision of the main exuma valley which is consistent with an important lateral supply of the main exuma valley prior to reaching the abyssal plain the main valley abruptly evolves into a deep canyon 5 km in width at its origin and as much as 10 km wide when it meets the abyssal plain through two major knickpoints named chutes with outsized height exceeding several hundred of meters in height both chutes are associated with plunge pools as deep as 200 m in the deepest pools the flows generate a hydraulic jump and resulting sediment accumulation when the canyon opens to the san salvador abyssal plain the narrow deep and strong flows release significant volume of coarse grained calcareous sediments in numerous turbidite layers interbedded with fine mixed siliciclastic and carbonate sediments transported by the western boundary undercurrent wbuc along the bahama escarpment carbonate gravity flows exiting the canyon decelerate at the abyssal plain level and construct a several kilometre wide coarse grained deep sea turbidite system with well developed lobe shape levees partially modified by the flow of strong contour currents along the bahama escarpment

compositional variations in calciturbidites due to sea level fluctuations late quaternary bahamas piston cores in tongue of the ocean bahamas revealed an alternating sequence of periplatform ooze and bankderived turbidites of the past 5 glacial and interglacial periods by using the point count method we have analyzed the composition of the turbidite sediment variations in the bank derived fraction are clearly linked to the glacial interglacial cycles nonskeletal components pellets ooids grapestones are most abundant in interglacial turbidites while skeletal components calcareous algae peneroplids and reef builders dominate in glacial turbidites we attribute this pattern to the exposure and flooding of the surrounding carbonate platforms during late quaternary sea level cycles because nonskeletal sediment is produced in the interior of the platforms its growth and subsequent export to the flanks are at a maximum when the banks are flooded i e during interglacial periods during glacials skeletal grains dominate because the banks are exposed and carbonate production is limited to a narrow belt of skeletal sands and fringing reefs the resulting compositional signal appeared to have a good correlation with aragonite variations in the periplatform ooze between the turbidites further compositional variation parallels the change in turbidite frequency described earlier highstand bundling frequency and composition of turbidites are both unaffected by diagenesis and therefore provide an excellent monitor of sealevel fluctuations

distinguishing tectonically and gravity driven synsedimentary deformation structures along the apulian platform margin gargano promontory southern italy abstract the assessment of deformation types within the slope of a carbonate platform can be complicated by the possible interaction of rooted tectonically induced and superficial gravity driven structures an ideal case study to document and distinguish tectonically and gravity driven structures is provided by the cretaceous slope to basin carbonates exposed in the gargano promontory southern italy these carbonates formed adjacent to the apulian platform margin which was oriented approximately ne sw to nw se along the southern and northern edges of the promontory respectively slump related folds are characterised by axial planes typically oriented either sub parallel or at small angles to the strike of the inferred paleoslope in fact the strike of folds is roughly ne sw in the southern portion of the study area whereas it is nw se in the northern part correspondingly gravity driven normal and reverse faults strike sub parallel and at acute angles to the adjacent apulian paleoslope cretaceous tectonic faults in the slope to basin carbonates form two principal sets striking nw se and wnw ese the former set is made up of normal faults and the latter one includes mainly oblique slip normal faults neither normal nor oblique slip normal faults show any relationship with the geometry of the paleoslope the results obtained from this study may help the interpretation of subsurface data in those geological contexts in which the interplay of gravitational and tectonic processes is responsible for deformation

fine grained versus coarse grained wave ripples generated experimentally under large scale oscillatory flow abstract wave ripples were generated in a wave tunnel under large scale oscillatory flow orbital diameter 1 4 5 m using two different grain sizes very fine sand and coarse sand the geometry of bed configurations that were produced varied strongly as a function of grain size small anorbital ripples wavelengths 10 cm heights 5 cm these results support the hypothesis advanced by leckie 1988 that large waves generate markedly different stratigraphic signatures in fine grained and coarse grained sediment

source rock distribution model of the periadriatic region the periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic sedimentary cycles tectonic evolution progressed from a triassic early jurassic liassic continental rifting stage on the northern edge of the african craton through an early jurassic middle liassic late cretaceous eocene oceanic rifting stage and passive margin formation to a final continental collision and active margin deformation stage in the late cretaceous eocene to holocene this evolution occurred in a transtensional and transpressional framework resulting from the oblique separation and convergence of the african and european plates extensive shallow water carbonate platform deposits covered large parts of the periadriatic region in the late triassic platform breakup and development of a platform to basin carbonate shelf morphology began in the late triassic and extended through the cretaceous on the basis of this paleogeographic evolution the regional geology of the periadriatic region can be expressed in terms of three main upper triassic paleogene sedimentary sequences the platform sequence sequence a the platform to basin sequence sequence b and the basin sequence sequence c these sequences developed during the initial rifting and subsequent passive margin formation tectonic stages three distinct episodes of source bed deposition can be identified middle upper triassic to lower jurassic liassic organic rich oil prone and mature source beds generally are structurally controlled and are closely associated with transtensional intraplatform basins formed in the early continental rifting stage the principal triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the periadriatic region are associated with sequence b areas the second episode of organic rich rocks deposition includes both shallow and deeper water facies of jurassic cretaceous age thin immature deep water epioceanic organic rich marls and shales are generally bathymetrically controlled these units are related to basin wide anoxic events in the tethys ocean and its submerged continental margin and are associated with sequence b areas middle upper cretaceous shallow water oil prone facies occur in isolated anoxic basins within carbonate platforms these source sequences are generally thicker and are associated with sequence a areas no major hydrocarbon accumulation can be directly attributed to the jurassic cretaceous epioceanic and intraplatform source rock sequences the third episode of source bed deposition characterizes the final active margin deformation stage and is represented by upper tertiary organic rich terrigenous units mostly gas prone these are essentially associated with turbiditic and flysch sequences of foredeep basins and have generated the greater part of the commercial biogenic gases of the periadriatic region

nutrient and temperature controls on modern carbonate production an example from the gulf of california mexico in addition to salinity and temperature nutrient concentrations in surface waters are known to have a significant impact on distribution of carbonate producing biota but have never been quantitatively evaluated against different temperatures along a latitudinal transect the western coast of the gulf of california mexico presents a natural laboratory for investigating the influence of oceanographic parameters such as salinity temperature and chlorophyll a a proxy for nutrients on the composition of a range of modern heterozoan and photozoan carbonate environments along a north south latitudinal gradient spanning the entire warm temperate realm 29 n 23 n chlorophyll a measured in situ at half hour resolution is highly variable throughout the year due to short term upwelling and increases significantly from the southern to northern gulf of california salinity in contrast fluctuates little and remains at an average of 35 from south to north carbonate production ranges from oligotrophic mesotrophic coral reef dominated shallow water areas minimum temperature 18 6 c through mesotrophic eutrophic red algal dominated inner shelf carbonate production in the central gulf minimum temperature 16 c and to molluscan bryozoan eutrophic inner to outer shelf environments minimum temperature 13 7 c the gulf of california data supplemented with oceanographic and compositional information from a database compiled from a spectrum of modern carbonate systems worldwide demonstrates the significance of nutrient control in the formation of heterozoan photozoan and transitional heterozoan photozoan carbonate systems and serves as a basis for more accurately interpreting fossil carbonates

three dimensional structure of the submarine flanks of la reunion inferred from geophysical data 1 la reunion indian ocean constitutes a huge volcanic oceanic system of which most of the volume is submerged we present a study of its submarine part based on the interpretation of magnetic and gravity data compiled from old and recent surveys a model of the submarine internal structure is derived from 3 d and 2 d models using constraints from previous geological and geophysical studies two large scale previously unknown buried volcanic construction zones are discovered in continuation of the island s construction to the east the alizes submarine zone is interpreted as the remnants of les alizes volcano eastward flank whose center is marked by a large hypovolcanic intrusion complex to the southwest the etang sale submarine zone is interpreted as an extension of piton des neiges probably fed by a volcanic rift zone over a large extent they were predominantly built during the matuyama period and thus probably belong to early volcanism a correlation exists between their top and seismic horizons recognized in previous studies and interpreted as the base of the volcanic edifice their morphology suggested a lithospheric bulging beneath la reunion not required to explain our data since the seismic interfaces match the top of our volcanic constructions the coastal shelf coincides with a negative bouguer anomaly belt often associated with magnetic anomalies suggesting a shelf built by hyaloclastites a detailed analysis of the offshore continuation of la montagne massif to the north confirms this hypothesis the gravity analysis confirms that the bathymetric bulges forming the northern eastern southern and western submarine flanks are predominantly built by debris avalanche deposits at the surface

segmentation and coalescence of cenozoic carbonate platforms northwestern great bahama bank seismic profiles over the northwestern great bahama bank reveal that it is formed by the coalescence of three smaller platforms and significant lateral progradation this conclusion is contrary to previous models which assumed that the bank is the result of continuous accumulation on one huge buildup in late cretaceous to early tertiary time a north south trending depression the straits of andros separated an eastern platform andros bank from a western platform bimini bank initially the straits of andros had dimensions similar to the modem tongue of the ocean but was progressively filled from east to west in early to middle tertiary time a second depression the bimini embayment formed within bimini bank by folding it had a maximum depth of about 470 m this depression was also filled from east to west in addition prograding systems built the western margin of bimini bank more than 25 km westward into the straits of florida

submarine landslides at subduction margins insights from physical models abstract submarine landslides which commonly develop along subduction margins at the front of accretionary prisms have recently been recognized as one of the most serious geohazards to investigate the mechanical processes involved in the development of these landslides a series of sandbox experiments were performed and the results were analyzed using the digital image correlation dic technique numerous slope failures which may be analogous to natural submarine landslides were produced on the model surface the slope failures can be classified as follows type i failures which are relatively small but are frequently developed on the lower parts of the slope and type ii failures which are relatively large and cover the entire slope but occur less frequently detailed observations reveal that the failure process can be divided into four stages 1 pre failure 2 steepening of the lower slope 3 type i failure and 4 type ii failure the minor type i slides act as precursors of major type ii failures each slope failure produces a topographic undulation triggering events in adjacent areas and a lateral migration of discrete slope failures although such experiments provide useful insight into slope failure processes a detailed 3d analysis of the failed sediment is vital if we are to understand the precise history of thrust activity at subduction margins recent and miocene accretionary prisms along the nankai trough japan display the geometric and lithologic characteristics of type i and type ii failures in their slide deposits

