field measurements of the flux and speed of wind blown sand a field experiment was conducted to measure the flux and speed of wind blown sand under known conditions in a natural setting the experiment run at pismo beach california involved a tract 100 m long parallel with the wind by 20 m wide the site was instrumented with four arrays of anemometers to obtain wind velocity profiles through the lower atmospheric boundary layer temperature probes to determine atmospheric stability and wind vanes to determine wind direction from these measurements wind friction speeds were derived for each experimental run in order to measure sand saltation flux a trench 3 m long by 10 m wide transverse to the wind direction by 0 5 m deep was placed at the downwind end of the tract and lined with 168 collector bins forming an egg box pattern the mass of particles collected in each bin was determined for four experimental runs in order to assess various sand trap systems used in previous experiments 12 leatherman traps one fryberger trap and one array of ames traps were deployed to collect particles concurrently with the trench collection particle velocities were determined from analysis of high speed 3000 and 5000 frames per second motion pictures and from a particle velocimeter sand samples were collected from the trench bins and the various sand traps and grain size distributions were determined fluxes for each run were calculated using various previously published expressions and then compared with the flux derived from the trench collection results show that bagnold s 1941 model and white s 1979 equation most closely agree with values derived from the trench comparison of the various collector systems shows that the leatherman and ames traps most closely agree with the flux derived from the trench although these systems tended to under collect particles particle speeds were measured from analysis of motion pictures for saltating particles in ascending and descending parts of their trajectories results show that particle velocities from the velocimeter are in the range 0 5 7 0 m s 1 compared to a wind friction velocity of 0 32 0 43 m s 1 and a wind velocity of 2 7 3 9 m s 1 at the height of the particle measurements descending particles tended to exceed the speeds of ascending particles by 0 5 m s 1

clastic domains of sandstones in central eastern venezuela trinidad and barbados heavy mineral and tectonic constraints on provenance and palaeogeography current models for the tectonic evolution of northeastern south america invoke a palaeogene phase of inter american convergence followed by diachronous dextral oblique collision with the caribbean plate becoming strongly transcurrent in the late miocene heavy mineral analysis of cretaceous to pleistocene rocks from eastern venezuela barbados and trinidad allow us to define six primary clastic domains refine our palaeogeographic maps and relate them to distinct stages of tectonic development 1 cretaceous passive margin of northern south america 2 palaeogene clastics related to the dynamics of the proto caribbean inversion zone before collision with the caribbean plate 3 late eocene oligocene southward transgressive clastic sediments fringing the caribbean foredeep during initial collision 4 oligocene middle miocene axial fill of the caribbean foredeep 5 late eocene middle miocene northern proximal sedimentary fringe of the caribbean thrustfront and 6 late miocene recent deltaic sediments flowing parallel to the orogen during its post collisional mainly transcurrent stage domain 1 3 sediments are highly mature comprising primary guayana shield derived sediment or recycled sediment of shield origin eroded from regional palaeogene unconformities in trinidad palinspastic restoration of neogene deformation indicates that facies changes once interpreted as north to south are in fact west to east reflecting progradation from the maturin basin into central trinidad across the nw se trending bohordal marginal offset distorted by about 70 km of dextral shear through trinidad there is no mineralogical indication of a northern or northwestern erosional sediment source until oligocene onset of domain 4 sedimentation paleocene middle eocene rocks of the scotland formation sandstones in barbados do show an immature orogenic signature in contrast to venezuela trinidad domain 2 sediments this requires 1 at least a bathymetric difference if not a tectonic barrier between them and 2 that the barbados deep water depocentre was within turbidite transport distance of the early palaeogene orogenic source areas of western venezuela and or colombia domains 4 6 from late oligocene show a strong direct or recycled influence of caribbean orogen igneous and metamorphic terranes in addition to substantial input from the shield areas to the south the delay in the appearance of common caribbean detritus in the east relative to the paleocene and eocene appearance of caribbean influenced sands in the west reflects the diachronous eastward migration of caribbean foredeep subsidence and sedimentation as a response to eastward younging collision of the caribbean plate and the south american margin

near bed mass flux profiles in aeolian sand transport high resolution measurements in a wind tunnel vertical profiles of the streamwise mass flux of blown sand in the near bed 17 mm region are analysed from high resolution measurements made using an optical sensor in a wind tunnel this analysis is complemented by detailed measurements of mass flux and mean velocity profiles throughout the boundary layer depth 0 17 m using passive chambered sand traps of small dimensions and armoured thermal anemometers respectively the data permit a preliminary analysis of the relations between the observed forms of the profiles of near bed fluid stress and horizontal mass flux within a carefully conditioned boundary layer profiles of mass flux density are found to be characterized by three regions of differing gradient with transitions at about 2 mm and 19 mm above the bed the exponential decay of mass flux with height is confirmed for elevations above 19 mm and when plotted as a function of u 2 g a parameter of mean vertical trajectory height in saltation the gradient of mass flux in this region scales with the wake corrected friction velocity u where u 0 30 m s 1 a separate near bed region of more intense transport below 19 mm is identified which carries 80 per cent of the total mass flux this region is evident in some previous field and wind tunnel data but not in profiles simulated by numerical models ventilated passive sand traps underestimate mass flux in this region by 37 per cent at slow or moderate wind speeds a third significant region below 2 mm is observed these regions are likely to be related to grain populations in successive saltation low energy ejections and intermittent bed contact respectively optical measurements reveal locally high grain concentrations at some elevations below 5 mm these heights scale with transport rate mass flux gradient and wind speed copyright 1999 john wiley sons ltd

oceanic plateau formation a cause of mass extinction and black shale deposition around the cenomanian turonian boundary the cenomanian turonian boundary 90 4 ma represents a major period of worldwide environmental disturbance the physical manifestations of this are elevated atmospheric and oceanic temperatures a significant sea level transgression and a period of widespread anoxia leading to the formation of oceanic black shales and the extinction of 26 of all genera elevated 13 c values and enrichment of trace elements in cenomanian turonian boundary sediments combined with a reduction in 87 sr 86 sr also imply a severe environmental perturbation at this time oceanic crustal production rates reached their highest level of the last 100 million years this was principally caused by extensive melting of hot mantle plumes at the base of the oceanic lithosphere and the development of vast areas up to 1 10 6 km 2 of thickened oceanic crust in the pacific and indian oceans the anomalous volcanism associated with the formation of these oceanic plateaux may have been responsible for the environmental disturbances c 90 ma these eruptions would also have resulted in the emission of large quantities of co 2 into the atmosphere leading to global warming additionally the emission of so 2 h 2 s co 2 and halogens into the oceans would have made seawater more acidic resulting in the dissolution of carbonate and further release of co 2 this run away greenhouse effect was probably put into reverse by the decline of the anomalous volcanic activity and by increased co 2 driven productivity in oceanic surface waters leading to increased organic carbon burial black shale deposition anoxia and mass extinction in the ocean basins

aeolian processes across transverse dunes i modelling the air flow this paper discusses a two dimensional second order closure model simulating air flow and turbulence across transverse dunes input parameters are upwind wind speed topography of the dune ridge and surface roughness distribution over the ridge the most important output is the distribution of the friction velocity over the surface this model is dynamically linked to a model that calculates sand transport rates and the resulting changes in elevation the sand transport model is discussed in a separate paper the simulated wind speeds resemble patterns observed during field experiments despite the increased wind speed over the crest the friction velocity at the crest of a bare dune is reduced compared to the upstream value because of the effect of stream line curvature on turbulence these curvature effects explain why desert dunes can grow in height in order to obtain realistic predictions of friction velocity it was essential to include equations for the turbulent variables in the model in these equations streamline curvature is an important parameter the main flaw of the model is that it cannot deal with flow separation and the resulting recirculation vortex as a result the increase of the wind speed and friction velocity after a steep dune or a slipface will be too close to the dune foot in the sand transport model this was overcome by defining a separation zone copyright 1999 john wiley sons ltd

