a paleohydrologic model for early proterozoic dolomitization and silicification abstract primary depositional features observed in the intertidal and supratidal facies of the 2 25 ga malmani dolomite including tepees and finely laminated domal stromatolites have equivalents in holocene salinas on the southern coast of australia the hydrological regime so important in the formation of these recent primary features is still active and so it has been possible to interpret the palaeohydrological significance of analogous features in the malmani dolomite the palaeoclimate of the malmani dolomite shoreline was probably humid to semi arid and the supratidal zone is interpreted as a zone of groundwater resurgence tepees indurated fenestral limestone sheets algal mats small domal stromatolites and intraclast breccias were forming on the supratidal flats in areas of periodically outcropping groundwaters in the shallow subsurface the mixing zone between these resurging continental groundwaters and the marine derived phreatic waters was probably a zone of secondary coarse grained dolomite precipitation and or chert nodule formation this groundwater controlled mixing zone model explains why such fabrics are restricted to porous and immediately adjacent units which at the time of diagenesis were below the regional water table in the upper supratidal zones above the regional water table no secondary dolomites or chert nodules could form nor could diagenetic fabrics form in the subtidal zone for there the stromatolitic mounds contained no palaeoaquifer

the influence of idealized heterogeneity on wet and dry planetary boundary layers coupled to the land surface abstract this manuscript describes numerical experiments investigating the influence of 2 30 km striplike heterogeneity on wet and dry convective boundary layers coupled to the land surface the striplike heterogeneity is shown to dramatically alter the structure of the convective boundary layer by inducing significant organized circulations that modify turbulent statistics the impact strength and extent of the organized motions depend critically on the scale of the heterogeneity relative to the boundary layer height zi the coupling with the land surface modifies the surface fluxes and hence the circulations resulting in some differences compared to previous studies using fixed surface forcing because of the coupling surface fluxes in the middle of the patches are small compared to the patch edges at large heterogeneity scales zi 18 horizontal surface flux gradients within each patch are strong enough to counter the surface flux gradients between wet and dry patches allowing the formation of

depositional facies and environments in the permian umm irna formation dead sea area jordan abstract the permian umm irna formation in central jordan consists of a 60 m thick sequence of clastic sediments which can be divided into two fluvial sedimentary facies the lowermost facies 1 is characterized by the presence of five sandstone dominated fining upward sequences each sequence comprising an erosively based coarse to fine grained trough cross bedded sandstone overlain and laterally intertonguing with maroon siltstone and silty shale containing locally abundant carbonaceous plant material the overlying facies 2 also consists of up to five fining upward sequences each comprising an erosively based coarse grained pebbly sandstone grading up through fine grained sandstone and siltstone into silty shale the sandstones are tabular and laterally persistent internally complex units structured by erosively bounded trough cosets the thickness and grain size of the sandstones and the proportion of siltstone and silty shale is much greater than in facies 1 it also contains abundant ferruginous concretions glaebules deposition occurred on an unconfined braidplain sloping northwestwards away from an elevated provenance arabo nubian shield in the south and east the lowermost facies 1 is regarded as a distal environmental equivalent of the overlying facies 2 deposition was largely controlled by period c shifts of the active channel tract influenced by a gradual increase in the elevation of the source area thereby promoting basinwide progradation and vertical stacking of the two major facies components the ferruginous concretions glaebules in facies 2 are thought to have resulted from diagenetic processes in the vadose zone of a humid possibly tropical climate characterized by alternating wet and dry seasons and strong leaching the fluvial depositional system drained basinwards into a shallow water marine depository along the southern margin of the tethys ocean the ocean may have exerted a maritime influence on the climate of the alluvial plain

zeolitic diagenesis of late quaternary fluviolacustrine sediments and associated calcrete formation in the lake bogoria basin kenya rift valley late quaternary fluviolacustrine siltstones mudstones and claystones loboi silts on the northern margins of the saline alkaline lake bogoria in the kenya rift valley contain up to c 40 authigenic analcime and minor natrolite the zeolitic sediments are reddish brown and up to 1 m thick the amount of analcime increases upward in the profile but decreases with distance from the lake the altered sediments show many pedogenic features including zeolitic root mats rootmarks concretions and carbonate rhizoliths residual patches of calcrete locally cap the zeolitic rocks the profile is interpreted as an exhumed palaeosol and land surface on the former margins of the lake the analcime occurs as submicroscopic 0 5 2 5 m subhedral and euhedral crystals which have an average si a 1 ratio of 2 33 as determined by x ray microanalysis or 2 18 d value of 639 analcime peak the analcime formed in lake marginal sediments soils by reaction of silicate detritus with na2co3 rich pore waters concentrated close to the land surface by evaporative pumping and evapotranspiration poorly ordered clay minerals were probably the main reactants authigenic illite may have been a by product of the reactions chemical analyses suggest that pore waters supplied some of na and possibly k and sio2 the associated calcrete and rhizoliths were formed during or shortly after the main period of zeolitic alteration the ca2 may have originated from infiltrating dilute runoff and groundwater authigenic smectite was precipitated in open porosity following analcime formation the zeolitic alteration at lake bogoria provides a relatively recent analogue for lake marginal zeolites found in many ancient saline alkaline lake sediments

turbulence structure above a vegetation canopy we compare the turbulence statistics of the canopy roughness sublayer rsl and the inertial sublayer isl above in the rsl the turbulence is more coherent and more efficient at transporting momentum and scalars and in most ways resembles a turbulent mixing layer rather than a boundary layer to understand these differences we analyse a large eddy simulation of the flow above and within a vegetation canopy the three dimensional velocity and scalar structure of a characteristic eddy is educed by compositing using local maxima of static pressure at the canopy top as a trigger the characteristic eddy consists of an upstream head down sweep generating hairpin vortex superimposed on a downstream head up ejection generating hairpin the conjunction of the sweep and ejection produces the pressure maximum between the hairpins and this is also the location of a coherent scalar microfront this eddy structure matches that observed in simulations of homogeneous shear flows and channel flows by several workers and also fits with earlier field and wind tunnel measurements in canopy flows it is significantly different from the eddy structure educed over smooth walls by conditional sampling based only on ejections as a trigger the characteristic eddy was also reconstructed by empirical orthogonal function eof analysis when only the dominant sweep generating head down hairpin was recovered prompting a re evaluation of earlier results based on eof analysis of wind tunnel data a phenomenological model is proposed to explain both the structure of the characteristic eddy and the key differences between turbulence in the canopy rsl and the isl above this model suggests a new scaling length that can be used to collapse turbulence moments over vegetation canopies

coherent structures in the boundary and cloud layers role of updrafts subsiding shells and environmental subsidence coherent structures such as updrafts downdrafts shells and environmental subsidence in the boundary and cloud layers of shallow convection are investigated using a new classification method using large eddy simulation data the new method first filters out background turbulence and small scale gravity waves from the coherent part of the flow composed of turbulent coherent structures and large scale transporting gravity waves then the algorithm divides this coherent flow into updrafts downdrafts shells subsidence ascendance and four other flow structures using an octant analysis the novel method can systematically track structures from the cloud free boundary layer to the cloud layer thus allowing systematic analysis of the fate of updrafts and downdrafts the frequency and contribution of the coherent structures to the vertical mass flux and transport of heat and moisture can then be investigated for the first time updrafts subsidence and downdrafts subsiding shells to a lesser extent are shown to be the most frequent and dominant contributors to the vertical transport of heat and moisture in the boundary layer contrary to previous perspective environmental subsidence transport is shown to be weak in the cloud layer instead downdrafts shells are the main downward transport contributors especially in the trade inversion layer the newly developed method in this study can be used to better evaluate the entrainment and detrainment of individual or an ensemble of coherent structures from the unsaturated boundary layer to the cloud layer