earthquake induced sediment failures on a 0 25 slope klamath river delta california on november 8 1980 a major earthquake magnitude 6 5 to 7 2 occurred 60 km off the coast of northern california a survey of the area using high resolution seismic reflection and side scan sonar equipment revealed the presence of extensive sediment failure and flows in a zone about 1 km wide and 20 km long that trends parallel to the shelf on the very gently sloping c and a prominent 1 to 2 m high seaward facing toe scarp on the outer margin of the terrace this toe scarp is sinuous appears to be nearly continuous for a distance of 20 km and closely parallels the 60 m isobath evidence indicates that the toe scarp is the terminus of lateral spreads and lobes of sediment flows side scan sonar records show evidence of gas vents and small 10 3 0 5 m high pressure ridges formed seaward of and parallel to the sediment flow scarp indicators of liquefaction sand boils and collapse craters are present on the sediment flow terrace extensive sediment failure occurred on a sea floor slope of less than 0 25 and we can unequivocally pinpoint the cause as an earthquake of known location magnitude and time

sedimentary dynamics and high frequency sequence stratigraphy of the southwestern slope of great bahama bank abstract new geophysical data from the leeward slope of great bahama bank show how contour currents shape the slope and induce re sedimentation processes along slope segments with high current control drift migration and current winnowing at the toe of slope form a deep moat here the slope progradation is inhibited by large channel incisions and the accumulation of large mass transport complexes triggered by current winnowing in areas where the slope is bathed by weaker currents the accumulation of mass transport complexes and channel incision is rather controlled by the position of the sea level large slope failures were triggered during the mid pleistocene transition and mid brunhes event both periods characterized by changes in the cyclicity or the amplitude of sea level fluctuations within the seismic stratigraphic framework of third order sequences four sequences of higher order were identified in the succession of the upper pleistocene these higher order sequences also show clear differences in function of the slope exposure to contour currents two stochastic models emphasize the role of the contour currents and slope morphology in the facies distribution in the upper pleistocene sequences in areas of high current influence the interplay of erosional and depositional processes form a complex facies pattern with downslope and along strike facies alterations in zones with lower current influence major facies alternations occur predominately in downslope direction and a layer cake pattern characterizes the along strike direction therefore this study highlights that contour currents are an underestimated driver for the sediment distribution and architecture of carbonate slopes

palaeogene neogene present day growth folding in the bahamian foreland of the cuban fold and thrust belt the santaren anticline constitutes the frontal termination of the cuban fold and thrust belt within the bahamian foreland new well and seismic data allow us to constrain in detail the evolution of this anticline pre growth and syntectonic partly post tectonic units separated by a major unconformity are associated with the santaren anticline their geometrical features are consistent with a detachment fold the precise age of the beginning of fold growth remains unknown however the complete record of well dated syntectonic sediments documents its kinematic evolution from mid eocene to pliocene present day and reveals an approximately constant and very slow growth rate from early miocene to pliocene present day the timing of evolution of the santaren anticline is not consistent with previous models that postulate that deformation associated with the cuban fold and thrust belt ended in the eocene our data suggest that the most external part of the cuban fold and thrust belt was still being deformed under a compressional regime during the late palaeogene neogene and probably during the quaternary we propose that this folding may result from compressive stresses transmitted approximately 400 km northwards from the actual plate boundary as a result of slow convergence between the n and s american plates

new insights into the morphology and sedimentary processes along the western slope of great bahama bank new high quality multibeam and seismic data image the western slope of the great bahama bank and the adjacent floor of the straits of florida the extensive survey reveals several unexpected large and small scale morphologies these include bypass areas channel leveelobe systems gullied slopes and products of slope instabilities at various scales including long slump scars at the lower slope and mass transport complexes that extend 30 km into the adjacent basin floor the toe of the slope is irregularly covered with deep water carbonate mounds the abundance of the individual morphological features varies from north to south from 26 00 n to 25 20 n the slope is dissected by numerous deep canyons that abruptly end southward where the slope is characterized by a smooth lower portion and small regularly spaced furrows in its upper part further south two long 25 50 km scars document instability at the lower slope one of these scars is the source area of a large mass transport complex in addition to this large scale feature several types of gravity induced sedimentary processes are revealed most of the morphologies and inferred processes of this carbonate system are similar to those observed in siliciclastic systems including mass transport complexes gravity currents initiated by density cascading and overspilling channeled turbidity currents for the first time a clear asymmetric channel levee system has been identified along the slope suggesting similitude in sorting processes between carbonate and siliciclastic systems and enhancing the reservoir bearing potential of carbonate slopes notable differences with siliciclastic systems include the lack of connection with the shallow and emerged part of the system i e bank top and the small size of the sedimentary system 2012 geological society of america

variability of cold water coral mounds in a high sediment input and tidal current regime straits of florida cold water coral mound morphology and development are thought to be controlled primarily by current regime this study however reveals a general lack of correlation between prevailing bottom current direction and mound morphology i e footprint shape and orientation as well as current strength and mound size i e footprint area and height these findings are based on quantitative analyses of a high resolution geophysical dataset collected with an autonomous underwater vehicle from three cold water coral mound sites at the toe of slope of great bahama bank the three sites 80 km2 total have an average of 14 mounds km 2 indicating that the great bahama bank slope is a major coral mound region at all three sites living coral colonies are observed on the surface of the mounds documenting active mound growth morphometric analysis shows that mounds at these sites vary significantly in height 1 to 83 m area 81 to 6 00 000 m2 shape mound aspect ratio 0 1 to 1 and orientation mound longest axis 0 to 180 the autonomous underwater vehicle measured bottom current data depict a north south flowing current that reverses approximately every six hours the tidal nature of this current and its intermittent deviations during reversals are interpreted to contribute to the observed mound complexity an additional factor contributing to the variability in mound morphometrics is the sediment deposition rate that varies among and within sites at most locations sedimentation rate lags slightly behind mound growth rate causing mounds to develop into large structures where sedimentation rates are higher than mound growth rates sediment partially or completely buries mounds the spatial distribution and alignment of mounds can also be related to gravity mass deposits as indicated by geomorphological features for example slope failure and linear topographic highs in the three dimensional bathymetry in summary variability in sedimentation rates current regime and underlying topography produce extraordinarily high variability in the distribution development and morphology of coral mounds on the great bahama bank slope

mesozoic tertiary tectonic evolution of albania in its regional eastern mediterranean context abstract research carried out since the opening of albania to the western geological community in the 1990s allows the geology and tectonics of this small balkan country to be integrated into an overall interpretation of neotethys in the eastern mediterranean region specifically greece and the former yugoslavia region albanian geology is most famous for the occurrence of contrasting ophiolites of jurassic age the country is sub divided into three main geotectonic units those in the west i e sazani ionian kruja krasta cukali and the albanian alps relate to the western margin of apulia effectively part of north africa from early mesozoic time onwards in the east is the korabi zone interpreted as a microcontinent located further northeast within neotethys between the two is the mirdita zone dominated by two contrasting jurassic ophiolites the western type ophiolite and the eastern type ophiolite taking account of evidence from greece and former yugoslavia the following tectonic evolution is proposed from early mesozoic time onwards neotethys in albania existed as a northward continuation of the pindos oceanic basin in greece pindos mirdita ocean a korabi microcontinent was rifted off apulia in the early mid triassic followed by passive margin subsidence until late middle jurassic time a rifted slow spreading mor type ophiolite formed within the western pindos mirdita oceanic basin in late triassic early late jurassic time using present co ordinates the shkoder peje scutari pec lineament in the north of albania is interpreted as an important transform fault zone that influenced the regional tectonic evolution during the entire mesozoic early tertiary rift drift emplacement history of the pindos mirdita ocean taking account of evidence from the greek and former yugoslavia ophiolites the easterly albanian ophiolites formed within the pindos mirdita ocean above a westward dipping intra oceanic subduction zone in the early late jurassic metamorphic soles were formed during initial intra oceanic displacement ca 162 174 m y and underlying melanges originated as subduction accretion complexes the mor western type ophiolite evolved into the iat boninitic eastern type ophiolite after subduction began during tithonian berriasian time trench margin collision emplaced the ophiolites eastwards over the korabi margin coupled with redeposition of ophiolitic and continental margin material as exotic blocks debris flow deposits and turbidites these were emplaced onto the upper surface of the ophiolitic thrust sheet during the latest stages of emplacement onto the korabi microcontinent following collision in the east oceanic crust remained within a small remnant pindos mirdita oceanic basin passive conditions were restored in the mid late cretaceous with shallow water carbonate deposition on microcontinental units and both pelagic and redeposited carbonates in basinal settings from the maastrichtian onwards africa eurasia convergence resulted in large scale westward thrusting deforming the apulian foreland in oligo miocene time the suture zone was re activated in oligo miocene time as the albanie thassalie piggy back type basin in central and southern albania albania as a whole was rotated 45 clockwise as part of the western aegean arc in post eocene time coastal and offshore albania experienced strong subsidence after early miocene time forming the periadriatic basin including the tirana depression interpreted as a foredeep related to continuing regional convergence southern albania experienced extensional tectonics in plio quaternary time related to southward roll back of the aegean active margin

lithospheric bulges recorded by regional unconformities the case of mesozoic tertiary apulia abstract cyclic shallow water carbonate sequences in the cretaceous of southern italy are punctuated by regional unconformities associated with bauxites and palaeokarst features direct and indirect evidence strongly suggests that despite their apparent plate interior position tectonics rather than eustasy was responsible for subaerial exposure long enough to form bauxites in plane stress related lithospheric arching caused by orogenic deformation along the distant active margins of apulia is invoked to explain the vertical stacking of a series of regional unconformities one of them marked by bauxites on land and under the sea the case history of apulian bauxites associated with a turonian arching allows a first estimate of the duration of a stress related distant perturbation of a subsiding passive continental margin

