dolomitization of the oligocene miocene bluff formation on grand cayman british west indies the oligocene miocene bluff formation on grand cayman is formed of hard white finely crystalline dolostone in which the precursor textures and fossil microstructures are commonly preserved the d

wind profiler observations of vertical motion and precipitation microphysics of a tropical squall line abstract data from a wind profiler located at darwin australia have been used to examine the vertical motions and precipitation microphysics in a well developed squall line both a mature and developing convective cell are well sampled the vertical motions within the mature cell are dominated by the effect of glaciation and a convective downdraft feeding a cold pool the strong updrafts are accompanied by supercooled water as much as 2 km above the freezing level the two cells are separated by a narrow region of deep descent the developing cell has a low level maximum in upward motion coinciding with high radar reflectivity below 3 km suggesting warm rain processes there is a large transition region with deep descent and a stratiform region with a classic up and downdraft circulation the precipitation characteristics show the aggregation of ice particles as they descend in the stratiform region over half of the rain is seen to evaporate between 4 and 2 km the cooling implied by this and the hea

subrainband structure and dynamic characteristics in the principal rainband of typhoon hagupit 2008 abstractthe principal rainband in tropical cyclones is currently depicted as a solitary and continuous precipitation region however the airborne radar observations of the principal rainband in typhoon hagupit 2008 reveal multiple subrainband structures these subbands possess many characteristics of the squall lines with trailing stratiform in the midlatitudes and are different from those documented in previous principal rainband studies the updraft and reflectivity cores are upright and elevated the updraft is fed by a low level radial outflow from the inner side the tangential wind speed shows a clear midlevel jet on the inner side of the reflectivity core except for the structural similarities the dynamics of the subbands is also similar to the squall lines the local environment near the subbands shows little convective inhibition modest instability and vertical wind shear the temperature retrieval shows a cold pool structure in the stratiform precipitation region the estimated vertical w

structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation abstract mechanisms responsible for meso and convective scale organization within a large tropical squall line that occurred on 22 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment are investigated using a three dimensional numerical cloud model the squall line occurred in an environment typical of fast moving tropical squall lines characterized by moderate convective available potential energy and moderate to strong vertical shear beneath a low level jet with weak reverse vertical shear above a well simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi linear to a three dimensional bow shaped structure over a 2 h period this transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40 60 km long bow shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge within enha

sequence stratigraphy in a marine moraine at the head of hardangerfjorden western norway evidence for a high frequency relative sea level cycle abstract the depositional architecture and stratigraphy of the haereid moraine a sedimentary ridge ca 1 5 km long and up to 113 m in height at the head of hardangerfjorden west norway have been reconstructed in a high resolution sequence stratigraphic framework information from ground penetrating radar gpr profiles outcrop sections and borehole data have been used in the analysis the basal forced regressive deposits comprise relicts of a gilbert type delta that commenced its development at the front of a grounded glacier on the seaward distal side of the ridge there is a major channel fill mouth bar complex covering large parts of the delta s former frontal slope and prodelta zone the complex occurs in the seaward lengthening of a fluvially incised channel and is interpreted as a lowstand to early transgressive succession of fluvial and fluvial estuarine facies the channel fill mouth bar complex and the dissected delta top have been planed off through transgressive ravinement and the delta top is overlain by an upvalley thinning sedimentary wedge 3 8 m thick and with a general landward onlapping and propagating internal bedform geometry this wedge is thought to be composed mainly of transgressive marine estuary mouth barrier facies on the landward proximal side of the ridge the transgressive deposits include a retrograding landward dipping foreset interpreted as relicts of a flood tidal delta overlain by possible washover fan deposits these deposits are again conformably overlain by laminated clay interpreted as the remains of a highstand mud drape the depositional sequence delineated in this study up to 20 m thick and comprising deposits of a lowstand wedge a transgressive and a highstand systems tract developed in response to a relative sea level rsl rise of 12 15 m this rsl rise which interrupted the general rsl fall following the deglaciation is correlated with the younger dryas transgression a regionally recorded sea level event the highstand mud drape was deposited as the rising rsl ultimately led to drowning of the moraine the highstand and transgressive deposits are erosively truncated by a thin gravelly lag deposited during final emergence in the early holocene

sedimentology and diagenesis of upper mississippian to lower permian strata talbot lake area jasper national park alberta in the talbot lake area the upper mississippian carbonate sequence comprises in ascending order the turner valley and mount head formations the mount head formation is informally divided into lower and upper members the rocks of the upper mississippian originated by sedimentation associated with successive shallowing upward sequences on the basis of the fossils lithologies textural characters and sedimentary structures the turner valley formation apparently resulted from sedimentation on open marine shoals and in a lagoon the lower member of the mount head formation from sedimentation in shallow subtidal to lower supratidal environments and the upper member of the mount head formation from deposition in upper intertidal to supratidal environments the paraconformity between the lower and upper members of the mount head formation records a short erosional break a disconformity between the upper mississippian carbonates and the upper permian ishbel group displays paleotopographic relief and pale

vertical velocity characteristics of deep convection over darwin australia abstract continuous vertical velocity measurements using a 50 mhz wind profiler located at darwin in northern australia during periods of active convection have been analyzed this dataset is dominated by continental type convection numerous examples of shallow deep and decaying convection were seen and it is shown that only the deep systems have substantial tilts to the draft structure the most intense updrafts occur above the freezing level but shallow convection also produces large amplitude vertical motions the strength of these updrafts in this dataset is very similar to other tropical oceanic data that observation is consistent with the idea that the magnitude of the updrafts is much less in the tropics than for intense midlatitude convection because the convective available potential energy is distributed over a much deeper layer in the tropics although more intense updrafts may be present at other tropical locations such as the tiwi islands north of darwin the size of the cores however

cathedral cave wellington caves new south wales australia a multiphase non fluvial cave cathedral cave is an outstanding example of a class of multiphase caves with largely non fluvial origins it contains large cavities such as cathedrals and cupolas characteristic of excavation by convection currents in rising waters smaller scale features such as rising half tubes pseudonotches curved juts projecting corners blades and bridges indicate intersection and exhumation of older cavities during the formation of younger ones it is possible to recognize at least ten significant phases of speleogenesis by morphostratigraphy in addition to the four generations of cave filling palaeokarst deposits intersected by the cave the cave we see today results from the progressive integration of a number of previously disconnected or poorly connected solution cavities copyright 2007 john wiley sons ltd

genesis of terrestrial oncoids cayman islands british west indies terrestrial oncoids up to 4 3 mm long are common in sinkholes that penetrate the dolostones of the oligocene miocene bluff formation on grand cayman and cayman brac the vaguely laminated terrestrial oncoids which generally lack a nucleus are formed of detrital material micrite clays dolomite calcified filaments and spores and insect fragments the abundant diverse assay of microorganisms includes six different types of filaments and five different types of spores which can be attributed to fungi algae and or cyanobacteria thin mats of mucus are commonly associated with the microorganisms the microorganisms contribute to the formation of the terrestrial oncoids by i calcification of the filaments and spores ii trapping and binding detrital material and iii binding with their mucus detrital material to the surface of the oncoids identification of terrestrial oncoids relies on i the recognition of a microbial assemblage ii the demonstration that the microorganisms played an ac

vhf radar observations of convectively generated gravity waves some new insights 1 vhf radar observations of tropical mesoscale convective systems have provided some new insights on convectively generated gravity waves over gadanki 13 5 n 79 2 e a tropical station in india present observations revealed disturbed tropopause structures and enhanced mass fluxes across the tropopause during the passage of deep convective systems the analysis suggest that during disturbed tropopause conditions not only the direct intrusion across the tropopause takes place but also the gravity wave activity associated with convection enhances in the lower stratosphere as compared to the stable tropopause conditions this result is a major outcome of the present study another noteworthy result from the present observations is the phase profile of convectively generated gravity waves which for the first time provided an opportunity to localize the source region of gravity waves

three dimensional kinematic and microphysical evolution of florida cumulonimbus part i spatial distribution of updrafts downdrafts and precipitation abstract this paper is the first in a three part study that examines the kinematic and microphysical evolution of florida cumulonimbus and focuses on the convective to stratiform transition of the storm this first paper lays the groundwork for the subsequent papers by defining the problem under study delineating the setting for the storm and describing the spatial distribution of updrafts downdrafts and precipitation high resolution radar data of a typical line of storms associated with the florida sea breeze is the centerpiece of this study the high resolution data reveal details of the internal structure of the squall line that were beyond the resolution of previous squall line studies radar reflectivity filled in between cells at upper levels as the storm evolved reflectivity values were only weakly associated with updraft and downdraft magnitude the updrafts and downdrafts in the storm tended to be irregular in their three dimensional shape and less than 5 km in horizontal extent at any giv

observations of tropical convection events using indian mst radar first results mesoscale convective events associated with severe weather play a significant role in troposphere stratosphere coupling processes deep convection occurs very often at tropical latitudes the convection events result in the transport of energy from the lower troposphere to the upper troposphere and stratosphere and may also affect global circulation in the indian tropical region meteorological convection events are a common occurrence during the months of may to december in the present study very high frequency radar located at gadanki 13 45 n 79 18 e a tropical station in india is used to make observations of winds turbulence and stable layer structures during the passage of convective events over the radar site under different synoptic situations radar observations of vertical velocity show enhanced up and down draughts during the passage of convection events height and time cross sections of radar observed signal to noise ratio clearly show distinct regions of enhanced signal intensity indicating height and time structures of enhanced atmospheric turbulence associated with the convection it is also noted that stable layer structures associated with the tropical tropopause are not well defined during the passage of convection this suggests weakening of stable layer structures during the convective activity the present observations also show enhanced mass flux both in upward and downward directions through the tropopause indicating mass exchange between troposphere and stratosphere during the period of convective activity

biogenic structures and micrite in stalactites from grand cayman island british west indies stalactites from modern and old caves developed in the bluff formation of grand cayman island contain laminae and bulbous masses of micrite intercalated with sparry calcite the micrite as well as some of the sparry calcite around it contains small up to 25 m long ovate to spherical bodies that have a high concentration of either manganese or iron such bodies may be of bacterial origin the micrite contains numerous calcified filaments that are probably of algal origin calcification of the filaments occurred either during life or shortly after death of the algae the algae played an important role in trapping and binding the micrite furthermore the algae may be directly or indirectly responsible for the formation of much of the micrite