carbonate evaporite sedimentary transitions in the badenian middle miocene basin of southern poland abstract in the badenian middle miocene paratethys basin of the carpathian foredeep gypsum deposits interfinger with and are covered by carbonates of the ratyn limestone laminar microbial deposits which form the bulk of the ratyn limestone at radruz southeastern poland show grumelous web and angular boxwork fabrics they also exhibit stromatolitic laminae and spar pseudomorphs after lenticular gypsum crystals these deposits show many striking similarities to laminated microbial boundstones reported from some south australian saline lakes the associated gypsum which occurs basinward of these microbial carbonate deposits is interpreted to have originated in a salina environment which was subjected to episodic subaerial exposure similar limestones often showing dedolomite fabrics co occur with gypsum in southern poland such limestones are commonly regarded as diagenetic products i e replacements of sulphate deposits because of the close association between limestones and gypsum previous interpretations have favoured a secondary origin for the carbonates this may be an oversimplification

paleoclimatic records of late triassic paleosols from central ethiopia abstract the present study documents the major paleosols types within the lower adigrat sandstone in the blue nile basin of central ethiopia with the aim of unraveling the paleoclimatic signatures embedded in them the paleosols developed within an 80 m thick siliciclastic succession deposited in a mixed tide and wave dominated incised valley estuary during the late triassic based on down profile variations in pedogenic features three major paleosol types i e types i ii and iii were identified type i paleosols dominate the lower part of the section and are interpreted as moderately well drained argillic vertisols the dominant pedogenic process was shrinking and swelling of expandable clays i e smectite through repeated wetting and drying cycles the morphologies and the mineralogy of the paleosols provide persuasive evidence for pedogenesis under semi arid subtropical climatic conditions with pronounced wet dry seasonality highly fluctuating soil moisture regime and deep groundwater table the presence of a calcic bk horizon deep in the profiles is consistent with elevated soil moisture deficits and low to moderate mean annual precipitation map type ii paleosols interpreted to represent vertic gleysols are more common in the middle part of the section the pervasive gleying reflects poor soil drainage and a shallow groundwater table where the soil is waterlogged most of the year these paleosols suggest a humid tropical climate characterized by alternating wet dry seasonality but with more wet months per year the top of the unit is dominated by type iii paleosols that represent gleyed oxisols reflecting a more humid equatorial climate marked by wet seasons elevated annual soil moisture content and a high water table the presence of plinthite laterite is in agreement with a wet equatorial climate characterized by extensive chemical weathering and long periods of landscape stability the observed vertical progression in the major paleosol types from vertsols to gleysols and oxisols implies a systematic change in the number of wet months most probably in response to regional tectonics and long term climate change because the number of wet months is in part related to latitude and monsoonal climates the upward stratigraphic trend in paleosol orders is interpreted to signal the northward or equatorward migration of the blue nile basin and central ethiopia within pangea from dry subtropical low latitudes in the early late triassic carnian norian toward the humid wet equatorial possibly monsoonal paleoclimatic zone in the late triassic norian rhaetian

neutral turbulent flow over forested hills numerical simulations of neutral turbulent flow over periodic forested hills are carried out using a first order turbulence closure scheme the forest is represented by the inclusion in the model of a canopy near the surface where additional drag is exerted on the flow as a result of the trees simulations with a more traditional roughness length parametrization of the surface which does not explicitly model the flow within the forest are also carried out for comparison comparison of simulations with existing wind tunnel data shows that the simple mixing length canopy closure scheme provides a good estimate of the mean flow over a forested hill and is a significant improvement on a traditional roughness length parametrization in this case the numerical results are seen to be in close agreement with existing linear analytical solutions for flow over a low and wide forested hill the model is used to investigate the breakdown of the analytical solution when the hill becomes steep and the perturbations to the flow are no longer linear even in the case of a gentle slope the analytical solution can break down when the hill is narrow or the canopy is deep and the vertical velocities near the top of the canopy become large this leads to a downwind shift in the surface pressure perturbation and an enhanced drag compared to a roughness length model model results also show enhanced flow separation in the presence of a canopy these results are important for a range of meteorological problems including the interpretation of flux measurements parametrization of orographic drag predicting wind damage to trees and calculating the yield from wind turbines royal meteorological society 2005 s b vosper s contribution is crown copyright

pseudospherulitic fibrous calcite in paleo groundwater unconformity related diagenetic carbonates paleocene of the ager basin and miocene of the madrid basin spain abstract massive decimeter thick intervals formed by mosaics of subspherical calcite crystals displaying an intracrystalline fibrous microfabric have been found in paleocene and miocene strata in spain the fibrous microfabric is marked by inclusion defined fibers that radiate from the central parts of the crystals which can be termed pseudospherulites and not spherulites because they are single crystals and not polycrystalline aggregates the horizons of pseudospherulitic calcite appear in meter scale laterally persistent levels of crystalline limestones that exhibit complex pseudospar fabrics they are interbedded with peritidal and or lacustrine deposits they grade downward into bedded dolomicrites and they can be linked to unconformities several meters higher in the section above intervening unaltered limestones the pseudospar zones are interpreted as early diagenetic paleo groundwater alteration products after dolomicrites the pseudospherulites are composed of low mg calcite with low contents of fe and mn and they have a stable isotope composition indicative of precipitation from meteoric water they form xenotopic mosaics in which goethite palygorskite and sepiolite may be present as inclusions and in the intercrystalline matrix cathodoluminescence microscopy reveals peripheral growth of the pseudospherulites which results from several phases of precipitation and even of dissolution the first phase of crystal growth may show rhombic habits and may contain corroded dolomite inclusions interpreted as an indication of growth at the expense of dolomicrite by a dissolution precipitation process the second phase of crystal growth is fibrous sensu stricto exhibits lobate growth laminae and shows indications of displacive growth the pseudospherulitic fabric is not relict and the pseudospherulites do not represent speleothems recrystallized microcodium or neomorphosed spherulitic carbonate instead they are interpreted as split crystals that grew within dolomicritic host sediments in part by dissolution precipitation and in part by displacement the hypothesis of a dolomicritic host is supported by the geological and diagenetic setting by the presence of corroded dolomite inclusions within the pseudospherulites and by the relationship between their growth and the authigenesis of sepiolite palygorskite and goethite the pseudospherulites grew in the shallow subsurface at or near the water table from predominantly oxidizing meteoric water and under periodically fluctuating geochemical conditions saturation redox caused by fluctuations of the water table during periods of subaerial exposure the presence of fossil bacteria within the pseudospherulites the anastomosing pattern of the inclusion defined fibers and the lobate growth forms of the fibrous calcite suggest some bacterial influence in the genesis of the pseudospherulitic fabric

palaeosols of the lower jurassic mishhor and ardon formations laterite derivative facies makhtesh ramon israel the lower jurassic sequence exposed at makhtesh ramon in the south western negev of israel comprises cyclic fluviatile sediments derived almost exclusively from the reworking of an older laterite terrain a succession of palaeosols having the characteristics of modern red brown earths has developed during periods of sub aerial exposure upon the fine grained overbank sediments a marked seasonal palaeoclimate with accompanying poor sub surface drainage conditions and some stagnation of ground water is reflected by the distribution and mottling patterns of the iron minerals with varying degrees of hydration precipitation of illuviated carbonate and sulphate minerals and the development of soil microrelief a complex history of pedogenesis and ground water alteration is shown by the rapid lateral facies change within this sequence into one dominated by high alumina flint clay and bauxite relict pedogenetic and sedimentological textural features of the combined palaeosol fluviatile sequence have been identified and mapped within the flint clay bauxite lithologies these features include irregular voids produced by solution of pedogenic sulphate nodules slickensided curviplanar surfaces of soil microrelief and depositional bedding the field relationships of these relicts indicate the overprinting of a younger chemical weathering event giving rise to the high alumina flint clay and bauxites the geometric shape of the upper bounding surface of the bauxite alteration zone is irregular and has an intrusive character with respect to the younger overlying unaltered sediments this together with abrupt changes in mottling patterns near the contact zone and subtle changes in mineralogy from a bauxitic assemblage at depth to one containing mixed layer clay minerals and carbonates nearer the contact leads to the conclusion that the later stages of chemical weathering occurred within a confined system where ground water movements were induced by intake of underlying aquifers