reconstructing 4000 years of mass movement and tsunami history in a deep peri alpine lake lake geneva france switzerland the study of mass movements in lake sediments provides insights into past natural hazards at historic and prehistoric timescales sediments from the deep basin of lake geneva reveal a succession of six large scale volumes of 22 x 10 6 to 250 x 10 6 m 3 mass transport deposits associated with five mass movement events within 2600 years 4000 cal bp to 563 ad the mass transport deposits result from i lateral slope failures mass transport deposit b at 3895 225 cal bp and mass transport deposits a and c at 3683 128 cal bp and ii rhone delta collapses mass transport deposits d to g dated at 2650 150 cal bp 2185 85 cal bp 1920 120 cal bp and 563 ad respectively mass transport deposits a and c were most probably triggered by an earthquake whereas the rhone delta collapses were likely to be due to sediment overload with a rockfall as the external trigger mass transport deposit g the tauredunum event in 563 ad known from historical records an earthquake mass transport deposit e or unknown external triggers mass transport deposits d and f independent of their origin and trigger mechanisms numerical simulations show that all of these recorded mass transport deposits are large enough to have generated at least metre scale tsunamis during mass movement initiation since the tauredunum event in 563 ad two small scale volumes of 1 to 2x10 6 m 3 mass transport deposits h and i are present in the seismic record both of which are associated with small lateral slope failures mass transport deposits h and i might be related to earthquakes in lausanne geneva possibly 1322 ad and aigle 1584 ad respectively the sedimentary record of the deep basin of lake geneva in combination with the historical record show that during the past 3695 years at least six tsunamis were generated by mass movements indicating that the tsunami hazard in the lake geneva region should not be neglected although such events are not frequent with a recurrence time of 0 0016 yr 1

soft sediment deformation within seismogenic slumps of the dead sea basin abstract the late pleistocene lisan formation preserved next to the dead sea provides exceptional 3 d exposures of folds and faults generated during soft sediment slumping and deformation it is possible to generate a range of four different scenarios associated with overprinting in a single slump event the progressive evolution of slump systems may be broadly categorised into initiation translation cessation relaxation and compaction phases thrust packages typically define piggyback sequences during slump translation with back steepening of imbricate faults leading to collapse of folds back up the regional palaeoslope detailed evaluation of slumped horizons may also permit structures to be traced across apparently separate and distinct slumped units the recognition that slumps may be reworked by younger seismically triggered events suggests that in some cases the seismic recurrence interval may be shorter than previously anticipated

geometry prediction for wave generated bedforms published data on wave generated bedform geometry from field and laboratory measurements are re evaluated in terms of relative fluid orbit diameter at the bed and a wave period parameter d 8t2 laboratory bedform data shows a strong dependence on these parameters however for very small values of the period parameter typically field data there is evidence that bedform length depends only on sediment grain size the disappearance of sediment bedforms at high fluid velocities apparently occurs through a decrease in bedform height improved methods for the prediction of bedform geometry under waves are provided in graphical form and computer code

3 d stratigraphic architecture sedimentary processes and controlling factors of cretaceous deep water resedimented carbonates gargano peninsula se italy abstract detailed geological mapping in 3 d supported by a lidar derived dom sedimentologic and biostratigraphic analyses and 3 d numerical modelling are used to characterise the stratigraphic architecture of deep water resedimented carbonate systems in the gargano peninsula se italy the base of slope succession spanning the upper aptian to danian p p was subdivided in five lithostratigraphic units that record the complex evolution and sedimentary dynamic along a segment of the apulian platform margin that was strongly influenced by syn sedimentary tectonic activity the characteristic location in a relay zone between the nw se trending platform margin and the e w oriented mattinata fault system favoured the existence of a transtentional zone from the upper aptian up to the end of the cretaceous the spatial distribution of the gravity flow deposits the stratal geometries the lateral facies changes and the biostratigraphic data demonstrate that the base of slope systems were sourced by distinct platform blocks characterised by different slope profiles abrupt to west and distally steepened to the north in this context the nature and origin of the resedimented carbonate material were controlled by the fracturation of the margin the response of the carbonate factory to relative sea level changes but were also strongly influenced by the slope profile this study demonstrates the relevance of combining traditional field work with numerical tools to improve the understanding of ancient sedimentary systems notably by mapping the stratal architecture and lithologies in continuity and at various scales on doms and by reconstructing the paleo topographies in 3 d

slope failures on the flanks of the western canary islands abstract landslides have been a key process in the evolution of the western canary islands the younger and more volcanically active canary islands el hierro la palma and tenerife show the clearest evidence of recent landslide activity the evidence includes landslide scars on the island flanks debris deposits on the lower island slopes and volcaniclastic turbidites on the floor of the adjacent ocean basins at least 14 large landslides have occurred on the flanks of the el hierro la palma and tenerife the majority of these in the last 1 million years with the youngest on the northwest flank of el hierro as recent as 15 thousand years in age older landslides undoubtedly occurred but are difficult to quantify because the evidence is buried beneath younger volcanic rocks and sediments landslides on the canary island flanks can be categorised as debris avalanches slumps or debris flows debris avalanches are long runout catastrophic failures which typically affect only the superficial part of the island volcanic sequence up to a maximum thickness of 1 to 2 km they are the commonest type of landslide mapped in contrast slumps move short distances and are deep rooted landslides which may affect the entire thickness of the volcanic edifice debris flows are defined as landslides which primarily affect the sedimentary cover of the submarine island flanks some landslides are complex events involving more than one of the above end member processes individual debris avalanches have volumes in the range of 50 500 km3 cover several thousand km2 of seafloor and have runout distances of up to 130 km from source overall debris avalanche deposits account for about 10 of the total volcanic edifices of the small relatively young islands of el hierro and la palma some parameters such as deposit volumes and landslide ages are difficult to quantify the key characteristics of debris avalanches include a relatively narrow headwall and chute above 3000 m water depth on the island flanks broadening into a depositional lobe below 3000 m debris avalanche deposits have a typically blocky morphology with individual blocks up to a kilometre or more in diameter however considerable variation exists between different avalanche deposits at one extreme the el golfo debris avalanche on el hierro has few large blocks scattered randomly across the avalanche surface at the other icod on the north flank of tenerife has much more numerous but smaller blocks over most of its surface with a few very large blocks confined to the margins of the deposit icod also exhibits flow structures longitudinal shears and pressure ridges that are absent in el golfo the primary controls on the block structure and distribution are inferred to be related to the nature of the landslide material and to flow processes observations in experimental debris flows show that the differences between the el golfo and icod landslide deposits are probably controlled by the greater proportion of fine grained material in the icod landslide this in turn relates to the nature of the failed volcanic rocks which are almost entirely basalt on el hierro but include a much greater proportion of pyroclastic deposits on tenerife landslide occurrence appears to be primarily controlled by the locations of volcanic rift zones on the islands with landslides propagating perpendicular to the rift orientation however this does not explain the uneven distribution of landslides on some islands which seems to indicate that unstable flanks are a weakness that can be carried forward during island development this may occur because certain island flanks are steeper extend to greater water depths or are less buttressed by the surrounding topography and because volcanic production following a landslide my be concentrated in the landslide scar thus focussing subsequent landslide potential in this area landslides are primarily a result of volcanic construction to a point where the mass of volcanic products fails under its own weight although the actual triggering factors are poorly understood they may include or be influenced by dyke intrusion pore pressure changes related to intrusion seismicity or sealevel climate changes a possible relationship between caldera collapse and landsliding on tenerife is not in our interpretation supported by the available evidence

marine biota response to clastic sediment influx a quantitative approach abstract there have been few quantitative studies of the effects of siliciclastic and volcaniclastic sediment influx on carbonate producing organisms from the geological record this study presents the results of quantitative field petrographic and acid digestion analyses of samples from three cenozoic shallow water mixed carbonate volcani siliciclastic depositional environments the miocene wonosari formation of south java the miocene batu putih limestone of east borneo and the eocene collsuspina limestone of northeast spain carbonate production in these systems is dominated by larger benthic foraminifera coralline algae and corals analyses of the quantity grainsize and type of volcani siliciclastic sediment within these mixed successions have allowed assessment of the influence of these factors on shallow water carbonate producers larger benthic foraminifera and coralline algae exhibit the greatest tolerance to siliciclastic sediment influx abundant up to 55 and 38 wt respectively at a range of grain sizes to coarse sand platy corals are also present within sediments containing a large proportion of insoluble material geologically averaged rates of clastic accumulation and their potential influences on carbonate producers inferred herein may be difficult to compare directly with the daily and seasonal fluctuations experienced by modern clastic influenced systems however this study may aid our understanding of the likely effects of increased clastic influx today commonly anthropogenically related to marine carbonate environments over longer time periods

bahamian carbonate platform development in response to sea level changes and the closure of the isthmus of panama in this paper we show that the development of the sediment architecture at the leeward toe of slope of great bahama bank ocean drilling project leg 166 bahama transect during the last 6 ma is not only a response to sea level fluctuations but also to major paleo oceanographic and climatic changes a major sequence boundary close to the miocene pliocene boundary dated at 5 6 5 4 ma is interpreted to reflect a major sea level drop that was followed by a sea level rise which led to the re flooding of the mediterranean sea at the end of the messinian and increasing sea surface temperatures at great bahama bank distinct erosional horizons occurred during the pliocene dated at 4 6 and 3 3 3 6 ma related to sea level change and the intensification of the gulf stream when the emergence of the isthmus of panama reached a critical threshold the gulf stream brings warm saline and nutrient poor waters to the bahamas starting at the early late pliocene boundary at 3 6 ma this paleo oceanographic reorganization in combination with enhanced sea level fluctuations associated with the late pliocene main intensification in northern hemisphere glaciation since 3 2 ma led to 1 a gradual change from a ramp type to a flat topped type morphology and 2 a change from a skeletal to a non skeletal dominated sedimentary system mainly peloidal increased sea level fluctuations during the second half of the pleistocene led to an intensified high stand shedding depositional pattern within the surrounding basins