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

accreted seamounts in north tianshan nw china implications for the evolution of the central asian orogenic belt the carboniferous bayingou ophiolitic melange is exposed in north tianshan accretionary complex in the southwestern part of the central asian orogenic belt caob the melange is mainly composed of serpentinised ultramafic rocks including harzburgite lherzolite pyroxenite dunite and peridotite pillowed and massive basalts layered gabbros radiolarian cherts pelagic limestones breccias and tuffs and displays block in matrix structures the blocks of ultramafic rocks gabbros basalts cherts and limestones are set in a matrix of serpentinised ultramafic rocks massive basalts and tuffs the basaltic rocks in the melange show significant geochemical heterogeneity and two compositional groups one ocean island basalt like and the other mid ocean ridge like can be distinguished on the basis of their isotopic compositions and immobile trace element contents such as light rare earth element enrichment in the former but depletion in the latter the more enriched basaltic rocks are interpreted as remnants fragments of seamounts derived from a deep mantle reservoir with low degrees 2 3 of garnet lherzolite mantle melting the depleted basalts most likely formed by melting of a shallower spinel lherzolite mantle source with 15 partial melting it is probable that both groups owe their origin to melting of a mixture between plume and depleted morb mantle the results from this study when integrated with previous work indicate that the junggar ocean crust comprising a significant number of seamounts was likely to have been subducted southward beneath the yili central tianshan block in late devonian early carboniferous the seamounts were scraped off and accreted along with the oceanic crust in an accretionary wedge to form the bayingou ophiolitic melange we present a model for the tectonomagmatic evolution of this portion of the caob involving prolonged intra oceanic subduction with seamount accretion

problems of scale in the modeling and interpretation of coastal dunes abstract coastal dune systems are studied at time scales from seconds to millennia and space scales from millimeters to kilometers present approaches to the study of coastal dunes make it difficult to integrate models and interpretations of these systems over these scale ranges and arrive at reasonable conclusions it is argued that identification of key controls on dune development measurement of those controls and synthesis of data describing past and present conditions and used as calibration points will improve the viability of coastal dune models theoretical and empirical advances are necessary to improve the reliability of predictions across a range of geomorphological scales attempts at linking theoretical systematic models process synoptic measurement and historical or paleoenvironmental synthetic approaches make explicit the recognition that at time scales of more than a few hours and space scales greater than a few hundred meters deterministic models become unstable vis a vis prototype environments process climatologies provide one means to link process based work with broader scaled analysis as scales increase such climatologies will become less appropriate as the data become less reliable or as the systems change or as the scales become too large relative to the process record lengths in these conditions specific data i e samples representing points in time and space become check points for calibrating models it should be possible ideally to integrate both up and down time and space scales this is not yet possible

jurassic cretaceous boundary age and mid ocean ridge type mantle source for shatsky rise basalt sills cored in lowermost berriasian sediments on shatsky rise in the northwest pacific yield a mean 4 0 ar 3 9 ar incremental heating age of 144 6 0 8 ma providing a minimum estimate on the age of the jurassic cretaceous boundary the largest part of the rise was emplaced at rates similar to those of several continental flood basalts the rise formed at an oceanic triple junction and the sills as well as lavas from two dredge sites exhibit an ocean ridge type nd pb sr isotope signature this signature is provisionally consistent with either a perisphere or meteorite impact model but is not predicted by the plume head model of plateau formation however no model can yet be rejected given the very sparse sampling of shatsky rise

evolution of middle america and the in situ caribbean plate model james k h 2009 evolution of middle america and the in situ caribbean plate model origin and evolution of the caribbean plate 328 127 138 james k h lorente m a pindell j l eds conference on geology of the area between north and south america with focus on the origin of the caribbean plate siguenza spain may 29 jun 02 2006

submarine basalts of the northern kerguelen plateau interaction between the kerguelen plume and the southeast indian ridge revealed at odp site 1140 during ocean drilling program leg 183 basaltic cores were retrieved from the northern kerguelen plateau nkp at site 1140 on the extreme north of the plateau 270 km north of the kerguelen archipelago amongst the six basement units recovered five were pillow basalts with fresh glassy rims together with flow lobes this is the first evidence for submarine eruption anywhere on the kerguelen plateau each flow unit has distinct geochemical and isotopic characteristics that span the range from southeast indian ridge seir mid ocean ridge basalt to tholeiitic transitional basalts derived from the kerguelen mantle plume relationships between element abundance ratios involving incompatible elements and isotopic ratios reflect mixing of near primary melts from an seir source and the kerguelen plume with an increasing role for an incompatible element rich end member in the order unit 1

ophiolite genesis and global tectonics geochemical and tectonic fingerprinting of ancient oceanic lithosphere ophiolites and discussions on their origin and significance in earth s history have been instrumental in the formulation testing and establishment of hypotheses and theories in earth sciences the definition tectonic origin and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century here we present a review of these ideas as well as a new classification of ophiolites incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological geochemical and tectonic processes during formation in different geodynamic settings we define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments their geochemical characteristics internal structure and thickness vary with spreading rate proximity to plumes or trenches mantle temperature mantle fertility and the availability of fluids subduction related ophiolites include suprasubduction zone and volcanic arc types the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle melting of the subducting sediments and repeated episodes of partial melting of metasomatized peridotites subduction unrelated ophiolites include continental margin mid ocean ridge plume proximal plume distal and trench distal and plume type plume proximal ridge and oceanic plateau ophiolites that generally have mid ocean ridge basalt morb compositions subduction related lithosphere and ophiolites develop during the closure of ocean basins whereas subduction unrelated types evolve during rift drift and seafloor spreading the peak times of ophiolite genesis and emplacement in earth history coincided with collisional events leading to the construction of supercontinents continental breakup and plume related supermagmatic events geochemical and tectonic fingerprinting of phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in earth history and it can be extended into precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the archean

age and geochemistry of the beata ridge primary formation during the main phase 89 ma of the caribbean large igneous province highlights at least parts of the beata ridge formed during the main clip stage at 95 83 ma sampling of numerous volcanic rocks indicates a broad extrusive magmatic event depleted and enriched geochemical signatures point to a heterogeneous mantle source geochemical heterogeneities can occur on a small scale of tens of kilometers abstract the caribbean large igneous province clip a cretaceous oceanic flood basalt province presumably formed at the initiation of the galapagos hotspot during the m81 cruise of the german r v meteor we sampled the beata ridge a prominent submarine structure in the caribbean sea belonging to the clip the ridge offers the opportunity to directly sample basement sequences of the central submarine part of the clip complementing numerous studies of accreted clip sequences exposed on land around the margins of this lip the majority of the recovered beata ridge samples are volcanic implying that at least parts of the beata ridge were formed during a large extrusive event in contrast to previous assumptions that the structure is primarily composed of intrusive rocks several stratigraphically controlled profiles were sampled along the western slope of the beata ridge using the remotely operated vehicle rov kiel 6000 and revealed variously alternating sequences of magmatic rocks lavas pillow breccias tuffs and gabbros and sediment plains we report new 40ar 39ar age and geochemical major and trace element sr nd hf pb isotope data for the recovered magmatic samples although the 40ar 39ar analyses display disturbed age spectra they suggest an age range of 92 4 76 9 ma thus our age data show for the first time that the beata ridge also formed during the main magmatic stage of the clip 95 83 ma previous studies suggested that the beata ridge was formed during a second lower volume magmatic phase of the clip 81 71 ma possibly related to decompression melting during an extensional phase in the caribbean most samples display relatively flat chondrite normalized rare earth element ree patterns commonly observed throughout the clip but light ree enriched and depleted compositions are also present the occurrence of enriched and depleted incompatible element and radiogenic isotope signatures implies a heterogeneous mantle source region as is observed for other lips worldwide since a high degree of geochemical variability is observed over short stratigraphic intervals within the rov profiles melt homogenization did not operate as effectively as commonly assumed for lips instead the plume head probably preserved some domains of enriched and depleted components whereas most of the melts during the main stage have intermediate compositions with flat ree patterns representing mixtures of the enriched and depleted components