the alteration of sparry calcite crystals in a vadose setting grand cayman island calcite crystals that cement the dolostone clasts in a karst breccia from grand cayman island have been substantially altered as a result of infestation by algae and or fungi as well as etching that may or may not be related to organic activity the features produced include 1 borings 2 constructive micrite envelopes 3 spiky calcite 4 almond shaped etch pits 5 crystal surfaces with a blocky topography and 6 etched crystal surfaces that suggest some of the crystals may have grown by spiral growth spar calcite crystals in a vadose setting can be subjected to complex chemical and physical processes that are commonly mediated by algae and or fungi these microorganisms are capable of removing caco3 from substrates via dissolution transporting that caco3 elsewhere and then directly or indirectly causing its reprecipitation during the calcification of their filaments and or the formation of the constructive micrite envelopes the extensive alteration of calcite cements in the karst brecci

association of tepees and palaeokarst in the ladinian calcare rosso southern alps italy the ladinian calcare rosso of the southern alps provides a rare opportunity to examine the temporal relationships between tepees and palaeokarst this unit comprises peritidal strata pervasively deformed into tepees repeatedly capped by palaeokarst surfaces mantled by terra rossa palaeokarsts characterized by a regional distribution across the southern alps occur at the base and at the top of the unit local palaeokarsts confined to this part of the platform occur within the calcare rosso and strongly affected depositional facies tepee deformation ranges from simple antiformal structures peritidal tepees to composite breccias floating in synsedimentary cements and internal sediments senile tepees peritidal tepees commonly occur at the top of one peritidal cycle in association with subaerial exposure at the cycle top while senile tepees affect several peritidal cycles and are always capped by a palaeokarst surface cements and internal sediments form up to 80 of the total rock volume of senile tepees the paragenesis of senile tepees is extremely complex and records several superimposed episodes of dissolution cement precipitation fibrous cements laminated crusts mega rays and deposition of internal sediments marine sediment and terra rossa petrographical observations and stable isotope geochemistry indicate that cements associated with senile tepees precipitated in a coastal karstic environment under frequently changing conditions ranging from marine to meteoric and were altered soon after precipitation in the presence of either meteoric or mixed marine meteoric waters stable isotope data for the cements and the host rock show the influence of meteoric water average 18o 5 8 while strontium isotopes average 87sr 86sr 0 707891 indicate that cements were precipitated and altered in the presence of marine triassic waters field relationships sedimentological associations and paragenetic sequences document that formation of senile tepees was coeval with karsting senile tepees formed in a karst dominated environment in the presence of extensive meteoric water circulation in contrast to previous interpretations that tepees formed in arid environments under the influence of vadose diagenesis tepees initiated in a peritidal setting when subaerial exposure led to the formation of sheet cracks and up buckling of strata this porosity acted as a later conduit for either meteoric or mixed marine meteoric fluids when a karst system developed in association with prolonged subaerial exposure relative sea level variations inducing changes in the water table played a key role in exposing the peritidal cycles to marine mixed marine meteoric and meteoric diagenetic environments leading to the formation of senile tepees the formation and preservation in the stratigraphic record of vertically stacked senile tepees implies that they formed during an overall period of transgression punctuated by different orders of sea level variations which allowed formation and later freezing of the cave infills

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

structure and evolution of a severe squall line over oklahoma abstract a squall line on 2 may 1979 developed in oklahoma in proximity to a synoptic scale cold front this line is analyzed during its growth and mature periods using radar satellite sounding and surface data some of the cells produced hail and many of the cell tops reached 16 km however there were no reports of tornadoes three main topics are addressed in the paper 1 examination of squall line and cell propagation mechanisms 2 the three dimensional structure of the squall line and individual cells during the mature period and 3 mass and moisture fluxes and precipitation efficiency comparison is made between the 2 may case and other tropical and midwest squall line cases the 2 may case does not exhibit a trailing stratiform anvil during the period mechanism requiring veering environmental wind shear in the lowest levels and 2 mechanism where the cell motion is eventually governed by the moisture convergence and lifting provided the convergence line the motion of the squall line defin

a preliminary morphology of precipitation systems in tropical northern australia a preliminary morphology of convective systems observed in the vicinity of darwin australia is presented several types of tropical convection during monsoonal and break season flow are identified using specific examples and compared with a range of systems observed worldwide in the general context of the bulk richardson number a significant spectrum of convective activity ranging from low shear and low convective available potential energy cape to high shear and moderate to high cape typical of mid latitude severe storms is identified significant differences between monsoonal flow and break season systems are apparent the formation of convective lines perpendicular to the low level shear and the apparent balance between advancing shallow cold pools and the shear are ubiquitous features convective scale downdraughts and mesoscale descent appear to be responsible for redistribution of 700 mb momentum to the planetary boundary layer pel the motion of the break season squall lines appears to result from an equilibrium between the cold pool and the undisturbed environmental pel flow deviations from this balance are hypothesized to result in the observed propagating and non propagating or slow moving modes examples of these modes are given showing the classical continuous development of new cells in a balanced state along the leading edge of long lived squalls and in the propagating case the discontinuous development of new cells on the cold pool ahead of the squall

kinematic and precipitation structure of the 10 11 june 1985 squall line abstract high frequency 90 min rawinsonde data from a special mesoscale network 26 sites have been combined with wind profiler dense automated surface network data 80 stations spaced 50 km apart and a series of high resolution dual doppler radar analyses in a common framework attached to a moving squall line system to form a comprehensive dataset describing the mature phase of the 10 11 june 1985 squall line observed during pre storm the dual doppler radar analyses covered a 200 300 km2 area from the leading edge of the convective line to the back edge of the trailing stratiform precipitation region thus providing high resolution wind information over a very broad portion of the storm system the comprehensive analysis is used to resolve several aspects of the trailing stratiform region that had remained unclear from previous studies first a difference in the horizontal scale was found between the mesoscale updraft which at upper levels was on the scale of the trailing stratiform cloud a

timing and genesis of early marine caymanites in the hydrothermal palaeokarst system of buda hills hungary abstract sedimentological biostratigraphic and magnetostratigraphic studies were carried out on five late eocene early oligocene profiles in the buda hills hungary the szepvolgy limestone formation accumulated on the pre eocene basement basal strata of the limestone consist of a thin conglomerate followed by a coralgal limestone the overlying limestone contains abundant nummulites discocyclina the contact between these two members is sharp the szepvolgy limestone body covering 60 65 km2 is considered a carbonate bank above the limestone the siliciclastic slope deposits of the pelagic and turbiditic buda marl and the euxinic tard clay accumulated a huge multiphase hydrothermal cave system developed in the szepvolgy limestone resulting in a long term composite palaeokarstic evolution lasting from the late eocene to the quaternary the first palaeokarst phase during the late eocene is represented by two generations of early marine cavity filling sediments of caymanite type deposited at sea level the earlier carbonate infilling is conformable while the younger siliciclastic one is disconformable with the bedding of the host rock bio and magnetostratigraphic studies indicate that deposition of the caymanites bearing palaeokarst host sequence started in the late eocene during chron c15r 35 3 ma and terminated in the early oligocene during chron c13n 33 ma two marker horizons are present the first is between the szepvolgy limestone and buda marl at 34 6 ma and the second horizon is between the buda marl and the tard clay at 33 5 ma the szepvolgy limestone deposited on a mobile shelf represents a deepening upward sequence interrupted by two lowstand events they can be correlated with the phd event of keller et al 1987 global distribution of late palaeogene hiatuses geology 15 199 203 and resulted in marine palaeokarstification the carbonate shelf with the infillings drowned at 34 6 ma the caymanites accumulated at about 35 2 35 0 ma and represent short term palaeokarstic events their deposition record was estimated in several thousand years

variability of the australian summer monsoon at darwin 1957 1992 abstract the variability of the australian summer monsoon is reexamined using data covering 35 monsoon seasons a new easily applied objective definition of active and break phases of the monsoon based solely on the zonal wind at darwin is proposed attempts to define wet westerly onsets are shown to be misleading since no clear relationship is found between westerly winds and rainfall on the timescales associated with the transition between active and break phases the resulting dates of monsoon onset at darwin differ from those reported in some recent studies resulting in significantly different relationships with the southern oscillation in particular the date of monsoon onset is shown to be significantly related to and hence predicted from prior values of the southern oscillation index also in contrast to a number of recent studies that have highlighted the so called 40 50 day oscillation in the australian summer monsoon no dominant timescales are found in the length of the active period

unconformities and porosity development in carbonate strata ideas from a hedberg conference the purpose of this paper is to highlight ideas from a hedberg conference concerning detection of unconformities and associated porosity in carbonate strata many types of information including cores and outcrops seismic data eustatic sea level curves wireline logs biostratigraphic data stable isotope trends cycle stacking patterns and tectonic and basin evolution models can be used to predict and or detect subaerial unconformities all methods of detecting subaerial exposure with these types of information have limits and pitfalls detailed analysis of the stratigraphy sedimentology and diagenetic history of a rock sequence from outcrop or core data is considered the most reliable means of detecting subaerial exposure though an integrated approach using all a ailable information is recommended the relationship between subaerial exposure and subsurface porosity in carbonates is not simple or easily predicted subsurface porosity is the product of many factors operating during deposition subaerial exposure and burial several concepts should be recognized when evaluating porosity associated with subaerial unconformities 1 carbonate diagenesis during subaerial exposure rearranges pore networks but usually does not increase the total porosity near surface dissolution can simply lower a topographic surface without increasing porosity within the host limestone in many cases total porosity in carbonates under unconformities is actually reduced during subaerial exposure 2 permeability is likely to change more than porosity during subaerial exposure increasing in some c ses but decreasing in others 3 pore systems evolve with time during subaerial exposure short periods of subaerial exposure 10 000 400 000 yr are often associated with greater porosity than long intervals of subaerial exposure 1 20 million yr prolonged subaerial exposure may change permeability less than porosity because high permeability karst related conduits can form quickly and persist for millions of years 4 many carbonates subjected to subaerial exposure have little or no porosity in the deep subsurface because compaction cementation and stratal collapse reduce porosity during burial 5 unconformity related diagenesis may enhance reservoir potential by creating pore systems that are resistant to compaction during deeper burial 6 vugs caverns and breccias can fo m in the deep subsurface because of dissolution by basinal fluids independent of subaerial exposure 7 lithologic changes at unconformities like shales overlying carbonates can influence the flow of subsurface fluids during end page 857 deeper burial resulting in deep burial dissolution localized along unconformities if subaerial exposure and exposure surfaces are integrated into a sequence stratigraphic paleogeographic and climatic framework systematic and hopefully predictable patterns will emerge however we do not fully understand the complex interplay between the factors critical to creating and preserving porosity in carbonates additional research is needed to quantify critical processes and products so we can reliably predict porosity associated with subaerial exposure during exploration in frontier basins and on a smaller scale during reservoir analysis