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

can humans force a return to a cretaceous climate abstract the modern pole to equator sea level temperature difference is about 50 c that of the mid cretaceous ranged from 30 c to as little as 24 c implying a much more equable climate this may have been caused by 1 reduction of the ice forced albedo of the polar regions 2 more efficient meridional energy transport by the atmosphere and ocean and 3 increased atmospheric greenhouse gas concentrations earth s icy polar regions stabilize its present inequable climate through the ice albedo feedback effect the polar ice results in permanent atmospheric highs that stabilize earth s wind systems in turn the stable winds drive the ocean currents and determine the location of the frontal systems that separate the low and high latitude oceanic gyre systems and bound the region where water sinks into the ocean interior as thermocline and intermediate water masses increased ocean heat transport can assist in making a more equable climate but unrealistic volume transports would be required to warm the polar regions to cretaceous levels the major factor forcing the equable climate of the cretaceous is now thought to be increased greenhouse gas concentrations dominated by co2 the modern rate of change in atmospheric concentration is greater than 200 ppmv per century and increasing this compares with 1 ppmv per century during the last deglaciation at current rates of fossil fuel burning atmospheric co2 levels will reach cretaceous levels of 2 times the pre industrial level about 2070 and 8 times the pre industrial level shortly after 2300 it is likely that cretaceous atmospheric co2 concentrations will last for many thousands to tens of thousands of years in addition to increased atmospheric greenhouse gas concentrations a return to climatic conditions resembling those of the cretaceous would require ice free poles and large changes in atmospheric and oceanic circulation arctic sea ice is melting much more rapidly than had been expected and the arctic ocean will soon be free of sea ice in summer the greenland ice sheet is melting more rapidly than expected because of greenhouse warming surface meltwater forms lakes and then flows down through crevasses and holes in the ice to lubricate the base allowing ice steams to flow much more rapidly the lifetime of the greenland ice sheet may be only a few hundred years the west antarctic ice sheet is inherently unstable being grounded on rock well below sea level the ice shelves blocking ice streams off west antarctica have begun to melt from beneath and break up as the southern ocean warms the east antarctic ice sheet has been regarded as highly stable but discovery of lakes beneath the ice and fast flowing ice streams raises questions about whether the ice sheet will ultimately succumb to global warming and disintegrate i conclude that a return to climatic conditions resembling those of the mid cretaceous is not only possible but also likely unless humanity can organize an effective campaign to stop co2 emissions to the atmosphere and remove some of the excess co2 already introduced

highstand versus lowstand deposition on carbonate platform margins insight from quaternary foreslopes in the bahamas abstract examples of both highstand and lowstand deposition have been identified on the upper platform slopes of the tongue of the ocean bahamas highstand deposits consist of a thick wedge of fine grained skeletal and non skeletal sands and carbonate muds derived predominantly from the platform and deposited on slopes of 25 28 these sediments were deposited subsequent to platform flooding and may be more than 30 m thick along open leeward margins in contrast lowstand deposits consists of coarse skeletal sands gravels and boulders deposited on primary depositional slopes of 35 45 these sediments were derived from fringing reefs along the marginal escarpment and deposited during the initial rise of sea level following the last lowstand these variations in depositional character result in a distinctive signature of highstand versus lowstand deposition for steep sided platforms and further elucidate the response of carbonate platforms to high magnitude 5th order scale 20 000 yrs fluctuations in sea level

on the architecture of intra formational mass transport deposits insights from the carbonate slopes of great bahama bank and the apulian carbonate platform abstract large sub tropical carbonate platforms shed huge volumes of sediment onto their adjacent slopes resulting carbonate successions are comprised of gravity flow beds turbidites debrites which are occasionally reworked into mass transport deposits mtds by the failure of inconsistently lithified portions of slope strata despite their significance in the depositional record the internal architecture of mtds along relatively tectonically stable and sediment producing carbonate platforms is poorly understood in comparison with counterparts in active compressional tectonic settings this study compares carbonate slope derived mtds imaged in seismic reflection data with those observed in outcrop the internal architecture of mtds from two case studies is presented the seismically imaged mtds in miocene recent carbonate slope deposits from the bahamas and mtds off the cretaceous apulian carbonate margin exposed in outcrops of the ionian basin albania understanding the large scale kilometers to tens of kilometers internal architecture of mtds in seismic is crucial for identification of these structures in outcrop in turn only outcrop studies allow the detailed analysis of the reworking style within these massive sediment bodies at a smaller scale meters to kilometers the internal architecture of the studied carbonate mtds testifies to the existence of an along slope continuum of deformation structures characterized by vertical partitioning into distinct mass flows during single mass transport events mass wasting processes are inferred from strain partitioning structures recording along slope and slope parallel architectural heterogeneities three deformation domains are recognized extensional headwall domain translational body domain and contractional toe domain confined mtds are limited by steep and deep lateral margins and frontal ramps that mark the boundaries between failed deposits and undisturbed strata vertical strain partitioning is pronounced in the toe domain upward intensification of deformation within mtds is common and corresponds to a top down reorganization of failed strata during downslope transport intra formational mtds along carbonate slopes that are lacking exotics such as the ones studied here differ from extra formational mtds occurring in compressional tectonic settings that form sedimentary melanges ductile layer deformation structures are predominant in carbonate mtds as opposed to block in matrix fabrics in sedimentary melanges the development of shear surfaces rather than ductile shear zones in the body and toe domains presents predictive in modern environments and diagnostic criteria in fossil examples of mass wasting events along carbonate slopes

bahama carbonate platforms the deep and the past abstract carbonate deposition prevailed for 150 ma in the bahama florida segment of the west atlantic margin and provides an interesting test for actualism present day facies patterns on the banks are controlled by the backward decrease of waves and tides and the concomitant increase of temperature and salinity variation in the troughs influx of sand and rubble from gravity flows varies with topography and distance from shallow water sources and allows one to define facies belts a rhythmic sequence of ooze and graded beds on the basin floors subdivided into a basin margin belt of coarse thick turbidites and basin interior with fine turbidites slope facies change with increase in height and declivity from accretionary to by pass to erosional regimes stratigraphic history of the bahamas is not simply a projection of the holo scene back in time both long term natural evolution decrease in subsidence upbuilding of the banks submarine erosion and outside factors climate eustacy have caused significant changes since the jurassic the bahamas seem to have evolved from a clastics evaporite province to a single carbonate evaporite platform and finally to an array of platforms and troughs during the platform trough stage the rate of upbuilding of the platforms decreased submarine canyon erosion increased platform flanks steepened as they grew higher and changed from accretionary to by pass to erosional slopes a change imposed by extraneous factors occurred in the pliocene when the great bahama bank changed from a giant reef rimmed atoll to a flat platform covered by oolites and peloid sands the bahamas share both long term trends as well as random changes by extraneous factors with other platforms in the geologic record compared to ancient platforms however they are unusually long lived and at a more advanced stage of growth they are deeply dissected by erosion their flanks are unusually high and steep and the troughs very narrow the neogene platform sequence is strongly controlled by eustatic sea level fluctuations

seismically induced slumps in lower maastrichtian peritidal carbonates of the apulian platform southern italy abstract in the southeastern murge apulian foreland southern italy a lower maastrichtian carbonate section showing soft sediment deformation structures is composed of peritidal lithofacies associations developed in a wide low energy inner platform system shear induced soft sediment deformation structures correspond to multilayer deformed horizons 1 5 to 2 m in thickness sandwiched between undeformed layers overturned and recumbent folds lying on decollement surfaces and asymmetrical fault inception folds allow us to interpret the observed deformed horizons as slump sheets the detailed description of the main morphological features of the deformed beds and the recognition of unconformable surfaces and undeformed beds between slumped beds allow us to distinguish three different events of deformation preferential orientation of slump folds has been measured and every slumped bed shows a different direction of shortening randomly oriented direction of shortening suggests that each deformation event was driven by the presence of local very gentle gradients developed in peritidal settings by excluding other potential trigger mechanisms of deformation the observed slumps are interpreted as seismically induced slides even if no data about the distance of the seismic source may be obtained near field earthquake tectonics affected the apulian platform during late cretaceous times

a unified model for bedform development and equilibrium under unidirectional oscillatory and combined flows the development of bedforms under unidirectional oscillatory and combined flows results from temporal changes in sediment transport flow and morphological response in such flows the bedform characteristics for example height wavelength and shape change over time from their initiation to equilibrium with the imposed conditions even if the flow conditions remain unchanged these variations in bedform morphology during development are reflected in the sedimentary structures preserved in the rock record hence understanding the time and morphological development in which bedforms evolve to an equilibrium stage is critical for informed reconstruction of the ancient sedimentary record this article presents results from a laboratory flume study on bedform development and equilibrium development time conducted under purely unidirectional purely oscillatory and combined flow conditions which aimed to test and extend an empirical model developed in past work solely for unidirectional ripples the present results yield a unified model for bedform development and equilibrium under unidirectional oscillatory and combined flows the experimental results show that the processes of bedform genesis and growth are common to all types of flows and can be characterized into four stages i incipient bedforms ii growing bedforms iii stabilizing bedforms and iv fully developed bedforms furthermore the development path of bedform growth exhibits the same general trend for different flow types for example unidirectional oscillatory and combined flows bedform size for example small versus large ripples bedform shape for example symmetrical or rounded bedform planform geometry for example two dimensional versus three dimensional flow velocities and sediment grain sizes the equilibrium time for a wide range of bed configurations was determined and found to be inversely proportional to the sediment transport flux occurring for that flow condition

high resolution stratigraphic forward modeling of a quaternary carbonate margin controls and dynamic of the progradation abstract the relationships between the margin sedimentary regime and the platform progradation are studied using forward stratigraphic numerical simulations on the leeward western prograding margin of the great bahama bank gbb during the quaternary 1 7 0 ma the corresponding sedimentary regime in the slope and the platform is well known from the odp leg 166 and bahamas drilling project wells located along the western line seismic transect however the sedimentary regime on the margin is not well established the coral reefal margin observed before between 1 7 and 0 8 ma in the well clino is not active anymore at present day and the holocene sedimentary regime is geometrically unable to account alone for the progradation this study is based on three 2d high resolution forward stratigraphic numerical modeling experiments with the software dionisosflow that include the platform margin and slope domains on the western line section in the same sedimentary models the results are compared to the six sedimentary cores and to the present day bathymetry in order to identify the more realistic scenario the three experiments test different models of carbonate sediment production and transport experiment 1 shows that the highstand shedding of the fine grained uncemented platform production is unable to reproduce the progradation and the present day profile experiments 2 and 3 incorporate cemented facies in the margin with the best results obtained with the cemented marginal wedges produced in experiment 2 during platform emersion from these results a high resolution interpretation of the margin seismic section is proposed this study shows that the platform progradation can be decoupled from the highstand shedding of the fine grained platform production it is dependent on the accumulation in front of the steep margin of coarse or cemented material before 0 8 ma this corresponds to the coral reef identified in clino the transition after 0 45 ma to 100 kyr large eustatic cycles with total platform flooding created two distinct marginal regimes 1 during platform flooding aggrading accumulation of non skeletal sands and 2 during platform emersion prograding cemented marginal wedges produced in situ

