on the height of the warm core in tropical cyclones abstractthe warm core structure of tropical cyclones is examined in idealized simulations using the weather research and forecasting wrf model the maximum perturbation temperature in a control simulation occurs in the midtroposphere 5 6 km in contrast to the upper tropospheric 10 km warm core that is widely believed to be typical this conventional view is reassessed and found to be largely based on three case studies and it is argued that the typical warm core structure is actually not well known in the control simulation the height of the warm core is nearly constant over a wide range of intensities from additional simulations in which either the size of the initial vortex or the microphysics parameterization is varied it is shown that the warm core is generally found at 4 8 km a secondary maximum often develops near 13 14 km but is almost always weaker than the primary warm core it is demonstrated that microwave remote sensing instruments are of insufficient resolution to detect this

sequence stratigraphy of the neoproterozoic infra krol formation and krol group lesser himalaya india a bstract a sequence stratigraphic study of terrigenous and carbonate rocks of the infra krol formation and krol group in the lesser himalaya fold and thrust belt of northern india was undertaken as part of a broader investigation of the significance of carbon isotope data in neoproterozoic successions eight regional stratigraphic discontinuities were traced over a distance of nearly 300 km and interpretations were anchored in a series of local studies involving the mapping of key beds and the measurement of closely spaced sections three of the regional surfaces are interpreted as sequence boundaries on the basis of 1 locally developed incised valleys 60 m deep 2 paleokarstic depressions with 50 m of mappable relief 3 subaerial dissolution and weathering products breccias and calcrete filling vertical fissures dikes cavities and shallow de pressions in underlying carbonate rocks and 4 small scale evidence for sub aerial exposure at an erosion surface the remaining five discontinuities are regional flooding surfaces identified on the basis of either facies changes with an abrupt upward deepening across the surface or transitions in facies stacking patterns typically from forestepping to backstepping a glacio eustatic origin is permitted although not required for the three sequence boundaries but no evidence has been found for marked lowering of sea level at other horizons a mismatch between the stratigraphic location of sequence boundaries and car bon isotope minima suggests that local diagenetic alteration or oceanographic phenomena unrelated to glaciation may be in part responsible for observed isotopic variation and that small ice sheets may have existed during apparently nonglacial times without producing either cap carbonates or negative carbon isotope excursions

distribution of helicity cape and shear in tropical cyclones abstract the previous study of helicity cape and shear in hurricane bonnie 1998 was extended to all eight tropical cyclones sampled by nasa during the convection and moisture experiments camex storms were categorized as having large or small ambient vertical wind shear with 10 m s 1 as the dividing line in strongly sheared storms the downshear mean helicity exceeded the upshear mean by a factor of 4 as in the previous study the helicity differences resulted directly from the tropical cyclone response to ambient shear with enhanced in up out flow and veering of the wind with height present downshear cape in strongly sheared storms was 60 larger downshear mean inflow near the surface and the depth of the inflow layer each were 4 times larger downshear at more than 30 of observation points outside the 100 km radius in the downshear right quadrant midlatitude empirical parameters indicated a strong likelihood of supercells no such points existed upshear in highly sheared storms much small

ordovician paleotopography as evidenced from original dips and differential compaction of dolostone and shale unconformably overlying precambrian basement on manitoulin island canada abstract the middle to basal upper ordovician lindsay formation unconformably overlies the paleoproterozoic bar river and lorrain formations on manitoulin island ontario canada representing a depositional hiatus of at least 1 7 billion years the paleoproterozoic inliers currently exposed as basement highs in the sheguiandah region comprised a 14 km2 area of quartz arenite archipelago during the middle to late ordovician inland sea transgression of north america the quartz arenite outcrop collectively covers an area of approximately 1 8 km2 high energy transport and reworking during wave and tropical storm activity along a high relief rocky shoreline is indicated by dolostone containing 2 5 m size rounded to subrounded quartz arenite boulders with percussion marks up to 4 5 m size subangular quartz arenite blocks consistent with mechanical breakage along joints fractures or bedding planes lenticular conglomerate beds and cracks in quartz arenite basement containing mixtures of dolostone quartz granules and fossiliferous debris with continued transgression organic rich carbonate muds were deposited under low energy conditions either on carbonate strata or directly on quartz arenite basement in restricted regions protected from the open sea clast size distribution in the dolostone clast rounding and the location of the shale quartz arenite unconformity relative to basement highs are all consistent with a longshore current running from the present northeast to southwest with the leeward sides of rocky islands protected from high wave and storm energy processes subsequent deposition of upper ordovician and silurian strata resulted in burial and differential compaction of the lindsay formation units the compaction may have been associated with fractures through which mg rich fluids migrated locally altering the lowermost lindsay formation to dolostone evidence for differential compaction is provided by bed thickening down dip of basement highs and boulder flanks and higher regional dips in shale beds proximal to basement highs compared with dolostone strata the relatively high angle strata of the lindsay formation are a result of the combined effects of paleotopography a high relief rocky shoreline and differential compaction