influence of averaging interval on shear velocity estimates for aeolian transport modeling abstract recent investigations of aeolian transport have focused on increasingly short time scales because of growing recognition that wind unsteadiness is a major factor in the dynamics of sediment transport however the statistical reliability of shear velocity u estimates becomes increasingly uncertain as averaging interval is decreased this study provides an empirical assessment of the influence of averaging interval on the reliability of u estimates the data consist of 15 min wind speed profiles 1 hz sampling collected at four coastal sites each profile was subdivided into progressively shorter fixed length time intervals and estimates of u and the 95 confidence interval for u were determined for each time block using standard statistical techniques the logarithmic model accurately represents the measured wind speed profiles even with relatively brief averaging intervals mean r 2 values remain robust down to block lengths as short as 10 20 s typically retaining better than 98 of the r 2 value found for the full length data sets fewer than 2 of the individual 10 s blocks had r 2 values less than 0 9 however mean confidence intervals typically expanded by 70 80 of the full record value as block length decreased from 900 to 10 s for highly log linear profiles this amounted to an absolute increase from about 8 to only 14 of u so that the additional information gained through the use of shorter averaging intervals may outweigh the increase in statistical uncertainty nevertheless given that rates of aeolian transport are generally modeled as a function of u 3 this increase in uncertainty may be significant for transport modeling thus very short averaging intervals should be used with caution when predicting aeolian sediment flux it is proposed that transport modeling should incorporate the shear velocity confidence interval as an indicator of the potential error associated with this source of uncertainty

la isla de gorgona colombia a petrological enigma a wide range of intrusive wehrlite dunite gabbro and olivine gabbro and extrusive komatiites picrites and basalts igneous rocks are found on the small pacific island of gorgona the island is best known for its 90 ma spinifex textured komatiites the only true phanerozoic komatiites yet discovered early work led to suggestions that the rocks of the island formed at a mid ocean ridge however more recent research supports an origin as part of a hot mantle plume derived oceanic plateau one of the main lines of evidence for this origin stems from the inferred high mantle source temperatures required to form the high mgo n15 wt komatiites and picrites another remarkable feature of the island considering its small size 8 2 5 km is the degree of chemical and radiogenic isotopic heterogeneity shown by the rocks this heterogeneity requires a mantle source region with at least three isotopically distinctive source regions two depleted and one enriched although these mantle source regions appear to be derived in significant part from recycled oceanic crust and lithosphere enrichments in 187os 186os and 3he in gorgona lavas and intrusive rocks suggest some degree of transfer of material from the outer core to the plume source region at dw modelling reveals that the komatiites probably formed by dynamic melting at an average pressure of 3 4 gpa leaving residual harzburgite trace element depletion in gorgona ultramafic rocks appears to be the result of earlier deeper melting which produced high mgo trace element enriched magmas the discovery of a trace element enriched picrite on the island has confirmed this model gorgona accreted onto the palaeocontinental margin of northwestern south america in the eocene and palaeomagnetic work reveals that it was formed at 26 8s it has been proposed that gorgona is a part of the caribbean colombian oceanic plateau ccop however the ccop accreted in the late cretaceous and was derived from a more equatorial palaeolatitude this evidence and differing geochemical signatures strongly suggests that gorgona and probably other coastal oceanic plateau sequences in colombia and ecuador belong to a completely different oceanic plateau to the ccop

an experimental study of multiple grain size ejecta produced by collisions of saltating grains with a flat bed collision data are presented from coloured high speed films of three size fractions of sand grains saltating over a bed of the total grain population each fraction was colour tagged and the proportion of each size ejected by grains colliding with the surface was recorded on a number of films taken as the bed was progressively eroded the results confirm earlier findings that v3 v1 0 5 0 6 vn v1 08 and the rebound angle increases with decreasing grain size ejected grains are examined in relation to their size the impactor size ejection speed and angle and the number of ejecta per collision in addition changes in grain parameters are observed with time for fine impactors ejection speeds generally increase with a decrease in ejecta size but the fine fraction does not follow this trend for the coarse and medium impactors ejection angles are typically between 40 and 60 with coarse grains having shallower mean angles than fine ejecta the number of ejections per collision increases with a decrease in particle size for each impactor size the general tendency for coarse particles to be ejected at lower speeds and shallower angles than fine particles will lead to sorting of the grain sizes there is poor correlation between the forward momentum loss of the saltating grams at collision and both the forward momentum of the ejected grains and the number of ejected grains much of the forward momentum of the saltating grains is transfered to creeping grains the composition and geometry of the bed are considered to be important factors in the evolution of the saltation cloud

groundwater in the celtic regions this book covers a diverse range of hydrogeological environments that occur in the celtic regions of britain and ireland these include hard rock aquifers of lower palaeozoic and precambrian age generally dominated by fracture flow within a shallow zone of weathering carboniferous limestone aquifers often characterized by conduit flows in karstic systems dual porosity permo triassic sandstone aquifers and quaternary deposits many of which form shallow granular aquifers the papers presented here address a number of current issues common to the celtic regions including groundwater protection policies groundwater management in karst aquifers groundwater development in quaternary aquifers groundwater evaluation in data scarce aquifers and groundwater supplies to small island communities

70 m y history 139 69 ma for the caribbean large igneous province it is commonly accepted that large igneous provinces are formed through catastrophic volcanic events occurring over vast areas within a few million years at the initiation of hotspots mantle plumes new 40ar 39ar ages 111 139 ma and geochemical results from the nicoya peninsula costa rica extend the age range of volcanism in the caribbean large igneous province to 70 m y 69 139 ma our results are not consistent with the formation of this vast igneous province through a single plume head at the initiation of a mantle plume such as the galapagos instead we propose that multiple oceanic intraplate igneous structures such as plateaus and hotspot tracks were accumulated through the subduction process the igneous structures could be remnants of the earlier history of the galapagos hotspot making it one of the oldest active hotspots on earth alternatively they could have been derived from several spatially distinct mantle melting events that sampled similar source material e g oceanic lithosphere of similar age

detecting impacts of sand grains with a microphone system in field conditions abstract this paper describes the miniphone an instrument to measure aeolian saltation this instrument is a modified electret microphone that detects the impacts of individual grains the unidirectional miniphone is inexpensive approximately us 10 small and poses minimal disruption to the wind field it can be sampled at rates up to 44 100 hz using commonly available sound card technology or it can be interfaced with a data acquisition system data from deployments on beaches on marco island fl usa and near shoalhaven heads nsw australia using sample rates of 44 100 hz and 6000 hz are presented an algorithm for identifying discrete impacts of grains is described the number of saltation impacts was not reduced when sub sampling a record from 44 100 hz to 6000 hz the most immediate use for the miniphone is for short term deployments to detect unsteadiness in the saltation field