wave formed sediment ripples transient analysis of ripple spectral development 1 a new method has been developed that models the changes a wave formed rippled sediment bed undergoes as it is actively evolving between two given equilibrium states due to a change in surface wave conditions the transient analysis of rippled beds has received very little attention within the literature dynamic changes within ripple parameters have implications for the estimation of flow dissipation and sediment transport by changing the bottom roughness height the method uses the spectral density function of the rippled bed and is based on a series of ripple growth and ripple transition experimental tests the ripple evolution model was developed from the well known logistic growth law fitting the general solution of the logistic nonlinear differential equation to the experimental data enabled the evolution rate of the bed to be determined for each experimental test it was concluded that there was no difference between the evolution rate determined from the ripple growth tests and the ripple transition tests this indicated that the two types of growth are special cases of the same evolution processes which is adequately modeled by the logistic growth equation a functional dependence was established between the ripple evolution rate and the shields parameter this allows the evolution rate to be estimated from flow and sediment properties the estimation of the rate at which rippled sediment beds evolve under a variable sea state has the potential to lead to significant improvements to the way ripple transition and hence bottom roughness is approximated in coastal wave models

oscillatory ripple geometry ripple geometry provides a bed roughness which governs the bed shear stress and the profile of eddy viscosity or diffusion coefficient required for the description of the sediment concentration profile or rate of sediment transport an analysis is made of ripple geometries using known tabulated laboratory and field data as well as water tunnel data obtained by the writer three different types of ripples can be identified sand light sediment and oscillating bed ripples they reflect different effects of the fluid shear stress and fluid acceleration on bed sediments it is also shown that when the bed shear stress or the amplitude of the water particle motion relative to the sediment size is small the resulting vortices are more regular with low turbulence intensity and the generated ripples are two dimensional they are called growing or vortex ripples which are strongly influenced by the amplitude of the water particle motion at the other extreme when the bed shear stress or the amplitude of the

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

seismic stratigraphy and geologic history of middle cretaceous through cenozoic rocks southern straits of florida multifold and singlefold seismic data and indirect ties to industry wells and deep sea drilling program and ocean drilling program sites are used to study the middle cretaceous to cenozoic history of the southern straits of florida since the late albian the southern straits of florida has evolved from a shallow water platform to a deep water trough this evolution is related in part to late albian middle cenomanian drowning and segmentation of a shallow water carbonate megabank which extended across the region since the late cretaceous shallow water deposition has continued around cay sal bank and along the southern margin of the south florida basin while deeper water deposition has persisted elsewhere evolution of the straits of florida is also related to late cretaceous middle eocene convergence between the north american and caribbean plates regional dip towards the cuban fold and thrust belt suggests that the southern straits of florida is an extension of the north cuban foreland basin a paleo florida current became active during the early paleocene along the northern limb of this foreland basin during this time the southern straits of florida was still relatively shallow and bottom currents persisted over most of the region rapid subsidence during the late eocene caused a change in depositional regimes from current dominated to predominantly pelagic hemipelagic sedimentation since the late eocene the florida current has influenced deposition only in the shallower parts f the southern straits of florida

contribution to the understanding of the ionian basin sedimentary evolution along the eastern edge of apulia during the late cretaceous in albania abstract integrated in the peri adriatic domain the ionian basin extended along a nw se direction during the late cretaceous limited on its sides by the apulian and the kruja platforms the basinal slope succession was studied in seven outcrops exposed in the albanian fold and thrust belt sedimentological investigations supported by bio and chronostratigraphy were performed on calcareous upper cretaceous hemipelagites gravity flow deposits and slumps the western part of the basin was studied revealing a strong influence of the apulian margin alternatively shedding sediment basinward by means of a tectonically controlled edge the late albian to cenomanian period is characterized by the settling of muddy debrites along the margin a deep basinal environment characterizes this period which prolongs until the santonian with no significant influx of the platform basinward this sedimentary setting abruptly changed at the end of the santonian with an important influx derived from both platforms coarsening and thickening upward sequences show a progressive increase in sediment shedding during the campanian the late campanian early maastrichtian period points out a major change on the resedimentation processes with the settling of several slumped units reworking thick sediment packages the latter can be traced along the apulian margin testifying of instabilities along the edge of apulia

rise and demise of the bahama grand banks gigaplatform northern margin of the jurassic proto atlantic seaway abstract an extinct 5000 km long jurassic carbonate platform and barrier reef system lies buried beneath the atlantic continental shelf and slope of the united states a revised stratigraphic framework a series of regional isopach maps and paleogeographic reconstructions are used to illustrate the 42 m y history of this bahama grand banks gigaplatform from its inception in aalenian early middle jurassic time to its demise and burial in berriasian valanginian time early early cretaceous aggradation progradation rates for the gigaplatform are comparable to those of the familiar capitan shelf margin permian and are closely correlated with volumetric rates of siliciclastic sediment accumulation and depocenter migration siliciclastic encroachment behind the carbonate tracts appears to have been an important impetus for shelf edge progradation during the early cretaceous sea level changes combined with eutrophication due to landward soil development and seaward upwelling and the presence of cooler upwelled waters along the outer shelf appear to have decimated the carbonate producers from the carolina trough to the grand banks this allowed advancing siliciclastic deltas to overrun the shelf edge despite a notable reduction in siliciclastic accumulation rates however upwelling did not extend southward to the blake bahama megabank so platform carbonate production proceeded there well into the cretaceous subsequent stepwise carbonate abatement characterized the blake plateau basin whereas the bahamas have maintained production to the present the demise of carbonate production on the northern segments of the gigaplatform helped to escalate deep water carbonate deposition in the early cretaceous but the sudden augmentation of deep water carbonate reservoirs in the late jurassic was triggered by other agents such as global expansion of nannoplankton communities

cyclicity and basin axis shift in a piggyback basin towards modelling of the eocene tremp ager basin south pyrenees spain

highest natural bed forms 1 fluid flow interacts with sedimentary beds forming waves of different kinds which are of considerable practical importance since they influence significantly the near bed flow both over and below the bed sediment transport and wave height attenuation we focus here on steep bed forms capable of producing flow separation in this case the large scale vorticity generated in the phenomenon of separation rules the process of friction which appears to be practically unaffected by sediment motion under the crests of the bed forms the mean shear force due to friction is balanced by the force that bed forms exert on the flow via pressure which can be calculated from the work of gimenez curto and corniero 2002 bed forms grow until they have a height such that friction at their troughs is negligible thus ceasing the motion of fluid and sediment this condition leads to a very simple expression for the limiting steepness which compares favorably with existing observations on bed form geometry under steady open channel flow as well as under oscillatory flow

siliciclastic and volcaniclastic influences on equatorial carbonates insights from the neogene of indonesia in active tectonic areas of humid equatorial regions nearshore shallow water environments are commonly sites of near continuous siliciclastic influx and or punctuated volcaniclastic input despite significant clastic influence neogene carbonates developed in se asia adjacent to major deltas or volcanic arcs and are comparable with modern mixed carbonate clastic deposits in the region research into delta front patch reefs from borneo and fore arc carbonate platform development from java is described and used to evaluate the effects of siliciclastic and volcaniclastic influx on regional carbonate sedimentation local changes in carbonate producing biota and sequence development regional carbonate development in areas of high siliciclastic or volcaniclastic input was influenced by the presence of antecedent highs changes in the amounts or rates of clastic input delta lobe switching or variations in volcanic activity energy regimes and relative sea level change a variety of carbonate producing organisms including larger benthic foraminifera some corals coralline algae echinoderms and molluscs could tolerate near continuous siliciclastic or volcaniclastic influx approximately equal to their own production rates these organisms adopted various strategies for coping with clastic input including a degree of mobility morphologies adapted to unstable substrate inhabitation or shedding sediment and shapes adapted to low light levels local carbonate production was also affected by energy regime clastic grain sizes and associated nutrient input clastic input influenced the inhabitable depth range for photoautotrophs the zonation of light dependent assemblages and the morphology and sequence development of mixed carbonate clastic successions this study provides data on the dynamic interactions between carbonate and non carbonate clastic sediments and when combined with information from comparable modern environments allows a better understanding of the effects of siliciclastic and volcaniclastic influx on carbonate production

numerical study of sediment transport above rippled beds under the action of combined waves and currents to study sediment suspension above ripples under the combined action of waves and currents a three dimensional numerical model has been developed based on the use of fluent software and an external sediment transport model the computer model has been tested against laboratory measurements involving oscillatory wave motion as well as cases of co linear waves with following and opposing currents with satisfactory results compared with the situation in which only waves are present called waves alone cases the effects from the steady current on both vortex shedding and sediment suspension above ripples have clearly been revealed by the model results in particular the vortices generated in combined waves and currents tend to stay low in the trough area of the ripple and are ejected earlier than those in the waves alone case at both the ripple crest and trough which leads to concentration peaks at different phases and with different magnitudes the model was also applied to a field case from a multi barred dissipative beach at egmond an zee in the netherlands to investigate the influences of a long shore current on cross shore sediment transport the model results show reasonable overall agreement with the field measurements as well as the important effects of the three dimensional flow structure on the sediment entrainment process close to the ripple surface which is very difficult to observe in such detail in field studies

on the incorporation of atmospheric boundary layer effects into a balanced model a method of coupling the thermal and frictional forcing in the atmospheric boundary layer to a semi geostrophic model of the internal dynamics is developed it is illustrated by two dimensional sea breeze simulations which are compared with those of a two dimensional primitive equation model it is demonstrated that the main features of the circulation on a horizontal scale larger than 20 km can be simulated with the semi geostrophic model but the detailed local circulations cannot

linking continental slope failures and climate change testing the clathrate gun hypothesis it has been suggested that the release of clathrates rather than expansion of wetlands is the primary cause of the rapid increases observed in the ice core atmospheric methane record during the pleistocene because submarine sediment failures can involve as much as 5000 gt of sediment and have the capacity to release vast quantities of methane hydrates one of the major tests of the clathrate gun hypothesis is determining whether the periods of enhanced continental slope failure and atmospheric methane correlate to test the clathrate gun hypothesis we have collated published dates for submarine sediment failures in the north atlantic sector and correlated them with climatic change for the past 45 k y more than 70 by volume of continental slope failures during the past 45 k y was displaced in two periods between 15 and 13 ka and between 11 and 8 ka both these intervals correlate with rising sea level and peaks in the methane record during the bolling allerod and preboreal periods these data support the clathrate gun hypothesis for glacial interglacial transitions the data do not however support the clathrate gun hypothesis for glacial millennial scale climate cycles because the occurrence of sediment failures correlates with heinrich events i e lows in sea level and atmospheric methane a secondary use of this data set is the insight into the possible cause of continental slope failures glacial period slope failures occur mainly in the low latitudes and are associated with lowering sea level this finding suggests that reduced hydrostatic pressure and the associated destabilization of gas hydrates may be the primary cause the bolling allerod sediment failures were predominantly low latitude suggesting an early tropical response to deglaciation e g enhanced precipitation and sediment load to the continental shelf or warming of intermediate waters in contrast sediment failures during the preboreal period and the majority of the holocene occurred in the high latitudes suggesting either isostatic rebound related earthquake activity or reduced hydrostatic pressure caused by isostatic rebound causing destabilization of gas hydrates