petroleum systems of oman charge timing and risks after 35 years of exploration creaming of the conventional plays in oman is nearly complete and consequently the search has commenced for new less obvious plays many of the new opportunities occur beyond the known hydrocarbon provinces and are considered to have significant charge risks to define these risks extensive basin modeling studies have been conducted in recent years modeling and empirical data show that mesozoic and cenozoic kitchen areas are restricted to western north oman the only areas currently buried at their maximum temperature large parts of north and central oman depend on lateral migration from these kitchens for their charge progressive uplift of the east flank and basin inversion since the middle paleozoic provides favorable conditions for long distance migration in the post carboniferous interval in central oman geochemical tracer molecules benzocarbazoles suggest that a north south trending reactivated basement grain has funneled charge up to 300 km southeastward charge risks increase in the deeper sequence in which eastward migrating hydrocarbons have to traverse the ghaba salt basin a pronounced syncline at depths greater than 3 km the south oman salt basin is currently cool because of shallow depths and hydrodynamic fluid flow activity the shallow post cambrian reservoirs rely on storage of early cambrian ordovician charge by the ara salt cambrian sequence followed by release of hydrocarbons as the salt edge retreats through time basin modeling has outlined the extent of the different petroleum systems and provided us with risk maps to guide our next exploration phase it has revitalized some of the mature plays for instance the gharif formation where oil exploration is now focused along late cretaceous and tertiary migration paths deeper sections are envisaged to have significant scope for gas

coupled dynamic thermodynamic forcings during tropical cyclogenesis part i diagnostic framework abstracta diagnostic framework to investigate the role of processes around and during tropical cyclogenesis is presented the key framework metric is the ratio of bulk differences of moist entropy over differences of angular momentum between an inner and outer region of a tropical disturbance or cyclone this ratio is hypothesized to decrease and become negative as both the high entropy core and low level vortex in the inner region amplify during tropical cyclogenesis the time tendency of this ratio can be split into two forcings a moist entropy forcing and an angular momentum forcing each forcing can be further divided into components comprising differences in net advective fluxes and nonadvective boundary fluxes of moist entropy or angular momentum between each region the framework provides a comprehensive way to compare the relative importance of processes leading to tropical cyclogenesis in a tractable consistent manner suggestions on how to apply the framework to numerical model output are given

facies stratigraphy and evolution of a middle ediacaran carbonate ramp khufai formation sultanate of oman the khufai formation is the oldest carbonate platform of the cryogenian to lowermost cambrian huqf supergroup a stratigraphic characterization of this unit includes detailed facies descriptions a sequence stratigraphic interpretation and evaluation of lateral heterogeneity and overall ramp evolution the khufai formation comprises one and one half depositional sequences with a maximum flooding interval near the base of the formation and a sequence boundary within the upper peritidal facies most of the deposition occurred during highstand progradation of a carbonate ramp facies tracts include outer ramp and midramp mudstones and wackestones ramp crest grainstone shoal deposits and extensive inner ramp microbially dominated peritidal deposits outcrops in the oman mountains are deep water deposits including turbiditic grainstone and wackestone interbedded with siliciclastic rich siltstone and crinkly laminite facies patterns and parasequence composition are variable both laterally across the outcrop area and vertically through time because of a combination of ramp morphology siliciclastic supply and possible syndepositional faulting the lithostratigraphic boundary between the khufai formation and the overlying shuram formation is gradational and represents significant flooding of the carbonate platform the stratigraphic characterization presented here along with the identification of key facies and diagenetic features will help further future exploration and production of hydrocarbons from the khufai formation