meteoric phreatic speleothems and the development of cave stratigraphy an example from tounj cave dinarides croatia abstract speleothems occurring in some caves of the carbonate dinarides line all channel surfaces and have been deposited from meteoric waters under phreatic conditions such phreatic speleothemic deposition modifies common experience l that meteoric phreatic conditions cause dissolutional widening of cave voids and 2 that speleothems imply vadose conditions the phreatic speleothems described here postdate an early polygenetic evolution of the cave voids and predate the last vadose stage they were likely produced during the late postglacial warming period when dissolved carbonate was amply supplied and when there was much water available for saturation of underground voids phreatic speleothems may be used as a tool for time correlation of internal deposits both within one cave and within a karst region they indicate an important stage in the history of the ground water regime of an area in general phreatic speleothems help in better understanding of the development of subterranean voids and related karst palaeokarst

temporal evolution of tertiary dolostones on grand cayman as determined by 87sr 86sr abstract on the cayman islands the tertiary bluff group brac formation cayman formation pedro castle formation is onlapped and overlain by the pleistocene ironshore formation on grand cayman the brac formation and cayman formation are formed of finely crystalline dolostones whereas the pedro castle formation is formed of finely crystalline dolostones dolomitized limestones and limestones no dolomite has been found in the ironshore formation dolostones in the bluff group which retained their original depositional textures and lack evidence of any recrystallization are formed of small typically 5 15 m long interlocking euhedral dolomite crystals dolomite cement is present in the brac formation and cayman formation but is very rare in the pedro castle formation most of the dolomite crystals are characterized by oscillatory zoning with alternating zones of low ca calcian dolomite and high ca calcian dolomite grand cayman is ideal for assessing the temporal evolution of tertiary dolostones because the dolostones are young have not been recrystallized and are geographically isolated by the deep oceanic waters around the island interpretation of 158 new 87sr 86sr ratios from the dolostones in the bluff group indicate that the succession underwent three time transgressive phases of dolomitization during the late miocene the late pliocene and pleistocene petrographically similar dolomite was produced during each phase of dolomitization that was mediated by the same type of fluid and the same general conditions dolomitization was part of a dynamic cycle of processes that followed major lowstands karst development during the lowstands preconditioned the limestones for dolomitization by increasing their porosity and permeability thus vast quantities of the dolomitizing fluids could freely circulate through the strata during the subsequent transgression dolomitization ceased once a stable highstand had been attained

the holocene sedimentary history of the kangerlussuaq fjord valley fill west greenland abstract west greenland has been intensively studied to reconstruct and better understand past relative sea level changes and deglacial history this study extends these efforts by linking sea level and deglacial history to the sedimentary infill successions of kangerlussuaq fjord and associated landward valleys based on published and new land and sea based geophysical data radiocarbon dates and geological observations we have characterized the infill and reconstructed the sedimentation history during the holocene based on a revised sea level curve and data presented in this paper we defined three depositional phases phase i 7000 yr bp is represented by dominant glaciomarine deposition associated with a tide water glacier system as the greenland ice sheet gis continued to retreat it became land based during phase ii 7000 1500 yr bp two separate depocenters formed keglen delta depocenter arose from a temporary stabilization phase of the gis and prograded rapidly over the glaciomarine deposits of phase i further inland proglacial lake formation and subsequent sedimentary infill associated with the ongoing gis retreat is represents the second depocenter the watson river connected both depocenters by a flood plain which transferred sediment from the gis to the keglen delta ongoing sea level fall due to glacio isostastic uplift combined with a gradually cooler and dryer climate resulted in terrace formation along the watson river flood plain around 4000 yr bp the gis margin reached its most landward location and began to advance to its present location the final phase phase iii

geochemical evidence of saharan dust parent material for soils developed on quaternary limestones of caribbean and western atlantic islands abstract most previous workers have regarded the insoluble residues of high purity quaternary limestones coral reefs and oolites as the most important parent material for well developed clay rich soils on caribbean and western atlantic islands but this genetic mechanism requires unreasonable amounts of limestone solution in quaternary time other possible parent materials from external sources are volcanic ash from the lesser antilles island arc and saharan dust carried across the atlantic ocean on the northeast trade winds soils on quaternary coral terraces and carbonate eolianites on barbados jamaica the florida keys united states and new providence island bahamas were studied to determine which if either external source was important caribbean volcanic ashes and saharan dust can be clearly distinguished using ratios of relatively immobile elements al 2 o 3 tio 2 ti y ti zr and ti th comparison of these ratios in 25 soils where estimated ages range from 125 000 to about 870 000 yr shows that saharan dust is the most important parent material for soils on all islands these results indicate that the northeast trade winds have been an important component of the regional climatology for much of the quaterary saharan dust may also be an important parent material for caribbean island bauxites of much greater age

evidence for the development of a superpermeability flow zone by bioturbation in shallow marine strata upper jubaila formation central saudi arabia abstract superpermeability super k flow zones in carbonate reservoirs are thought to be controlled by bioturbation related burrow networks e g burrow pores of thalassinoides to improve the current understanding this study investigated thalassinoides and associated passive fill in the upper jubaila member of the upper jurassic jubaila formation central saudi arabia analysis of the elemental and mineralogical compositions of powder samples from the passive fill and burrow matrix and thin sections of selected burrow matrix samples were conducted to determine the origin of the passive fill the goal herein is to infer the flow properties of the bioturbated strata of the upper jubaila member based on the occurrence of this passive fill in the burrow pores of the thalassinoides compared to the burrow matrix the analyzed passive fill exhibit marked differences in elemental composition suggesting a much younger and different origin than that of the marine carbonates of the upper jubaila member a cao plus mgo concentration below 28 and an elevated sio2 plus al2o3 concentration above 45 suggest a clay dominated passive fill the reddish and brownish colorations of the passive fill are attributed to the presence of iron oxyhydroxides as indicated by the elevated fe2o3 concentration a mean of 5 8 1 7 and a mineralogical composition with elevated percentages of goethite and hematite the normalized rare earth element ree pattern of the passive fill is consistent with that of lithogenous siliciclastic sources which are likely deposited in a well oxygenated environment as suggested by the redox sensitive elements and normalized rees these sources probably originate in hot humid environment as indicated by the chemical index of alteration cia 80 the above geochemical data suggest that the passive fill was derived from soils similar to mediterranean terra rossa soils and postdate the formation of burrow pores in the thalassinoides bearing strata this could have occurred after exposure of the upper jubaila member terra rossa soil most likely reached the thalassinoides bearing strata from the surface through vertical fractures and karst features filled burrow pores fractures along bedding plains and even intercrystalline pores the occurrence of terra rossa soil in the burrows and intercrystalline pores of the thalassinoides bearing strata implies that the pore system of the upper jubaila member possessed connected pathways that enabled soil infiltration followed by simultaneous precipitation in the burrows and intercrystalline pores the presence of these connected burrow pores containing shafts with diameters ranges from 1 to 5 cm suggests a superpermeable storage capacity and presence of a superflow unit in the upper jubaila member this study provides an excellent example to better understand the controls of super k zones in carbonate reservoirs

evolution of quasi two dimensional squall lines part i kinematic and reflectivity structure abstract doppler radar observations that establish common patterns in the evolution of the reflectivity and flow structures of squall lines are described a number of squall lines have been analyzed with unprecedented time resolution in order to identity these patterns all of the squall lines appeared to be approximately two dimensional and featured a solid leading edge at some time during their life cycle instead of being composed of discrete cells separated by echo free regions a large variety of intensities and evolution lime scales was observed it is shown that squall lines of this type evolve through identifiable stages of reflectivity structure this evolution appears to be strongly related to changes that occur in the kinematic structure as a typical system evolves a rearward sloping zone of horizontal vorticity predominantly associated with vertical shear develops on the scale of the system presumably driven by the horizontal buoyancy gradients across the system the vorticity that is gen

vertical motion structure in maritime continent mesoscale convective systems results from a 50 mhz profiler abstract wind profiler data wore used to determine the vertical motion structure in four tropical mcsoscale convective systems mcss which occurred during the down under doppler and electricity experiment dundee near darwin northern territory australia three of the mcss occurred during the monsoon break convective regime and one occurred during the monsoon regime in the break regime cases each with a leading convective and trailing stratiform region structure the wind profiler sampled low level convective cells on the leading edge of the convective region trailed by deeper updrafts of comparable magnitude surface rainfall measurements from a network of raingauges showed two comparable peaks in rainfall intensity that roughly corresponded to the passage of low level and deep convective updraft 71 80 of the system total rainfall was associated with the passage of the convective line in the stratiform region the profiler data showed generally weak vertical drafts 1 m s 1 and the presenc

the isotopic composition of strontium of the early jurassic north mountain basalts nova scotia the initial isotopic composition of strontium of the early jurassic north mountain basalts was determined for two of three flow units the lower unit and upper unit each unit was sampled along the outcropping basalts over a distance of 170 km the initial 87sr 86sr ratios are remarkably constant for each unit for the lower unit the initial ratios range from 0 70591 to 0 70609 for the upper unit the range is 0 70675 0 70687 the relatively high ratio could represent tapping of a magma source in an isotopically heterogeneous mantle alternatively the magma could have resided for a time in the lower crust and assimilated crustal material thereby increasing the radiogenic 87sr content mixing had to have been very efficient as indicated by similar initial ratios over considerable distances with the extrusion of the upper unit an isotopically different part of the mantle was tapped or more likely the magma was retained within the lower crust long enough to assimilate additional crustal material an