late carboniferous high end t ehf t granitoids enclaves and dikes in western junggar nw china ridge subduction related magmatism and crustal growth abstract we report results of petrologic geochronological and geochemical investigation of the late carboniferous diorites granodiorites amphibole am bearing granites and associated dioritic and monzonitic enclaves and mafic and granitic dikes in the keramay area of the western junggar region of central asian orogenic belt caob zircon u pb dating suggests that they were generated in the late carboniferous 316 304 ma the diorite and granodiorite compositions extend over a wide range of sio2 53 70 wt sr 240 602 ppm and mg 41 58 values and are characterized by moderately fractionated rare earth element ree patterns nb ta depletion and relatively low y and yb contents the mafic dikes consist of dolerites diorite porphyries and minor granodiorite porphyries and have variable sio2 51 59 wt and high mg cr and ni values with the exception of two samples with relatively high heavy ree hree contents the mafic dikes exhibit trace element characteristics similar to diorites and granodiorites the am bearing granites and a granite porphyry dike sample have high levels of sio2 73 77 wt hrees e g yb 3 46 15 7 ppm and low mg cr and ni contents along with clearly negative eu ba and sr anomalies similar to typical a type granites all granitoids enclaves and dikes in this region have high positive end t 7 13 to 9 74 and zircon ehf t 10 to 16 values and moderate initial 87sr 87sr ratios 0 7004 0 7049 mineral composition data suggest that the parental magmas for mafic dikes are similar to cenozoic sanukitoids in the setouchi arc area japan and were possibly generated under water rich and high oxygen fugacity nno 1 5 to nno 2 7 conditions they most likely originated from partial melting of a mantle source variably modified by subducted oceanic crust derived melts and minor fluids and subsequently underwent fractional crystallization the diorites and granodiorites were possibly generated by magma mixing between enriched lithospheric mantle and juvenile lower crust derived magmas coupled with minor crystal fractionation the am bearing granites and granite porphyry dike were produced by partial melting of juvenile crustal materials at shallow crustal levels taking into account widespread contemporaneous magmatism including morb type basalts and slab derived adakites in western junggar we suggest that the keramay intrusive rocks were generated in a special arc setting related to ridge subduction and resultant slab window which played an important role in the crustal growth of the caob

constraints on aeolian sediment transport to foredunes within an undeveloped backshore enclave on a developed coast abstract landforms present in undeveloped beach enclaves located between properties developed with houses and infrastructure are often left to evolve naturally but are influenced by the human structures near them this field study evaluates how buildings and sand trapping fences change the direction of wind approach reduce wind speed and restrict fetch distances for sediment entrainment thereby reducing the potential for aeolian transport and development of dunes in enclaves field data were gathered in an 80 m long 44 m deep beach enclave on the ocean shoreline of new jersey usa comparison of wind characteristics in the enclave with a site unaffected by buildings revealed that offshore winds in the enclave are reduced in strength and altered in direction by landward houses increasing the relative importance of longshore winds vertical arrays of anemometers on the foredune crest foredune toe and berm crest in the enclave revealed increasing wind speed with distance offshore with strongest winds on the berm crest vertical cylindrical traps on the foredune crest foredune toe mid backshore berm crest and upper foreshore revealed the greatest rate of sediment transport on the berm crest sediment samples from the beach and from traps revealed limited potential for aeolian transport because of coarse grain sizes strong oblique onshore winds are common in this region and are normally important for transporting sand to dunes the length of an enclave and the setback distance on its landward side determine the degree to which sediment delivered by oblique winds contributes to dune growth the landward edge of the enclave defined by a sand fence near the dune toe is sheltered along its entire length from winds blowing at an angle to the shoreline of 25 or less a foredune set back this distance in an enclave the length of an individual lot about 20 m would be sheltered at an angle of 57 or less reducing the opportunity for dune building by onshore winds reduced potential for aeolian transport in enclaves implies that human actions may be required to build dunes artificially to protect buildings and roads from storm overwash

sand transport dynamics after a foredune breach a case study from schoorl the netherlands near schoorl in the netherlands a gap was created in the foredunes during a nature development project in 1997 this resulted in considerable aeolian sand transport and allowed the sea to enter the swale valley behind the foredunes during storm events from 1997 to 2002 a monitoring program was carried out and various data sets were collected this study used a part of those data to investigate the effects of a foredune breach on sand transport dynamics the main focus was on the aeolian transport of sediment through the gap in the dunes after the breach calcareous beach sand was transported into the swale valley where exclusively decalcified sand was present this enabled a study of the spatial aspects of transport based on six data sets of carbonate content that were collected during the 1997 2002 period grids of carbonate content were interpolated and analysed together with data on geomorphology topography and wind characteristics the results provided insight on the displacement speed of the deposition front of calcareous sand the influence of transport barriers and the correlation of transport directions with wind data in addition the study led to the observation that the trend of increase of available digital data during the last two decades is significant in facilitating the study of sand transport at the landscape scale this is encouraging given the fact that the practical use of existing sand transport models in this context remains limited c 2006 elsevier b v all rights reserved

a new instantaneous aeolian sand trap design for field use a new aeolian sediment trap is described which can give up to 1 hz measurement frequency in held conditions the trap adopts a circular horizontal trap design with a load cell connection to give continuous unobtrusive trap measurement of sediment flux simultaneous velocity recording is carried out using an anemometer trap construction costs are approximately pound 200 initial results in held conditions using a direct comparison of wind velocity data sampled at an equivalent frequency have given a first order relationship between sediment flux and velocity the trap enables simultaneous sampling of wind velocity and sediment flux at a sufficiently short interval to enable investigation of sediment transport dynamics under a variety of field conditions

the basaltic volcanism of the dumisseau formation in the sierra de bahoruco sw dominican republic a record of the mantle plume related magmatism of the caribbean large igneous province abstract the basaltic volcanism of the dumisseau fm in the sierra de bahoruco sw dominican republic offers the opportunity to study on land the volcanism of the caribbean large igneous province clip it consists of an at least 1 5 km thick sequence of submarine basaltic flows and pyroclastic deposits intruded by doleritic dykes and sills three geochemical groups have been identified low ti tholeiites group i high ti transitional basalts group ii and high ti and lree enriched alkaline basalts group iii these geochemical signatures indicate a plume source for all groups of basalts which are compositionally similar to the volcanic rocks that make up various clip fragments in the northern region of the caribbean plate trace element modelling indicates that group i magmas are products of 8 20 melting of spinel lherzolite group ii magmas result 4 10 melting of a mixture of spinel and garnet lherzolite and group iii basalts are derived by low degrees 0 05 4 of melting of garnet lherzolite dynamic melting models suggest that basalts represent aggregate melts produced by progressive decompression melting in a mantle plume there is no compositional evidence for the involvement of a caribbean supra subduction zone mantle or crust in the generation of the basalts two 40 ar 39 ar whole rock ages reflect the crystallisation of group ii magmas at least in the late campanian 74 ma and the lower eocene 53 ma all data suggest that the dumisseau fm is an emerged fragment of the clip which continues southward through the beata ridge

