impact cratering in sandstone the memin pilot study on the effect of pore water abstract planetary surfaces are subjected to meteorite bombardment and crater formation rocks forming these surfaces are often porous and contain fluids to understand the role of both parameters on impact cratering we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter sized steel spheres we utilized a 40 m two stage light gas gun to achieve impact velocities of up to 5 4 km s 1 cratering efficiency ejection velocities and spall volume are enhanced if the pore space of the sandstone is filled with water in addition the crater morphologies differ substantially from wet to dry targets i e craters in wet targets are larger but shallower we report on the effects of pore water on the excavation flow field and the degree of target damage we suggest that vaporization of water upon pressure release significantly contributes to the impact process

on the formation and propagation of nonlinear internal boluses across a shelf break high resolution two and three dimensional numerical simulations are performed of first mode internal gravity waves interacting with a shelf break in a linearly stratified fluid the interaction of nonlinear incident waves with the shelf break results in the formation of upslope surging vortex cores of dense fluid referred to here as internal boluses that propagate onto the shelf this paper primarily focuses on understanding the dynamics of the interaction process with particular emphasis on the formation structure and propagation of internal boluses onshelf a possible mechanism is identified for the excitation of vortex cores that are lifted over the shelf break from where from the simplest viewpoint they essentially propagate as gravity currents into a linearly stratified ambient fluid

nearshore internal bores and turbulent mixing in southern monterey bay 1 we observed transient stratification and mixing events associated with nearshore internal bores in southern monterey bay using an array of instruments with high spatial and temporal resolution the arrival of the bores is characterized by surging masses of dense cold water that tend to stratify the water column the bore is followed by a gradual drop in the temperature throughout the water column over several hours defined here as the bore period until a sharp warm front relaxation followed by high frequency temperature fluctuations returns the column back to nearly its original state defined here as the mixing period mixing periods revealed increased temperature variance at high frequencies n as well as a greater percentage of events where dynamic instabilities may be present ri 0 25 suggesting active mixing of the stratified water column turbulent dissipation rates in the stratified interior during the mixing period estimated using the technique of isopycnal slope spectra revealed mean values the same order of magnitude as near bed bottom generated turbulence observations indicate that local shear produced turbulent kinetic energy by the warm front relaxations dominates mixing in the stratified interior the non canonical nature of these bore and relaxation events is also investigated with a numerical model and the dynamics are shown to depend on the internal iribarren number our results suggest that nearshore internal bores interacting with local bathymetry dramatically alter local dynamics and mixing in the nearshore with important ecological implications

chemical modification of projectile residues and target material in a memin cratering experiment in the context of the memin project a hypervelocity cratering experiment has been performed using a sphere of the iron meteorite campo del cielo as projectile accelerated to 4 56 km s 1 and a block of seeberger sandstone as target material the ejecta collected in a newly designed catcher are represented by 1 weakly deformed 2 highly deformed and 3 highly shocked material the latter shows shock metamorphic features such as planar deformation features pdf in quartz formation of diaplectic quartz glass partial melting of the sandstone and partially molten projectile mixed mechanically and chemically with target melt during mixing of projectile and target melts the fe of the projectile is preferentially partitioned into target melt to a greater degree than ni and co yielding a fe ni that is generally higher than fe ni in the projectile this fractionation results from the differing siderophile properties specifically from differences in reactivity of fe ni and co with oxygen during projectile target interaction projectile matter was also detected in shocked quartz grains the average fe ni of quartz with pdf about 20 and of silica glasses about 24 are in contrast to the average sandstone ratio about 422 but resembles the fe ni ratio of the projectile about 14 we briefly discuss possible reasons of projectile melting and vaporization in the experiment in which the calculated maximum shock pressure does not exceed 55 gpa

observations of the internal tide in monterey canyon abstract data from two shipboard experiments in 1994 designed to observe the semidiurnal internal tide in monterey canyon reveal semidiurnal currents of about 20 cm s 1 which is an order of magnitude larger than the estimated barotropic tidal currents the kinetic and potential energy evidenced by isopycnal displacements of about 50 m was greatest along paths following the characteristics calculated from linear theory these energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of monterey bay energy propagated shoreward during the april experiment itex1 whereas a standing wave that is an internal seiche was observed in october itex2 the difference is attributed to changes in stratification between the two experiments higher energy levels were present during itex1 which took place near the spring phase of the fortnightly 14 8 days cycle in sea level while itex2 occurred close to the neap phase further evide

searching for distal ejecta on the craton the sedimentary effects of meteorite impact abstractdistal ejecta from meteorite impacts are rare and hard to spot in the field because of their thinness 5 mm diameter sediments and produce high flow regime bedforms megaripples dunes upper plane beds and possi

interaction between an inclined gravity current and a pycnocline in a two layer stratification a series of laboratory experiments were conducted to investigate the characteristics of a dense gravity current flowing down an inclined slope into a quiescent two layer stratification the presence of the pycnocline causes the gravity current to split and intrude into the ambient at two distinct levels of neutral buoyancy as opposed to the classical description of gravity currents in stratified media as being either a pure underflow or interflow the splitting behaviour is observed to be dependent on the richardson number ri unicode stix x1d70c of the gravity current formulated as the ratio of the excess density and the ambient stratification for low ri unicode stix x1d70c underflow is more dominant while at higher ri unicode stix x1d70c interflow is more dominant as ri unicode stix x1d70c increases however we find that the splitting behaviour eventually becomes independent of ri unicode stix x1d70c additionally we have also identified two different types of waves that form on the pycnocline in response to the intrusion of the gravity current an underflow dominated regime causes a pycnocline displacement where the speed of the wave crest is locked to the gravity current whereas an interflow dominated regime launches an internal wave that moves much faster than the gravity current head or interfacial intrusion

ejecta from impact craters an important feature of impacts into solar system bodies is the fate of crater ejecta the near surface material launched during the highly dynamic crater formation process laboratory measurements of impact crater ejecta from 18 studies are summarized the data are examined and used to assess our understanding of how the ejecta velocity and mass distributions depend on the conditions of an impact event the effects of impact speed on the ejecta are reasonably well understood but the dependences on target properties such as strength and porosity are only poorly constrained a point source scaling model for the ejecta mass and velocity distributions is developed and fit to the data for several classes of materials distinguished by porosity

geochemical processes between steel projectiles and silica rich targets in hypervelocity impact experiments abstract the possibility of fractionation processes between projectile and target matter is critical with regard to the classification of the impactor type from geochemical analysis of impactites from natural craters here we present results of five hypervelocity memin impact experiments poelchau et al 2013 using the cr v co mo w rich steel d290 1 as projectile and two different silica rich lithologies seeberger sandstone and taunus quartzite as target materials our study is focused on geochemical target projectile interaction occurring in highly shocked and projectile rich ejecta fragments in all of the investigated impact experiments whether sandstone or quartzite targets the ejecta fragments show i shock metamorphic features e g planar deformation features pdf and the formation of silica glasses ii partially melting of projectile and target and iii significant mechanical and chemical mixing of the target rock with projectile material the silica rich target melts are strongly enriched in the projectile tracer elements cr v and fe but have just minor enrichments of co w and mo inter element ratios of these tracer elements within the contaminated target melts differ strongly from the original ratios in the steel the fractionation results from differences in the reactivity of the respective elements with oxygen during interaction of the metal melt with silicate melt our results indicate that the principles of projectile target interaction and associated fractionation do not depend on impact energies at least for the selected experimental conditions and water saturation of the target partitioning of projectile tracer elements into the silicate target melt is much more enhanced in experiments with a non porous quartzite target compared with the porous sandstone target this is mainly the result of higher impact pressures consequently higher temperatures and longer reaction times at high temperatures in the experiments with quartzite as target material

early stage ejecta velocity distribution for vertical hypervelocity impacts into sand the ejecta dynamics during main stage excavation flow in a cratering event have previously been well characterized particularly for vertical impacts in this experimental study we present new results addressing the early time low angle high speed component of the ejecta velocity distribution as a function of time for hypervelocity vertical impacts into sand although this regime represents a very small portion of total ejected mass in laboratory experiments it comprises a greater percentage of growth for larger craters