radar observations of updrafts downdrafts and turbulence in fair weather cumuli abstract observations from a 94 ghz radar are used to define the vertical structure of marine fair weather cumuli doppler spectra obtained from the radar provide mean vertical velocities as well as detailed spectral shapes that can be used to infer small scale vertical velocity shear illuminate cloud microphysical processes and provide estimates of turbulence dissipation rates these new observations facilitate the analysis and understanding of in cloud circulations and the physical processes involved since the cloud boundaries and dimensions are mapped along with the internal structure of the clouds coincident observations from a 915 mhz radar wind profiler were used to further define the turbulence structure in and around the clouds the observations document the detailed vertical and horizontal dimensions of updraft and downdraft circulations in the clouds observed the two cumuli studied in detail have similar circulation patterns an updraft core surrounded by downdrafts although the clouds ha

estimating mass and momentum fluxes in a line of cumulonimbus using a single high resolution doppler radar we present a method to derive the vertical wind field at a scale of 1 2 km from a high resolution doppler radar by performing vertical scans in the plane of the mean wind and tracking turbulent features on a scale of several hundred metres in the radial velocity field between consecutive scans the method is applied to a line of cumulonimbus clouds observed by the high resolution chilbolton radar in southern england the storm was not a squall line since it was propagating parallel rather than perpendicular to its length a sequence of scans was taken over an hour long period from these scans we derive the u and w components of the wind updraughts of up to 15 m s 1 are found from these observations the mass flux of a typical storm cell was estimated over the 50 min lifetime of the cell the total mass of air transported from the boundary layer to the upper troposphere was found to be around 50 megatonnes the profile of hour averaged momentum flux against height was then calculated and compared to the vertical shear of the mean horizontal wind it was found that above 4 5 km the momentum flux was down gradient with an equivalent eddy diffusivity of around 103 m2s 1 below this height however the flux was counter gradient with an equivalent eddy diffusivity of around 103m2s 1 we propose a mechanism to explain this behaviour involving the prevalence of precipitation cooling and descent on the downshear side of convergence lines a synthesis of the major wind flows in the storm reveals that despite superficial appearance the storm did not fit the usual multi cell paradigm in which gust fronts play a key roll in triggering new cells downwind rather the convergence lines associated with the convection were more akin to warm frontal surfaces that remain tied to the base of each cell new cells tending to form upwind of older cells copyright 2008 royal meteorological society

petrography and significance of zoned dolomite cements from the cayman formation miocene of cayman brac british west indies abstract cavities in dolostones from the cayman formation miocene from cayman brac commonly contain complex cement successions that record three main phases of diagenesis phase i cements formed of low ca calcian dolomite lcd and high ca calcian dolomite hcd are divided into monomineralic lcd crystals oscillatory zoned lcd hcd crystals and step zoned hcd lcd crystals dissolution during phase ii produced dolomite crystals with hollow cores hollow growth zones and hollow crosscutting zones calcite precipitated during phase iii filled many of the cavities that had not been filled by the dolomite cements etching shows that the lcd is formed of blocky subcrystals that have their long axes perpendicular to the growth surfaces whereas hcd is characterized by a modulated structure that is evident as growth parallel slightly sinuous strands 10 20 nm wide the contrast in crystallographic microstructures supports the notion that lcd and hcd are distinct types of dolomite two levels of variability that operated on different time scales controlled diagenesis in the cayman formation of cayman brac long term variability controlled the evolution from dolomite precipitation to dolomite dissolution to calcite precipitation short term variability controlled variations in the physiochemical environments that characterized each phase of diagenesis thus during phase i diagenesis short term fluctuations in water chemistry and or crystal growth patterns controlled the mol caco3 in the dolomite cement crystals similarly short term variations in pore water compositions controlled the style of dolomite dissolution during the second phase of diagenesis

petrography of finely crystalline cenozoic dolostones as revealed by backscatter electron imaging case study of the cayman formation miocene grand cayman british west indies abstract finely crystalline cenozoic island dolostones like those found in the cayman formation on grand cayman are commonly assumed to be petrographically and compositionally homogeneous backscatter electron images bsei however show that the constituent dolomite crystals 3 content moreover such images allow 1 depiction of growth patterns in the constituent crystals irrespective of their origin 2 recognition of replacive dolomite as opposed to dolomite cement and 3 delineation of stratigraphic packages in the dolomite cements that reflect different episodes of cementation integration of this information forms the basis for paragenetic interpretations of the dolostones on grand cayman the miocene cayman formation can be divided into friable high porosity dolostones and hard low porosity dolostones backscatter electron images show that the hard dolostones are characterized by complex arrays of zoned dolomite cements that have occluded most of the pores caymanite an internal sediment has occluded many of the larger cavities in contrast the high porosity dolostones contain little cement and no internal sediments precipitation of the cements and the deposition of internal sediments were related to the passage of large volumes of water through some of the dolostones thus the hard low porosity dolostones are found in the cap rock of the formation in coastal locations and in areas close to solution widened fractures conversely the friable high porosity dolostones form the lower porous unit of the formation in the interior of the island where the passage of water was more restricted

dynamics of marine glacier termini read from moraine architecture allostratigraphic mapping of the internal facies architecture of marine moraines reveals the development history of ice contact sedimentary systems the new method for a high resolution analysis of the dynamic stratigraphy of moraines provides important information on the ice front behavior glacier dynamics and regional climatic conditions based on a series of case studies of the moraines of temperate glaciers in norway an allostratigraphic model is suggested as a conceptual guide for the field analysis of ice contact deposits based on outcrop sections as well as seismic or ground penetrating radar profiles

a middle proterozoic palaeokarst unconformity and associated sedimentary rocks elu basin northwest canada a major palaeokarst erosion surface is developed within the middle proterozoic elu basin northwestern canada this palaeokarst is named the sub kanuyak unconformity and truncates the parry bay formation a sequence of shallow marine dolostones that were deposited within a north facing carbonate platform under a semi arid climate the sub kanuyak unconformity exhibits up to 90 m of local relief and also formed under semi arid conditions when parry bay dolostones were subaerially exposed during a relative sea level drop of about 180 m caves and various karren developed within the meteoric vadose and phreatic zones their geometry size and orientation were largely controlled by northwest and northeast trending antecedent joints bedding and lithology near surface caves later collapsed forming valleys and intervening towers or walls and plains minor terra rossa formed on top of highs karstification was most pronounced in southern parts of bathurst inlet but decreased northward probably reflecting varying lengths of exposure time along a north dipping slope the kanuyak formation is up to 65 m thick and partially covers the underlying palaeokarst it consists of six lithofacies i breccia formed during collapse of caves as reworked collapse breccia and regolith ii conglomerate representing gravel dominated braided fluvial deposits iii sandstone deposited as braided fluvial and storm dominated lacustrine deposits iv interbedded sandstone siltstone and mudstone of sheet flood origin v dolostones formed from dolocretes and quiet water lacustrine deposits and vi red beds representing intertidal marine mudflat deposits rivers flowed toward the northwest and northeast within karst valleys and caves lakes were also situated within valleys marine mudflat sediments completely cover the palaeokarst to the north a regional correlation of the sub kanuyak unconformity with the intra greenhorn lakes disconformity within the coppermine homocline suggests that similar styles of karstification occurred over an extensive region the elu basin palaeokarst however was developed more landward and was exposed for a longer period of time than the coppermine homocline palaeokarst

ongoing long term evolution of an unconformity that originated as a karstic surface in the late miocene a case study from the cayman islands british west indies abstract on grand cayman and cayman brac karst development on the upper surface of the cayman formation during the late miocene lowstand produced the cayman unconformity on grand cayman this led to the development of a deep atoll shaped depression on the western part of the island the ensuing lower pliocene transgression buried that unconformity and led to deposition of sediments that now form the pedro castle formation today on grand cayman the dolostones of the cayman formation remain largely buried on the western half of grand cayman but are widely exposed on the central and eastern parts of the island where they have been subjected to extensive weathering over the last 4 3 ma although the situation is similar on cayman brac uplift of the central core led to removal of the pedro castle formation and much of the cayman formation karst development on both islands reflects the interplay between neogene sea level changes climate and tectonic uplift today weathering is further modifying the cayman unconformity on the eastern parts of both islands the cayman unconformity on the central and eastern parts of grand cayman is characterized by karst landforms including a peripheral rim sinkholes solution widened joints and photolineaments surface traces of joints and or faults the westward tilting of cayman brac 4 3 ma to 400 ka led to more severe weathering of the exposed cayman formation that included 1 enhancement of the peripheral rim and karst features on the upslope margin and 2 higher denudation rates than on grand cayman during the messinian the denudation rate on the west end of grand cayman was 0 03 0 10 mm yr 1 in contrast the denudation rate over the an estimated period of 4 9 to 6 2 ma for the eastern half of grand cayman has been about 0 01 mm yr 1 whereas on the east end of cayman brac it has been 0 03 0 04 mm yr 1 on both islands substantial thicknesses of strata have been lost to erosion and the cayman unconformity has been subject to ongoing modification over a period of 4 9 to 6 2 ma

deciphering the impact of sea level changes and tectonic movement on erosional sequence boundaries in carbonate successions a case study from tertiary strata on grand cayman and cayman brac british west indies abstract the stratigraphic architecture of carbonate successions that develop on geographically isolated islands reflects the balance between sea level highstands lowstands and tectonic activity this is readily apparent in the tertiary carbonate sequences on the cayman islands that are formed of the bluff group which includes the brac formation lower oligocene cayman formation middle miocene and pedro castle formation middle pliocene these strata are overlain by the pleistocene ironshore formation the unconformities that define the boundaries between these formations are variable because some developed during one cycle of past erosion others developed through two or more past erosional cycles and some are still developing today some unconformities like the one at the top of the cayman formation are geographically variable because they underwent different developmental histories in different areas the challenge with architectural complex successions like those on the cayman islands is that of deciphering the impact of sea level changes as opposed to tectonic influences during sea level lowstands the older carbonate successions were exposed on land and modified by surface and subsurface karst development at the same time marine erosional processes affected the coastal areas surface karst modification which commonly produced rugged topographies with erosional relief at least 62 m was controlled largely by rainfall runoff and stratal dip weathering on grand cayman at the end of the miocene for example produced a dish shaped topography with elevated peripheral rims in contrast uplift of the east end of cayman brac between the late pliocene 3 6 ma and 400 ka elevated the basal part of the cayman formation 33 m above sea level subsequent karst development which is still ongoing today removed most of the cayman formation on the eastern part of the island and produced peripheral rims that are higher than those on grand cayman during some lowstands like that between the late pliocene and 400 ka coeval coastal erosion led to the development of coastal benches that cut into the older carbonate strata the combination of karst development in the islands interiors and coastal erosion produced complex rugged topographies that strongly influenced patterns of deposition during the following highstand the complex stratigraphic architecture of the carbonate successions on the cayman islands reflects the variable impact of tectonics karst development and coastal erosion that was associated with each lowstand highstand cycle