design and field test of a continuously weighing tipping bucket assembly for aeolian sand traps a new tipping bucket assembly t bass for aeolian sand traps has been designed and field tested with encouraging results it facilitates high frequency monitoring of sediment flux over extensive time periods and therefore offers improved performance over other continuously weighing mechanisms that are generally limited to either a small total load capacity or poor resolving ability the t bass is a modified version of the tipping bucket meteorological rain gauge mounted on a cantilever and pulley system linked to an electronic load cell as trapped sand accumulates in one of the buckets the increasing mass exerts a downward force on the cantilever arm which translates into a slight deflection of the thin beam element of the load cell the resulting voltage output is proportional to the load and the analogue signal may be monitored by a data acquisition system eventually the bucket fills to capacity and tips the sediment load is emptied into a reservoir container the other bucket of the bucket pair is positioned beneath the funnel and the system is automatically reset to zero load for continued measurement in this way a high frequency record of sediment accumulation is obtained field testing of five prototypes demonstrated that the t bass can be configured to yield i linear calibrations for conversion of voltage to gram weight with r2 values exceeding 0 99 ii weight resolution of 0 99 ii weight resolution of 0 1 g or better depending on load cell specifications and bucket capacity and iii detailed temporal information order of 1 s on sediment flux allowing investigation of its relation to attributes of the wind field suggested modifications may produce improved performance in future versions copyright 1998 john wiley sons ltd

storm impacts and shoreline recovery mechanisms and controls in the southern north sea abstract storm impacts play a significant role in shoreline dynamics on barrier coastlines furthermore inter storm recovery is a key parameter determining long term coastal resilience to climate change storminess variability and sea level rise over the last decade four extreme storms with strong energetic waves and high still water levels resulting from high spring tides and large skew surge residuals have impacted the shoreline of the southern north sea the 5th december 2013 storm with the highest run up levels recorded in the last 60 years resulted in large sections of the frontline of the north norfolk coast being translated inland by over 10 m storms in march and november 2007 also generated barrier scarping and shoreline retreat although not on the scale of 2013 between 2008 and 2013 a calm period recovery dominated barrier position and elevation but was spatially differentiated alongshore for one study area scolt head island no recovery was seen this section of the coast is being reset episodically landwards during storms by contrast the study area at holkham bay showed considerable recovery between 2008 and 2013 with barrier sections developing seaward through foredune recovery the third study area brancaster bay showed partial recovery in barrier location and elevation results suggest that recovery is promoted by high sediment supply and onshore intertidal bar migration at rates of 40 m a 1 these processes bring sand to elevations where substrate drying enables aeolian processes to entrain and transport sand from upper foreshores to foredunes we identify three potential sediment transport pathways that create a region of positive diffusivity at holkham bay during calm periods a general westward movement of sediment from the drift divide at sheringham sources the intertidal bar and foredune development at holkham bay however during and following storms the drift switches to eastward not only on the beach itself but also below the 7 m isobath sediment from the eroding barrier at brancaster bay and especially scolt head island also sources the sediment sink of holkham bay knowledge of foredune growth and barrier recovery in natural systems are vital aspects of future coastal management planning with accelerated sea level rise and storminess variability

terraced fills of pleistocene and holocene age in the rheidol valley wales the legacy of repeated pleistocene glaciations has endowed many welsh river valleys with locally thick successions of glacial and alluvial sediments investigations of a well preserved flight of terraced sediments with good exposures at capel bangor on the afon rheidol mid wales has allowed its quaternary valley fill stratigraphy to be examined in detail study has revealed five terraced fills consisting of seven distinct sedimentary units these range from late devensian ice contact and ice marginal deposits to holocene high sinuosity stream sediments with episodes of man induced accelerated deposition of fine grained alluvium and to aggradation and subsequent incision associated with historic metal mining examination of general sedimentary properties e g granulometry sedimentary structures terrace surface morphology show both differences in the pattern and controls of deposition and also progressive changes over late devensian and holocene times the sediments of the rheidol valley record the response and subsequent recovery of a drainage basin to glaciation and the increasing influence of man on sediment yields channel processes and sediment quality

aeolian sand transport a wind tunnel model wind sand transport is an important geological process on earth and some other planets formulating the wind sand transport model has been of continuing significance majority of the existing models relate sand transport rate to the wind shear velocity based on dynamic analysis however the wind shear velocity readapted to blown sand is difficult to determine from the measured wind profiles when sand movement occurs especially at high wind velocity moreover the effect of grain size on sand transport is open to argument detailed wind tunnel tests were carried out with respect to the threshold velocity threshold shear velocity and transport rate of differently sized loose dry sand at different wind velocities to reformulate the transport model the results suggest that the relationship between threshold shear velocity and grain size basically follow the bagnold type equation for the grain size d 0 1 mm however the threshold coefficient a in the equation is not constant as suggested by bagnold but decreases with the particle reynolds number the threshold velocity at the centerline height of the wind tunnel proved to be directly proportional to the square root of grain diameter attempts have been made to relate sand transport rate to both the wind velocity and shear velocity readapted to the blown sand movement the reformulated transport model for loose dry sand follows the modified o brien rindlaub type equation q f1 d 1 ru 2 g v3 or the modified bagnold type equation q f2 d 1 rt 0 25 g u 3 where q is the sand transport rate the sand flux per unit time and per unit width in kg m 1 s 1 is the air density 1 25 kg m 3 g is the acceleration due to gravity 9 81 m s 2 ru vt v rt u t u v is the wind velocity at the centerline of the wind tunnel in m s 1 vt is the threshold velocity measured at the same height as v in m s 1 u is the shear velocity with saltating flux in m s 1 u t is threshold shear velocity in m s 1 f1 d 1 475 24 93 62d d f2 d 1 41 4 98exp 0 5 ln d 1 55d 0 57 2 d is the grain diameter in mm and d is the reference grain diameter equals 0 25 mm the bagnold s equation that asserts for a given wind drag the rate of movement of a fine sand is less than that of a coarse sand is not supported by the reformulated models

on the prediction of bed load sand transport rate in air this paper discusses the parameterization of aeolian mass transport rate beginning with a critical discussion of four different forms of the prediction equation following this recent progress in understanding the physics of the aeolian system is used to suggest an alternative approach which provides some new insights into the prediction of mass flux the primary object of the paper is not to add another transport rate equation to those already present in the literature but rather to discuss the transport system in relation to the physical processes showing to some extent why reliable transport rate prediction has so far been elusive

aeolian sand transport an optimized model consideration of the available equations for prediction of aeolian sand transport led to the development of a model which relies on optimization techniques for the production of improved performance the model has been applied to the characterization of dunesand movement in coastal environments in eastern australia

late jurassic oceanic crust and upper cretaceous caribbean plateau picritic basalts exposed in the duarte igneous complex hispaniola abstract four distinct rock units have been recognized near el aguacate in the janico juncalito la vega area of the duarte complex dominican republic 1 serpentinites crosscut by numerous diabasic dikes 2 basalts interbedded with late jurassic ribbon cherts 3 picrites and ankaramites relatively enriched in incompatible trace elements and 4 amphibolites and gneissic amphibolites chemically similar to oceanic plateau basalts similar ar ar ages of late magmatic amphibole from a picrite and hornblende from an amphibolite documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty decl