cosmogenic nuclide age constraints on middle stone age lithics from niassa mozambique abstract the late phases of the middle stone age msa in the east african rift system ears are known for their evolutionary shifts and association with bottlenecks transcontinental expansion and climatic fluctuations the chronology of msa sites contemporaneous with these eco demographic upheavals is uncertain because of the scarcity of datable sites and the poor understanding of their depositional and erosional histories we apply terrestrial cosmogenic nuclide dating in a stratigraphic section with a complex exposure history to the study of the luchamange beds a widespread sedimentological unit underlying msa sites from the shores of lake niassa mozambican ears we use an innovative approach which may be applicable elsewhere to calculate their age using a monte carlo based bayesian model that links depth profiles of 26al and 10be and uses other geomorphic and cosmogenic nuclide age constraints on episodic erosion and burial the age of the basal luchamange beds is 42 77 15 ka and the msa occupation on top is 29 3 11 ka these dates suggest temporal overlap between msa and the earliest later stone age and diversity in cultural manifestations at the end of the msa

new termite trace fossils galleries nests and fungus combs from the chad basin of africa upper miocene lower pliocene abstract four new trace fossils of termites are described from the upper miocene and lower pliocene continental sandstones of the northern chad basin coatonichnus globosus ichnogenus and ichnospecies nov is a large ellipsoidal termite calie 20 40 cm in diameter more or less flattened at both poles it is morphologically very similar to the nest of extant termite hodotermes mossambicus from south africa it exhibits an internal shelved pattern of modern hodotermitidae such as the superposition of flat chambers separated vertically by ramps columns walls and pillars it is interpreted as the nest of an ancestral species of hodotermes hodotermitidae the new ichnospecies vondrichnus planoglobus is composed of dense swarms of tens of chambers connected by a net of straight galleries developed in a single plane the chambers 5 12 cm in diameter have a spherical shape with a planar base generally short galleries connect each chamber to the straight main tunnel of meter to decameter scale length vondrichnus planoglobus is interpreted as polychambered diffuse nests of fungus growing termites macrotermitinae termitidae microfavichnus alveolatus ichnogenus and ichnospecies nov is a small scale alveolar mass 3 8 cm by 2 4 cm the base of the construction is flat to concave it is entirely composed of a sub horizontally layered alveolar like structure composed of a regular juxtaposition of millimetre scale round pellets or balls mylospheres microfavichnus alveolatus is interpreted as fossilized fungus combs of fungus growing termites macrotermitinae termitidae termitichnus schneideri ichnospecies nov is a large scale extremely flattened construction 15 60 cm in diameter and 6 18 cm in height the internal shelved pattern is composed of flat chambers separated by columns walls and pillars each level is connected by ramps an external wall surrounds the framework constructed one to several peripheral funnel shaped tunnels occur sub perpendicular to the construction this new termitichnus ichnospecies is interpreted as being a possible central hive of the vondrichnus planoglobus net

channel hydrodynamics of submerged flexible vegetation with seepage abstractthe presence of aquatic vegetation changes the flow characteristics in a channel the impact of the presence of submerged flexible vegetation in a channel with an additional parameter such as downward seepage is analyzed in the present work two patterns staggered and uniform and two different vegetation spacing 15 and 10 cm center center were adopted experiments were conducted for the case of no seepage 10 seepage and 15 seepage velocity profiles show the presence of an inflection point near the top of the vegetation where maximum reynolds stress is achieved the velocity profiles measured in the unobstructed region of uniform pattern are higher compared to the velocity measured in line with the vegetation stems downward seepage increases the velocity reynolds stress and turbulent intensities in the average range of 10 15 as compared to the no seepage case higher order turbulent statistics such as moment analysis quadrant analysis and turbulent kinetic budget are derived through

observations of flow and turbulence in the nocturnal boundary layer over a slope measurements were conducted on an eastern slope of the salt lake basin slb as a part of the vertical transport and mixing experiment vtmx conducted in october 2000 of interest was the nocturnal boundary layer on a slope in particular katabatic flows in the absence of significant synoptic influence extensive measurements of mean flow turbulence temperature and solar radiation were made from which circulation patterns on the slope and the nature of stratified turbulence in katabatic winds were inferred the results show that near the surface 25 50 m the nocturnal flow is highly stratified and directed downslope but at higher levels winds strongly vary in magnitude and direction with height and time implying the domination of upper levels by air intrusions these intrusions may peel off from different slopes surrounding the slb have different densities and flow at their equilibrium density levels the turbulence was generally weak and continuous but sudden increases of turbulence levels were detected as the mean gradient richardson number dropped to rig about unity with a short timescale fluctuated on the order of a few tens of seconds while modulating with rig a longer along slope internal waves sloshing timescale of about half an hour the mixing efficiency or the flux richardson number of the flow was found to be a strong function of similar to that found in laboratory rig experiments with inhomogeneous stratified shear flows the eddy diffusivities of momentum and heat were evaluated and they showed a systematic variation with when scaled with the shear length scale and the rms rig vertical velocity of turbulence

dolomitization and sulfate reduction in the mixing zone between brine and meteoric water in the newly exposed shores of the dead sea pleistocene dolomites are associated either with evaporative processes such as in sabkhas and playas or with a mixing zone where mixing between two different solutions e g seawater and groundwater takes place we report here on the very recent formation of dolomite at shallow depths 6 12 cm in newly exposed gypsum rich sediments on the western shores of the dead sea sem and eds analysis as well as x ray diffraction analysis indicate that this dolomite is euhedral and close to ideal dolomite in composition these dolomite crystals differ from anhedral detrital ca rich dolomites from the cretaceous section of the watershed found in the whole section taking into account the sedimentation rate at the shore vicinity the maximal age of the euhedral dolomite was estimated as less than 60 years in the three profiles analysed euhedral dolomite was most abundant at a single layer where the gypsum content was locally lowered due to bacterial reduction of sulfate the sediments solution at the dead sea shore localities represent a mixing zone between dead sea residual solution and subsurface freshwater springs under such conditions formation of dolomite occurs at highly saline environment where very high mg ca ratios are attained

mesozoic unconformities in israel characteristics mode of origin and implications for the development of the tethys abstract nine breaks in the mesozoic stratigraphic column of israel are described in terms of their hiatus type of contact residual deposits and areal extent using these criteria and by reference to published global eustatic sea level curves three of the stratigraphic breaks are correlated with global eustatic sea level lowstands triassic jurassic boundary toarcian aalenian late turonian coniacian one probably represents a condensed sequence resulting from a rapid sea level rise middle callovian four are related primarily to rifting and extension tectonics of the incipient anisian carnian pliensbachian sinemurian or evolving early neocomian tethys and one reflects a folding phase of the syrian arc fold system related to the early closure stages of the tethys campanian maastrichtian by careful scrutiny of stratigraphic breaks on the margins of the arabian craton and by recognition of eustacy related events important stages in the tectonic evolution of the tethys can be reconstructed