a 10be chronology of south western scandinavian ice sheet history during the lateglacial period we present 34 new cosmogenic 10be exposure ages that constrain the lateglacial bolling preboreal history of the scandinavian ice sheet in the lysefjorden region south western norway we find that the classical lysefjorden moraines earlier thought to be entirely of younger dryas age encompass three adjacent moraines attributed to at least two ice sheet advances of distinctly different ages the 10be age of the outermost moraine 14 0 0 6 ka n 4 suggests that the first advance is of older dryas age the innermost moraine is at least 2000 years younger and was deposited near the end of the younger dryas 11 4 0 4 ka n 7 after abandonment of the innermost lysefjorden moraine the ice front receded quickly towards the head of the fjord where recession was interrupted by an advance that deposited the trollgaren moraine at 11 3 0 9 ka n 5 10be ages from the inboard side of the trollgaren moraine suggest final retreat by 10 7 0 3 ka n 7 the late culmination of the younger dryas advance contrasts with other sectors of the scandinavian ice sheet where the margin appears to have culminated earlier during the younger dryas stadial followed by retreat during the middle and late part of the younger dryas

hydrogeochemistry of grand cayman british west indies implications for carbonate diagenetic studies abstract groundwater in the dolostone aquifers of the bluff group oligocene miocene on grand cayman is divided into fresh lightly and highly brackish and saline type i and ii zones according to chemical characteristics that were determined during a 3 year 1985 1988 monitoring program brackish and type i saline waters display the greatest variation in chemical properties whereas the type ii saline water has the most stable chemical characteristics most groundwaters from these dolostone aquifers are thermodynamically capable of precipitating calcite and or dolomite the saturation indices for these minerals however vary through time and space even in the context of small water lens simple mixing of fresh and sea water cannot explain the chemistry of the water found in the joint and karst controlled dolostone aquifers of grand cayman deviation from a simple mixing model is due to variations caused by tidal fluctuation the rate of rain water recharge influx of ca rich groundwater from the surrounding limestone aquifers influx of co 2 rich surface water from sinkholes and swamps and water rock interactions dissolution and precipitation of calcite and dolomite sustained groundwater abstraction from a lens can significantly alter the hydrochemistry of the water lens this suggests that hydrochemical characterization of small fresh water lenses like those on grand cayman cannot be based on spot or short term sampling interpretation of such fluids in terms of calcite dolomite precipitation and or dissolution must be treated with caution if the data base has not been derived from long term monitoring

termination of the arabian shelf sea stacked cyclic sedimentary patterns and timing oligocene miocene oman abstract in the janabah region of southeastern oman oligocene miocene limestones of the shuwayr warak and ghubbarrah formations are widely exposed they were deposited on an extensive shallow carbonate platform that was part of the arabian shelf and located on the gulf of aden s northeastern rift shoulder which emerged during the early miocene the uppermost part of the studied sedimentary succession developed immediately before the permanently subaerial exposure of the carbonate platform cyclic changes of intertidal and subtidal facies document a fluctuating relative sea level at different frequencies and a continuous decline of accommodation single erosive surfaces with palaeokarst cavities and caliche crusts separate larger depositional cycles these disconformities imply relatively long episodes of subaerial exposure and are interpreted to have been formed during lowstands of third order sea level cycles that denuded the platform taxonomic studies of the accompanying mollusc faunas and certain benthic foraminifers allow a correlation of the recognised subaerial disconformities with the ru4 ch1 to ch4 aq1 sequence boundaries of hardenbol et al hardenbol j thierry j farley m b jacquin t graciansky p c vail p r 1998 mesozoic and cenozoic sequence chronostratigraphic framework of european basins in graciansky c p hardenbol j jacquin t vail p r eds mesozoic and cenozoic sequence stratigraphy of european basins society for sedimentary geology special publication 60 13 603 this demonstrates that the termination of the arabian shelf sea must be back dated from the middle burdigalian to the early aquitanian

diagenetic processes associated with unconformities in carbonate successions on isolated oceanic islands case study of the pliocene to pleistocene sequence little cayman british west indies abstract the youngest part of the neogene carbonate succession on little cayman is a thin

collapse of marine based outlet glaciers from the scandinavian ice sheet abstract we present a reconstruction of the timing and retreat rates of more than 2000 m thick younger dryas yd fjord glaciers in western norway using a detailed chronology of 10 be exposure ages from lateral moraines and 14 c dated end moraines a primary conclusion is that ice margins retreated up the 120 170 km long fjords at mean rates of 240 340 m yr 1 during the early holocene we further show that part of the south western sector of the scandinavian ice sheet collapsed in two distinct steps the first step occurred between 19 5 and 18 5 ka bp as break up of the norwegian channel ice stream which drained the ice sheet during the last glacial maximum lgm the second step was the rapid retreat up the fjords mentioned above dated to 11 6 11 1 ka bp during the intervening 7000 years no net retreat occurred despite oscillations of the ice margin this stepwise ice margin retreat strongly contrasts with the more monotonic decay of the ice sheet as a whole indicating that water depths set the pace for climate triggered ice margin retreat in this part of the ice sheet calving and melting of marine margins has dominated mass loss from modern ice sheets in recent decades however the mechanisms and long term 100 1000 yr rate of ice front retreat is less certain and empirical examples such as those given here may help in developing better numerical models

a major re growth of the scandinavian ice sheet in western norway during allerod younger dryas abstract distinct younger dryas yd moraines are mapped more or less continuously around the scandinavian ice sheet in most areas there is no evidence to suggest that a glacial re advance took place during the yd either because it did not happen or because older deposits have been removed by glacial erosion in contrast we here present 90 radiocarbon dates from 36 different sites that were overrun by a major ice sheet advance in the area between hardangerfjorden and sognefjorden sw norway thus this region is exceptional for examining the glacial response to the climate shifts across allerod yd the re growth of the ice sheet in this sector commenced during the allerod interstadial it expanded along 600 800 m deep fjords reaching a thickness of up to 2000 m we produce time distance diagrams for two lobes for both the outermost coast became ice free close to 15 cal ka bp i e at the onset of the bolling the hardangerfjorden lobe re advanced during the older dryas 14 cal ka bp an event that was not replicated for the herdla lobe farther north both lobes reached their most landward position before re advancing at 13 5 13 0 cal ka and obtained their maximum extent at the very end of the yd 11 5 cal ka the late culmination of the advance is accurately dated and differs from most of the scandinavian ice sheet margin where the maximum was reached during early or middle yd we also present a time distance diagram from the last glacial maximum to the ice divide showing two step retreat fast retreat occurs 21 20 and 11 5 10 cal ka bp separated by a period of almost no net retreat 20 11 5 cal ka bp which contrasts with much more even retreat in other parts of the scandinavian ice sheet

downdrafts within high plains cumulonimbi i general kinematic structure abstract this paper presents results from a comprehensive investigation in which observations from several case studies an integrated with three dimensional cloud model results to examine the general kinematic structure of downdrafts associated with high plains precipitating convection one particular downdraft type the low level precipitation associated downdraft is the focus of this paper general airflow and trajectory patterns within low level downdrafts are convergent from 0 8 km upwards to downdraft top typically less than 5 km agl observed mass flux profiles often increase rapidly with height as a result of strong buoyancy forcing below the melting level inflow to the low level downdraft although vertically continuous can be separated into two branches the up down branch originating within the planetary boundary layer initially rises up to 4 km and then descends within the main precipitation associated downdraft the midlevel branch usually more pronounced during early downdraft stages ori

microarchitecture of dolomite crystals as revealed by subtle variations in solubility implications for dolomitization abstract despite their small size most dolomite crystals in the dolostones of the miocene cayman formation on grand cayman are zoned with a core formed of high calcium calcian dolomite hcd encased by a cortex formed of low calcium calcian dolomite lcd these two different types of dolomite are separated by a sharp well defined cortical boundary acid etching shows that the hcd cores are characterized by numerous growth defects including twinning modulations and dissolution slots whereas the lcd that forms the cortex contains far fewer and less well developed growth defects the fact that the hcd is far more soluble than the lcd is attributed to its higher caco 3 content and greater density of growth defects the cortical boundary that separates the hcd core from the lcd cortex is a discontinuity that may have developed as a response to a change in diagenetic regimes or a change in the composition of the dolomitizing fluids deciding between these two possibilities however is difficult because the small size of the crystals precludes collection of data needed to resolve the issue irrespective of the underlying cause the development of the zoning is critical from a diagenetic perspective because the hcd with its high caco 3 content and high density of growth defects is far more prone to dissolution than the lcd cortex thus zoned crystals of this type are highly susceptible to diagenetic modifications that will lead to the development of hollow crystals dedolomite or inside out dolomite

radar facies of paraglacial barrier systems coastal new england usa analysis of a large data base of ground penetrating radar gpr profiles from both natural and developed paraglacial barriers along the coast of new england has allowed identification of eight reflection configurations that characterize this type of mid to high latitude coastal environment bedrock anchor points yield primarily hyperbolic configurations whereas glacial anchor points and sediment source areas are characterized by chaotic parallel and tangential oblique configurations beaches and dunes produce predominantly sigmoidal oblique hummocky reflection free and bounding surface configurations back barrier sediments may yield basin fill configurations but generally include abundant signal attenuating units the gpr data calibrated with information from cores were collected across swash aligned and drift aligned barriers in a variety of wave and tidal energy settings application of a 120 mhz antenna as used in this study enables portrayal of a range of sedimentary units from individual bedforms on single records to entire barrier elements using large numbers of intersecting gpr sections at maximum vertical resolutions that vary between 0 2 m and 0 7 m the most important drawback of gpr in the coastal environment is attenuation of the electromagnetic em signal by layers of salt marsh peat or by brackish or salty groundwater primarily along barrier edges this disadvantage is offset by many benefits data can be collected at rates of several km per day making gpr an excellent reconnaissance tool a core that is used in the calibration of gpr data can be matched with great accuracy to its position on the complementary gpr record allowing detailed correlation between lithostratigraphy and reflection configuration