petrological statistical approach to interpret recent and subrecent lagoon subfacies idku nile delta of egypt abstract an approach combining petrology and statistics cluster analysis is developed to better distinguish a series of subfacies in surficial and short core samples from idku lagoon in the northwestern nile delta egypt the method integrates lithology physical and biogenic structures grain size and composition of the sand size fraction seven lithofacies eight grain size types and six clusters reveal comparable geographic distributions that are a direct response to geomorphic setting and depositional processes both of which have been modified by man although positioned in an arid setting and affected by anthropogenic factors land reclamation pollutants regional subfacies distribution patterns in idku lagoon are largely a function of the spatial configuration of freshwater dominated to brackish to higher salinity dominated near inlet zones typical of lagoons receiving significant freshwater input within idku a northern depositional province near the inlet and along the coastal sand barrier is defined by associations of terrigenous and coarse grained sediment types a southern province bounded by lagoon margins and marshes is characterized by finer grained sediment types with a high biogenic content recording lower energy levels the petrological statistical approach is used to identify and interpret lagoon subfacies in older to 6000 years b p core sections in idku region and in former abu qir lagoon additionally cluster analysis serves to determine specific lagoon subfacies from hand samples alone whether from surface grabs or cores this is based on a comparison of lithofacies and clusters determined for surficial and short core samples in the idku region to test the method a separate cluster analysis also using surficial and short core samples was used to define manzala lagoon subfacies in the northeastern nile delta results are generally comparable to those obtained in the idku study and show a close relation among manzala lagoon subfacies geomorphic configuration and depositional processes the petrological statistical method could be applied to other regions and also to the geological record

abstract new model for tectonic evolution of neoproterozoic cambrian huqf supergroup basins oman oman has prolific reservoirs within salt of precambrian cambrian age but exploration efforts have been restricted due to limited understanding of the tectonostratigraphic framework new ages constrain the rift related abu mahara group to have been deposited between 730 and 700 ma whereas shelf facies of the overlying nafun group were deposited between 600 and 550 ma this 100 my unconformity precludes a simple relationship between abu mahara crustal extension and nafun regional subsidence due to thermal decay the nafun group is temporally continuous into the ara group the onset of ara subsidence occurred at ca 550 548 ma and was accompanied by a shift to arid climate and uplift of basement blocks to form smaller basins that accumulated salt and carbonates the youngest ara strata are earliest cambrian in age ghadir manquil mirbat subsidence is related to extension at ca 725 ma of a composite basement terrain comprising older archean basement blocks stitched by older pan african ca 800 ma arcs which was sutured to the younger terrains of the arabian shield at ca 625 ma nafun regional subsidence started at this time and is considered here to relate to dynamic depression of the lithosphere associated with subduction of oceanic lithosphere beneath the arabian plate subduction is inferred to have occurred from the northeastern margin of gondwanaland eastern oman where an andean margin resulted in orographic retroarc desiccation in addition to uplift of basement blocks where subduction dip was gentle analogous to the bolivian segment of the andes volcanic ashes and calderas within the ara group record subduction related melting of the crust in a retroarc setting

controls on facies and sequence stratigraphy of an upper miocene carbonate ramp and platform melilla basin ne morocco abstract upwelling of cool seawater paleoceanographic circulation paleoclimate local tectonics and relative sea level change controlled the lithofacies and sequence stratigraphy of a carbonate ramp and overlying platform that are part of a temporally well constrained carbonate complex in the melilla basin northeastern morocco at melilla from oldest to youngest a third order depositional sequence within the carbonate complex contains 1 a retrogradational transgressive warm temperate type rhodalgal ramp 2 an early highstand progradational bioclastic platform composed mainly of a temperate type bivalve rich molechfor facies and 3 late highstand progradational to downstepping subtropical tropical type chlorozoan fringing porites reefs the change from rhodalgal ramp to molechfor platform occurred at 7 0 0 14 ma near the tortonian messinian boundary during a late stage in the development of the bioclastic platform a transition from temperate type molechfor facies to subtropical tropical type chlorozoan facies occurred and is bracketed by chron 3an 2n 6 3 6 6 ma comparison to a well dated carbonate complex in southeastern spain at cabo de gata suggests that upwelling of cool seawater influenced production of temperate type limestone within the ramp and platform at melilla during postulated late tortonian early messinian subtropical tropical paleoclimatic conditions in the western paleo mediterranean region the upwelling of cool seawater across the bioclastic platform at melilla could be related to the beginning of siphoning of deep cold atlantic waters into the paleo mediterranean sea at 7 17 ma the facies change within the bioclastic platform from molechfor to chlorozoan facies may be coincident with a reduction of the siphoning of atlantic waters and the end of upwelling at melilla during chron 3an 2n the ramp contains one retrogradational parasequence and the bioclastic platform three progradational parasequences minor erosional surfaces that bound the upper surface of the ramp and upper surface of the oldest platform parasequence are related to relative falls in sea level induced by local volcanism and associated tectonic uplift these local relative falls had little influence on a broader scale rise to stillstand in relative sea level that controlled development of the transgressive and early highstand systems tracts represented in the ramp and platform respectively