tepees in peritidal carbonates origin via earthquake induced deformation with example from the middle cambrian of western canada abstract tepee structures are common in many ancient carbonate tidal flat successions and because analogues are known from tropical coastal areas they are well established as evidence for synsedimentary lithification of subaerially exposed carbonate sediment existing explanations involving desiccation thermal expansion and contraction fluctuating groundwater pore pressure or diagenetic force of crystallization do not adequately account for the style and degree of deformation seen in some examples such as those in the middle cambrian cathedral formation of the southern rocky mountains western canada these tepees provide evidence for essentially instantaneous events causing brittle failure of decimetre thick crusts of ooidal and pisoidal grainstone followed by their dilation rupturing separation tilting and shingling they can be explained as breccias generated by sporadic episodes of strong ground motion from earthquakes that emanated from a syndepositionally active fault system nearby variably directed tensile and compressive stresses broke crusts shifted them upwards and shuffled them laterally subsequent microbial encrustation and vigorous flushing by seawater in the resulting shelter cavities led to rapid stabilization by cementation recognition of the role of seismically induced deformation in explaining some tepee structures furnishes a proxy for synsedimentary tectonism and adds another member to the family of seismites which reflect a range of rheological properties of unlithified and lithifying sediments

groundwater ferricretes from the silurian of ireland and permian of the spanish pyrenees abstract haematite nodule horizons occur in alluvial lacustrine deposits from the mill cove formation silurian of dingle ireland and the unidad roja superior permian of the spanish pyrenees these horizons generally less than 1 m thick are not associated with palaeosol profiles but are hosted by laminated or structureless bioturbated mudstones to sandstones the sequences contain weakly developed calcrete profiles the haematite nodules are interpreted as having formed around fluctuating water tables and are analogous to present day groundwater ferricretes laterites or plinthites fe2 mobilised during periods of reducing groundwaters was segregated into ferric oxide nodules during falls in the water table or during influxes of oxygenated meteoric waters the prevailing climate during deposition of both sequences was probably semi arid and the presence of ferricrete like horizons is not evidence of humid climates the horizons represent early diagenetic effects not related to prevailing soil moisture regime

interaction between turbulent flow and sea breeze front over urban like coast in large eddy simulation turbulent flow and its interaction with a sea breeze front sbf over an urban like coast with a regular block array were investigated using a building resolving computational fluid dynamics model it was found that during daytime with an offshore ambient flow streaky turbulent structures tended to grow within the convective boundary layer cbl over a warm urban surface ahead of the sbf the structures were organized as streamwise streaks at an interval of a few hundred meters which initiated at the rooftop level with strong wind shear and strengthens in the cbl with moderate buoyancy the streaks then interacted with the onshore propagating sbf as it made landfall the sbf which was initially characterized as a shallow and quasi linear feature over the sea developed three dimensional structures with intensified updrafts at an elevated frontal head after landfall frontal updrafts were locally enhanced at intersections where the streaks merged with the sbf which greatly increased turbulent fluxes at the front the frontal line was irregular because of merging tilting and transformation effects of vorticity associated with streaky structures inland penetration of the sbf was slowed by the frictional effect of urban like surfaces and turbulent flow on land the overall sbf intensity weakened after the interaction with turbulent flow these findings aid understanding of local weather over coastal cities during typical sea breeze conditions

nodular and enterolithic gypsum the sabkha tization of salt flat playa west texas abstract the sediment in the continental sabkha of salt flat west texas is typically millimeter laminated and composed of evaporitic and diagenetic minerals including gypsum dolomite halite calcite and aragonite these laminated evaporites were originally deposited on the floor of a late pleistocene perennial brine lake and now constitute the matrix of the modern sabkha sediments in the playa as climate changed from the more humid phase of the pleistocene to the more arid conditions of the holocene the lake dried up and these laminated evaporites were deflated into gypsum dunes or overprinted by a sabkha related hydrology near surface gypsum rich layers were transformed by capillary evaporation into coalescing nodular horizons at the same time in shallow vadose sediments less than 1 2 m subsurface the gypsum was dissolved and replaced either by halite or dolomite diagenetic gypsum was co precipitated as gypsum overgrowths and a patchwork of cement from a highly saline interstitial brine avg 156 000 mg l tds these processes of early diagenetic enlargement and coalescence of gypsum crystals created holocene gypsum nodules within the laminated host sediment diffuse growth of nodules in the lower vadose zone created chicken wire textures gypsum growth in the upper vadose zone was often concentrated along particular layers and formed enterolithic bands pleistocene lacustrine evaporites were in effect sabkhatized by a fall in the lake water level

structural analysis of soil microrelief in palaeosols of the lower jurassic laterite derivative facies mishhor and ardon formations makhtesh ramon israel abstract a sequence of palaeosols developed on exposed overbank sediments of successive alluvial cycles of the lower jurassic laterite derivative facies ldf at makhtesh ramon contains well developed penecontemporaneous soil microrelief structures the folded structures commonly show overthrusting and vary in wave length and amplitude they are characterized by slickensided surfaces cuspate in cross section with the curviplanar deformed surfaces oriented concave up the palaeosol stratigraphy is well established over the entire makhtesh ramon area and this afforded the opportunity of obtaining controlled structural measurements on the folded surfaces and their associated slickensided striae as a means of providing data for reconstruction of the fold geometry stereographic projection of the poles to the ldf fold surfaces on two separate palaeosol horizons from several localities together with the slickensided striae were plotted on the lower hemisphere of a schmidt equal area net the ldf folds were seen to be symmetrical and asymmetrical structures with a gently plunging fold axis of 4 10 maximum and minimum dip values of the cuspate curviplanar surface sp 1 were well emphasized by the plots 20 and 30 for symmetrical structures and data from the two horizons obtained from several localities showed remarkable uniformity a second slickensided curviplanar surface of deformation sp 2 shows the same range of dip values as sp 1 and intersects the sp 1 surface normal to the sp 2 fold axis the internal arrangement of symmetry elements within the ldf folds remains approximately constant regardless of the large variation between the gross morphological parameters such as amplitude and wavelength and this appears to be a reflection of the response of a soil with inherent anisotropies to stress the geometry of the ldf structure resembles that of linear or wavy gilgai the sp 1 surface therefore is most likely the result of upthrusting on the edges of drainage rills affected by differential wetting the sp 2 surface bears a constant geometric relationship with sp 1 and is therefore considered to have formed penecontemporaneously during the upthrusting of the sp 1 blocks a rectangular surface fracture pattern parallel to and normal to topographic slope is considered to be an alternative means of initiating the upward growth of the soil microrelief features

waving plants and turbulent eddies new large eddy simulations of flow over a flexible plant canopy by dupont et al j fluid mech 2010 this issue vol 652 pp 5 44 have produced apparently paradoxical results work over the last three decades had suggested that turbulent eddies could lock onto to the waving frequency of uniform cereal canopies their new simulations contradict this view although a resolution may lie in the essentially three dimensional nature of the instability process that generates the dominant eddies above plant canopies

turbulent reynolds stress and quadrant event activity in wind flow over a coastal foredune recent research on quasi instantaneous turbulent kinematic reynolds stresses rs u w and decomposed quadrant event activity e g ejections and sweeps over dunes in fluvial settings and in wind tunnels has shown that turbulent stresses at the toe of a dune often exceed time averaged streamwise shear stress u 2 estimates it is believed that semi coherent turbulent structures are conveyed toward the bed along concave streamlines in this region and that impact of these structures cause fluctuations in local surface stresses that assist in grain entrainment this has been hypothesized to explain how sand is supplied to the windward slope through a region of flow stagnation toward the crest surface stress increases and becomes dominated by streamwise accelerations resulting from streamline compression and convexity that suppress vertical motions high frequency 32 hz measurements of turbulent wind flow from 3 d ultrasonic anemometers are analyzed for oblique onshore flow over a vegetated coastal foredune in prince edward island canada reynolds stress and quadrant activity distributions varied with height 0 60 m and 1 66 m and location over the dune in general quadrant 2 ejection u 0 and quadrant 4 sweep activity u 0 w 0 w 0 and quadrant 3 inward interaction u 0 w 0 activity on the lower stoss slope significant ejection and sweep event activity was most frequent 85 to 92 ejections plus sweeps whereas at the upper crest significant ejection and sweep activity became less frequent while significant outward and inward interactions increased in frequency 25 to 36 an exuberance effect i e changing shape of quadrant frequency distribution skewed toward ejection and sweep activity is observed whereby streamline compression and convexity effects inhibit vertical fluctuations in flow and thus reduce the frequency of ejections and sweep activity toward the crest in separated flow in the lee of the crest quadrant distributions were more symmetrical as a result of more mixed multi directional flow these trends in turbulent event distributions and reynolds stress have implications for sediment transport dynamics across the dune and may help to explain sand transport potential and dune maintenance for example areas with a high frequency of ejection and sweep activity may have higher rates of sediment entrainment and transport whereas areas with lower ejection and sweep activity and an increase in outward and inward interactions which contribute negatively to reynolds stress generation may experience a greater potential for deposition further research on associations between quadrant event activity and coincident sand transport is required to confirm this hypothesis and the resultant significance of the flow exuberance effect in aeolian dune morphodynamics