petrographic and geochemical features of sinkhole filling deposits associated with an erosional unconformity on grand cayman abstract on grand cayman exposures of dolostones belonging to the cayman formation miocene represent an erosional unconformity that has been developing since the late pliocene 3 6 ma sinkholes that developed during this time have remained open or become partly to fully filled with various combinations of rootcrete breccias loose limestone and dolostone lithoclasts and white red and orange limestones these sinkhole filling deposits have different geochemical attributes to the neogene and pleistocene marine carbonates that form the bedrock of the island the deposits in the sinkholes formed in response to the variations of sea level climate exposure and vegetation that developed during the period when the erosional unconformity was developing the rootcrete oncoids red and orange limestones are terrestrial in origin whereas the limestone and dolostone lithoclasts and white limestones are derived from marine deposits on the erosional unconformity intense root activity led to the formation of rootcrete and terrestrial oncoids but also selectively blackening reworked marine carbonates the red and orange limestone matrices which formed under more arid conditions contrast with the other sinkhole filling deposits that formed during periods when the climate was semi arid to humid the distinctive ree signatures of the sinkhole filling deposits which are different from those of the bedrock limestones and dolostones can probably be attributed to trace amount of terra rossa and or airborne saharan derived dust that are present in those deposits

observed structure of mesoscale convective systems and implications for large scale heating mesoscale convective cloud systems that produce large amounts of rain in mid latitudes and most of the rain in the tropics consist of a combination of convective and stratiform cloud the convective regions contain numerous deep cells that are often but not always arranged in lines the stratiform region is an outgrowth of the convective ensemble it lies adjacent to the convective region and is seeded by ice particles detrained from convective towers sometimes it lies to the rear of a propagating convective line while on other occasions it surrounds the convection the heating of the large scale environment by a mesoscale convective system is affected by both the convective and stratiform regions although processes such as melting and radiation are important the net heating by a system is dominated by condensation and evaporation associated with vertical air motions this paper reviews recent observational evidence regarding the mean vertical motion profiles in the convective and stratiform regions of mesoscale convective systems and the implications of these mean motions for the vertical distribution of heating of the large scale environment in both the convective and the stratiform regions vertical motions have been determined by various techniques including composites of rawinsonde and aircraft wind data single and dual doppler precipitation radar analyses and wind profiler observations in stratiform regions these data consistently show mean vertical velocity that is upward in the upper troposphere and downward in the lower troposphere the level separating upward from downward motion is located from 0 to 2 km above the 0 c level depending on location within the stratiform region diagnostic calculations show that these vertical motion profiles imply heating of the upper troposphere and cooling of lower levels by stratiform region processes data on vertical motions in the convective regions are less consistent from case to case these data sometimes indicate that the mean vertical velocity in convective regions is maximum in the lower troposphere in other cases the data indicate a maximum in the high troposphere diagnostic calculations show that heating profiles diagnosed from these two types of profile are quite different the first having a maximum of heating in the lower troposphere while the second has a maximum in the middle troposphere although it is difficult to determine whether or not the differences in estimates arise from different types of observations analysis methods or sampling strategies it seems likely that they stem from differences in the large scale environment of the different mesoscale systems the ubiquitous occurrence of stratiform regions in mesoscale convective systems and hurricanes together with their consistent heating profiles which systematically concentrate heating in upper levels while cooling lower levels are a major consideration in evaluating the interaction of mesoscale systems with the large scale environment however the consistency of the stratiform profiles from case to case indicates that the variability of net convective plus stratiform heating profiles from case to case lies primarily in the variation of the convective region profiles from one case to another it is suggested that future work should focus on the convective region vertical profiles of vertical motion and heating and on the large scale environmental factors that may control the variation of these profiles from case to case

sedimentary facies and depositional architecture of ice contact glaciomarine systems abstract the characteristics of ice contact glaciomarine systems are reviewed based on a range of weichselian and holocene examples from the fjordal basins in norway and svalbard these depositional systems occur as large morphological ridges end moraines including push moraines which are coarse grained and show large scale foreset bedding the paper addresses some of the major problems with regard to the recognition classification and stratigraphic analysis of these systems the ice proximal glaciomarine systems are classified here into three categories 1 ice contact submarine fans 2 ice contact deltas and 3 glaciofluvial deltas this classification integrates morphological and sedimentological criteria and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common non glacial deltaic systems the emphasis is on the criteria for the recognition of the ice contact glaciomarine systems i e ice contact fans and ice contact deltas and their discrimination from common gilbert type deltas and fan deltas the review further focuses on ice contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations it is shown that both the periods of ice front stability and changes in the ice front position as well as the magnitude and rate of those changes are all recorded in the ice contact depositional system the sedimentary record further reflects glacio isostatic sea level changes and local palaeogeography a new conceptual model is suggested which places these ice contact glaciomarine systems in a dynamic stratigraphic context the model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework and is meant to be a guide for the analysis of the sedimentary record of ice contact systems

mass flux characteristics of tropical cumulus clouds from wind profiler observations at darwin australia abstractcumulus parameterizations in weather and climate models frequently apply mass flux schemes in their description of tropical convection mass flux constitutes the product of the fractional area covered by convection in a model grid box and the vertical velocity in cumulus clouds however vertical velocities are difficult to observe on gcm scales making the evaluation of mass flux schemes difficult here the authors combine high temporal resolution observations of in cloud vertical velocities derived from a pair of wind profilers over two wet seasons at darwin with physical properties of precipitating clouds cloud top heights cth convective stratiform classification derived from the darwin c band polarimetric radar to provide estimates of cumulus mass flux and its constituents the length of this dataset allows for investigations of the contributions from different cumulus cloud types namely congestus deep and overshooting convection to the overall mass flux and of the influence of large

characteristics of vertical velocity cores in different convective systems observed over gadanki india abstract the indian mesosphere stratosphere troposphere mst radar measurements during the passage of 60 convective systems are used to study the vertical air velocity w characteristics of tropical convection the up and downdraft cores and various stages types of convection shallow deep and decaying are discerned from radar time intensity maps of w the characteristics of cores speed size orientation vertical extent gravity wave activity etc at different stages of convection are discussed with the help of three case studies the cores stratified based on the type of convection are mostly erect in nature in all types of convective systems except for deep updraft cores a considerable percentage 35 of deep updraft cores show inclined structure with elevation angles as low as 0 20 the variation of the horizontal wind field with height and the internal dynamics of mesoscale convective systems mcss are thought to be responsible for this geometry further the vertical extent of draft

the influence of the shear induced pressure gradient on thunderstorm motion abstract in the present investigation we propose a simple theory to explain how a veering environmental wind shear vector can cause an initially symmetric updraft to grow preferentially to the right of the shear vector and acquire cyclonic rotation the explanation offered is based on linear theory which predicts that interaction of the mean shear with the updraft produces favorable vertical pressure gradients along its right flank to asses the validity of linear theory for large amplitude updrafts the three dimensional shallow anelastic equations are numerically integrated using a simple parameterization for latent heating within a cloud and the linear and nonlinear forcing terms are separately analyzed these results suggest that although the nonlinear effects strongly promote splitting of the updraft the linear forcing remains the dominant factor in preferentially enhancing updraft growth on the right flank we believe this differential forcing is a major contributor to the observed predominance o

analysis of convectively generated gravity waves in mesoscale model simulations and wind profiler observations the characteristics of convectively generated gravity waves during an episode of deep convection near the coast of wales are examined in high resolution mesoscale simulations with the met office unified model and in observations from a mesosphere stratosphere troposphere wind profiling doppler radar in this episode deep convection reached the tropopause and generated vertically propagating high frequency waves in the lower stratosphere that produced vertical velocity perturbations of order of 1 ms 1 wavelet analysis is applied in order to determine the characteristic periods and wavelengths of the waves both in the simulations and in the observations the wavelet spectra contain several distinct preferred scales indicated by multiple spectral peaks the peaks are most pronounced in the horizontal spectra at several wavelengths less than 50 km although these peaks are most clear and of largest amplitude in the highest resolution simulations with 1 km horizontal grid length they are also evident in coarser simulations with 4 km horizontal grid length peaks also exist in the vertical and temporal spectra at approximately 2 5 4 5 km and 10 30 min respectively with good agreement between simulation and observation two dimensional wave number frequency spectra demonstrate that each of the selected horizontal scales contains peaks at each of the preferred temporal scales revealed by the one dimensional spectra alone copyright 2008 royal meteorological society

convective updraught evaluation in high resolution nwp simulations using single doppler radar measurements this study presents an evaluation of the size and strength of convective updraughts in high resolution simulations by the uk met office unified model um updraught velocities have been estimated from range height indicator rhi doppler velocity measurements using the chilbolton advanced meteorological radar as part of the dynamical and microphysical evolution of convective storms dymecs project based on mass continuity and the vertical integration of the observed radial convergence vertical velocities tend to be underestimated for convective clouds due to the undetected cross radial convergence velocity fields from the um at a resolution corresponding to the radar observations are used to scale such estimates to mitigate the inherent biases the analysis of more than 100 observed and simulated storms indicates that the horizontal scale of updraughts in simulations tend to decrease with grid length the 200 m grid length agreed most closely with the observations typical updraught mass fluxes in the 500 m grid length simulations were up to an order of magnitude greater than observed and greater still in the 1 5 km grid length simulations the effect of increasing the mixing length in the sub grid turbulence scheme depends on the grid length for the 1 5 km simulations updraughts were weakened though their horizontal scale remained largely unchanged progressively more so for the sub kilometre grid lengths updraughts were broadened and intensified horizontal scale was now determined by the mixing length rather than the grid length in general simulated updraughts were found to weaken too quickly with height the findings were supported by the analysis of the widths of reflectivity patterns in both the simulations and observations