the modification of bottom boundary layer turbulence and mixing by internal waves shoaling on a barrier reef abstractresults are presented from an observational study of stratified turbulent flow in the bottom boundary layer on the outer southeast florida shelf measurements of momentum and heat fluxes were made using an array of acoustic doppler velocimeters and fast response temperature sensors in the bottom 3 m over a rough reef slope direct estimates of flux richardson number rf confirm previous laboratory numerical and observational work which find mixing efficiency not to be a constant but rather to vary with frt reb and rig these results depart from previous observations in that the highest levels of mixing efficiency occur for frt 1 suggesting that efficient mixing can also happen in regions of buoyancy controlled turbulence generally the authors find that turbulence in the reef bottom boundary layer is highly variable in time and modified by near bed flow shear and stratification driven by shoaling internal waves

impact crater formation in icy layered terrains on mars we present numerical simulations of crater formation under martian conditions with a single near surface icy layer to investigate changes in crater morphology between glacial and interglacial periods the ice fraction thickness and depth to the icy layer are varied to understand the systematic effects on observable crater features to accurately model impact cratering into ice a new equation of state table and strength model parameters for h2o are fitted to laboratory data the presence of an icy layer significantly modifies the cratering mechanics observable features demonstrated by the modeling include variations in crater morphometry depth and rim height and icy infill of the crater floor during the late stages of crater formation in addition an icy layer modifies the velocities angles and volumes of ejecta leading to deviations of ejecta blanket thickness from the predicted power law the dramatic changes in crater excavation are a result of both the shock impedance and the strength mismatch between layers of icy and rocky materials our simulations suggest that many of the unusual features of martian craters may be explained by the presence of icy layers including shallow craters with well preserved ejecta blankets icy flow related features some layered ejecta structures and crater lakes therefore the cratering record implies that near surface icy layers are widespread on mars

observation of very large and steep internal waves of elevation near the massachusetts coast 1 we report on near bottom waves of elevation with amplitude nearly half the 25 m water column very steep and propagating into a sheared turbulent wave guide the waves contained trapped cores transporting parcels of water shoreward these large waves depart strongly from weakly nonlinear and weakly nonhydrostatic conditions and challenge established paradigms they can also represent an important factor in the across shore transport of plankton and contaminants

scale dependent dispersion within the stratified interior on the shelf of northern monterey bay abstractautonomous underwater vehicle measurements are used to quantify lateral dispersion of a continuously released rhodamine wt dye plume within the stratified interior of shelf waters in northern monterey bay california the along shelf evolution of the plume s cross shelf lateral width provides evidence for scale dependent dispersion following the 4 3 law as previously observed in both surface and bottom layers the lateral dispersion coefficient is observed to grow to 0 5 m2 s 1 at a distance of 700 m downstream of the dye source the role of shear and associated intermittent turbulent mixing within the stratified interior is investigated as a driving mechanism for lateral dispersion using measurements of time varying temperature and horizontal velocities both an analytical shear flow dispersion model and a particle tracking model generate estimates of the lateral dispersion that agree with the field measured 4 3 law of dispersion without explicit appeal to any assumed turbulence structure

northern monterey bay upwelling shadow front observations of a coastally and surface trapped buoyant plume 1 during the upwelling season in central california northwesterly winds along the coast produce a strong upwelling jet that originates at point ano nuevo and flows southward across the mouth of monterey bay a convergent front with a mean temperature change of 3 77 0 29c develops between the warm interior waters and the cold offshore upwelling jet to examine the forcing mechanisms driving the location and movement of the upwelling shadow front and its effects on biological communities in northern monterey bay oceanographic conditions were monitored using cross shelf mooring arrays drifters and hydrographic surveys along a 20 km stretch of coast extending northwestward from santa cruz california during the upwelling season of 2007 may september the alongshore location of the upwelling shadow front at the northern edge of the bay was driven by regional wind forcing through an alongshore pressure gradient buoyancy forces due to the temperature change across the front and local wind forcing the diurnal sea breeze the upwelling shadow front behaved as a surface trapped buoyant current which is superimposed on a poleward barotropic current moving up and down the coast up to several kilometers each day we surmise that the front is advected poleward by a preexisting northward barotropic current of 0 10 m s 1 that arises due to an alongshore pressure gradient caused by focused upwelling at point ano nuevo the frontal circulation onshore surface currents breaks the typical two dimensional wind driven cross shelf circulation offshore surface currents and introduces another way for water and the material it contains e g pollutants larvae to go across the shelf toward shore

scaling and reproducibility of craters produced at the experimental projectile impact chamber epic centro de astrobiologia spain the experimental projectile impact chamber epic is a specially designed facility for the study of processes related to wet target e g marine impacts it consists of a 7 m wide funnel shaped test bed and a 20 5 mm caliber compressed n2 gas gun the target can be unconsolidated or liquid the gas gun can launch 20 mm projectiles of various solid materials under ambient atmospheric pressure and at various angles from the horizontal to test the functionality and quality of obtained results by epic impacts were performed into dry beach sand targets with two different projectile materials ceramic al2o3 max velocity 290 m s 1 and delrin max velocity 410 m s 1 23 shots used a quarter space setting 19 normal 4 at 53 from horizontal and 14 were in a half space setting 13 normal 1 at 53 the experiments were compared with numerical simulations using the isale code differences were seen between the nondisruptive al2o3 ceramic and the disruptive delrin polymer projectiles in transient crater development all final crater dimensions when plotted in scaled form agree reasonably well with the results of other studies of impacts into granular materials we also successfully validated numerical models of vertical and oblique impacts in sand against the experimental results as well as demonstrated that the epic quarter space experiments are a reasonable approximation for half space experiments altogether the combined evaluation of experiments and numerical simulations support the usefulness of the epic in impact cratering studies

ejecta from experimental impact craters particle size distribution and fragmentation energy abstract the particle size distribution psd of impact crater ejecta is an important parameter that is useful for understanding the formation of natural craters the distribution of space debris the influence of impact events on climate and energy partitioning in impact events 11 impact experiments into dry and water saturated sandstone were performed and analyzed the experiments span a range of impact velocities from 2 5 to 5 3 km s 1 using projectile sizes from 2 5 to 12 mm kinetic impact energies between 874 and 80 338 j were achieved ejecta of these experiments was collected and the psd was measured and quantified with power law fits the resulting power law exponents lie between 2 54 and 2 74 our results do not show an influence of impact energy or impact velocity on the psd of impact ejecta a significant increase in the psd values was found from dry to water saturated sandstone targets we suggest that water saturation of the target has multiple effects on ejecta fragmentation a comparison of our experimental data with data from the literature shows no correlation between the target material lithology and the ejecta psd interestingly literature data for disruption experiments revealed a strong influence imparted energy density on the d values psd values were used to calculate the energy spent for target fragmentation and show that the fraction of impact energy used for comminution is in the lower single digit percentage

circulation and larval distribution in internal tidal bore warm fronts internal tidal bore warm fronts were observed during the summer of 1996 off the coast of southern california warm bore fronts had concentrating currents resulting from high frequency internal motions and from a larger two way flow the two way flow featured surface currents onshore and bottom currents offshore a sharp thermocline depression and high frequency large amplitude internal motions followed the leading edge of the bore with downwelling currents on the trailing side of the crest of the nonlinear internal waves and upwelling currents in front of the crest warm bores propagated onshore with a propagation speed c that ranged from 10 6 to 19 6 cm s 1 while time averaged frontal currents varied from 11 2 to 17 6 cm s 1 in the shallowest bin in one out of three cases c which implied that there were faster currents than the rate of advance of the front and which implied that the origin of surface frontal material is behind the front not in front of it three invertebrate larval taxa were found at all sites across fronts but only two intertidal barnacles pollicipes polymerus and chthamalus spp were concentrated at the front s surface while the subtidal bryozoan membranipora spp was not frontal pollicipes were more concentrated than were chthamalus the frontal downwelling currents observed suggested that concentrated larvae would have to swim upward in order to maintain depth pollicipes were abundant on the offshore warm side of the fronts but were absent or rare on the onshore colder side suggesting that the origin of frontal pollicipes was behind the front although an alternative cannot be ruled out conclusively chthamalus were more abundant at depth than at the surface at all sites except at the front where this pattern was reversed the origin of frontal chthamalus is uncertain membranipora were more abundant on the onshore colder side of the fronts and abundances were usually higher at depth than at surface lack of accumulation in this species may be due to its limited swimming capability