a plate tectonic model for the mesozoic and early cenozoic history of the caribbean plate abstract we present a model in which the caribbean plate is an intra american feature formed along the caribbean spreading center as opposed to the current model that considers the caribbean plate as a far travelled crustal segment that formed in the pacific region paleomagnetic data which cover an age range from jurassic through paleocene indicate the ophiolite complexes in costa rica and panama formed in an equatorial position the ophiolites did not fundamentally change their position relative to south america since their origin basaltic rocks of the lower part of the ophiolites are of mid ocean ridge type suggesting formation at a spreading center they are interpreted to have formed as part of the proto caribbean crust at a spreading axis in an intra american position during jurassic and early cretaceous times the upper part of the ophiolites is mainly built up by island arc and intraplate basalts the island arc basalts evolved at the central american landbridge which started in the middle cretaceous the intraplate basalts are related to the caribbean plateau basalt which thickened and stiffened the caribbean crust in middle cretaceous to probably campanian times changes in relative plate motions along the middle american convergent plate margin are reflected by orientations and time sequences of paleostress tensors calculated from fault slip data in southern mexico and costa rica kinematic indicators from mylonite zones display sinistral movement along secondary shear zones within the southern mexican crustal complexes and along the northern boundary of the chortis block in the motagua polochic fault system this reflects the eastward drift of the chortis block since the beginning of the cenozoic at this time the chortis block became part of the caribbean plate which moved more than 1000 km towards the east relative to the north and south american plates during the cenozoic

evaluation of aeolian sand transport equations using intertidal zone measurements saunton sands england sand transport rates were measured using a vertical sand trap along the intertidal zone of a beach in north devon england together with simultaneous monitoring of the wind speed on the beach and moisture levels in the surface layers of sand the results of 88 sand trap samples in a wide range of wind speeds showed that moisture levels up to 14 in the top 1 2 mm of the beach sand have no discernible effect on the transport rates transport rates measured from areas of the beach where the moisture was below this level are compared with the rates predicted by seven expressions based on theoretical and wind tunnel research together with the empirical results of other published research measured transport rates range from 0 0001 to 0 22 kg m 1 s 1 the results indicate that expressions based on a power relation between the wind speed and the transport rate and which include a threshold velocity term provide the best estimates of the observed transport rates

field measurement and numerical modelling of aeolian mass flux distributions on a sandy beach the vertical and horizontal distributions of aeolian mass flux were measured at oceano dunes california and these data were used to evaluate a numerical model of saltation grain size analyses showed that the distributions of the modal sediment size class corresponded closely to those of the total sediment population and modelling thus focused on replicating the distributions of the mean grain size although much previous work has assumed that the mean launch speed of saltating particles varies in proportion to shear velocity simulations using a constant mean launch speed were found to yield the closest approximations to the mass flux distributions observed in the field both exponential and gamma distributions of launch velocity produced realistic simulations although the latter approach required the inclusion of an additional reptation component to achieve good results a range of mean launch angles and an equivalent sphere correction were also found to generate comparable results providing the other input parameters could be varied freely all the modelling approaches overestimated the proportion of mass flux occurring at the bottom of the vertical distributions and underestimated the proportion occurring at the upwind end of the horizontal distributions no theoretical shortcoming that would account for these small but systematic discrepancies could be identified and experimental error thus represents a more plausible explanation the conclusion that mean grain launch speeds are essentially constant and independent of shear velocity suggests that the additional kinetic energy extracted by grains under more energetic wind conditions is largely transferred to the bed and that increases in the transport rate are therefore driven primarily by the ejection of additional grains it is suggested that the kinetic energy of rebounding grains is constrained by the ability of the bed to resist deformation equivalent to a plastic limit hence grains of larger mass diameter rebound from the bed at lower speeds and follow shorter lower trajectories as has been widely observed previously

the effect of surface slope on saltation threshold a new wind tunnel has been constructed to study the mass transport properties of wind blown sand this report on the first set of experiments in the new wind tunnel concerns the effect of slope on threshold friction speed the results of this series of static threshold experiments and one dynamic threshold experiment for a range of particle diameters and bed slope angles show that provided the effects of reynolds number variation and interparticle cohesive force are accounted for the static friction angle is independent of slope and close in value to the measured static angle of response

field evaluation of some sand transport models fluorescent tracer procedures originally developed for research on fluvial sediment movement were used to monitor the movement of three commercially purchased sands in a natural dune environment results were compared with estimates of transport rates from three theoretical models estimates from models by bagnold 1941 and hsu 1971 were larger by as much as one order of magnitude than the rates observed in the tracer study the model of a a kadib 1965 provided closer correspondence to observed transport rates for medium sand mean diam 0 653 mm but underestimated rates for coarse sand mean diam 0 992 mm

observations of collisions of saltating grains with a granular bed from high speed cine film high speed photography was used to record saltating sand grains colliding with a horizontal noncohesive bed of similarly sized grains impacting grain bed interaction is discussed in general the process as observed from the films is then described in terms of the apparent bed contact length abcl and various parameters of the impacting grains and any ejected grains examples are given of typical behaviour of bed grains in response to impacting grains of different sizes saltating grains that are large in comparison to the bed grains they encounter at collision can churn up the surface layers of soils and sediments so that previously buried grains become available for entrainment this process is discussed in relation to the potential release of dust particles into the airflow

upper crustal structure of the western colombian basin caribbean sea multichannel seismic reflection profiles show that most of the western colombian basin is underlain by a large oceanic plateau the crust of this plateau has a smooth upper surface an oceanic velocity structure and a thickness at least twice that of typical oceanic crust locally well defined reflections within the plateau crust are related to layered basalt flows and interbedded sediments a mounded reflection pattern within acoustic basement at the crest of the plateau mono rise may represent volcanic knolls smooth surfaced basement of the western colombian basin is probably equivalent to the upper cretaceous basement complex below seismic reflection horizon b in the central venezuelan basin and resembles the basements of some cretaceous oceanic plateaus and aseismic rises in the western pacific an area of apparently typical oceanic crust lies adjacent to the colombian basin plateau and may represent relatively unmodified oceanic crust upon which the plateau was constructed reflections within the flank of the colombian basin plateau appear to overlap this crust indicating that the plateau is younger than the oceanic crust oceanic plateau crust extends to panama and costa rica without apparent structural break and may be continuous with the basement complex of southern central america

mafic pegmatites intruding oceanic plateau gabbros and ultramafic cumulates from bolivar colombia evidence for a wet mantle plume

aeolian sediment supply at a mega nourishment abstract mega nourishments are intended to enhance growth and resilience of coastal dunes on medium to long time scales by stimulation of natural sediment transport processes the growth and resilience of coastal dunes largely depends on the presence of a continuous supply of aeolian sediment a recent example of a mega nourishment is the 21 mm 3 mega nourishment known as the sand motor the sand motor is intended to nourish the entire holland coast over a period of two decades four years of bi monthly topographic measurements of the sand motor domain provide an opportunity to analyze spatiotemporal variations in aeolian sediment supply using an aeolian sediment budget analysis it appears that more than 58 of all aeolian sediment deposits originate from the low lying beaches that are regularly reworked by waves aeolian sediment supply from higher beaches diminished after half a year after construction of the sand motor likely due to the formation of deflation lag deposits that constitute a beach armor layer the compartmentalization of the sand motor in armored and unarmored surfaces suggests that the construction height is an important design criterion that influences the lifetime and region of influence for any mega nourishment