tepee shaped agglutinated microbialites an example from a famennian carbonate platform on the lennard shelf northern canning basin western australia distinctive metre scale antiformal structures are well developed in a famennian carbonate platform in the chedda cliffs area of the lennard shelf reef complexes the structures are distinguished by chevron shaped crests and thickened cores and contain abundant non skeletal allochems ooids pisoids peloids and intraclasts of silt to pebble size and variably developed laminations and fenestrae the internal morphology and pervasive occurrence of fenestral clotted and wavy laminated fabrics suggest that these structures are microbial mounds composed of agglutinated stromatolites and thrombolites microbial fabrics most probably originated through sediment trapping and binding by microbial mats with early lithification involving microbial calcification and cementation of trapped sediment the facies and stratigraphic context of the mounds support a shallow subtidal transitional backreef to reef flat setting however alone these mounds do not provide unequivocal environmental information other large antiformal structures in famennian platforms on the lennard shelf previously described as tepee structures show morphological similarities to the chedda cliffs mounds which suggests that these other structures may also be microbial mounds the presence of microbial mounds in platform successions further highlights the importance of microbial communities in the lennard shelf reef complexes

tepees modern southern australia and ancient permian texas and new mexico a comparison abstract tepee structures are forming today about the edges of a number of holocene groundwater lakes coastal salinas in the coastal zone of south australia tepees form by the groundwater induced deformation of an extensive sheet of fenestral limestone known as a veneer boundstone underlying the veneer boundstone is an extremely porous aquifer known as a boxwork boundstone areas of groundwater resurgence in these salinas are characterized by an association of tepee structures boxwork boundstones and stromatolites the tepees in these salinas are termed groundwater or boxwork tepees to emphasize the importance of resurging groundwater in their formation preliminary studies of tepee structures in the back reef strata of guadalupian age in the guadalupe mountains of west texas and new mexico has shown that these tepees are also groundwater tepees such tepee structures in the guadalupe mountains are often associated with remnants of an underlying boxwork boundstone and or an underlying sandy palaeoaquifer they are tepees which formed in zones of groundwater resurgence at a time when the nearby reef was a subaerially exposed barrier limestone sheets composed of vadose pisolites were deformed coincident with tepee formation this association implies that vadose pisolites like tepees formed in areas of periodic groundwater resurgence characterized by a complex schizohaline hydrological regime

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

calcrete and palustrine assemblages on a distal alluvial floodplain a response to local subsidence miocene of the duero basin spain abstract in the upper miocene of the eastern duero basin two carbonate units cu 1 and cu 2 display a lateral transition from distal alluvial floodplain red mudstones to calcrete and an upwards transition from calcrete to palustrine facies the carbonate content in the calcrete increases upwards as shown in sequences from red or reddish brown mudstones with diffuse calcification to nodular calcrete facies to massive calcretes the palustrine facies display a broad range of textures related to the degree of exposure peloidal intraclast textures formed during the most prolonged phases of exposure and are those most commonly seen in the palustrine facies the transition from calcrete to palustrine facies occurs in two ways 1 as an indurated limestone level with mixed features of calcrete and palustrine facies and 2 a well delimited boundary between the two facies which show very similar characteristics in the vicinity of this boundary the 13cpdb and 18opdb values of the calcretes are similar to those of the palustrine facies this is because their genesis was related to groundwaters which inherited the isotopic signature of meteoric waters good covariance between 13c and 18o palustrine values r 0 78 is typical of lakes in semi arid regions with long water residence times in closed basins the calcrete palustrine association records a progressive decrease in the terrigenous supply and a continuous elevation of the groundwater table until it intersected with the surface to create a pond the rise in the groundwater table resulted from local subsidence that was not compensated by terrigenous supply leading to a lowering of the floodplain changes in the thickness of palustrine facies from central to marginal pond areas with ubiquitous exposure features suggest that the pond was progressively filled up by bio chemical carbonate precipitation balancing the available space created by subsidence this maintained the shallow character of the pond deposits

calcrete conglomerate case hardened conglomerate and cornstone a comparative account of pedogenic and non pedogenic carbonates from the continental siwalik group punjab india the occurrence of authigenic carbonates formed in three different environmental situations within the continental siwalik group has been used to compare the lithological and petrographic characters of the contrasted lithofacies the three lithofacies are 1 calcrete conglomerate 2 case hardened conglomerate 3 cornstone pedogenic nodular calcrete the calcrete conglomerate facies laterally intertongues with the channel conglomerates it consists of pisolites which are interpreted to have formed from carbonate rich spring waters emerging on to the gravelly substrate of dry abandoned channels the laminae characteristics of these pisolites are distinctly different from those of marine origin and also from comparable biogenic materials case hardened conglomerate occurs in the youngest part of the siwalik stratigraphic column in boulder conglomerates having limestone as the principal clast component this lithofacies has resulted from cementation of the conglomerate through continued dissolution and re precipitation of calcite by meteoric water downwards from the surface it displays a coarsely crystalline sparry calcite cement with no evidence for displacive growth or replacement by calcite cornstones nodular calcrete occur in several sedimentary cycles of the middle siwalik sub group these are immature and commonly associated with thinly bedded sandstones levee and red shales overbank this lithofacies is a result of concentration of carbonate through capillary action associated with pedogenic activity ooids developed in cornstone are essentially micritic in nature and usually composed of less than five indistinct laminae

palaeoclimatic significance of changes in clay mineralogy across the jurassic cretaceous boundary in england and france abstract clay mineralogical changes across the jurassic cretaceous boundary from the northern to the southern part of western europe show similar patterns in the mudrocks exposed on the yorkshire coast the paralic sediments of the dorset wessex basin and the jura and vocontian trough of s e france this comprises a change from smectite poor sediments in the jurassic with correspondingly abundant illite and kaolinite to sediments with abundant smectite in the jurassic cretaceous boundary beds depleted in kaolinite this change occurs in the oxfordian in the south to latest volgian in the north of the study area kaolinite reappears in abundance in the late ryazanian or stratigraphic equivalent in all the locations studied comparison with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest jurassic earliest cretaceous aridity the onset of which appears to be diachronous across w europe possible causes for the climatic change towards aridity are examined the orographic effect of mountains or plateaus to the east of the study area is considered most likely

lateritization and ground water alteration phenomena in the triassic budra formation south western sinai field and laboratory investigations of the triassic budra formation of wadi budra south west sinai have demonstrated the existence of surface pedogenic laterites developed within overbank facies of fluviatile sediments during times of hiatus the laterite profiles up to 7 m thick comprise a zone of high iron concentrations 21 47 73 17 which includes a concretionary unit and either overlies a zone of slightly mottled host rock or rests directly upon unaltered sandstone a pallid zone is noticeably absent the primary depositional horizontal fabric of the finely laminated sediments of the overbank facies has strongly influenced the final fabric of the laterite the pronounced alternations of iron rich pisolitic and iron deficient laminae highlight the influence of inherent fabric primary bedding on pedogenesis the micromorphology of the laterites is characterized by bimasepic plasmic fabrics abundant elongate voids partially infilled with cryptocrystalline kaolinite and an abundance of randomly oriented skew planes illuviation of clay minerals to considerable depths is evident sesquioxidic and kaolinitic glaebules concentrated within the concretionary units of the laterite have a flattened ellipsoidal shape and occur as both massive and concentrically structural varieties at gebel mussaba salama to the north zoned iron mineralization occurs at various levels within the fluviatile sandstones which underlie the overbank facies this is interpreted as being a non pedogenic ground water alteration phenomenon induced by a rising water table within the buried alluvial channels iron mineralization probably records minor fluctuations of the water table during standstill periods lateritization in the triassic budra formation provides important evidence that the widely recorded late triassic lateritization and bauxitization event of the neighbouring east mediterranean countries extended south to the continental areas bordering the tethyan ocean