application of nondestructive testing methods to study the damage zone underneath impact craters of memin laboratory experiments within the framework of the multidisciplinary experimental and modeling impact research network memin research group the damage zones underneath two experimentally produced impact craters in sandstone targets were investigated using several nondestructive testing ndt methods the 20 20 20 cm sandstones were impacted by steel projectiles with a radius of 1 25 mm at approximately 5 km s 1 resulting in craters with approximately 6 cm diameter and approximately 1 cm depth ultrasound us tomography and vibrational analysis were applied before and after the impact experiments to characterize the damage zone and micro computer tomography l ct measurements were performed to visualize subsurface fractures the newly obtained experimental data can help to quantify the extent of the damage zone which extends to about 8 cm depth in the target the impacted sandstone shows a local p wave reduction of 18 below the crater floor and a general reduction in elastic moduli by between approximately 9 and approximately 18 depending on the type of elastic modulus the results contribute to a better empirical and theoretical understanding of hypervelocity events and simulations of cratering processes

the tattered curtain hypothesis revised coastal jets limit cross shelf larval transport exchange and retention of coastal waters modulate dispersal of marine larvae affecting marine ecosystem dynamics a hypothesis was put forward in the 1980s describing the coastal upwelling front as a tattered curtain that retains larvae this front was envisioned to be broken up by squirts and eddies hitting the coast under upwelling relaxation events here we revise this hypothesis by using an idealized ocean model of an eastern boundary upwelling current and an idealized particle larvae model appropriate for shelf spawning benthic species modeled larval settlement patterns were controlled by retention in the core of the upwelling jet bounded by regions of high velocity shear on the flanks of the jet squirts filaments poleward moving eddies and meanders modulated settlement patterns locally while dense packets moved equatorward within the upwelling jet correlation between settlement i e particles 20 40 d old 10 km from shore and wind was low for a lagged wind product r 0 33 and moderate for a 20 d integrated wind product r 0 62 we determined that it is not upwelling relaxation but sustained moderate upwelling that can result in a highly retentive jet that entrains larvae and acts as a barrier to cross shelf transport however the amount of retention is highly variable settlement was low after strong persistent upwelling completely tattered the jet jet cores in general should act as important retentive transport barriers across diverse coastal systems a view supported by dynamical theory modeling studies and larval recruitment observations

observations of polarity reversal in shoaling nonlinear internal waves observations off the new jersey coast document the shoaling of three groups of nonlinear internal waves of depression over 35 km across the shelf each wave group experienced changing background conditions along its shoreward transit despite different wave environments a clear pattern emerges nearly symmetric waves propagating into shallow water develop an asymmetric shape in the wave reference frame the leading edge accelerates causing the front face to broaden while the trailing face remains steep this trend continues until the front edge and face of the leading depression wave become unidentifiable and a near bottom elevation wave emerges formed from the trailing face of the initial depression wave and the leading face of the following wave the transition from depression to elevation waves is diagnosed by the integrated wave vorticity which changes sign as the wave s polarity changes sign this transition is predicted by the sign change of the coefficient of the nonlinear term in the kdv equation when evaluated using observed profiles of stratification and velocity

experimental ejection angles for oblique impacts implications for the subsurface flow field a simple analytical solution for subsurface particle motions during impact cratering is useful for tracking the evolution of the transient crater shape at late times a specific example of such an analytical solution is maxwells z model which is based on a point source assumption here the parameters for this model are constrained using measured ejection angles from both vertical and oblique experimental impacts at the nasa ames vertical gun range data from experiments reveal that impacts at angles as high as 45 to the targets surface generate subsurface flow fields that are significantly different from those created by vertical impacts the initial momentum of the projectile induces a subsurface momentum driven flow field that evolves in three dimensions of space and in time to an excavation flow field during both vertical and oblique impacts a single stationary pointsource model specifically maxwells z model however is found inadequate to explain this detailed evolution of the subsurface flow field during oblique impacts because 45 is the most likely impact angle on planetary surfaces a new analytical model based on a migrating point source could prove quite useful such a model must address the effects of the subsurface flow field evolution on crater excavation ejecta deposition and transient crater morphometry

hypervelocity impacts on dry and wet sandstone observations of ejecta dynamics and crater growth this study deals with the investigation of highly dynamic processes associated with hypervelocity impacts on porous sandstone for the impact experiments two light gas accelerators with different calibers were used capable of accelerating steel projectiles with diameters ranging from 2 5 to 12 mm to several kilometers per second the projectiles impacted on dry and water saturated seeberger sandstone targets the study includes investigations of the influence of pore water on the shape of the ejecta cloud as well as transient crater growth the results show a significant influence of pore water on ejecta behavior steeper ejecta cone angles are observed if the impacts are conducted on wet sandstones the transient crater grows at a faster rate and reaches a larger diameter if the target is water saturated in our experiments target porosity leads to smaller crater sizes compared with nonporous targets water within the pore space reduces porosity and counteracts this process power law fits were applied to the crater growth curves the results show an increase in the scaling exponent with increasing pore space saturation

observations of nonlinear internal waves on the outer new england continental shelf during the summer shelfbreak primer study observations are presented of nonlinear internal waves on the outer new england continental shelf during the summer shelfbreak primer study conducted between july 26 and august 5 1996 current and temperature measurements were made with an upward looking acoustic doppler current profiler adcp located on the 147 m isobath near the shelfbreak and three vertical thermistor moorings located upshelf data from the adcp and two nearby thermistor chains show energetic internal tides propagating at roughly 0 9 m s 21 to the north northwest nearly perpendicular to the local topography with 10 15 cm s 21 horizontal currents and 15 30 m vertical displacements these waves evolve rapidly within a 5 8 km range into an undular internal tidal bore cross isobath barotropic tidal currents responsible for generating the internal tides are in the 5 12 cm s 21 range the bore formation is highly variable there is evidence of a correlation between internal tide steepening and a shelfbreak front jet orientation that is oppositely directed to the internal tide propagation there is no correlation between steepening and the jet s vertical shear statistics of the undular bores show rms travel time fluctuations from 0 8 to 1 7 hours and average tidal bore durations from 12 to 9 hours the average undular bore speed is 0 9 m s 21 with an rms fluctuation of 0 4 m s 21 the number of high frequency waves in the bore varies from 0 to 8 near the shelfbreak and increases to 30 waves 26 7 km upshelf the observed distribution function of temporal spacing between high frequency internal waves is spread between 4 and 20 min

facies sequences of the middle upper jurassic carbonate platform amran group in the sana a region republic of yemen rocks of the amran group in the sana a region of yemen disconformably overlie the kohlan formation and unconformably underlie the tawilah group sea level rises have produced landward migration of facies belts and the development of deeper water facies over shallow ones the geometry of the depositional environments identified has enabled the passage of relatively short lived transgressive regressive cycles of sedimentation to be recognized three facies associations are introduced 1 carbonate platform facies 2 carbonate marl alternation facies and 3 shallow water coral and stromatoporoid build up facies these facies are widely distributed and the whole sequence reflects deposition on a broad platform upon which shoals separated platform carbonates from basin sedimentation and an open marine environment the repetition and interfingering of both fining and shallowing upward cycles within the study areas suggest that deposition occurred within the same basin with slightly different conditions in different places the main factors controlling their deposition are sea level changes and tectonics