case studies of developing east pacific easterly waves this paper contains a study of developing east pacific easterly waves observed during the summer of 1991 with aircraft in situ and radar data and geosynchronous infrared satellite imagery the circulation and divergence profiles surface momentum and entropy fluxes as well as 700 mb and 975 mb saturated and actual equivalent potential temperatures were measured repeatedly for three disturbances that evolved into east pacific hurricanes as the disturbances develop the level of maximum updraught mass flux decreases which leads to increased convergence at low levels this process appears to be coupled to an increase in the mid level relative humidity which in turn suppresses the development of convective downdraughts comparison of the respective tendencies of convergence and surface friction to spin up and spin down a developing disturbance suggests that friction is unimportant in the early stages of development however as the surface circulation develops the two effects become comparable in magnitude if surface friction is deposited through a fairly deep layer of the troposphere the observations appear to rule out boundary layer ekman balance in these developing systems though more accurate observations of the eddy fluxes of absolute vorticity into such systems are needed to answer this question with certainty

genesis of hurricane julia 2010 within an african easterly wave developing and nondeveloping members from wrf letkf ensemble forecasts abstractin this study the predictability of and parametric differences in the genesis of hurricane julia 2010 are investigated using 20 mesoscale ensemble forecasts with the finest resolution of 1 km results show that the genesis of julia is highly predictable with all but two members undergoing genesis despite the high predictability substantial parametric differences exist between the stronger and weaker members notably the strongest developing member exhibits large upper tropospheric warming within a storm scale outflow during genesis in contrast the nondeveloping member has weak and more localized warming due to inhibited convective development and a lack of a storm scale outflow a reduction in the rossby radius of deformation in the strongest member aids in the accumulation of the warmth while little contraction takes place in the nondeveloping member the warming in the upper troposphere is responsible for the development of meso scale surface pressure falls and a meso surface low i

neoproterozoic peritidal phosphorite from the sete lagoas formation brazil and the precambrian phosphorus cycle the neoproterozoic sete lagoas formation ca 610 ma of the sao francisco basin brazil is a succession of siltstone limestone and phosphorite phosphorite forms part of a previously unrecognized 150 to 200 m thick unconformity bounded depositional sequence lithofacies stacking patterns indicate that deposition was punctuated by higher order fluctuations in base level that produced aggradational parasequences these shallowing upward cycles record the progradation of phosphate rich intertidal flats over shallow subtidal deposits as accommodation filled the presence of mudcracks authigenic chert nodules lack of coarse terrigenous clastics and the abundance of silt with fine abraded quartz grains suggests accumulation along an arid coastline with significant aeolian input delivery of phosphorus adsorbed on aeolian fe oxyhydr oxide and clay is interpreted as having stimulated phosphogenesis in peritidal environments lithofacies associations indicate that windblown phosphorus promoted the establishment of cyanobacterial communities along the coast which produced photosynthetic oxygen and the suboxic conditions necessary for the precipitation of authigenic carbonate fluorapatite as in other precambrian phosphatic systems nearshore oxygen oases were a prerequisite for phosphorite accumulation because redox sensitive phosphogenic processes were pushed into the sediment to concentrate phosphorus in more distal anoxic environments phosphorite could not form because these biotic and abiotic processes were suspended in the water column which cycled phosphorus in sea water rather than at the sediment water interface such shallow water phosphorite is unlike larger younger neoproterozoic phanerozoic phosphatic deposits inferred to have formed in deeper upwelling related environments the increasing size of phosphatic deposits through the latest precambrian is interpreted as reflecting the progressive ventilation of the oceans during the neoproterozoic oxygenation event and resultant expansion of phosphogenic environments into distal settings the widespread cycling of bioavailable phosphorus at the sea floor not only produced the first true phosphorite giants but may have also been an important precondition for the evolution of multicellular animals