wetland sedimentation and associated diatoms in the pleistocene olorgesailie basin southern kenya rift valley abstract the olorgesailie basin in the southern kenya rift valley contains a variety of lacustrine wetland and terrestrial facies that were laid down during the last 1 2 million years this study integrates diatom ichnofossil and rhizolith silica and carbonate evidence in order to identify and characterize shallow wetland deposition at the top member 14 ca 493 ka of the olorgesailie formation a key feature of these deposits is the presence of facies with aquatic indicators diatoms that are overprinted by ichnofossils and rhizoliths that suggest drier conditions diatom floras include several fresh water aulacoseira spp and saline indicators such as thalassiosira rudolfi t faurii cyclotella meneghiniana and anomoeoneis sphaerophora the main indicators of shallow fresh to mildly saline waters include epithemia argus rhopalodia gibberula encyonema muelleri and synedra spp three main suites of ichnofossils indicate varying water table depths during their formation these consist of 1 horizontal tunnels that suggest saturated substrates 2 vertical burrows formed in substrates with relatively lower water tables and 3 termite hymenopteran and beetle ichnofossils that indicate dry substrates member 14 of the olorgesailie formation also contains carbonate and siliceous rhizoliths which occur both together and separately four possible models are suggested to explain the silica and carbonate rhizolith formation 1 a complex of spring fed marshes and dry areas 2 ephemeral wetlands and floodplains 3 wetlands with abundant organic decay and 4 initial carbonate rhizoliths that were replaced by silica preservation of cellular structures and the reworking and incorporation of rhizoliths in overlying younger strata suggest that they formed early during diagenesis

the influence of subaquatic springs in lacustrine sedimentation origin and paleoenvironmental significance of homogenites in karstic lake banyoles ne spain abstract banyoles 42 08 n 2 45 e is the largest and deepest lake of karstic tectonic origin in the iberian peninsula the lake comprises two basins and six sub circularly shaped sub basins fed by subaquatic springs periods of intense groundwater inflow in the deepest sub basins lead to the fluidization and re suspension of previously deposited sediments and subsequent settling forming homogenite deposits on the southern basin intermediate platforms the multiproxy analysis of sediment cores combined with high resolution seismic stratigraphy 3 5 khz pinger and multi frequency chirp surveys allows a precise reconstruction of depositional environments and related hydrological variability and groundwater inflow during the last ca 7 6 cal kyr bp according to the age model based on 137cs 210pb and ams 14c dating homogenite deposition occurred between 7 2 and 5 5 cal kyr bp stopped during the middle holocene 5 5 2 8 cal kyr bp and greatly increased during the last two millennia with a total of 17 homogenite layers individually up to 75 cm thick the onset of this unique sedimentation mode at ca 3 cal kyr bp coincides with an increase in lake level evidenced by the onlapping of fine grained distal sediments over coarser massive carbonate rich littoral deposits a detailed multidisciplinary study of the homogenites sedimentology physical properties high resolution elemental geochemistry mineral composition grain size organic matter content and sem combined with seismic stratigraphy demonstrates that the fluidization events triggering the formation of the homogenites were caused by higher and more intense local groundwater inflow related to increased rainfall during the late holocene and likely intensified by land use changes during the last millennium

the sedimentology and accretionary styles of an ancient gravel bed stream the budleigh salterton pebble beds lower triassic southwest england abstract three accretionary styles are present in the fluvial conglomerates and pebbly sandstones of the lower triassic budleigh salterton pebble beds bspb of east devon the lower portions of this 20 30 m sequence are dominated by extensive 50 m sheets or narrow lenses of planar cross bedded conglomerate sets 1 3 m thick these abruptly pass both downstream and laterally into horizontally bedded conglomerates cross bedded sandstones and muddy sandstones this accretionary style reflects deposition from linguoid shaped macroforms whose distal margins were bounded by slipfaces they accreted at anabranch confluences and as bank attached bars in relatively confined and channelised gravel bed streams lateral facies changes represent macroform evolution resulting from changing discharges or abandonment of a channel reach followed by accretion of a new macroform the upper portions of the bspb mainly comprise couplets of horizontally bedded conglomerate overlain by large scale trough cross bedded sandstone the conglomerate shows local channel macroform relief and lateral and downstream transitions into sets of gently dipping conglomerate this style of accretion represents deposition in less confined and less channelised fluvial systems by relatively low relief gravel macroforms and large sand dunes the third style recognised in the bspb is much more localised it consists of wedge like sets of large scale trough cross bedded conglomerate the sets are formed by erosion and subsequent fill of scours cut into a thick sandy substrate techniques of lateral profile analysis and hierarchical ordering of bounding surfaces can usefully be applied to some parts of the bspb this is important as the approach was originally developed for the deposits of sand bed streams however this approach is more difficult to apply to fluvial conglomerates because of the cryptic nature of some gravel stratification the appearance and character of some hierarchies of bounding surfaces may differ from their equivalents in fluvial sandstones

optimal control of katabatic flows within canopies what slope angle favours the development of katabatic flow is still an open question some studies have clarified that katabatic winds are stronger on steep slopes while others have demonstrated that katabatic winds are stronger on gentle slopes here we explore the control mechanisms of katabatic flow using a simplified theoretical model in an attempt to clarify the causes of the paradoxical findings our results indicate that optimal conditions for katabatic flows within canopies are synergistically controlled by terrain angle canopy structure and thermal condition through a simple equation where is terrain slope lc 1 cda is canopy length scale cd is drag coefficient a is leaf area density vt rc is a thermal factor rc is a cooling rate is ambient lapse rate and b is a constant this theoretical prediction implies that gentle slopes are optimal for katabatic flow developments in stably stratified air while steep slopes are optimal in weak or near neutral stratification canopy effect is significant in the control of katabatic flows only on gentle slopes copyright 2012 royal meteorological society

secondary currents and very large scale motions in open channel flow over streamwise ridges it is widely acknowledged that streamwise ridges on the bed of open channel flows generate secondary currents scs a recent discovery of meandering long streamwise counter rotating vortices in open channel flows known as very large scale motions vlsms raises a question regarding the interrelations between vlsms and scs in flows over ridge covered fully rough beds to address it we conducted long duration experiments using stereoscopic particle image velocimetry covering a range of ridge spacings s from approx 0 4 to approx 4 flow depths h for a benchmark no ridge case the flow is quasi two dimensional in the central part of the channel exhibiting a strong spectral signature of vlsms as expected with ridges on the bed at s lessapprox 2h two sc cells are formed between neighbouring ridges and vlsms are entirely suppressed suggesting that ridge induced scs prevent the formation of vlsms by absorbing their energy or overpowering their formation at the same time velocity auto and cross spectra reveal a new feature that can be explained by low amplitude meandering of the alternating low and high momentum flow regions associated with instantaneous manifestations of scs two point velocity correlations and smooth velocity field reconstructions using proper orthogonal decomposition further support the validity of this effect its origin is probably due to the instability related to the presence of inflection points in the spanwise distribution of the streamwise velocity within the sc cells these results have implications for bed friction in open channels where the friction factor may increase if depth scale scs are present or decrease under conditions of sub depth scale scs and suppressed vlsms