sequence stratigraphy of a tidally dominated carbonate siliciclastic ramp the tithonian early berriasian of the southern neuquen basin argentina the tithonian berriasian vaca muerta carrin cura and picun leufu formations in the southern neuquen basin were deposited on a tidally dominated mixed carbonate siliciclastic ramp basinal outer middle shallow and back ramp facies associations are recognized and a sequence stratigraphic analysis reveals that the ramp record consists of three shallowing upwards sequences ti1 ti2 and ti3 set within a lower order progradational cycle a higher order of cyclicity is superimposed on to the middle ti2 sequence the majority of the ramp facies belong to the transgressive and highstand systems tracts however at the base of ti2 a lowstand systems tract is identified characterized by a basal unconformity and an abrupt basinward shift of the shallow marine lithofacies transgressive systems tracts were characterized by slow sedimentation rates and rapid sea level rises that affected carbonate productivity highstand systems tracts show the greatest carbonate productivity and an increased progradation rate on account of a reduction in accommodation space generation palaeogeography played a major role in the development of the depositional systems partial isolation from the pacific ocean reflecting the growth of the andean magmatic arc and geographic restriction due to tectonic inversion in the central part of the basin resulted in a meso macrotidal regime that produced a tidally dominated sedimentary record in the shallow and back ramp environments coeval anoxic conditions in the central part of the neuquen basin favoured distal ramp and basinal black shale deposition during episodes of relative sea level rise

bathymetry and paleoecology of silurian bethic assemblages late llandoverian new york state late llandoverian marine shales in new york state are highly fossiliferous and provide and opportunity to examine gradients of biofacies the williamson and willowvale formations llandoverian c6 were deposited during a major transgressive episodes in and adjacent to the axis of a narrow ne sw trending central appalachian foreland basin the williamson shale is a black to dark green graptolite bearing unit of the upper clinton group of western new york state it grades eastward into gray fossiliferous shales and coquinoidlimestones of the willowvale formation orientation analysis of graptolites monograptus clintonensis indicates paleoccurents dominantly from the northeast to east the presence of rippled cross laminated sandstone beds tempestites within dark gray graptolitic facies of the lower williamson indicates that the darl shale facies was deposited in dysaerobic to marginally aerobic water slightly below storm wave base poorly fossiliferous green shales higher in the willimason appear to slow deposition in dysaerobic water and suggest a gradual deepening graded brachipod coquinoid limestones interpreted as storm layers occur near the middle and top of the williamson and in the willovale shale and indicate deposition of these sediments above maximum storm wave base the faunas of the williamson and willowvale shales are subdivisible into five vertically and laterally adjacent associations as follows a ichnofossil chondrites b monograptid chonetes cornutus c eopletodonta atrypta d palaeocyclus bryozoan and e eocoelia chonetes cornutus associations this spectrum of fossil associations appears to parallel the increasing frequency of bottom disturbance by waves and currents from deeper basinal areas to higher energy outer and low energy inner shallow shelf settings the fossil associations of the williamson a c probably belong to the deeper benthic assemblages 4 5 but developed in environments within to slightly below storm wave base about 50 80 m deep the willowvale fauna c d representing benthic assemblages 3 4 inhabited somewhat shallower better oxygenated environments of the photic zone probably at depths of approximately 20 50 m the easternmost to slightly southeastward equivalent of williamson willowvale fauna e evidently represents shallow water benthic assemblage 2 these conclusions indicate the need for a critical reevaluation of the bathymetric relations of benthic assemblages 3 5 a new interpretations of approximate depths for this range is presented herein

the memin research unit scaling impact cratering experiments in porous sandstones the memin research unit multidisciplinary experimental and modeling impact research network is focused on analyzing experimental impact craters and experimental cratering processes in geological materials memin is interested in understanding how porosity and pore space saturation influence the cratering process here we present results of a series of impact experiments into porous wet and dry sandstone targets steel iron meteorite and aluminum projectiles ranging in size from 2 5 to 12 mm were accelerated to velocities of 2 5 7 8 km s 1 yielding craters with diameters between 3 9 and 40 cm results show that the target s porosity reduces crater volumes and cratering efficiency relative to nonporous rocks saturation of pore space with water to 50 and 90 increasingly counteracts the effects of porosity leading to larger but flatter craters spallation becomes more dominant in larger scale experiments and leads to an increase in cratering efficiency with increasing projectile size for constant impact velocities the volume of spalled material is estimated using parabolic fits to the crater morphology yielding approximations of the transient crater volume for impacts at the same velocity these transient craters show a constant cratering efficiency that is not affected by projectile size

laboratory impacts into dry and wet sandstone with and without an overlying water layer implications for scaling laws and projectile survivability scaling laws describing crater dimensions are defined in terms of projectile velocity and mass densities of the materials involved strength of the target and the local gravity here the additional importance of target porosity and saturation and an overlying water layer are considered through 15 laboratory impacts of 1 mm diameter stainless steel projectiles at 5 km s 1 into a an initially uncharacterized sandstone porosity 17 and b coconino sandstone porosity 23 the higher porosity dry sandstone allows a crater to form with a larger diameter but smaller depth than in the lower porosity dry sandstone furthermore for both porosities a greater volume of material is excavated from a wet target than a dry target by 27 30 comparison of our results with pi scaling dimensionless ratios of key parameters characterizing cratering data over a range of scales suggests that porosity is important for scaling laws given that the new data lie significantly beneath the current fit for ice and rock targets on a v versus 3 plot v gives cratering efficiency and 3 the influence of target strength an overlying water layer results in a reduction of crater dimensions with larger craters produced in the saturated targets compared to unsaturated targets a water depth of approximately 12 times the projectile diameter is required before craters are no longer observed in the targets previous experimental studies have shown that this ratio varies between 10 and 20 gault and sonett 1982 in our experiments 25 of the original projectile mass survives the impact

sedimentology facies and depositional environments of the rochester shale silurian wenlockian in western new york and ontario abstract in western new york and ontario the rochester shale silurian wenlockian clinton group is everywhere divisible into lower lewiston and upper burleigh hill stoney creek members thin units within these members are traceable east to west for distances exceeding 100 km without substantial change in lithology or fossil content in contrast abrupt lateral facies changes occur within the rochester shale along short north south sections for example niagara gorge such stratigraphic evidence suggests that rochester shale facies belts are elongate east west parallel both to a northern paleoshoreline and also to the present outcrop trend the rochester shale consists of sparsely to richly fossiliferous gray shaley mudstone with abundant interbedded carbonates including intrasparrudites lenticular biosparites and biomicrites calcarenites and laminated pelmicrites calcisiltites such interbeds provide evidence for episodic concentration and transport of carbonate sediments by storm wave action on a gently southwards sloping shelf calcarenite lenses were formed as erosion lag deposits in regions within storm wave base finer debris winnowed from such areas formed suspension clouds which flowed downslope depositing storm silt calcisiltite and mud layers a crinoidal bank facies wiarton accumulated in the area of the algonquin arch during rochester deposition adjacent shelf areas to the south received a mixture of terrigenous muds from southeastern source areas taconics and detrital carbonate sediments from the wiarton shoal forming argillaceous carbonates and or calcareous shales stoney creek upper burleigh hill during times of low sedimentation this area became the site of abundant bryozoan growth bryozoan belt lewiston b d and e farther southward basinward facies comprise a mixture of sparsely fossiliferous mudstones and storm silt layers lewiston c lower burleigh hill vertical facies changes in the rochester shale are attributed to north south shifting of environmental belts due to migration of the northern paleoshoreline as a whole the formation comprises two eustatic trangressive regressive cycles the lewiston member represents a nearly symmetrical cycle of deepening units a c and shallowing units c e while the upper units burleigh hill stoney creek reflect aspects of an asymmetrical shallowing upward hemicycle during the last event allodapic carbonate sedimentation was considerably increased as a result of migrating crinoidal bars inhibiting the growth of bryozoans and other organisms the rochester shale provides a paradigm for interpreting numerous marine units in western new york which exhibit layer cake arrays of facies

local diurnal wind driven variability and upwelling in a small coastal embayment the oceanic response to high frequency local diurnal wind forcing is examined in a small coastal embayment located along an understudied stretch of the central california coast we show that local diurnal wind forcing is the dominant control on nearshore temperature variability and circulation patterns a complex empirical orthogonal function ceof analysis of velocities in san luis obispo bay reveals that the first mode ceof amplitude time series which accounts for 47 9 of the variance is significantly coherent with the local wind signal at the diurnal frequency and aligns with periods of weak and strong wind forcing the diurnal evolution of the hydrographic structure and circulation in the bay is examined using both individual events and composite day averages during the late afternoon the local wind strengthens and results in a sheared flow with near surface warm waters directed out of the bay and a compensating flow of colder waters into the bay over the bottom portion of the water column this cold water intrusion into the bay causes isotherms to shoal toward the surface and delivers subthermocline waters to shallow reaches of the bay representing a mechanism for small scale upwelling when the local winds relax the warm water mass advects back into the bay in the form of a buoyant plume front local diurnal winds are expected to play an important role in nearshore dynamics and local upwelling in other small coastal embayments with important implications for various biological and ecological processes