how to recognize crescentic bedforms formed by supercritical turbidity currents in the geologic record insights from active submarine channels submarine channels have been important throughout geologic time for feeding globally significant volumes of sediment from land to the deep sea modern observations show that submarine channels can be sculpted by supercritical turbidity currents seafloor sediment flows that can generate upstream migrating bedforms with a crescentic planform in order to accurately interpret supercritical flows and depositional environments in the geologic record it is important to be able to recognize the depositional signature of crescentic bedforms field geologists commonly link scour fills containing massive sands to crescentic bedforms whereas models of turbidity currents produce deposits dominated by back stepping beds here we reconcile this apparent contradiction by presenting the most detailed study yet that combines direct flow observations time lapse seabed mapping and sediment cores thus providing the link from flow process to depositional product these data were collected within the proximal part of a submarine channel on the squamish delta canada we demonstrate that bedform migration initially produces back stepping beds of sand however these back stepping beds are partially eroded by further bedform migration during subsequent flows resulting in scour fills containing massive sand as a result our observations better match the depositional architecture of upstream migrating bedforms produced by fluvial models despite the fact that they formed beneath turbidity currents

seismically induced slump on an extremely gentle slope 1 of the pleistocene tecopa paleolake california a superbly exposed 5 km 2 slump is developed in middle pleistocene lacustrine deposits of the tecopa basin california united states a subhorizontal detachment

the upper cretaceous carbonates of the gargano murge region southern italy a model of platform to basin transition the outcrops in gargano murge region are good examples of the upper cretaceous carbonate systems of the peri adriatic area they enable the architecture and the processes of the platform to basin transition to be studied in detail the platform carbonates are juxtaposed to the deeper marine carbonates by the intermediary of a faulted scarp the base of slope is characterized by bioclastic and conglomeratic aprons interbedded with pelagic mudstones the outer shelf domain which was the prolific source of rudistid bioclastic aprons is not preserved the platform is mainly built of mud dominated transgressive systems tracts whereas highstand systems tracts are developed as bioclastic base of slope aprons the volume of the resedimented bioclasts largely exceeds the volume of missing outer shelf indicating that carbonate production and sediment bypass are more critical for this stratigraphic response than carbonate erosion the lowstands which were controlled by tectonic deformations are characterized by base of slope breccia and blocks eroded from the shelf edge this erosion resulted in the progressive retreat of the shelf edge the best potentials for hydrocarbon reservoir are found in the bioclastic base of slope aprons formed during the cenomanian and maastrichtian highstands this model is considered as an analog for the hydrocarbon reservoirs formed by the deep marine deposits of cretaceous tamabra limestone in the gulf of mexico

the northwest african slope apron a modern analogue for deep water systems with complex seafloor topography the northwest african slope apron is an interesting modern analogue for deep water systems with complex seafloor topography a sediment process map of the northwest african continental margin illustrates the relative roles of different sedimentary processes acting across the entire margin fine grained pelagic and hemipelagic sedimentation is dominant across a large area of the margin and is considered to result from background sedimentary processes alongslope bottom currents smooth and mould the seafloor sediments and produce bedforms such as erosional furrows sediment waves and contourite drifts downslope gravity flows debris avalanches debris flows and turbidity currents are infrequent but important events on the margin and are the dominant processes shaping the morphology of the slope and rise the overall distribution of sedimentary facies and morphological elements on the northwest african margin is characteristic of a fine grained clastic slope apron however the presence of numerous volcanic islands and seamounts along the margin leads to a more complex distribution of sedimentary facies than is accounted for by slope apron models in particular the distribution and thickness of turbidite sands are controlled by the location of the break of slope which is itself controlled by the pre existing submarine topography

detailed measurements of velocities and suspended sand concentrations over full scale ripples in regular oscillatory flow the knowledge and modeling of wave induced sand transport over rippled beds still has significant shortcomings which is partly related to a lack of measurements of the detailed processes from controlled laboratory experiments we have carried out new measurements of the detailed time dependent velocity and suspended sand concentration field around vortex ripples for regular oscillatory flow conditions the fact that the ripples were mobile and the flow conditions were full scale makes these measurements unique we made velocity measurements for 14 different flows and concentration measurements for three of these flows the velocity and concentration field above ripples are dominated by the generation and ejection of vortices on the ripple flanks around the time of flow reversal vortex formation results in near ripple flow reversals ahead of free stream reversals and velocity maxima near the ripple crest that are much higher than the free stream maxima asymmetry in the free stream produces steady circulation cells with dominant offshore mean flow up the ripple lee slope balanced by weaker onshore streaming up the ripple stoss slope as well as higher up in the flow the time and bed averaged horizontal velocity profile comprises an offshore streaming near the bed and an onshore drift higher up in the flow the vortices are responsible for three main concentration peaks one just after on offshore flow reversal associated with the passage of a sand laden vortex followed by two smaller peaks due to advected suspension clouds generated by vortex action at the neighboring onshore ripples the sand flux field measured for one typical asymmetric flow condition is dominated by an offshore flux associated with the suspended sand cloud generated by vortex shedding from the ripple s lee slope around the time of on offshore flow reversal the net time averaged current related and wave related horizontal sand fluxes are generally offshore directed and mostly contained within 1 5 ripple heights above the ripple crest the wave related suspended transport component is larger but the contribution of the current related suspended sand transport cannot be neglected in addition to the measured offshore net transport of suspended sand there is an onshore directed transport very close to the ripple surface the total net transport is in the offshore direction for this specific asymmetric flow condition

evolution of the adriatic carbonate platform palaeogeography main events and depositional dynamics abstract the adriatic carbonate platform adcp is one of the largest mesozoic carbonate platforms of the perimediterranean region its deposits comprise a major part of the entire carbonate succession of the croatian karst external or outer dinarides which is very thick in places more than 8000 m and ranges in age from the middle permian or even upper carboniferous to the eocene however only deposits ranging from the top of the lower jurassic toarcian to the top of the cretaceous can be attributed to the adcp defined as an isolated palaeogeographical entity although the entire carbonate succession of the karst dinarides was deposited within carbonate platform environments there were different types of carbonate platforms located in different palaeogeographical settings carboniferous to middle triassic mixed siliciclastic carbonate deposits were accumulated along the gondwanian margin on a spacious epeiric carbonate platform after tectonic activity culminating by regional middle triassic volcanism recorded throughout adria the african promontory a huge isolated carbonate southern tethyan megaplatform abbreviated as stm was formed with the area of the future adcp located in its inner part tectonic disintegration of the megaplatform during the middle to late early jurassic resulted in the establishment of several carbonate platforms including the adriatic apenninic and apulian separated by newly drowned deeper marine areas including the adriatic basin as a connection between the ionian and belluno basins lagonero basin and the area of the slovenian and bosnian troughs the adcp was characterised by predominantly shallow marine deposition although short or long periods of emergence were numerous as a consequence of the interaction of synsedimentary tectonics and eustatic changes also several events of temporary platform drowning were recorded especially in the late cretaceous when synsedimentary tectonics became stronger leading up to the final disintegration of the adcp the thickness of deposits formed during the 125 my of the adcp s existence is variable between 3500 and 5000 m the end of adcp deposition was marked by regional emergence between the cretaceous and the palaeogene deposition during the palaeogene was mainly controlled by intense synsedimentary tectonic deformation of the former platform area some carbonates mostly eocene in age were deposited on irregular ramp type carbonate platforms surrounding newly formed flysch basins and the final uplift of the dinarides reached its maximum in the oligocene miocene the adriatic carbonate platform represents a part although a relatively large and well preserved one of the broader shallow water carbonate platform that extended from ne italy to turkey although its continuity is somewhat debatable in the area near albanian greece boundary this large carbonate body which was deformed mostly in the cenozoic including a significant reduction of its width needs a specific name and the central mediterranean carbonate platform is proposed abbreviated to cmcp although the local names such as adcp for its nw part should be kept to enable easier communication and to facilitate description of local differences in platform evolution

mass movement induced tsunami hazard on perialpine lake lucerne switzerland scenarios and numerical experiments previous studies of the sediments of lake lucerne have shown that massive subaqueous mass movements affecting unconsolidated sediments on lateral slopes are a common process in this lake and in view of historical reports describing damaging waves on the lake it was suggested that tsunamis generated by mass movements represent a considerable natural hazard on the lakeshores newly performed numerical simulations combining two dimensional depth averaged models for mass movement propagation and for tsunami generation propagation and inundation reproduce a number of reported tsunami effects four analysed mass movement scenarios three based on documented slope failures involving volumes of 5 5 to 20 8 106 m3 show peak wave heights of several metres and maximum runup of 6 to 10 m in the directly affected basins while effects in neighbouring basins are less drastic the tsunamis cause large scale inundation over distances of several hundred metres on flat alluvial plains close to the mass movement source areas basins at the ends of the lake experience regular water level oscillations with characteristic periods of several minutes the vulnerability of potentially affected areas has increased dramatically since the times of the damaging historical events recommending a thorough evaluation of the hazard

sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow an experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action wave induced oscillatory flow conditions near the seabed were simulated at full scale 1 1 in a new large oscillating water tunnel two sets of experiments series a and b were carried out during series a bed forms and wave cycle averaged suspended sediment concentrations were measured under sinusoidal waves series b focused on measurement of the wave cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows upper shoreface conditions and was aimed at the verification of quasi steady formulas for the description of cross shore sediment transport bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness only the measured ripple dimensions under asymmetric waves series b showed good agreement with nielsen s 1979 relations for most of the series b experiments the bed was plane sheet flow the net sediment transport was directed onshore and the measured transport rates showed a strong correlation with the velocity moment an empirical quasi steady transport model is proposed which is based on the new tunnel data and other existing data sets the limitations of the quasi steady model approach became clear in the rippled bed regime and through the presence of a consistent influence of the wave period in plane bed conditions in rippled bed conditions the suspended concentration profiles followed a negative exponential distribution for most of the experiments the measured concentration decay length showed a linear relation with the ripple height in plane bed sheet flow conditions the measured suspended concentration profiles followed a negative power function the power or concentration decay parameter was constant 2 1 for a wide range of velocity conditions it is suggested that the mobile bed sheet flow layer has a strong damping effect on the mixing of suspended sediments turbulence damping