evaluation of δ13c chemostratigraphy for intrabasinal correlation vendian strata of northeast siberia integrated sedimentologic stratigraphic and geochemical 13 c 18 o fe mn and sr data from vendian cambrian carbonate ramp deposits of the northeast siberian platform olenek uplift and kharaulakh mountains region are used to constrain primary time dependent oscillations in the carbon isotope record and to evaluate 13 c chemostratigraphy for high resolution intrabasinal correlation the vendian 13 c record of northeast siberia reflects global variations seen elsewhere by displaying in ascending order a strong positive isotopic shift to values near 6 herein named the p interval an intermediate interval of relatively little isotopic change i interval which shows in some sections a monotonic decrease in 13c from 2 at the base to near 0 at the top and a negative excursion to 4 n interval just beneath the vendian cambrian boundary in addition to secular isotopic shifts these strata exhibit local small scale signals related to intrabasinal variations in subsidence erosion and diagenetic alteration e g degradation of organic matter dolomitization and hydrothermal and burial effects these local intrabasinal processes in some cases have modified both the magnitude and form of the primary isotopic excursions which are used as the basis for correlation in all studies carbon isotope profiles provide an important method to evaluate intrabasinal variations in subsidence erosion and stratigraphic completeness these profiles reflect increasing subsidence along the platform to basin transition whereas progressive truncation of isotopic profiles along this trend illustrate pronounced uplift and erosion of ramp strata along unconformity surfaces

the role of vortical hot towers in the formation of tropical cyclone diana 1984 abstract a high resolution 3 km horizontal grid spacing near cloud resolving numerical simulation of the formation of hurricane diana 1984 is used to examine the contribution of deep convective processes to tropical cyclone formation this study is focused on the 3 km horizontal grid spacing simulation because this simulation was previously found to furnish an accurate forecast of the later stages of the observed storm life cycle the numerical simulation reveals the presence of vortical hot towers or cores of deep cumulonimbus convection possessing strong vertical vorticity that arise from buoyancy induced stretching of local absolute vertical vorticity in a vorticity rich prehurricane environment at near cloud resolving scales these vortical hot towers are the preferred mode of convection they are demonstrated to be the most important influence to the formation of the tropical storm via a two stage evolutionary process i preconditioning of the local environment via diabatic production of mul

evolution of a terminal neoproterozoic carbonate ramp system buah formation sultanate of oman effects of basement paleotopography the buah formation is a carbonate unit of late neoproterozoic age exposed in the jabal akhdar of northern oman and the huqf region of central oman the buah formation is interpreted as a distally steepened storm dominated ramp containing inner ramp tidally influenced oolitic shoal and back shoal lagoon fades and storm dominated mid ramp facies a slope break separates mid ramp facies from outer ramp facies characterized by accumulation of redeposited carbonates on gently inclined slopes 1 2 degrees combined facies stacking patterns and outcrop correlation via 1 3 c profiles suggest that buah carbonates formed as a highstand systems tract characterized by a general upward shallowing of facies and strong lateral progradation on a regional scale buah facies distributions across oman were controlled by the presence of basement highs defining areas of reduced subsidence which promoted lateral progradation of the buah carbonate ramp for tens of kilometers while the faster subsiding areas became sites of deep water deposition