cross shore deformation of a surfzone released dye plume by an internal tide on the inner shelf abstractan inner shelf is dye plume that formed following a 3 84 h early morning surfzone sz dye release off of imperial beach california is analyzed with in situ and aerial remotely sensed o

taphonomy and depositional dynamics of devonian shell rich mudstones abstract fossil preservation e g articulation of multi element skeletons provides important insights into depositional dynamics detailed taphonomic analysis of marine mudstones and associated shell beds from the middle devonian of western new york indicates that these beds record primarily episodic sediment deposition of short duration we propose a storm winnowing mud blanketing model to explain the variety of shell and mudstone beds observed and to explain apparent onshore offshore gradients of shell bed characteristics shell beds themselves appear to have accumulated during relatively long spans of time ranging up to perhaps thousands of years most are internally complex and exhibit evidence for multiple events of burial and exhumation by winnowing shell accumulation facilitated colonization of the seafloor by hard substrate encrusting organisms these contributed to increasingly complex communities that were ultimately destroyed and permanently blanketed by thick mud layers the sparsely fossiliferous mudstones which compose up to 85 of the hamilton stratigraphic section mainly record very abrupt inputs of sediment in some instances taphonomy of enclosed fossils indicates deposition of layers up to several centimeters thick prior to compaction within hours to a few days in turn some sequences of shell and mudstone beds were deposited within the life span of single colonial organisms and thus also record only relatively short spans of time overall this reinforces our conclusions that most time in mudstone sequences must be represented by discontinuities at sharp surfaces or thin condensed beds that bound more or less continuous bundles of shell and mudstone beds again these often subtle discontinuities can be recognized on the basis of taphonomic criteria many complex shell beds as well as simple shell beds can be traced along depositional strike for tens of kilometers condensed shell beds only a few centimeters thick can commonly be correlated for 100 to 200 km along and across depositional strike the correlatable nature of shell beds apparently reflects the temporal contrast between these beds and enclosing muds on a regional scale shell beds represent integrated accumulations that were deposited over spans of tens to thousands of years conversely the mud layers that blanketed and terminated shell bed accumulations may represent very rapid depositional events spanning hours to days which are locally isochronous thus the study of taphonomy of shell beds reveals a good deal of detail about their depositional history these studies imply that the stratigraphic record is even more episodic and discotinuous than commonly recognized episodic deposition implies that while the stratigraphic record of epeiric seas may be adequate for examining details of community succession and paleontology it probably can not generally be used for microevolutionary studies other than examination of patterns of stasis

connecting wind driven upwelling and offshore stratification to nearshore internal bores and oxygen variability this study utilizes field observations in southern monterey bay ca to examine how regional scale upwelling and changing offshore shelf conditions influence nearshore internal bores we show that the low frequency wind forcing e g upwelling relaxation time scales modifies the offshore stratification and thermocline depth this in turn alters the strength and structure of observed internal bores in the near shore an internal bore strength index is defined using the high pass filtered potential energy density anomaly in the nearshore during weak upwelling favorable conditions and wind relaxations the offshore thermocline deepens in this case both the amplitude of the offshore internal tide and the strength of the nearshore internal bores increase in contrast during strong upwelling conditions the offshore thermocline shoals toward the surface resulting in a decrease in the offshore internal tide amplitude as a result cold water accumulates in the nearshore nearshore pooling and the internal bore strength index decreases empirical orthogonal functions are utilized to support the claim that the bore events contribute to the majority of the variance in cross shelf exchange and transport in the nearshore observed individual bores can drive shock like drops in dissolved oxygen do with rapid onset times while extended upwelling peri ods with reduced bore activity produce longer duration low do events

barotropic and baroclinic m2 tides in the monterey bay region abstract a high resolution 250 m primitive equation model is used to simulate the depth averaged and baroclinic m2 tides in the monterey bay region the model shows a high level of skill in comparisons with sea level observations adcp current observations within the submarine canyon are reasonably well reproduced the modeled depth averaged currents have a complex spatial pattern with magnitudes in excess of 0 1 m s 1 near moss landing during the second half of flood ebb tide the flow is into out of the bay through the canyon but out of into the bay over the shelf regions this depth averaged flow pattern is not evident in a diagnostic run implying a feedback between the internal tides and the pressure gradient in the bay the depth integrated baroclinic total minus depth averaged energy fluxes show a complex beamlike pattern due to the interaction of energy from multiple sources the beams have magnitudes up to 1 kw m 1 interspersed with regions of near zero depth integrated flux energy en

transport by breaking internal gravity waves on slopes we use the results of a direct numerical simulation dns with a particle tracking model to investigate three dimensional transport by breaking internal gravity waves on slopes onshore transport occurs within an upslope surge of dense fluid after breaking offshore transport occurs due to an intrusion of mixed fluid that propagates offshore and resembles an intermediate nepheloid layer inl entrainment of particles into the inl is related to irreversible mixing of the density field during wave breaking maximum onshore and offshore transport are calculated as a function of initial particle position and can be of the order of the initial wave length scale for particles initialized within the breaking region an effective cross shore dispersion coefficient is also calculated and is roughly three orders of magnitude larger than the molecular diffusivity within the breaking region particles are transported laterally due to turbulence that develops during wave breaking and this lateral spreading is quantified with a lateral turbulent diffusivity lateral turbulent diffusivity values calculated using particles are elevated by more than one order of magnitude above the molecular diffusivity and are shown to agree well with turbulent diffusivities estimated using a generic length scale turbulence closure model based on a favourable comparison of dns results with those of a similar two dimensional case we use two dimensional simulations to extend our cross shore transport results to additional wave amplitude and bathymetric slope conditions

the extra large light gas gun of the fraunhofer emi applications for impact cratering research abstract the extra large light gas gun xllgg at the fraunhofer ernst mach institut emi efringen kirchen germany is a two stage light gas gun that can accelerate projectile masses of up to 100 g up to velocities of 6 km s 1 the accelerator s set up allows various combinations of pump and launch tubes for applications in different fields of hypervelocity impact research in the framework of the memin multidisciplinary experimental and modeling impact research network program the xllgg is used for mesoscale cratering experiments with projectiles made of steel and of iron meteorites and targets consisting of sandstone and other rocks the craters produced with this equipment reach a diameter of up to 40 cm a size unique in laboratory cratering research with the implementation of neural networks the acceleration process is being optimized currently yielding peak velocities of 7 8 km s 1 for a 100 g projectile here we summarize technical aspects of the xllgg

crater ejecta scaling laws fundamental forms based on dimensional analysis a model of crater ejecta is constructed using dimensional analysis and a recently developed theory of energy and momentum coupling in cratering events general relations are derived that provide a rationale for scaling laboratory measurements of ejecta to larger events specific expressions are presented for ejection velocities and ejecta blanket profiles in two limiting regimes of crater formation the so called gravity and strength regimes in the gravity regime ejecta velocities at geometrically similar launch points within craters vary as the square root of the product of crater radius and gravity this relation implies geometric similarity of ejecta blankets that is the thickness of an ejecta blanket as a function of distance from the crater center is the same for all sizes of craters if the thickness and range are expressed in terms of crater radii in the strength regime ejecta velocities are independent of crater size consequently ejecta blankets are not geometrically similar in this regime for points away from the crater rim the expressions for ejecta velocities and thickness take the form of power laws the exponents in these power laws are functions of an exponent that appears in crater radius scaling relations thus experimental studies of the dependence of crater radius on impact conditions determine scaling relations for ejecta predicted ejection velocities and ejecta blanket profiles based on measured values of are compared to existing measurements of velocities and debris profiles

unusual preservation of the trace fossil conostichus in middle silurian carbonate facies of indiana usa the long ranging plug shaped ichnofossil conostichus attributed to solitary polypoid cnidarians is most commonly described in the paleozoic from fine grained siliciclastic sediments with few de