origin and diagenetic evolution of gypsum and microbialitic carbonates in the late sag of the namibe basin sw angola abstract ephemeral evaporitic conditions developed within the uppermost part of the transgressive late sag sequence in the namibe basin sw angola leading to the formation of extensive centimetre to metre thick sulphate bearing deposits and correlative microbialitic carbonates rich in pseudomorphs after evaporite crystals the onshore pre salt beds examined in this study are located up to 25 m underneath the major mid aptian evaporitic succession which is typified at the outcrop by gypsiferous bambata formation and in the subsurface by the halite dominated loeme formation carbonate evaporite cycles mostly occur at the top of metre thick regressive parasequences which progressively onlap and overstep landward the former faulted rift topography or fill major pre salt palaeo valleys the sulphate beds are made up of alabastrine gypsum associated with embedded botryoidal nodules dissolution related gypsum breccia and are cross cut by thin satin spar gypsum veins nodular and fine grained fabrics are interpreted as being diagenetic gypsum deposits resulting from the dissolution and recrystallisation of former depositional subaqueous sulphates whereas gypsum veins and breccia result from telogenetic processes the carbonates display a broader diversity of facies characterised by rapid lateral variations along strike thin dolomitic and calcitic bacterial mediated filamentous microbialitic boundstones enclose a broad variety of evaporite pseudomorphs and can pass laterally over a few metres into sulphate beds dissolution related depositional breccias are also common and indicate early dissolution of former evaporite layers embedded within the microbialites sulphate and carbonate units are interpreted as being concomitantly deposited along a tide dominated coastal supra to intertidal sabkha and constitute high frequency hypersaline precursor events prior to the accumulation of the giant saline mid aptian bambata and loeme formations petrographic and geochemical analyses reveal successive dissolution recrystallisation and cementation phases that occurred during burial uplift and exhumation implying a complex diagenetic evolution of both gypsum and carbonates influenced by pore fluids of diverse composition which distinctly varied from meso to telogenetic domains

the holocene non tropical coastal and shelf carbonate province of southern australia abstract carbonate dominant sediments are currently forming and accumulating over the extensive marine shelf of the passive margin of southern australia a dearth of continental detritus results from both a very low relief and a predominantly arid climate the wide continental shelf is bathed by cold upwelling ocean waters that support luxuriant growths of bryozoans and coralline algae together with sponges molluscs asteroids benthic and some planktonic foraminifera the open ocean coast is battered by a persistent southwest swell resulting in erosion of calcrete encrusted pleistocene eolianites much sediment is reworked and overall shelf sedimentation rates are low high energy microtidal beach dune systems occur between headlands and along the very long ocean beach in the coorong region the northern more arid coastal areas also contain saline lakes that precipitate gypsum from infiltrated sea water and display marginal facies of aragonite boxwork to fenestral carbonate crusts with stromatolites and tepee structures in contrast the southern seasonally humid coorong region has a predominantly continental groundwater regime where sulphate is rare and the high summer evaporation precipitates dolomite magnesite and aragonite muds fenestral crusts breccias tepees and some stromatolites are also present st vincent and spencer gulfs both afford some protection from ocean swell but tidal amplitude and currents increase and a depth and inundation related zonation of plants and animals is established muddy carbonate sand accumulates on the sea floor below 30 m where filter feeding bryozoans bivalves and sponges dominate in shallower regions seagrass meadows contain a rich fauna that results in rapid accumulation of an unsorted muddy bioclastic sand mangrove woodlands backed by saline marsh with cyanobacterial mats are common and accumulate mud rich and gastropod bearing sediment as tidal amplitude and desiccation increase northward into both gulfs a supratidal zone bare of vegetation sabkha becomes the site for deposition of gypsum rich and fenestral calcitic mud

geochemical and mineralogical investigations of the lower jurassic flint clay bearing mishhor and ardon formations makhtesh ramon israel abstract the lower jurassic section at makhtesh ramon in the northeastern negev of israel comprises a sequence of fluviatile sediments of laterite composition post depositional chemical weathering has resulted in marked facies changes whereby the clastic sequence passes laterally into high alumina flint clays and bauxites goldbery 1979 a geochemical and mineralogical investigation was initiated on 216 samples from several key sections of the facies change to obtain a more refined definition of the diagenetic overprint to reconstruct the history of chemical weathering and finally to recognize the parent material of the unaltered laterite sediments results are presented herein on major and trace element composition normative mineralogical composition kaolinite crystallinity and porosity and density measurements kaolinite crystallinity values proved to be a good indicator of intensity of leaching showing a marked decline in ordering with increase of diagenetic reorganization on the basis of mineralogical parameters it was possible to subdivide the section of flint clays and bauxites generated under karstic conditions into four units bivariate plots of al2o3 vs several elements within the section plotted into four distinctive fields coinciding with the subdivision enrichment depletion ratios calculated from the element concentrations within these flint clays against element concentrations of the clastic parent material of the karstic infill led to the reconstruction of a multi cyclic leaching event whose signature is left in each of the four units at least 3 individual episodes of leaching related to a rising water table and punctuated by still stands could be recognized zr tio2 nb y plots of stable elements using the diagram of floyd and winchester 1978 for determination of source rocks indicated a rhyolite or alkaline rhyolite provenance for the clastic laterite detritus

flow over a hill covered with a plant canopy we develop an analytical model for atmospheric boundary layer flow over a hill that is covered with a vegetation canopy the slope of the hill is assumed to be small enough that the flow above the canopy can be treated within the linear framework of hunt perturbations to the flow within the canopy are driven by the pressure gradient associated with the flow over the hill in the upper canopy this pressure gradient is balanced by downwards turbulent transport of momentum and the canopy drag the flow there can be calculated from linearized dynamics which show that the maximum streamwise winds are where the perturbation pressure is at a minimum i e near the crest of the hill deep within the canopy the pressure gradient associated with the flow over the hill is balanced by the canopy drag here the nonlinear canopy drag this nonlinear balance shows how the streamwise winds are largest where the perturbation pressure gradient is largest i e on the upwind slope of the hill in the lee of the hill this nonlinear solution shows how the pressure gradient decelerates the wind deep within the canopy leading to separation with a region of reversed flow when the canopy is sufficiently deep coupling between the out of phase flows within and above the canopy means that the maximum velocity is further upwind of the hill crest than in flow over a rough hill while the extra turbulent mixing caused by the canopy significantly reduces the magnitude of the velocity speed up over the hill finally we find that there is no formal limit process where the solutions with a canopy yield the well known solutions for flow over a rough hill this finding calls into question the very use of a roughness length in accelerating or decelerating turbulent boundary layers copyright 2004 royal meteorological society

kalkowsky s stromatolites revisited lower triassic buntsandstein harz mountains germany abstract the term stromatolite was proposed by kalkowsky 1908 z dt geol ges 60 68 125 for structures he discovered in the carbonates of the lower triassic buntsandstein of the harz mountains in central germany we have re examined these localities to clarify kalkowsky s descriptions and to deduce the environmental conditions of stromatolitic growth the lower buntsandstein was deposited in a closed lacustrine basin the central european permo triassic basin the depositional environment was a playa lake with variable salinity in the centre of the basin oolite beds are intercalated in the mainly siliciclastic succession which is composed of 20 fining upward cycles thought to have been produced by climatic variations stromatolites occur almost exclusively on the surface of oolite beds stromatolitic structures consist of millimetre thick laminated crusts and centimetre high branching columnar forms smaller and bigger 2 m high domes are composed of secondary order columns and intercalated crusts occasionally upper surfaces of the domes are pitted due to syndepositional dissolution despite of the overall intense sparitization two groups of stromatolitic microstructures can be distinguished spongy fenestrate and fan like fabrics the spongy fenestrate fabric is similar to that one caused by the recent cyanobacteria phormidium calothrix and dichothrix and the fan like fabric to rivularia laminated crusts called stromatoid by kalkowsky are interpreted as being of cement origin and formed by quick precipitation the change from columnar to domical forms may reflect changes of hydrodynamic conditions clear photoautotrophism suggests that cyanobacteria or eukaryotes were the dominant organisms involved in the formation of kalkowsky s stromatolites influx of ooids or siliciclastic mud interrupted or terminated the stromatolitic growth the morphology growth pattern and fabrics of stromatolites were most likely controlled by ecological factors which all seem to be related to the general hydro climatic evolution of the lower buntsandstein