irreversible change of the oceanic carbon cycle in the earliest cambrian high resolution organic and inorganic carbon chemostratigraphy in the three gorges area south china the terminal neoproterozoic and its transition into the cambrian witnessed major evolutionary and geochemical changes large fluctuations in the carbon isotope ratio for inorganic carbon 13ccarb across the precambrian cambrian boundary pc c boundary indicate a significant change in the oceanic carbon cycle at that time this work presents the first high resolution 13corg chemostratigraphy of drill core samples across the pc c boundary in the three gorges area south china and discusses carbon cycles based on the relation between 13corg and 13ccarb we found that changes of 13corg and 13ccarb values were decoupled during the significant negative excursion of 13ccarb across the pc c boundary suggesting the presence of a huge organic carbon pool ocp previously the large ocp was inferred to have been established in the terminal proterozoic and to have disappeared at the end of the mid ediacaran shuram excursion in contrast our study suggests that the large ocp lasted until the early nemakit daldynian stage on the other hand in the middle nemakit daldynian to atdabanian the 13ccarb and 13corg changed in parallel as observed normally in the phanerozoic in order to evaluate these scenarios quantitatively we performed numerical simulations and calculated the time evolution of the 13ccarb masses of the inorganic and organic carbon pools and the fluxes between them as a result we show that the observed negative 13ccarb excursion with steady 13corg can be produced by enhanced primary productivity and remineralization of the large ocp if the rate constant for removal of organic carbon was considerably lower than that of today the end of the decoupled negative 13ccarb excursion is attributable to an increase in the removal rates of inorganic and organic carbon from the ocean the enhanced flux of organic carbon burials eliminated the large ocp so that the modern style carbon cycle was established by the early nemakit daldynian stage the inferred rapid increases of both organic and inorganic carbon burial rates in the middle nemakit daldynian stage were likely caused by the appearance of planktonic metazoans with guts making fecal pellets and by the first skeletal animals the biological innovations may have changed the oceanic carbon cycle irreversibly just after the pc c boundary

soils in the semi arid area of the el melah lagoon ne tunisia variability associated with a closing evolution abstract soils of the semi arid area of the el melah coastal lagoon ne tunisia with a closing evolution dynamic were studied aiming 1 the chemical and mineralogical characterization of surface and subsurface layers of soil profiles from locations previously submerged and of soils developed on dunes 2 to evaluate the dependence on the environment conditions of the geochemical patterns of the soils and 3 to determine chemical and mineralogical variations with the emersion of the sediments resulting from the decrease in the extent of the area permanently covered by water in the lagoon the compositional results obtained showed significant differences depending on the environment littoral plain old dunes and sandy spit but soils of the different environmental zones studied do not appear to be significantly polluted as far as trace elements are concerned among the elements studied high element sc ratios and variations were found for as sb and zn antimony is more concentrated in coarser samples suggesting its adsorption in fe or mn oxides coating quartz grain surfaces arsenic and zinc may be incorporated into the carbonates structure as well as adsorbed on or coprecipitated with iron oxides zinc may also be significantly incorporated in clay minerals iron was found to be more oxidized in the cultivated soil from the old dune strand and more reduced in the sandy spit where ankerite occurs suggesting the reduction of fe3 in oxide hydroxides by microorganisms and incorporation of fe2 in carbonates ree patterns particularly the hree lree are correlated with carbonates indicating preferential incorporation of the hree in carbonates and of the lree in clay minerals iron oxides high ga contents were found in soils and sediments rich in clay minerals al suggesting its incorporation in clay minerals structure therefore ga may be used as an indicator of the clay minerals proportion in sediments and soils carbonates sulphates besides fe and or mn oxides and clay minerals appear to play an important role on the trace elements distribution

extinction of cloudina and namacalathus at the precambrian cambrian boundary in oman biostratigraphic carbon isotope and u pb zircon geochronological data from the ara group of oman indicate an abrupt last appearance of cloudina and namacalathus coincident with a large magnitude but short lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the precambrian cambrian boundary u pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542 0 0 3 ma consistent with previous age constraints from siberia and namibia combined with the global biostratigraphic record these new data strengthen hypotheses invoking mass extinction within terminal proterozoic ecosystems at or near the precambrian cambrian boundary