modification of an oceanic plateau aruba dutch caribbean implications for the generation of continental crust the generation of the continental crust may be connected to mantle plume activity however the nature of this link and the processes involved are not well constrained an obstacle to understanding relationships between plume related mafic material and associated silicic rocks is that later tectonic movements are liable to obscure the original relationships particularly in ancient greenstone belts studies of younger analogous regions may help to clarify these relationships on the island of aruba in the southern caribbean a sequence of partly deformed mafic volcanic rocks intruded by a predominantly tonalitic batholith is exposed the mafic lavas show geochemical and isotopic affinities with other basaltic picritic and komatiitic rocks that crop out elsewhere in the caribbean these are well documented as belonging to an 88 91 ma plume related oceanic plateau which is allochthonous with respect to the americas and is thought to have been formed in the pacific region the 85 to 82 ma tonalitic rocks share some geochemical characteristics high sr and ba low nb and y with archaean tonalite trondhjemite granodiorite ttg suites field relationships suggest that deformation of the plateau sequence possibly related to collision with a subduction zone was synchronous with intrusion of the aruba batholith new incremental heating 40ar 39ar dates combined with existing palaeontological evidence show that cooling of the batholith occurred shortly after eruption of the plateau basalt sequence sr nd isotopic data for both rock suites are uniform 87sr 86sri 0 7035 endi 7 whereas pb isotopes are more variable plateau sequence 206pb 204pb 18 6 19 1 207pb 204pb 15 54 15 60 208pb 204pb 38 3 38 75 aruba batholith 206pb 204pb 18 4 18 9 207pb 204pb 15 51 15 56 208pb 204pb 38 0 38 5 this suggests that there has been a minor sedimentary input into the source region of the batholith however the limited time interval between basaltic and tonalitic magmatism makes a normal subduction related origin for the tonalites improbable instead models involving derivation of tonalite from partial melting of the plateau sequence or alternatively genesis in an unusual subduction zone environment are investigated

cretaceous basaltic terranes in western colombia elemental chronological and sr nd isotopic constraints on petrogenesis accreted terranes comprising mid to late cretaceous picrites basalts and dolerites occur in three north south trending belts in western colombia in the central cordillera western cordillera and along the pacific coast the geochemistry of these rocks is consistent with an oceanic plateau plume related origin and they most probably formed in the pacific as part of the caribbean oceanic plateau these igneous rocks display small but significant inter cordillera variations being younger and more depleted in incompatible trace element ratios and with more positive end values to the west the igneous rocks of the pacific coast serrania de baudo are dated at 73 78 ma 40ar 39ar and those of the western cordillera at 90 ma whereas the volcanics of the central cordillera are believed to be older than 100 ma most of the igneous rocks are basaltic and it is suggested that they have fractionated from picritic primary magmas generated by partial melting within a hot mantle plume variable and positive end values reveal that the plume must have been heterogeneous originating from a mantle source with a long term history of depletion partial melt modelling suggests that the composition of the basalts requires at least some input from a mantle source region containing garnet and that the extent of partial melting required to reproduce the composition of the erupted basalts is of the order of 20 mixing of melts from different depths either in the mantle melting column or during fractionation in lithospheric magma chambers can explain the relative homogeneity of basaltic lavas erupted to form this and other oceanic plateaux the caribbean colombian oceanic plateau may have formed at an oceanic spreading centre and valuable comparisons can be made between iceland and the caribbean colombian plateau

effect of source width and tidal elevation changes on aeolian transport on an estuarine beach data from a moderate energy meso tidal beach on the east side of delaware bay new jersey usa revealed the significance of both beach width as a source for aeolian transport and the effect of tidal rise on source width wind speeds averaged over 17 1 min recorded 6 m above the crest of a 0 5 m high dune ranged from 11 6 to 12 7 m s 1 during the experiment the highest observed rate of transport on the beach was 0 0085 kg m 1 s 1 monitored at rising low tide when the average wind speed was 11 6 m s 1 across 0 35 mm diameter surface sediments the wind direction was oblique to the shoreline creating a source width of 34 m the reduction in the width of the beach as a source for aeolian transport during rising tide was approximately arithmetic whereas the reduction in volume of sediment trapped was exponential aeolian transport effectively ceased when source width was less than 8 m wind conditions moisture content of the surface sediments and presence of binding salts did not appear to vary dramatically and no coarse grained lag deposit formed on the surface of the beach the decrease in rate of sediment trapped through time in the tidal cycle is attributed to differences in source width sediment deposited in the litter behind the active beach by strong winds during the rising tide was eroded during the high water period by the high waves and storm surge generated by these winds and net losses of sediment were observed despite initial aeolian accretion

multiple plume events in the genesis of the peri caribbean cretaceous oceanic plateau province the oceanic crust fragments exposed in central america in north western south america and in the caribbean islands have been considered to represent accreted remnants of the caribbean colombian oceanic plateau ccop on the basis of trace element and nd sr and pb isotopic compositions we infer that cumulate rocks basalts and diabases from coastal ecuador have a different source than the basalts from the dominican republic the latter suite includes the 86 ma basalts of the duarte complex which are light rare earth element ree enriched and display relative to normal mid ocean ridge basalts nmorb moderate enrichments in large ion lithophile elements together with high nb ta pb and low th contents moreover they exhibit a rather restricted range of nd and pb isotopic ratios consistent with their derivation from an ocean island type mantle source the composition of which includes the himu high 238u 204pb component characteristic of the galapagos hotspot in contrast the 123 ma ecuadorian oceanic rocks have flat ree patterns and relative to nmorb are depleted in zr hf th and u moreover they show a wide range of nd and pb isotopic ratios intermediate between those of ocean island basalts and nmorb it is unlikely on geochemical grounds that the plume source of the ecuadorian fragments was similar to that of the galapagos in addition because of the nne motion of the farallon plate during the early cretaceous the ecuadorian oceanic plateau fragments could not have been derived from the galapagos hotspot but were likely formed at a ridge centered or near ridge hotspot somewhere in the se pacific

a floating element drag plate for direct measurement of bed shear stress during eolian transport abstract this report outlines the design of an inexpensive floating element drag plate developed to obtain direct measurements of bed shear stress during eolian saltation shear stress measurements obtained from the drag plate during a field test are evaluated in comparison with estimates of shear velocity derived from an adjacent mast of rotating cup anemometers in terms of their correspondence with measurements of the transport rate obtained from a load cell based electronic sediment trap the two approaches provide a comparable level of explanation for transport rates averaged over intervals of several minutes however the drag plate provides a substantially improved level of explanation for 15 second intervals and also for the instantaneous 1 hz transport measurements it is suggested that the drag plate approach has considerable potential for investigating high frequency fluctuations in eolian transport rates

tectonic evolution of the caribbean the development of the caribbean is discussed in terms of modern tectonic theory the nature of the site on which the caribbean formed is examined and the development of the rifted margins of the caribbean is described constraints on caribbean evolution from the relative motions of north and south america are briefly examined and the caribbean oceanic plateau is discussed the great island arc system of the caribbean is addressed in detail emphasizing the way the great arc of the caribbean was segmented the role of central america in caribbean history is briefly considered

wavelet power spectra of aeolian sand transport by boundary layer turbulence 1 this letter reports on wavelet spectral analysis of collocated time series of streamwise wind speed and aeolian sand transport collected at 0 04 m above the bed in a field experiment on top of a large sand mound in a desert environment results suggest three distinct spatio temporal scales of interaction between boundary layer turbulence and sediment transport a long term scale associated with the regional mixing layer an integral time scale associated with the internal boundary layer and a streamer scale associated with the inertial subrange eddy cascade and saltation inertia