internal solitary waves control offshore extension of mud depocenters on the nw iberian shelf abstract hydrodynamic conditions and near bottom sediment transport on the nw iberian shelf associated with a 5 day storm in september 2014 were monitored during the post storm relaxation period active bottom sediment transport by internal solitary waves isws on a mid shelf mud depocenter located in between 110 and 130 m water depth wd was observed to explore the potential of internal waves in sediment transport and its link to development of mid shelf mud depocenters we apply a weakly nonlinear model based on the variable coefficient gardner equation to estimate the flow fields and bottom shear stress induced by shoaling of mode 1 long internal solitary waves shoreward propagation of the isws in three representative periods pre intra and post storm is simulated respectively transformation of the internal wave from a single sech2 shape characterized by negative polarity and small amplitude to a dispersive trailing wave packet with varying amplitude and inverse polarity are satisfactorily reproduced model results indicate enhancement of the maximum orbital velocity of the isws during and after the storm on the outer shelf 130 220 m wd including the seaward margin of the mud depocenter bottom shear stress consequently becomes strong enough 0 1 pa to winnow unconsolidated sediment and constrains the offshore extension of the depocenter the enhanced bottom orbital velocity and the asymmetry in the excursion direction of mode 1 long isws in the post storm period prove to be efficient in transporting fine grained sediment across shelf our results suggest that mid shelf mud depocenters are not necessarily areas under permanently calm conditions where fine grained sediment can settle straightforwardly they could also result from convergent sediment transport from both onshore and offshore directions and sediment may go through numerous cycles of resuspension transport deposition before its ultimate lasting burial

direct evidence of deep water intrusions onto the continental shelf via surging internal tides 1 near bottom diurnal thermocline shoaling and diurnal baroclinic currents were observed from time series data of water temperature salinity pressure and velocity collected from august 2006 to january 2007 in the nearshore zone off the huntington beach where the local inertial frequency is higher than the diurnal frequency poleward of the diurnal critical latitude during the stratified season the deep offshore cold dense water when shoaled into shallow water along the bottom was often trapped for a few hours and dissipated in the nearshore region water depth of 10 20 m during the ebb phase of the diurnal surface tide it appears that perturbations propagating onshore along the shoaled isopycnals can form an upslope surging front and an internal bolus our data allow the application of theoretical lab criteria for internal hydraulic jumps internal bolus formation and internal wave breaking and all criteria are fulfilled during a part of the tidal shoaling cycle nonlinear advection associated with the internal boluses causes higher close to 3 spectral falloff rate of near bottom temperature with frequency than the canonical garret munk spectra 2 in the range of 0 1 1 0 cph implying strong scattering of tidal energy toward smaller scales we are able to directly calculate the offshore eddy heat flux by cold water intrusion onto the shelf resulting from this process similar impacts and implications are expected for the biogeochemical quantities as well as for the role of subinertial internal waves on turbulent mixing in the immediate proximity of the generating region i e sloping bottom

suspended particulate layers and internal waves over the southern monterey bay continental shelf an important control on shelf mud belts 1 physical and optical measurements taken over the mud belt on the southern continental shelf of monterey bay california documented the frequent occurrence of suspended particulate matter features the majority of which were detached from the seafloor centered 9 33 m above the bed in fall 2011 an automated profiling mooring and fixed instrumentation including a thermistor chain and upward looking acoustic doppler current profiler were deployed at 70 m depth for 5 weeks and from 12 to 16 october a long range autonomous underwater vehicle performed across shelf transects individual spm events were uncorrelated with local bed shear stress caused by surface waves and bottom currents nearly half of all observed spm layers occurred during 1 week of the study 9 16 october 2011 and were advected past the fixed profiling mooring by the onshore phase of semidiurnal internal tide bottom currents at the start of the 9 16 october period we observed intense near bed vertical velocities capable of lifting particulates into the middle of the water column this updraft event appears to have been associated with nonlinear adjustment of high amplitude internal tides over the mid and outer shelf these findings suggest that nonlinear internal tidal motions can erode material over the outer shelf and that once suspended this spm can then be transported shoreward to the middle and shallow sections of the mud belt this represents a fundamental broadening of our understanding of how shelf mud belts may be built up and sustained

the role of internal tides in the nutrient enrichment of monterey bay california abstract semidiurnal internal tides in monterey canyon are shown to be partially responsible for macronutrient enrichment of surface waters in monterey bay california ctd time series at five stations in the canyon revealed the presence of semidiurnal internal tides with heights between 50 and 120 m p thermistor data demonstrated an internal tidal bore at the head of the canyon data and theory suggest that internal tidal bores may be breaking due to either shear instability or direct overturning thereby enriching the immediate area near the canyon head transects normal to monterey canyon showed a 20 m thick lens of 12 c water moving out of the canyon at high internal tide this lens was then pinched off from the canyon and led to a density induced divergence the nutrient transport associated with the internal tidal divergence could support as much as 30 of the daily primary productivity in the northern part of monterey bay during non upwelling periods

a crater and its ejecta an interpretation of deep impact we apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the deep impact event an important question is whether the cratering event was gravity or strength dominated the answer gives important clues about the properties of the surface material of tempel 1 gravity scaling was assumed in pre event calculations and has been asserted in initial studies of the mission results because the gravity field of tempel 1 is extremely weak a gravity dominated event necessarily implies a surface with essentially zero strength the conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution we address that feature here and conclude that even strength dominated craters would result in a plume that appeared to remain attached to the surface we then calculate the plume characteristics from scaling laws for a variety of material types and for gravity and strength dominated cases we find that no model of cratering alone can match the reported observation of plume mass and brightness history instead comet like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few hour time frame with such mechanisms and to within the large uncertainties either gravity or strength craters can provide the levels of estimated observed mass thus the observations are unlikely to answer the questions about the mechanical nature of the tempel 1 surface

storm effects on siliciclastic and carbonate shelf sediments in the medial silurian succession of pennsylvania abstract upper llandoverian through wenlockian strata in the pennsylvania part of the northern appalachian basin formed on a gentle epeiric ramp that extended from marginal tidal flats through coarser grained mid shelf shoals to a muddy basin center over approximately 10 million years the composition of the accumulating sediment evolved from siliciclastic to carbonate while the ramp maintained a relatively similar configuration and position below sea level and while storm generated processes continued as the major producers of sediment characteristics in both siliciclastic and carbonate parts of the succession sedimentary structures and their sequences are generally similar with only a small number of dissimilar features resulting from the differences in composition small scale coarsening and shallowing upward sequences are present in both mid shelf bar and basin transition deposits although specific sequence characteristics are different in siliciclastic and carbonate parts such sequences record cyclic fluctuations of relative sea level while the composition of the sediment evolved over this extended period the gentle ramp gradient was maintained largely by the processes generated by storms such processes were more effective because of the fluctuations of relative sea level

quaternary continental stratigraphy and neocatastrophism abstract recent papers on pre quaternary stratigraphy have emphasized that the rock record represents only a small portion of geologic time with the gaps representing the majority of elapsed time quaternary continental stratigraphy also yields such evidence in abundance time between dated organic sites in glaciated areas is commonly depicted as filled by glacial ice yet there is much evidence of rapid sedimentation and most deposits could be laid down in short time spans non glaciated areas yield similar evidence because of gaps over which depositional rates are averaged calculated rates are often lower than they really are continental stratigraphy requires attention from many workers supported by much improved dating methods to establish time spans and gaps for the rock record

internal tide pools prolong kelp forest hypoxic events this study uses field observations within a single kelp bed in southern monterey bay california to evaluate the retention of cold hypoxic water within depressions in the rocky reef following relaxation of internal wave events just as tide pools in the rocky intertidal zone persist in depressions following the relaxation of surface waves and tides internal tide pools persist in depressions in the subtidal reef following the relaxation of internal waves when internal waves contain low dissolved oxygen do water the duration of hypoxic events can be extended for organisms within the pooling zone additionally we suggest that internal wave run up can cause the early arrival of cold hypoxic water in these same areas thereby extending hypoxic events further together internal tide pools and wave run up extend event durations by 20 on average however some events are extended up to 160 of the regional scale event length which may be more ecologically relevant than the mean extension when internal waves contain other environmental covariates e g low ph nutrients internal tide pools are expected to create a similar time extension and patchy landscape in these quantities we attribute the slowing of the relaxation of sub thermocline water within pooling zones to retention within the reef itself rather than a drag effect of the kelp bed following hypoxic internal bores internal tide pools cause a period of extreme spatial variability in the do and temperature field which is likely to impact the distribution and behavior of local organisms