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

distribution and geometry of facies and early diagenesis the key to accommodation space variation and sequence stratigraphy upper cretaceous congost carbonate platform spanish pyrenees abstract through only moderate structural deformation the upper cretaceous carbonates of the tremp region in the spanish pyrenees can be studied in the form of a platform to basin cross section comparable in scale to that of a seismic section this study examines the upper turonian to mid coniacian congost platform and its associated basinal succession the sedimentology facies geometries and cycle stacking patterns along with evidence of exposure of the platform are interpreted in terms of fluctuations in relative sea level and variations in accommodation space differences in the facies and early diagenesis of carbonates from different parts of the congost platform suggest two separate phases of platform development an earlier more land ward platform was dominated by clinoforms prograding on to a sloping basin floor with a thin lagoonal sand bank facies upon the platform itself supplying abundant excess sediment to the clinoforms a later more basin ward platform has a more complex internal geometry of depositional units and marginal rudist coral buildups the interpretations are used to propose a new sequence stratigraphic architecture for the congost platform involving two sequences the second produced through dynamic forced regression sequence boundaries are characterised by subaerial exposure on the platform top that can be correlated with hardgrounds and or glauconitic horizons within the more basinal locations overlain by deeper water facies the presence of a submarine onlap surface and down slope slide deposits immediately above the sequence boundary suggests that the major transgressive event that followed sequence boundary development was brought about by local extensional tectonic activity the small scale cyclicity within the sequences and the major falls in sea level that produced the sequence boundaries are interpreted to have resulted largely from eustatic processes probably with tectonic enhancement

caymanite a cavity filling deposit in the oligocene miocene bluff formation of the cayman islands caymanite is a laminated multicoloured white red black dolostone that fills or partly fills cavities in the bluff formation of the cayman islands the first phase of caymanite formation occurred after deposition lithification and karsting of the oligocene cayman member the second phase of caymanite formation occurred after joints had developed in the middle miocene pedro castle member caymanite deposition predated dolomitization of the bluff formation 2 5 ma ago caymanite is formed of mudstones wackestone packstones and grainstones allochems include foraminifera red algae gastropods bivalves and grains of microcrystalline dolostone sedimentary structures include planar laminations graded bedding mound shaped laminations desiccation cracks and geopetal fabrics original depositional dips ranged from 0 to 60 although caymanite originated as a limestone dolomitization did not destroy the original sedimentary fabrics or structures the sediments that formed caymanite were derived from

vhf radar echoes in the vicinity of tropopause during the passage of tropical cyclone first observations from the gadanki mst radar first observations on the characteristics of vhf radar echoes in the vicinity of tropopause vot during depression or passage of tropical cyclone made using the gadanki mst radar are presented the most significant and new observation is that signal to noise ratio snr in zenith and off zenith beams are nearly equal in the vot when a cyclone is located close to the radar site during depression however a slight decrease in echo strength with zenith angle was found observations made during such disturbed conditions are in contrast to the usual aspect sensitive characteristics of the radar echoes spectral widths during disturbed atmospheric conditions in general are found to be much larger than that of normal condition further spectral widths observed in the vertical beam during cyclone are considerably larger than that during normal condition these features however have not been noticed at other height regions during such atmospheric conditions all these observations clearly indicate preferential enhancement in turbulence activity in the vot these observations constitute the first experimental evidence of such a zenith angle dependence of vhf radar echo characteristics in the vot during depression and cyclone these results are presented and discussed in the light of present understanding of turbulence activity in the vot

timing of the younger dryas glacial maximum in western norway this study precisely constrains the timing of the younger dryas yd glacial maximum in south western norway by utilizing sediment records from lake basins two of the basins located on the distal side of the mapped herdla halsnoy moraine received meltwater directly from the ice sheet only when the ice margin reached its maximum extent during the yd in the cores the ice maximum is represented by well defined units with meltwater deposits dominantly laminated silt plant macrofossils in the sediment sequences are common and we obtained 18 radiocarbon ages from one of the cores by applying bayesian age depth modelling we obtained a precise date for this meltwater event and thereby also for the timing of the yd glacial maximum we conclude that the ice sheet advance culminated at the halsnoy moraine at 11 760 120 cal a bp and that the ice margin stayed in this position for 170 120 years the subsequent retreat started at 11 590 100 cal a bp i e close to the yd holocene boundary withdrawal was probably triggered by abrupt climatic warming at this time copyright 2011 john wiley sons ltd

vertical velocity in oceanic convection off tropical australia abstract time series of 1 hz vertical velocity data collected during aircraft penetrations of oceanic cumulonimbus clouds over the western pacific warm pool as part of the equatorial mesoscale experiment emex are analyzed for updraft and downdraft events called cores an updraft core is defined as occurring whenever the vertical velocity exceeds 1 m s 1 for at least 500 m a downdraft core is defined analogously over 19 000 km of straight and level flight legs are used in the analysis five hundred eleven updraft cores and 253 downdraft cores are included in the dataset core properties are summarized as distributions of average and maximum vertical velocity diameter and mass flux in four altitude intervals between 0 2 and 5 8 km distributions are approximately lognormal at all levels examination of the variation of the statistics with height suggests a maximum in vertical velocity between 2 and 3 km slightly lower or equal vertical velocity is indicated at 5 km near the freezing level virtual t

void filling deposits in karst terrains of isolated oceanic islands a case study from tertiary carbonates of the cayman islands caves fossil mouldic cavities sinkholes and solution widened joints are common in the cayman and pedro castle members of the bluff formation oligocene miocene on grand cayman and cayman brac because they have been subjected to repeated periods of karst development over the last 30 million years many voids contain a diverse array of sediments and or precipitates derived from marine or terrestrial environs mineral aerosols and groundwater exogenic sediment was transported to the cavities by oceanic storm waves transgressive seas runoff following tropical rain storms and or in groundwater at least three periods of deposition were responsible for the occlusion of voids in the cayman and pedro castle members voids in the cayman member were initially filled or partly filled during the late oligocene and early miocene this was terminated with the deposition of the pedro castle member in the middle miocene subsequent exposure led to further karst development and void filling sedimentation in both the cayman and pedro castle members speleothems are notably absent the void filling deposits formed during these two periods which were predominantly marine in origin were pervasively dolomitized along with the host rock 2 5 million years ago the third period of void filling deposition after dolomitization of the bluff formation produced limestone various types of breccia terra rossa speleothemic calcite and terrestrial oncoids most of these deposits formed since the sangamon highstand 125 000 years ago voids in the present day karst are commonly filled or partly filled with unconsolidated sediments study of the bluff formation of grand cayman and cayman brac shows that karst terrains on isolated oceanic islands are characterized by complex successions of void filling deposits that include speleothems and a variety of sediment types the heterogenetic nature of these void filling deposits is related to changes in sea level and climatic conditions through time

vertical motion characteristics of tropical cyclones determined with airborne doppler radial velocities abstract vertical motions in seven atlantic hurricanes are determined from data recorded by doppler radars on research aircraft the database consists of doppler velocities and reflectivities from vertically pointing radar rays collected along radial flight legs through the hurricane centers the vertical motions are estimated throughout the depth of the troposphere from the doppler velocities and bulk estimates of particle fallspeeds portions of the flight tracks are subjectively divided into eyewall rainband stratiform and other regions characteristics of the vertical velocity and radar structure are described as a function of altitude for the entire dataset and each of the four regions in all of the regions more than 70 of the vertical velocities range from 2 to 2 m s 1 the broadest distribution of vertical motion is in the eyewall region where 5 of the vertical motions are 5 m s 1 averaged over the entire dataset the mean vertical velocity is upward at all altitudes mean downward mot

cave fills in miocene pliocene strata on cayman brac british west indies implications for the geological evolution of an isolated oceanic island abstract an 8 m high wall in a quarry on the west end of cayman brac exposes the upper part of the cayman formation miocene the lower part of the overlying pedro castle formation pliocene and the cayman unconformity which is a karstic unconformity that separates these formations the modern day karst surface caps the pedro castle formation this exposure also includes cross sections through two filled caves the lower cave 8 m long up to 2 5 m high and upper cave 23 m long up to 2 m high that are housed in the cayman formation and pedro castle formation respectively the lower cave is filled with caymanite which is formed of laminated varicolored dolomitized mudstones and grainstones that contain scattered marine fossils e g foraminifera red algae this cave connected to the cayman unconformity by a small diameter tunnel evolved as part of the karst system that developed during the messinian lowstand 7 3 5 3 ma the cave was filled and dolomitized prior to deposition of the pedro castle formation the upper cave is filled with a wide spectrum of lithotypes including dolostones calcareous mudstones terra rossa gastropod coquina coated grains and speleothems u th dating indicates that some of the flowstones are 500 000 years old whereas others are only 21 000 years old dolostones and mudstones in the basal part of the upper cave contain marine fossils foraminifera red algae whereas the younger deposits are devoid of such fossils the upper cave and its deposits developed after the sediments of the pedro castle formation had been deposited and lithified development of the cave filling deposits which includes a clear transition from marine to non marine influences was controlled by eustatic sea level changes and or westward tectonic tilting of cayman brac that occurred after the pedro castle formation became exposed probably during the late pliocene

the age fauna and palaeoenvironment of the late triassic fissure deposits of tytherington south gloucestershire uk important vertebrate faunas occur in fissure deposits of late triassic jurassic age in sw britain although the faunas are well described their age and palaeoenvironment remain poorly understood one such fissure system was documented in detail during quarrying operations at tytherington and has yielded in situ palynomorphs that add much information concerning its age and palaeoenvironment significantly the tytherington fauna is of the sauropsid type that has generally been dated as norian or pre penarth group transgression and was also regarded as representing a distinct upland fauna the palynomorphs which include a significant marine component demonstrate that the tytherington triassic fissures are infilled with late triassic rhaetian sediments that match specific levels in the westbury formation in addition many of the tytherington solutional fissures probably formed during the rhaetian and are consistent with a fluctuating saline to freshwater environment there is no prima facie evidence of solutional formation and infilling of the reptile bearing deposits before the rhaetian trangression the fissure reptile fauna which includes the early dinosaur thecodontosaurus inhabited a small fire swept limestone island in the rhaetian sea the features of the herpetofauna are entirely consistent with this island model which has quaternary analogues