mesoscale interactions in tropical cyclone genesis with the multitude of cloud clusters over tropical oceans it has been perplexing that so few develop into tropical cyclones the authors postulate that a major obstacle has been the complexity of scale interactions particularly those on the mesoscale which have only recently been observable while there are well known climatological requirements these are by no means sufficient a major reason for this rarity is the essentially stochastic nature of the mesoscale interactions that precede and contribute to cyclone development observations exist for only a few forming cases in these the moist convection in the preformation environment is organized into mesoscale convective systems each of which have associated mesoscale potential vortices in the midlevels interactions between these systems may lead to merger growth to the surface and development of both the nascent eye and inner rainbands of a tropical cyclone the process is essentially stochastic but the degree of stochasticity can be reduced by the continued interaction of the mesoscale systems or by environmental influences for example a monsoon trough provides a region of reduced deformation radius which substantially improves the efficiency of mesoscale vortex interactions and the amplitude of the merged vortices further a strong monsoon trough provides a vertical wind shear that enables long lived midlevel mesoscale vortices that are able to maintain or even redevelop the associated convective system the authors develop this hypothesis by use of a detailed case study of the formation of tropical cyclone oliver observed during toga coare 1993 in this case two dominant mesoscale vortices interacted with a monsoon trough to separately produce a nascent eye and a major rainband the eye developed on the edge of the major convective system and the associated atmospheric warming was provided almost entirely by moist processes in the upper atmosphere and by a combination of latent heating and adiabatic subsidence in the lower and middle atmosphere the importance of mesoscale interactions is illustrated further by brief reference to the development of two typhoons in the western north pacific

dual aircraft investigation of the inner core of hurricane norbert part i kinematic structure abstract on 24 25 september 1984 air motions and physical processes in the eyewall region of hurricane norbert were investigated with two national oceanic and atmospheric administration noaa aircraft operations center aoc wp 3d research aircraft one aircraft equipped with the airborne doppler radar flew repeated radial penetrations of the eyewall mapping the three dimensional wind field throughout a 40 km radius of the storm center these data provide the first complete documentation of the three dimensional wind field of the inner core of a hurricane on spatial scales of 10 25 km in the horizontal and 1 km in the vertical and temporal scales of 1 2 h the wind field was asymmetric and the asymmetry varied with altitude as altitude increased the location of the maximum tangential wind sloped upwind from left of the storm track at 1 km altitude to right of the storm track above 3 km the radial wind at 1 km altitude was inward in front of the storm and outward behind this pattern in the radial

role of cumulus congestus in tropical cyclone formation in a high resolution numerical model simulation abstractthe role of cumulus congestus shallow and congestus convection in tropical cyclone tc formation is examined in a high resolution simulation of tropical cyclone fay 2008 it is found that cumulus congestus plays a dominant role in moistening the lower to middle troposphere and spinning up the near surface circulation prior to genesis while deep convection plays a key role in moistening the upper troposphere and intensifying the cyclonic circulation over a deep layer the transition from the tropical wave stage to the tc stage is marked by a substantial increase in net condensation and potential vorticity generation by deep convection in the inner wave pouch region this study suggests that tc formation can be regarded as a two stage process the first stage is a gradual process of moisture preconditioning and low level spinup in which cumulus congestus plays a dominant role the second stage commences with the rapid development of deep convection in the inner pouch region after the air colum

depositional history of the middle proterozoic castner marble and basal mundy breccia franklin mountains west texas abstract the ca 1260 ma castner marble is composed of six metamorphosed lithologies stromatolitic limestone cryptalgalaminite massive limestone hornfels mudstone and tuff rhythmite and flat pebble conglomerate on the basis of the associations of these lithologies the castner marble can be divided into three distinct intervals a lower section containing stromatolitic and cryptalgalaminite units a middle section with thick hornfels and massive limestone beds and an upper section of rhythmites interlaminated to thinly interbedded carbonate and hornfels with interbedded flat pebble conglomerate the castner succession was deposited during a transgressive event on a low energy carbonate ramp the contact between the castner marble and the overlying basaltic mundy breccia marks a catastrophic event or series of events in which rhythmite units were disrupted and or displaced along arcuate detachment surfaces and redeposited as lenses of rhythmite megabreccia unconformably overlying intact rhythmite sequences these megabreccia lenses consist of large locally deformed rhythmite blocks in a matrix of muddy flat pebble conglomerate one megabreccia lens contains intervals bearing irregular shaped basalt clasts possible hyaloclastite layers and pod like basalt intrusions this polymictic lens may have been produced by submarine syn eruptive mixing of basalt and sediment local basalt intrusions may be part of the feeder system for this material and also the overlying basaltic mundy breccia the mundy breccia covered the irregular topography created by the megabreccia lenses locally loading and deforming the megabreccia into flame like structures the polymictic carbonate and basalt nature of one lens and presence of load features suggests that little time elapsed between deposition of the castner marble and the mundy breccia and therefore that the mundy breccia was most likely deposited in a submarine setting