ejection behavior characteristics in experimental cratering in sandstone targets within the frame of the memin research unit multidisciplinary experimental and numerical impact research network impact experiments on sandstone targets were carried out to systematically study the influence of projectile mass velocity and target water saturation on the cratering and ejection processes the projectiles were accelerated with two stage light gas guns ernst mach institute onto fine grained targets seeberger sandstone with about 23 porosity collection of the ejecta on custom designed catchers allowed determination of particle shape size distribution ejection angle and microstructures mapping of the ejecta imprints on the catcher surface enabled linking of the different patterns to ejection stages observed on high speed videos the increase in projectile mass from 0 067 to 7 1 g correlates with an increase in the total ejected mass ejecta angles however are similar in range for all experiments the increase in projectile velocity from 2 5 to 5 1 km s 1 correlates with a total ejecta mass increase as well as in an increase in comminution efficiency and a widening of the ejecta cone a higher degree of water saturation of the target yields an increase in total ejecta mass up to 400 with respect to dry targets higher ejecta velocity and a steeper cone these data in turn suggest that the reduced impedance contrast between the quartz grains of the target and the pores plays a primary role in the ejecta mass increase while vaporization of water determines the ejecta behavior concerning ejecta velocity and particle distribution

breaking of internal kelvin waves shoaling on a slope in stratified flow breaking of internal waves over slopes induces resuspension of bottom sediments and transport of mass when internal waves shoal and break flow dynamics and mass transport diff

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

erosion of tortonian phosphatic intervals in upwelling zones the role of internal waves abstract during the miocene the upwelling is assumed to be important in the formation of many mediterranean phosphate deposits in carbonate platform successions there are different types of upwelling mechanisms such as equatorial upwellings ice edge upwellings and coastal upwellings the carbonate platforms are mainly affected by wind driven coastal upwelling systems during upwelling season the seawater in coastal areas is strongly density stratified and the permanent pycnocline rises inshore forming an inclined frontal layer the liaison between upwellings and internal waves is widely documented in the literature internal waves result from perturbations of the hydrostatic equilibrium where balance is sustained between the force of gravity and buoyant restoring force many perturbations of the pycnocline can propagate as an internal wave in a coastal upwelling a key role for wave propagation is played by permanent pycnocline the run up swash currents develop during the break of internal waves and produce erosional processes in particular the backwash return flow may induce the erosion of seafloor sediments and transport these sediments downslope as bedload erosion of phosphate rich intervals has been extensively documented the deposition of gravity flow sediments is followed by intervals of non deposition incipient lithification phosphogenesis and erosion in this work we evaluate the role of internal waves in the formation of the resedimented phosphate rich intervals characterising the basal portion of the hemipelagic orbulina marls these marls are deposited on the low angle latium abruzzi carbonate ramp and represent deposition in a foreland basin during the initial stages of evolution of the central apennine belt during the early tortonian age

observations of nonlinear internal wave run up to the surfzone abstractthe cross shore evolution of nonlinear internal waves nliws from 8 m depth to shore was observed by a dense thermistor array and adcp isotherm oscillations spanned much of the water column at a variety of periods at times nliws propagated into the surfzone decreasing temperature by 1 c in 5 min when stratification was strong temperature variability was strong and coherent from 18 to 6 m depth at semidiurnal and harmonic periods when stratification weakened temperature variability decreased and was incoherent between 18 and 6 m depth at all frequencies at 8 m depth onshore coherently propagating nliw events had associated rapid temperature drops t up to 1 7 c front velocity between 1 4 and 7 4 cm s 1 and incidence angles between 5 and 23 front position t and two layer equivalent height ziw of four events were tracked upslope until propagation terminated front position was quadratic in time and normalized t and ziw both decreased collapsing as a linearly decaying funct

near bed solibores over the continental slope in the faeroe shetland channel abstract on two occasions within a 12 day measurement period in the faeroe shetland channel strongly nonlinear wave trains were observed at the sea bed propagating up the continental slope in water depths 450 m the events were separated by a period of 4 days and whilst resembling in appearance a density current running up a slope are termed solibores displaying the properties of both turbulent internal bores and nonlinear internal solitary waves isw each solibore displays a steep leading edge followed by a train of nonlinear waves with amplitudes of o 10 m and periods of 5 20 min wave induced particle velocities are consistent with isw whilst a zone of strong horizontal convergence at the leading edge of the solibores causes the formation of a rotor with flow in the opposite sense to a forward overturning surface wave in both cases upward vertical velocities 10 cm s 1 are immediately followed by a return downward flow of equal magnitude a ctd and microstructure transect conducted during the passage of the first solibore illustrates its behaviour as an up slope intrusion of cold dense water with concurrent rates of turbulent dissipation e of o 10 7 w kg 1 and resulting in short term maximum vertical diffusivities kz of o 10 1 m2 s 1 in the long term however kz 140 days which again indicate intermittency in periods of enhanced sediment flux the solibores are consistent with the results of numerical and laboratory experiments on hydraulic jumps resulting from shoaling isw the influence of the slope is proposed to be the reason for their slightly different forms and effects on sediment transport thus the first solibore propagating directly up the slope is proposed to result from an overturning hydraulic jump caused by kinematic instabilities and which subsequently forms a horizontal density intrusion the second solibore represents a dispersive wave train due its oblique direction of propagation which reduces the effective bottom slope allowing dispersion to balance nonlinear effects and prohibiting overturning

climatic versus tectonic control on storm cyclicity in mesoproterozoic koldaha shale vindhyan supergroup central india abstract the 1 2 ga old koldaha shale central india reveals three orders of depositional cyclicities in its basal storm dominated shelf succession visual appraisal as well as fourier and mem analyses concurs in this respect only the major storm events at intervals of a few thousands of years have left recognizable imprints interbedding of storm sandstones and fairweather shales is apparently climate controlled packaging of about seven such climatic cycles results the second order cyclicity befitting eccentricity cycles of contemporary scale nonetheless for the erratic storm bed thickness trends within the cycles some other factor s might have played a role the third order cycles are more dominantly correlatable with basinal tectonics

sensing of upslope passages of frontal bores across the trench slope break of the japan trench the circum pacific trench slope system is one of the most spectacular topographic features of the earth we report the relatively frequent occurrence of upslope passages 50 times a year of internal bores in the japan trench system observations were made using a triaxial accelerometer a tiltmeter and a current meter at the seafloor 3400 m deep during 10 months from 2013 to 2014 we detected 42 tilt events from the records of the accelerometer and confirmed their consistency with the tiltmeter records the tilt occurred always landward by 1 10 rad with a rise time on the order of 1000 s and return to the original with a much longer recovery time the current and temperature records available for the first two events indicated that landward tilting was associated with an upslope current with a speed of several cm s and a temperature drop of several tens of m c the temperature remained cold even after the current had diminished all of these observations implied the frontal passages of upslope advancing bores which caused the instrument to be tilted landward the observational site was located at the trench slope break separating the trench slope sloping supercritically or near critically for the m2 internal tide from the fore arc basin sloping subcritically this unique locality suggested the internal tide origin of the observed bores although other possibilities could not be precluded bores generated on the trench slope may play a role for upslope transportation of suspended sediments stirred up by deep submarine landslides

observations of internal wave packets propagating along shelf in northern monterey bay internal waves of depression were observed propagating along shelf and into northern monterey bay california ca on the inner shelf these waves had amplitudes approximately equal to the thermocline depth 4 m and were unstable to shear and mix the thermocline isopycnal gradient spectra showed that the wave packets lead to an elevated mean dissipation rate of 2 63 10 5 m3 s 2 for up to 2 hours after wave passage the proximity to the surface created strong surface convergences that can actively transport buoyant material such as plankton back into the bay the wave packets were observed regularly over the upwelling season across multiple years suggesting they may have large effects on the documented spatial variation of phytoplankton and larvae on the inner shelf the timing of the waves suggests they are not formed by tides interacting with bathymetry but are generated by buoyant plume propagation