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

response of sand ripples to change in oscillatory flow ripples take time to evolve to a new equilibrium state in response to a change in wave generated oscillatory flow the paper presents results from flow tunnel experiments designed to examine oscillatory flow transient ripple processes under controlled full scale laboratory conditions the experiments include study of the growth of ripples from flat bed and the evolution of existing ripples to new equilibrium ripples in response to a step change in the flow in general ripples evolve through a combination of two main processes i from a flat bed or from a bed consisting of ripples that are smaller than the equilibrium ripples through a combination of slide and merge ii from a bed consisting of ripples that are larger than the equilibrium ripples through a combination of split and merge the experimental results show that equilibrium ripple geometry is independent of initial bed morphology while the time to reach equilibrium is largely independent of the initial bed and the equilibrium ripple size the time to reach equilibrium depends strongly on the mobility number and a new empirical equation relating mobility number and the number of flow cycles to equilibrium is proposed this equation is combined with a simple exponential function for ripple height growth or decay to produce a new empirical model for ripple height evolution which gives a reasonably good overall agreement with the measurements the model is based on experiments involving one sediment size only and further work is needed to develop the model for other sand sizes

geometric characteristics of coarse sand ripples generated by oscillatory flows a full scale experimental study abstract the shape of vortex ripples generated by wave boundary layers determines the local hydrodynamics and sediment motions and therefore is critical for understanding coastal sediment transport in the rippled bed regime in this study coarse sand vortex ripples were generated by periodic oscillatory flows mimicking full scale field conditions in an oscillatory water tunnel a laser based bottom profiler was applied for measuring the movable bed s profile the observed ripple development from a flat bed is in agreement with many previous studies small ripple marks appeared within a couple of flow periods and gradually became 3 dimensional 3 d transient ripples which eventually evolved to equilibrium 2 dimensional 2 d ripples after o 100 1000 flow periods the shape of equilibrium 2 d ripple was studied based on a representative ripple profile obtained by ensemble averaging a periodic ripple train the shape of ripples formed under sinusoidal flows become increasingly sinusoidal as the flow becomes stronger larger shields parameter or wave period becomes longer which is possibly because the influence of coherent vortex becomes more significant wave nonlinearities have different effects on the ripple shape generally speaking wave skewness makes ripples onshore leaning while wave asymmetry makes ripples crests sharper and troughs flatter our measurements also revealed some detailed geometric characteristics i e the roundness of ripple crests and the maximum local slope along ripple flanks

sedimentary dynamics along carbonate slopes bahamas archipelago hydroacoustic and sedimentological data in the santaren channel covering both the leeward slope of great bahama bank and the windward slope of cay sal bank allow new insights into carbonate platform slope sedimentation the data document the interplay between depositional and erosive processes on both slopes through time and provide information on the current regime and its influence on the slope sedimentary processes this study emphasizes the diversity and complexity of the slope morphology and the sediment distribution of the youngest high frequency sequence which has developed since the last glacial maximum the processes triggering slope failures and the formation of channels and gullies differ on both slopes at the leeward slope of the great bahama bank extensive slope failures occurred primarily during sea level lowering following an interglacial these slope failures created a slope morphology that channelizes the exported platform sediments during the subsequent highstand at the windward slope of cay sal bank contour currents and the local tectonic regime are responsible for slope failures during sea level lowstands downwelling induces turbidity currents the interaction of turbidity and contour currents leads to the formation of a system of furrows and slope parallel sediment ridges the discovered heterogeneities in slope sedimentation improve the understanding of carbonate slope sedimentation and provide implications for sequence stratigraphic interpretation of carbonate platform slopes

the meaning of stromatolites stromatolites document microbial interactions with sediments and flowing water throughout recorded earth history and have the potential to illuminate the long term history of life and environments modern stromatolites however provide analogs to only a small subset of the structures preserved in archean and proterozoic carbonates thus interpretations of secular trends in the shapes and textures of ancient columnar stromatolites require nonuniformitarian scale dependent models of microbial responses to nutrient availability seawater chemistry influx of sediment grains shear and burial models that integrate stromatolite scales macroscopic organization and shapes could also help test the biogenicity of the oldest stromatolites and other structures whose petrographic fabrics do not preserve direct evidence of microbial activity an improved understanding of stromatolite morphogenesis in the presence of oxygenic and anoxygenic microbial mats may illuminate the diversity of microbial metabolisms tha

a model for the simulation of coupled flow bed form evolution in turbulent flows 1 we develop a three dimensional numerical model to simulate bed form dynamics in a turbulent boundary layer in the numerical model hydrodynamics is solved in a moving generalized boundary fitted curvilinear coordinate system such that the domain boundary exactly follows complex time dependent bed form geometry the resolved turbulent features are computed via large eddy simulation while the subgrid scale turbulent motions are modeled with a dynamic mixed model a second order accurate arbitrary lagrangian eulerian method is used to guarantee conservation of sediment mass while the grid moves arbitrarily due to the motion of the bed transport of suspended load is modeled using the eulerian approach with a pickup function as the bottom boundary condition for sediment entrainment at the bed transport of bed load and suspended load are combined in a mass balance equation for the bed which evolves due to the spatiotemporally varying bed stress induced by the turbulent flow field above the bed and gravity gravity induced avalanche flow motion of the bed in turn affects the flow field in a coupled hydrodynamic moving bed simulation in which bed features evolve due to resolved details of the turbulent flow we compare different bed elevation models and demonstrate the capability of the present model through simulation of sand ripple formation and evolution induced by turbulence in an oscillatory flow a resolution study demonstrates the need for fine grid resolution to resolve a bulk of the near wall turbulence which is essential for bed form initiation

unifying large and small wave generated ripples 1 frequently in field and laboratory studies of wave generated bed forms on beds of sandy sediments both large and small wave generated ripples lwrs and swrs are observed and in some situations may be superimposed upon one another the present paper examines relationships between measured wave conditions and the geometry of lwrs and swrs and shows that existing empirical equations used to predict the dimensions of swrs perform badly for lwrs to address this problem relationships found between ripple geometry and the wave reynolds number are used as the basis for new expressions for prediction of ripple height wavelength and steepness that improve the accuracy of existing approaches for both lwrs and swrs the present results indicate strongly that swrs and lwrs are related and their superposition in certain conditions reflects the time lag between the response of the bed to changing hydrodynamic conditions they must be considered therefore when estimating the total bed roughness in a range of practical engineering and numerical modeling applications

bed forms created by simulated waves and currents in a large flume 1 the morphology and evolution of bed forms created by combinations of waves and currents were investigated using an oscillating plate in a 4 m wide flume current speed ranged from 0 to 30 cm s maximum oscillatory velocity ranged from 20 to 48 cm s oscillation period was 8 s except for one run with 12 s period and the median grain size was 0 27 mm the angle between oscillations and current was 90 60 or 45 at the end of each run the sand bed was photographed and ripple dimensions were measured ripple wavelength was also determined from sonar images collected throughout the runs increasing the ratio of current to wave i e oscillatory velocity decreased ripple height and wavelength in part because of the increased fluid excursion during the wave period increasing the ratio of current to waves or decreasing the angle between current and waves increased the three dimensionality of bed forms during the runs ripple wavelength increased by a factor of about 2 the average number of wave periods for evolution of ripple wavelength to 90 of its final value was 184 for two dimensional ripples starting from a flat bed bed form orientations at the end of each run were compared to four potential controlling factors the directions of waves current maximum instantaneous bed shear stress and maximum gross bed form normal transport mgbnt the directions of waves and of mgbnt were equally good predictors of bed form orientations and were significantly better than the other two factors

genesis of limestone megabreccias and their significance in carbonate sequence stratigraphic models a review a re appraisal of the factors controlling the deposition of carbonate megabreccias and their sequence stratigraphic significance is presented based on an examination of the mechanisms for instigating carbonate seafloor slope instability and a review of the depositional settings of these distinctive rock deposits limestone megabreccias have classically been interpreted as formed by the catastrophic collapse of high angle metastable oversteepened carbonate platform margins however a review of megabreccia occurrence shows that these deposits formed on a broad range of carbonate slope angles and that metastable oversteepened slopes are not necessary for their genesis a re evaluation constructed from first principles of mechanisms promoting submarine gravitational instability indicates that pore water overpressure of confined aquifer horizons beneath the seafloor rather than slope oversteepening is the critical control on megabreccia deposition catastrophic release of overpressure may initiate gravitational instability of previously kinematically stable slopes the relative importance of endogenic processes intrinsically linked to the depositional system and exogenic processes operating independently in generating megabreccias is assessed two particularly important mechanisms in generating megabreccias are endogenic processes causing overpressure at discrete hydrologically confined horizons beneath the seafloor during relative sea level falls and increases in stress as pore fluid drains from the sediment when the platform top becomes subaerially exposed during relative lowstands of sea level the increased likelihood of megabreccia genesis during relative sea level falls is supported by an empirical trend identified from a review of the stratigraphic distribution of documented megabreccias exogenic causes of gravitational instability with inherently random periodicity especially seismicity may account for the small number of documented megabreccias that do not conform to this underlying trend the proposed endogenic pattern favouring megabreccia deposition during relative sea level falls is important in a sequence stratigraphic context megabreccia deposits may build volumetrically significant toe of slope wedges and aprons during relative lowstands of sea level partially compensating for the decrease loss in the supply of fresh granular sediment as the platform top carbonate factory contracts lowstand wedges and aprons in carbonate systems therefore generally differ in composition from equivalent highstand deposits in being composed not of calciturbidite deposits but of megabreccias cannibalized from the upper slope