convection waves observations of gravity wave systems over convectively active boundary layers widespread gravity wave systems have been found to exist over convectively active boundary layers cbls in the presence of vertical wind shear in contrast to mountain waves these convection waves occur over flat terrain and are ubiquitous over fields of shallow fair weather cumuli or clear air thermals they extend vertically to at least 9km a m s l probably to the tropopause first discovered by glider pilots as thermal waves they have now been systematically investigated by research aircraft during the ncar convection wave project which also incorporates an effort in numerical simulation the flight results are reported in this paper while the numerical simulations are described in a companion paper typical wavelengths of convection waves were found to range from 5 to 15 km average 9 km and typical vertical motion amplitudes from 1 to 3 m s 1 in all cases vertical wind shear exceeded 3 10 3s 1 under these conditions cloud tops were measured to move with relative velocities of 8 to 10 m s 1 against their environment hence they present an obstacle to the surrounding airflow the analogy to mountainous obstacles launching gravity waves into the atmosphere is suggestive and borne out by the aforementioned numerical simulations which describe this process step by step the interaction between the cbl and the overlying stable layers is studied by spectral and cross spectral analysis of aircraft data including coherence and phase relations between wave motions and cloud population underneath consideration is given to other potential sources of the observed gravity waves at this stage the conclusions of our pilot study may be considered tentative some implications for further research are also discussed

quantification of macroscopic subaerial exposure features in carbonate rocks abstract the macroscopic features that characterize subaerial exposure surfaces in carbonates are well known but their significance has not been quantitatively evaluated this study presents such an analysis in the lower oligocene suwannee limestone of west central florida eleven cores were point counted on a foot by foot basis for the abundance of caliche rhizoliths karst breccia open vugs infiltrated sediment fractures and pedogenic alteration these features occur at and below intraformational exposure surfaces which represent hiatuses estimated at 104 to 105 years and an uppermost sequence bounding unconformity representing 0 5 myr as revealed by sr isotope data statistical analyses of the point count data reveal only a few significant relationships 1 the hierarchy of exposure surfaces and by inference duration of exposure is differentiated only at a marginally significant level by sediment filled vugs preferentially associated with the sequence boundary duration of exposure did not have a significant impact on the relative abundance of all other features 2 proximity 5 ft to both types of surfaces fractures open vugs and infiltrated sediment show no proximal or distal preference for either type of surface 3 depositional texture has no statistically significant affect on the presence or abundance of the exposure features with the exception that rhizoliths and open vugs are preferentially more abundant in packstones relative to grainstones this is interpreted to be the result of a soil moisture effect factor analysis defines four factors that explain 46 to 52 of the total variance in the abundance data relative to the sequence boundary and the intraformational surfaces respectively the loading of each exposure feature on each factor is the same with respect to both types of surfaces which is further evidence that the abundance of exposure features is independent of duration of exposure factor 1 is interpreted to be the amplitude of base level changes and controls the abundance of karst breccia factor 2 is interpreted to be abundance of vegetation and relates to the abundance of rhizoliths and fractures factor 3 is interpreted to be a combination of soil zone pco2 and the availability of water and affects the abundance of pedogenic overprinting caliche and open vugs factor 4 is stratigraphic proximity to the sequence boundary which controls the presence of sediment filled voids the amount of uncorrelated unique variance associated with infiltrated sediments pedogenic overprinting caliche and open vugs is large 60 meaning that feature abundance is also influenced by other unidentified site specific factors these results demonstrate that quantifying the abundance of macroscopic subaerial exposure features in limestones has the potential to yield more insight into the significance of those features than a mere qualitative assessment this is particularly true when assessing the potential role of the many variables that can affect the development of these features

the signature of mid latitude convection observed by vhf wind profiling radar 1 the signature of mid latitude convection observed by a 46 5 mhz wind profiling radar at aberystwyth uk 52 4 n 4 0 w is demonstrated by way of a case study a key feature of such radars is their ability to measure the vertical air velocity directly even under conditions of precipitation higher frequency radars which have more typically been used for such studies measure the net effect of hydrometeor terminal velocities and the air motion under such conditions the radar is capable of observing both updrafts and downdrafts with peak updrafts of the order of 10 m s 1 the signature of convection additionally consists of enhanced values of the radar return spectral width which cannot be interpreted in terms of turbulence intensity and reduced reliability of the corresponding radar derived horizontal wind components when convection reaches the uppermost troposphere the radar return signal power can be anomalously large leading to the radar derived tropopause altitude being overestimated the presence of convection is confirmed by thermal infrared satellite imagery of high topped clouds use is also made of radiosonde and uhf wind profiler data

average vertical motions in the tropical atmosphere observed by a radar wind profiler on pohnpei 7 n latitude 157 e longitude abstract average vertical profiles of the vertical wind obtained under clear sky conditions as weal as under conditions of both light to moderate and heavy rainfall am presented from data obtained using a radar wind profiler located on the island of pohnpei latitude 7 n longitude 157 e the average profiles for the precipitation conditions were obtained insofar as possible under conditions similar to those present within the stratiform and convective regions of tropical mesoscale convective complexes comparison between the vertical wind profiles obtained from the wind profiler and vertical wind profiles obtained earlier by wore conventional methods i e deduced from the convergence divergence of mesoscale horizontal winds shows that while the general features of the profiles obtained by both techniques are similar the profiler results exhibit somewhat more detail the profiler is able to resolve long term average vertical motions down to the cm s 1 subsidence that occurs under clear air condi

lateglacial and early holocene palaeoclimatic reconstruction based on glacier fluctuations and equilibrium line altitudes at northern folgefonna hardanger western norway northern folgefonna c 23 km 2 is a nearly circular maritime ice cap located on the folgefonna peninsula in hardanger western norway by combining the position of marginal mor aines with ams radiocarbon dated glacier meltwater induced sediments in proglacial lakes draining northern folgefonna a continuous high resolution record of variations in glacier size and equili brium line altitudes elas during the lateglacial and early holocene has been obtained after the termination of the younger dryas c 11 500 cal yr bp a short lived 100 150 years climatically induced glacier readvance termed the jondal event 1 occurred within the preboreal oscillation pbo c 11 100 cal yr bp bracketed to 10 550 10 450 cal yr bp a second glacier readvance is named the jondal event 2 a third readvance occurred about 10 000 cal yr bp and corresponds with the erdalen event 1 recorded at jostedalsbreen an exponential relationship between mean solid winter precipitation and ablation season temperature at the ela of norwegian glaciers is used to reconstruct former variations in winter precipitation based on the corresponding ela and an indepen dent proxy for summer temperature compared to the present the younger dryas was much colder and drier the jondal event 1 pbo was colder and somewhat drier and the jondal event 2 was much wetter the erdalen event 1 started as rather dry and terminated as somewhat wetter varia tions in glacier magnitude elas and corresponding palaeoclimatic reconstructions at northern folge fonna suggest that low altitude cirque glaciers lowest altitude of marginal moraines 290 m in the area existed for the last time during the younger dryas these low altitude cirque glaciers of sug gested younger dryas age do not fit into the previous reconstructions of the younger dryas ice sheet in hardanger copyright 2005 john wiley sons ltd

characteristics of deep tropical and subtropical convection from nadir viewing high altitude airborne doppler radar abstract this paper presents observations of deep convection characteristics in the tropics and subtropics that have been classified into four categories tropical cyclone oceanic land and sea breeze vertical velocities in the convection were derived from doppler radar measurements collected during several nasa field experiments from the nadir viewing high altitude er 2 doppler radar edop emphasis is placed on the vertical structure of the convection from the surface to cloud top sometimes reaching 18 km altitude this unique look at convection is not possible from other approaches such as ground based or lower altitude airborne scanning radars the vertical motions from the radar measurements are derived using new relationships between radar reflectivity and hydrometeor fall speed various convective properties such as the peak updraft and downdraft velocities and their corresponding altitude heights of reflectivity levels and widths of reflectivity cores are estimated the most significant

open and filled karst features on the cayman islands implications for the recognition of paleokarst the dolostones of the oligocene miocene bluff formation on the cayman islands are characterized by well developed surficial interface and subsurface karst features that are open or filled with speleothems and sediment some of the open caves show evidence of a minimum of two stages of development related to dissolution in the phreatic zone and the vadose zone the development of speleothemic formations e g stalactites stalagmites columns is limited in some caves but extensive in others some of the caves have limited amounts of sediment on their floors in these caves the speleothems and sediments are still formed of caco3 and thus contrast sharply with the dolostone of the bluff formation in which they occur some of the joints sinkholes and caves are filled with breccia caymanite terra rossa terra rossa breccia pisolitic limestone and speleothems although filled such karst features are analogous to the open karst features that occur elsewhere on the islands the filling of joints sinkh

radar characteristics of storms in the sydney area abstract the characteristics of radar echoes for 12 thunderstorm days in the vicinity of sydney australia in the summer of 1995 96 have been examined using an objective methodology for storm identification and tracking the spatial distribution of identified storms shows a maximum in frequency and intensity along the east side of the mountains that lie inland from the coast characteristics such as storm volume area and height are shown to have a lognormal frequency distribution reflectivity also has a skewed frequency distribution with a prevalence of lower reflectivity storms both the maximum reflectivity and storm height are shown to be correlated with the logarithm of storm volume although small storms predominate the bulk of precipitation flux comes from the relatively few large scale storms it is also shown that storms generally move or propagate in a direction slightly to the left of the mass weighted mean wind for the surface to 300 hpa layer at a speed slightly less than the mean speed

vertical motions in intense hurricanes abstract hurricane vertical motion properties are studied using aircraft measured 1 hz time series of vertical velocity obtained during radial penetrations of four mature hurricanes a total of 115 penetrations from nine flight sorties at altitudes from 0 5 to 6 1 km are included in the data set convective vertical motion events are classified as updrafts or downdrafts if the vertical velocity was continuously positive or negative for at least 500 m and exceed an absolute value of 0 5 m s 1 over 3000 updrafts and nearly 2000 downdrafts are included in the data set a second criteria was used to define stronger events called cores this criteria required that upward or downward vertical velocity be continuously greater than an absolute value of 1 m s 1 for at least 500 m the draft and core properties are summarized as distributions of average and maximum vertical velocity diameter and vertical mass transport in two regions eyewall and rainband in both regions updrafts dominated over downdraft

the tilt of the leading edge of mesoscale tropical convective lines abstract the tilt with height of the leading edge of seven mesoscale convective lines in gate is determined by two independent methods when averaged over time and along the line axis the tilt is found to he surprisingly shallow between 20 and 35 degrees from the horizontal this is distinct from the slopes of the individual towers which can be much steeper the line leading edge slope corresponds to the ratio of the vertical to horizontal velocity relative to the line motion of representative embedded convective cores