in situ measurements of impact induced pressure waves in sandstone targets in the present study we introduce an innovative method for the measurement of impact induced pressure waves within geological materials impact experiments on dry and water saturated sandstone targets were conducted at a velocity of 4600 m s using 12 mm steel projectiles to investigate amplitudes decay behavior and speed of the waves propagating through the target material for this purpose a special kind of piezoresistive sensor capable of recording transient stress pulses within solid brittle materials was developed and calibrated using a split hopkinson pressure bar experimental impact parameters projectile size and speed were kept constant and yielded reproducible signal curves in terms of rise time and peak amplitudes pressure amplitudes decreased by 3 orders of magnitude within the first 250 mm i e 42 projectile radii the attenuation for water saturated sandstone is higher compared to dry sandstone which is attributed to dissipation effects caused by relative motion between bulk material and interstitial water the proportion of the impact energy radiated as seismic energy seismic efficiency is in the order of 10 3 the present study shows the feasibility of real time measurements of waves caused by hypervelocity impacts on geological materials experiments of this kind lead to a better understanding of the processes in the crater subsurface during a hypervelocity impact

the degeneration of internal waves in lakes with sloping topography in a laboratory study we quantified the temporal energy flux associated with the degeneration of basin scale internal waves in closed basins the system is two layer stratified and subjected to a single forcing event creating available potential energy at time zero a downscale energy transfer was observed from the wind forced basin scale motions to the turbulent motions where energy was lost due to high frequency internal wave breaking along sloping topography under moderate forcing conditions steepening of nonlinear basin scale wave components was found to produce a high frequency solitary wave packet that contained as much as 20 of the available potential energy introduced by the initial condition the characteristic lengthscale of a particular solitary wave was less than the characteristic slope length leading to wave breaking along the sloping boundary the ratio of the steepening timescale required for the evolution of the solitary waves to the travel time until the waves shoaled controlled their development and degeneration within the domain the energy loss along the slope the mixing efficiency and the breaker type were modeled using appropriate forms of an internal iribarren number defined as the ratio of the boundary slope to the wave slope amplitude wavelength this parameter allows generalization to the oceanographic context analysis of field data shows the portion of the internal wave spectrum for lakes between motions at the basin and buoyancy scales to be composed of progressive waves both weakly nonlinear waves sinusoidal profile with frequencies near 10 24 hz and strongly nonlinear waves hyperbolic secant squared profile with frequencies near 10 23 hz the results suggest that a periodically forced system may sustain a quasi steady flux of 20 of the potential energy introduced by the surface wind stress to the benthic boundary layer at the depth of the pycnocline

the effect of stokes drift and transient rip currents on the inner shelf part i no stratification abstractthis is part ii of a two part study focused on stokes drift and transient rip current trc effects on the unstratified part i and stratified this paper inner shelf part i focuses on funwavec coupled ocean atmosphere wave sediment transport coawst coupling and trc effects on mixing and exchange on an unstratified inner shelf here two simulations r3 and r4 are performed on a stratified inner shelf and surfzone with typical bathymetry stratification and wave conditions r3 is a coawst only simulation no trcs while r4 has funwavec coawst coupling with trcs in r4 trcs lead to patchy near surface cooling vertical isotherm displacement and increased water column mixing for both r3 and r4 the mean lagrangian circulation has two nearly isolated surfzones and inner shelf overturning circulation cells with a stronger r4 inner shelf circulation cell the r4 inner shelf vertical velocity variability is 2 3 times stronger than a simulation with trcs and no stratification relative

a simple model of mixing in stratified tidal flows we use a simple model of vertical mixing in a stratified tidal flow to study flows that might be observed in shallow estuaries in the model flow is driven by a specified surface pressure gradient due to barotropic tidal motions the model incorporates two means for accomplishing vertical mixing 1 shear instability and 2 bottom mixed layer deepening by turbulence produced at the estuary bottom and in the shear layer at the top of the mixed layer we discuss model results that show how the combined action of shear instability and tidal stirring accomplishes vertical mixing the interaction between the instabilities that develop because of the substantial tidal timescale velocity shear caused by stratification is the key feature of mixing shear instability weakens the stability of the mixed layer allowing stirring to efficiently entrain lighter fluid into the mixed layer the importance of shear is found to depend on the stability of the water column and on the relative importance of frictional forces

crater morphology in sandstone targets the memin impact parameter study hypervelocity 2 5 7 8 km s 1 impact experiments into sandstone were carried out to investigate the influence of projectile velocity and mass target pore space saturation target projectile density contrast and target layer orientation on crater size and shape crater size increases with increasing projectile velocity and mass as well as with increasing target pore space saturation craters in water saturated porous targets are generally shallower and larger in volume and in diameter than craters from equivalent impacts into dry porous sandstone morphometric analyses of the resultant craters 5 40 cm in diameter reveal features that are characteristic of all of our experimental craters regardless of impact conditions i a large central depression within a fragile light colored central part and ii an outer spallation zone with areas of incipient spallation two different mechanical processes grain fragmentation and intergranular tensile fracturing are recorded within these crater morphologies zone i approximates the shape of the transient crater formed by material compression displacement comminution and excavation flow whereas ii is the result of intergranular tensile fracturing and spallation the transient crater dimensions are reconstructed by fitting quadric parabolas to crater profiles from digital elevation models the dimensions of this transient and of the final crater show the same trends both increase in volume with increasing impact energy and with increasing water saturation of the target pore space the relative size of the transient crater in percent of the final crater volume decreases with increasing projectile mass and velocity signifying a greater contribution of spallation on the final crater size when projectile mass and velocity are increased

shock wave profile study of tuff from the nevada test site shock wave equation of state and release behavior of tuff from the nevada test site were measured in the range 8 to 107 gpa by recording shock wave profiles produced by impact of projectiles accelerated by a two stage light gas gun shock wave profiles were measured with a fast optical interferometer hugoniot sound speed and effective gruneisen parameter data were determined from the profiles the specimen geometry allows direct observation of the shape of the leading edge of the shock in which complex compressive dynamics caused by pore crushing or phase transitions can manifest themselves the tuff specimens were tested in both a water saturated and semidry state hydration of the rock increases both the shock and sound speeds for a given compression the us up relation for our water saturated tuff is slightly nonlinear and can be approximated as us 2 00 1 42 up for 0 up 6 km s and us 2 29 1 29up for 0 up 3 km s for semidry tuff at pressures less than 18 gpa us 1 70 1 28up

non intrusive measurements of crater growth abstract an experimental technique to measure crater growth is presented whereby a high speed video captures profiles of a crater forming after impact obtained using a vertical laser sheet centered on the impact point unlike previous so called quarter space experiments where projectiles were launched along a transparent plexiglas sheet so that growth of half a crater could be viewed the use of the laser sheet permits viewing changes in crater shape without any physical interference to the cratering process this technique indicates that for low velocity impacts 300 m s into 220 m glass beads that are without cohesion and where the projectile is not disrupted craters initially grow somewhat proportionally but that later their depths remain essentially constant while their diameters continue to expand in addition these experiments indicate that as the impact velocity increases the rate of growth and the transient depth to diameter ratio at the end of ejecta excavation decreases these last two observations are probably due to the large time of penetration of the projectile which becomes a significant fraction of the time of crater formation this is contrary to the expectations for the scaling rules which assumes a point source very high curtain angles 45 are also seen and could be due to the low friction angle of the target significant crater modification which is rarely seen in quarter space experiments is also observed and appears to be controlled by the dynamic angle of repose of the target these latter observations indicate that differences in target friction angles may need to be considered when determining near rim ejecta mass distributions and large scale crater modification processes on the planets

observations of shoaling nonlinear internal bores across the central california inner shelf abstractwe present observations of shoaling nonlinear internal bores off the coast of central california the dataset includes 15 moorings deployed during september october 2017 and cross shore shi