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

the hydrological significance of holocene tepees stromatolites and boxwork limestones in coastal salinas in south australia abstract holocene groundwater lakes salinas are common in the coastal zone of south australia they usually contain an evaporitic carbonate sequence that surrounds a central gypsum unit to form a bull s eye pattern of sediment distribution in the salina the evaporitic carbonates can be subdivided into three units a boxwork boundstone unit a veneer boundstone unit and an algal boundstone unit these units contain many interesting structures including tepees stromatolites and mound springs all of which show a megapolygonal outcrop pattern the salina carbonates have formed under a hydrological regime that has changed little since its inception some 6000 years ago consequently it has been possible to interpret the hydrological significance of the salina carbonates the salinas are fil ed by schizohaline surface waters whose water levels and salinities fluctuate seasonally all of the salina carbonates form where marine derived groundwater resurges from a surrounding dune aquifer into the margin of the salina tepee structures form in the veneer boundstone as a response to groundwater induced seasonal changes in the pore pressures of the underlying boxwork sediments the recognition of such groundwater tepees or other groundwater controlled structures in ancient carbonate sequences could aid paleohydrological interpretation of the ancient basin

can a simple dynamical system describe the interplay between drag and buoyancy in terrain induced canopy flows abstractunder nonneutral stratification and in the presence of topography the dynamics of turbulent flow within a canopy is not yet completely understood this has among other consequences serio

comparison of sequences formed in marine sabkha subaerial and salina subaqueous settings modern and ancient marine evaporites occurring in modern subaqueous salina settings and subaerial sabkha settings are different subaqueous holocene evaporites occur as shoaling upward lacustrine sequences up to 10 m thick they are evaporite dominated and are composed primarily of bottom nucleated crystals that may be deposited as massive laminated or rippled units each coastal lake is dominated by laminated evaporites with subordinate carbonate sediments in plan view they show a well developed bull s eye pattern with a sulfate center and a carbonate rim in contrast subaerial sabkha evaporites occur as part of a laterally prograding shoaling upward peritidal sequence in which the supratidal unit is usually no more than 1 m thick sabkha sequences are matrix dominated not ev porite dominated with the bulk of the sulfate phase occurring as diagenetic nodules enteroliths or diapirlike structures these sulfates were formed during syndepositional diagenesis by replacement and displacement processes the various facies of the sequence tend to accumulate in belts parallel with the shoreline relative to the sea level or the brine level sabkhas tend to form over paleotopographic highs whereas salinas tend to occur in paleotopographic lows some of the characteristics that distinguish holocene subaerial and subaqueous evaporite sequences can be used to do the same for similar ancient facies even when gypsum has been converted to nodular anhydrite the distinction is important for it can be used by explorationists in the oil industry to define the paleotopography of the associated underlying porous and nonporous carbonates

mixing layers and coherent structures in vegetated aquatic flows 1 to date flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow with vegetative drag treated as an extension of bed drag however recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer this paper presents laboratory measurements obtained from a scaled seagrass model that demonstrate the applicability of the mixing layer analogy to aquatic systems specifically all vertical profiles of mean velocity contained an inflection point which makes the flow susceptible to kelvin helmholtz instability this instability leads to the generation of large coherent vortices within the mixing layer observed in the model at frequencies between 0 01 and 0 11 hz which dominate the vertical transport of momentum through the layer the downstream advection of these vortices is shown to cause the progressive coherent waving of aquatic vegetation known as the monami when the monami is present the turbulent vertical transport of momentum is enhanced with turbulent stresses penetrating an additional 30 of the plant height into the canopy

approaches to middle stone age landscape archaeology in tropical africa the southern montane forest grassland mosaic ecosystem in the humid subtropics southern rift valley of africa comprised the environmental context for a large area in which modern human evolution and dispersal occurred variable climatic conditions during the late pleistocene have ranged between humid and hyperarid changing the character of the ecosystem and transforming it at different points in time into a barrier a refuge and a corridor between southern and eastern african populations alluvial fans presently blanket the areas adjacent to major river systems which were key areas of prehistoric human habitation these sets of variables have created conditions that are both challenging and advantageous to conduct archaeological research lateritic soil development has resulted in poor organic preservation and facilitated insect bioturbation which has demanded an integrated micro macro scale approach to building a reliable geochronology an integrated field and analytical methodology has also been employed to identify the nature and degree of post depositional movement in alluvial deposits which preserve a wide range of spatial integrity levels in buried stone artifact assemblages between 47 and 30 ka in karonga northern malawi this paper describes the methodological advances taken toward understanding open air middle stone age archaeology in sub tropical africa and explores the inferential potential for understanding pleistocene human ecology in the important southern rift valley region

analytical models for the mean flow inside dense canopies on gentle hilly terrain simplifications and scaling arguments employed in analytical models that link topographic variations to mean velocity perturbations within dense canopies are explored using laboratory experiments laser doppler anemometry lda measurements are conducted in a neutrally stratified boundary layer flow within a large recirculating flume over a train of gentle hills covered by a dense canopy the hill and canopy configuration are such that the mean hill slope is small and the hill is narrow in relation to the canopy h l 1 and lc l 1 where h is the hill height l the half length and lc the canopy adjustment length scale the lda data suggest that the often criticized linearizations of the advective terms turbulent shear stress gradients and drag force appear reasonable except in the deep layers of the canopy as predicted by a previous analytical model the lda data reveal a recirculation region within the lower canopy on the lee slope adjusting the outer layer pressure perturbations by a virtual ground that accounts for the mean streamline distortions induced by this recirculation zone improves this model s performance for the velocity perturbations in the deeper layers of the canopy a new analytical model which retains a balance between mean horizontal advection mean pressure gradient and mean drag force but neglects the turbulent shear stress gradient is developed the proposed model reproduces the lda measurements better than the earlier analytical model which neglected advection but retained the turbulent shear stress gradient in the lower layers of the canopy and near the hill top this finding is consistent with the fact that the earlier model was derived for tall hills in which advection inside the canopy remains small in essence the newly proposed model for the narrow hill studied here assumes that in the deeper layers of the canopy the spatial features of the mean flow perturbations around their background state can be approximated by the inviscid mean momentum equation we briefly discuss how to integrate all these findings with recent advances in canopy lidar remote sensing measurements of general topography and canopy height copyright 2008 royal meteorological society

distinguishing early groundwater alteration effects from pedogenesis in ancient alluvial basins examples from the palaeogene of southern portugal colour mottling and horizons of secondary carbonates are common in ancient alluvial sequences and are normally interpreted as pedogenic features they have been used to assess palaeoclimates soil drainage conditions and deposition rates palaeogene alluvial deposits in the sado and lisbon basins of portugal exhibit prominent colour variations and mottle patterns as well as carbonate accumulations both at the bases of fining upwards cyclothems and as thick units up to 20 m capping alluvial megasequences however these colour and carbonate features are interpreted as the products of shallow saline reducing groundwaters unrelated to pedogenesis such non pedogenic products are easily mistaken for soil formed ones and criteria for differentiating the two are reviewed to assist interpretations in other alluvial deposits key criteria are thickness gradational tops and bases absence of soil horizon features occurrence in coarser alluvium and prevalence of hydromorphic colour and mottling patterns