magma source evolution beneath the caribbean oceanic plateau new insights from elemental and sr nd pb hf isotopic studies of odp leg 165 site 1001 basalts ocean drilling project leg 165 sampled 38 m of the basaltic basement of the caribbean plate at site 1001 on the hess escarpment the recovered section consists of 12 basaltic flow units which yield a weighted mean ar ar age of 80 9 0 9 ma the basalts 6 4 8 5 wt mgo are remarkably homogeneous in composition and are more depleted in incompatible trace elements than n morb depleted initial radiogenic isotope ratios end 11 1 to 11 9 ehf 15 2 to 16 9 87sr 86sr 0 7025 0 7028 206pb 204pb 18 34 18 50 207pb 204pb 15 42 15 51 208pb 204pb 37 64 37 90 reveal a long term history of depletion although the site 1001 basalts are superficially similar to n morb radiogenic isotopes in conjunction with incompatible trace element ratios show that the basalts have more similarity to the depleted basalts and komatiites of gorgona island this chemical composition strongly implies that the site 1001 basalts are derived from a mantle plume depleted component and not from depleted ambient upper mantle therefore the site 1001 basalts are both compositionally and tectonically a constituent part of the caribbean oceanic plateau mantle melt modelling suggests that the site 1001 lavas have a composition which is consistent with second stage melting of compositionally heterogeneous mantle plume source material which had already been melted most likely to form the 90 ma basalts of the plateau the prolonged residence 10 ma of residual mantle plume source material below the region confirms computational model predictions and places significant constraints on tectonic models of caribbean evolution in the late cretaceous

seismic stratigraphy and structure of the caribbean igneous province multichannel seismic reflection profiles reveal the tectonic and stratigraphic complexity of the caribbean province a smooth reflector b forms the top of widespread cretaceous volcanic flows drilled during dsdp leg 15 and odp leg 165 in addition we also show other seismic evidence of volcanism sills and dipping horizons the southern parts of the venezuela and colombia basins are underlain by rough basement that shows many characteristics of oceanic crust several thick volcanic plateaus separated by deep basins with thin crust comprise the caribbean volcanic province in the venezuela basin only normal oceanic crust is present but in other basins this crust is underlain by underplated volcanic material the crust of the venezuela basin is less than 5 km thick and was probably formed in the pacific during the jurassic refraction data indicate that a thin layer 2v is formed by original oceanic crust overlain by a thin volcanic layer an intra basement reflection sub b marks the top of original oceanic crust that is sandwiched between an upper volcanic layer and lower underplated material this underplated layer forms a very thick layer 3v beneath the beata and nicaragua volcanic plateaus the upper part of layer 3v is gabbroic and outcrops on the beata ridge the thickening occurs mainly in the high velocity lower part of layer 3v and is attributed to the presence of magnesian rocks picrites or ultramafic cumulates a highly reflective horizon r is located at the top of this layer we present a model where the galapagos plume is 2500 km wide but has narrow heads that formed the caribbean volcanic plateaus separated by deep basins the caribbean igneous province is compared to similar volcanic features in the indian ocean kerguelen plateau and in the western pacific ocean ontong java plateau nauru and pigafetta basins the thick plateaus of the caribbean province resemble the kerguelen and ontong java plateaus whereas the deep basins present some similarities with the nauru and pigafetta basins the caribbean igneous province is younger 90 75 ma than the indian and pacific plateaus 110 130 ma however several geological evidences from land and geophysical offshore observations indicate that the onset of volcanic activity in the caribbean province could be as old as 115 ma

a field experiment on the role of small scale wind gustiness in aeolian sand transport estimates of aeolian sand transport generally use an average wind speed to assess the wind energy to determine if variation in small scale wind gustiness on the order of several seconds duration has a significant effect on sand movement detailed field measurements were made of wind speed and transport rate average wind speed and several gust parameters were derived from the wind data the results indicate that small scale gust information does not improve prediction of transport rates

wind blown sand on beaches an evaluation of models five models for predicting rates of aeolian sand transport were evaluated using empirical data obtained from field experiments conducted in april 1994 at a beach on inch spit co kerry republic of ireland measurements were made of vertical wind profiles to derive shear velocity estimates beach slope and rates of sand transport sediment samples were taken to assess characteristics of grain size and surface moisture content estimates of threshold shear velocity were derived using grain size data after parsing the field data on the basis of the quality of shear velocity estimation and the occurrence of blowing sand 51 data sets describing rates of sand transport and environmental conditions were retained mean grain diameter was 0 17 mm surface slopes ranged from 0 02 on the foreshore to about 0 11 near the dune toe mean shear velocities ranged from 0 23 m s 1 just above the observed transport threshold to 0 65 m s 1 rates of transport ranged from 0 02 kg m 1 h 1 to more than 80 kg m 1 h 1 these data were used as input to the models of bagnold bagnold r a 1936 the movement of desert sand proc r soc london a157 594 620 kawamura kawamura r 1951 study of sand movement by wind translated 1965 as university of california hydraulics engineering laboratory report hel 2 8 berkeley zingg zingg a w 1953 wind tunnel studies of the movement of sedimentary material proc 5th hydraulics conf bull 34 iowa city inst of hydraulics pp 111 135 kadib kadib a a 1965 a function for sand movement by wind university of california hydraulics engineering laboratory report hel 2 8 berkeley and lettau and lettau lettau k and lettau h 1977 experimental and micrometeorological field studies of dune migration in k lettau and h lettau eds exploring the world s driest climate university of wisconsin madison ies report 101 pp 110 147 correction factors to adjust predictions of the rate of transport to account for the effects of slope and moisture content were calculated using the models of bagnold bagnold r a 1973 the nature of saltation and bed load transport in water proc r soc london ser a 332 473 504 and belly belly p y 1964 sand movement by wind u s army corps eng cerc tech mem 1 washington d c 38 pp respectively none of the models was able to produce a strong correspondence between measured and predicted rates of transport best results were obtained using the bagnold and zingg models and the kadib model was the least viable of this group the influence of sediment moisture content appeared to be the critical factor in degrading model viability overall none of the models is adequate for general applications to coastal aeolian environments where moisture content complications tend to override the predictive competence of the simple transport formulations c 1998 elsevier science b v

the petrogenesis of gorgona komatiites picrites and basalts new field petrographic and geochemical constraints gorgona island colombia is remarkable not only because it contains the only phanerozoic komatiites but also because it has mafic to ultramafic lavas with a wide range of compositions from moderately enriched to extremely depleted relative to bulk earth the komatiite flows are in many respects similar to archaean komatiites they formed from mgo rich 18 liquids and have upper spinifex zones and lower cumulate zones the cumulate zones of archaean komatiites contain many solid grains in contrast more than 90 of the olivine in the gorgona cumulates is highly skeletal this combined with the fact that the gorgona cumulate zones are thinner than those in archaean komatiites suggests that the komatiite magma became strongly superheated en route to the surface the komatiites have trace element contents intermediate between those of the basalts and the ultramafic tuffs some basalts have isotope compositions indicative of long term enrichment in incompatible elements whereas other basalts and ultramafic volcanics have isotopic signatures that imply corresponding depletion it is apparent that the plume source region of the gorgona magmas was markedly heterogeneous with at least two source components contributing to the observed variation in composition this heterogeneity may have resulted from the incorporation of different components into the plume source or it may be the result of complex melting and melt extraction processes during the ascent of a heterogeneous plume despite earlier suggestions that there may have been a significant age gap between depleted komatiite and basalt flows and the enriched basal new 4oar 39ar dating of basalts and gabbros are more consistent with all being generated at 87 ma during formation of the caribbean colombian plateau possibly at the galapagos hotspot