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

carbonate mounds in the santaren channel bahamas a current dominated periplatform depositional regime abstract new hydroacoustic data high resolution multichannel seismic reflection data ctd casts and sampling document the dominance of bottom currents and the occurrence of carbonate mounds in the santaren channel off great bahama bank and cay sal bank based on these data sets three types of carbonate mounds have been identified in water depths between 285 and 685 m their distribution is strongly related to the present current regime bank driven sediments are caught up by the currents and redeposited mainly in the channel center resulting in the accumulation of giant confined drifts flanked by moats the moats at the banks toe of slope are formed by a southward and northward flowing water mass respectively mainly antarctic intermediate water and subtropical underwater the observed carbonate mounds are concentrated in these moats mound type 1 has an elongated shape parallel to the prevailing bottom current direction a gently inclined flank facing the water flow and a steep flank in its current shadow its upstream flank is covered by a thin sediment wedge whereas the lee side is marked by a parabolic scour type 1 occurs at both bank margins but mainly off great bahama bank consisting of cold water coral rubble floating in a sediment matrix and is thus interpreted as cold water coral mound by contrast type 2 mounds are restricted to the cay sal margin and have a predominately conical outline bottom samples including living sessile crinoids show that its surface must be lithified and colonized by macroepibenthos except corals the mounds are situated in pockmark like depressions that are underlain by fluid escape structures like pipes and chimneys these fluid pathways are generated by a network of fractures mound type 2 is probably formed by abiotic carbonate precipitation however a chemoherm nature cannot be ruled out mound type 3 has a conical to polygonal shape and occurs off cay sal bank and great bahama bank it is surrounded by a scour which is elongated in downcurrent and crescent in upcurrent direction a sediment bulge formed at its front this type is consistent with blocks and boulders colonized by macroepibenthos and related to gravity controlled mass movements at the steep bank slopes principally two habitats can be distinguished the great bahama bank periplatform deep water province dominated by mound type 1 and the cay sal bank slope to basin province occupied by mound type 2 that is associated with pockmark like structures mound type 3 occurs in both habitats physical water mass properties for the existence of cold water corals are limited to a depth range of ca 430 to 685 m with seawater densities of 26 93 to 27 29 kg m and temperatures below 13 c their dominance off great bahama bank might be addressed to a more effective food supply induced by local downwelling

size distribution of submarine landslides and its implication to tsunami hazard in puerto rico 1 we have established for the first time a size frequency distribution for carbonate submarine slope failures using detailed bathymetry along the northern edge of the carbonate platform north of puerto rico we show that the cumulative distribution of slope failure volumes follows a power law distribution the power law exponent of this distribution is similar to those for rock falls on land commensurate with their interpreted failure mode the carbonate volume distribution and its associated volume area relationship are significantly different from those for clay rich debris lobes in the storegga slide norway coupling this relationship with tsunami simulations allows an estimate of the maximum tsunami runup and the maximum number of potentially damaging tsunamis from landslides to the north shore of puerto rico

ripple morphology under oscillatory flow 1 prediction 1 recent laboratory and field experiments have shown the inability of existing oscillatory flow ripple predictors to accurately predict both ripple size and ripple planform geometry however at this time only partial adaptations of these predictors have been proposed to account for the observed discrepancies with new experimental data the present work starts by presenting a comprehensive data set compiled from 27 literature studies and our own experimental data which are presented in a companion paper dimensional analysis is used both to clarify the importance of the different variables involved in the development of ripples and to generate the basic dimensionless framework for the study of ripple morphology under oscillatory flow several ripple size and planform geometry predictors are contrasted against the compiled data set afterward a new ripple wavelength and height predictor and a new planform geometry predictor are proposed which overcome several of the limitations found in the earlier formulations the new predictors emphasize the existence of local and global sediment transport mechanisms over a ripple bed each of them acting at different scales in particular sediment size is found to have an important effect on the size and geometry of bed forms that can be generated by oscillatory flows

sand ripples generated by regular oscillatory flow abstract the prediction of ripple geometry is a necessary precursor to the prediction of sand transport under waves for ripple regime conditions the paper begins with a comparison of four existing methods for predicting the geometry of sand ripples generated by oscillatory flow the comparison points to substantial differences between ripple dimensions predicted by the methods especially for field scale conditions ripple geometry experiments carried out in a large oscillatory flow tunnel are then described the experiments involved a range of sand sizes and sinusoidal and asymmetric flows with periods and velocities typical of field conditions comparison of measured and predicted ripple geometries leads to the recommendation that the method of mogridge davies and willis be used to predict ripple geometry for field scale oscillatory flows the nielsen method yields good predictions of ripple length but the rapid fall off in ripple steepness predicted by the nielsen method at high mobility number is not supported by the measurements the lengths and heights of symmetric ripples produced by sinusoidal flows are found to be similar to the lengths and heights of asymmetric ripples produced by equivalent asymmetric flows three dimensional ripples occur with fine sand in long period flows typical of field conditions the dimensions of these ripples cannot be predicted using methods developed for two dimensional ripples previously suggested criteria for predicting the occurrence of three dimensional ripples fail when tested against a wide range of flow and sand conditions the occurrence of three dimensional ripples and the effects of ripple and flow history on ripple geometry require further research

stratigraphy and structure of southern blake plateau northern florida straits and northern bahama platform from multichannel seismic reflection data approximately 2 100 km of 24 fold multichannel seismic reflection data reveal much about the subsurface geology for a large part of the continental margin east of florida discordance between the westward dipping pre breakup sediments and the eastward sloping basement along the edge of the blake plateau is interpreted as an effect of a splinter of continental margin derived from the african plate by a spreading center jump in the middle jurassic early rifting centered under the main part of the blake plateau became inactive as a spreading center jump shifted the active rift to east of the present blake escarpment along the blake spur magnetic anomaly in the northern florida straits the data reveal that the breakup unconformity underlain by triassic lower jurassic arkosic volcaniclastics extends from southern florida to the western bahama banks these volcaniclastics are associated with the rift crust of intermediate nature formed just prior to and during breakup of the north american and african continental plates back reef platform deposits of limestones dolomites and evaporites of late jurassic to albian age extend from the blake bahama escarpment westward beneath florida these deposits formed what once was a megabank extending over a wider area than the present smaller isolated bahama banks the formation of the florida straits and bahama channels occurred during the cenomanian transgression only on the present bahama banks and florida platform did shallow water carbonate deposition persist to maintain a shallow bank environment evidence of recurring scour by current erosion is found in the florida straits erosional events apparently occurred in the middle cenomanian middle paleocene early middle eocene and eocene oligocene which coincidentally are times of lower eustatic sea level according to vail et al 1977a this evidence of florida current scour indicates that the current was present as far back as the cenomanian major faulting appears to have dropped the northeast providence channel relative to the western bahamas after the albian submarine erosion and bank buildup created the channels and smaller relief features like great abaco knoll beginning in about the cenomanian a carbonate bank margin and reef complex was present along the bahama escarpment since the middle jurassic apparently these organic buildups seeded on originally shallow structural relief on oceanic basement created during the spreading center jump to the position of the blake spur magnetic anomaly the bank margin apparently has retreated at least 15 km from a late jurassic earliest cretaceous position now marked by a bench below the au unconformity active faulting occurred along the great abaco fracture zone at least through the late cretaceous and perhaps into the tertiary these relatively young tectonic events together with the post albian faults in providence channel indicate interactions between the atlantic and caribbean plates and that extensions of faulting have taken place far to the northeast of cuba and the greater antilles

spatial variability of the wave bottom boundary layer over movable rippled beds observations of the spatially dependent velocity field over movable bed forms subjected to slightly skewed and asymmetric regular wave forcing were collected the dynamics between the ripple elements is dominated by coherent vortices characterized by the swirling strength and evidenced in the temporal and spectral characterization within the boundary layer spectral energy in the second harmonic 3f0 is amplified at the ripple slopes and is consistent with the location of the expected strongest pressure gradients first moment and second moment velocity statistics were used to address the spatial variability of the intra ripple hydrodynamics estimates of displacement and momentum thicknesses and mom are smaller than suggested by the higher harmonics but consistently highlight areas of adverse and favorable pressure gradients shear stress and roughness estimates were inferred by fitting a logarithmic model to first moment and second moment statistics of the velocity field the maximum shields parameter was observed to peak at the stoss slope of asymmetric ripples during the strongest and shorter half wave period onshore first moment roughness estimates are similar in magnitude to bed load parameterizations provided by li et al 1997 and about a factor of 3 larger than second moment estimates assessment of the vertical transfer of horizontal momentum derived using a reynolds decomposition suggests that stresses inferred from the logarithmic law using first moment velocity statistics appropriately reproduce the mean momentum transfer for the longer and weaker offshore half wave period

long term event stratigraphy of the apulia platform margin upper jurassic to eocene gargano southern italy abstract the upper jurassic to eocene apulia platform margin and the eastward transition to the adjacent basinal deposits are well exposed in the gargano promontory southern italy a carbonate block that is part of the slightly deformed foreland of the southern apennine thrust belt the long term stratigraphy of this margin and slope transect is punctuated by five major dynamic phenomena that subdivide the succession into six second order sequences these events include 1 a valanginian drowning unconformity 2 an early aptian albian drowning and demise of the platform 3 late albian cenomanian platform margin failures 4 a santonian campanian retreat of the platform margin and 5 eocene uplift and platform margin collapse the first event is documented worldwide and is probably eustatic in origin the second is concomitant with some oceanic anoxic events oae the last three processes are probably related to foreland reaction to subduction and collision in the dinarides and hellenides thrust belts the ultimate cause of the albian cenomanian failures is more problematic a worldwide eustatic regression is documented at this time but regional geology seems to favor tectonic uplift

a possible bridge between adria and africa new palaeobiogeographic and stratigraphic constraints on the mesozoic palaeogeography of the central mediterranean area abstract dinosaur records in central and southern italy testify to the occurrence of a diverse dinosaur fauna on the apennine and apulian carbonate platforms at least from the tithonian to the santonian most of the palaeogeographic reconstructions show these domains as topographically isolated areas separated by deep pelagic basins and far from emerged continental areas thus they hardly justify the long lasting occurrence of these terrestrial vertebrates recent studies on the mesozoic panormide carbonate platform western sicily yielded important stratigraphical and palaeontological data which provide evidence for a convincing explanation of this unresolved problem the recent discovery of a theropod bone in mid cretaceous peritidal levels of the panormide platform as well as the anomalous subsidence of this palaeogeographic domain strongly support the existence of a crustal sector filtering bridge which connected africa to adria