sedimentation during carbonate ramp to slope evolution in a tectonically active area bowland basin dinantian northern england the bowland basin northern england contains a series of carbonates and terrigenous mudstones deposited during the ivorian to early brigantian two regional depositional environments are indicated by facies and facies associations wackestone packstone and calcarenite facies indicate deposition in a carbonate ramp environment while lime mudstone wackestone calcarenite and limestone breccia conglomerate facies often extensively slumped represent a carbonate slope environment stratigraphic relations suggest that the depositional environment evolved from a ramp into a slope through the dinantian two main sediment sources are indicated by the sequence an extra basinal terrigenous mud source and a supply of carbonate from the margins of the basin deposition from suspension and from sediment gravity flows in situ production and remobilization of sediment during sedimentary sliding were important processes operating within the basin periods of enhanced tectonic activity in the late chadian to early arundian and late asbian to early brigantian are indicated by basin wide horizons of sedimentary slide and mass flow deposits both intervals were marked by a decline in carbonate production resulting from inundation and uplift emergence the first of these intervals separates deposition on a seafloor with gentle topography carbonate ramp from a situation where major lateral thickness and facies variations were present and deposition took place in a carbonate slope environment the second interval marks the end of major carbonate deposition within the bowland basin and the onset of regional terrigenous sedimentation

evolution of an early proterozoic foreland basin carbonate platform lower pethei group great slave lake north west canada the taltheilei utsingi mclean and blanchet formations form a 175 390 m thick carbonate platform to basin succession in the lower part of the paleoproterozoic pethei group preserved in the eastern arm of great slave lake carbonates accumulated along the south east margin of the slave craton within a foredeep formed during the collision of the slave and churchill cratons the rocks include eight predominantly microbial carbonate facies that comprise five facies associations representing 1 shallow water rimmed shelf 2 shallow water open shelf 3 shallow water ramp 4 upper slope and deep ramp and 5 lower slope and basin plain environments microbialite facies grew by organically mediated precipitation of spar and micritic cement and trapping and binding of lime mud these wholly subtidal facies typically reflect progressive shallowing and changing geometry of the lower pethei sea floor from ramp to open shelf to shallow rimmed shelf with associated slope and basin plain deposition repeated relative sea level changes influenced platform growth this resulted in five shallowing upward packages each separated by an incipient drowning event of varying magnitude antecedent topography and the size of the preceding drowning event strongly influenced the initial growth of each interval this repeated pattern is attributed to interaction between a the inherent tendency of microbial carbonates to aggrade vertically b changing sedimentation rates and c readjustments of relative base level the lower pethei succession is one of few paleoproterozoic examples of carbonate platform growth within a foreland basin it has 1 a low gradient profile 2 extensive slope and basin plain carbonate production and sedimentation 3 no ooids 4 minor terrigenous clastic sediments and 4 a mobile submergent shelf rim lacking substantial carbonate sand shoals

mixed carbonate siliciclastic sedimentation in forebulge grabens an example from the ediacaran bambui group sao francisco basin brazil abstract mixed carbonate siliciclastic successions have been described in multiple phanerozoic sedimentary settings recording the dynamic interplay of tectonics eustasy climate in situ carbonate production and variations in siliciclastic sediment supply the ediacaran bambui 1st order sequence i e bambui group covers most of the intracratonic sao francisco basin southeast brazil and encompasses thick packages of carbonate and fine to coarse grained siliciclastic strata recording a marine foreland basin stage that developed in the sao francisco plate during the neoproterozoic early paleozoic west gondwana assembly the ediacaran deposits unconformably overlie archean paleoproterozoic metamorphic assemblages of the sete lagoas basement high and fill a series of kilometer long grabens in the southern sao francisco basin seismic data reveal that these troughs developed through the extensional reactivation of ancient basement structures along with the tectonically driven forebulge uplift of the sete lagoas high in the early evolutionary stages of the bambui basin cycle based on the detailed description of continuous drill cores of a well recently drilled during hydrocarbon exploration campaigns we recognized two transgressive regressive 2nd order sequences preserved within one of the focused grabens i sequence 1 includes the glaciogenic deposits of the basal carrancas formation that grade upward into the carbonate ramp successions of the sete lagoas formation ii sequence 2 contains the siliciclastic dominated and deep water to deltaic strata of the serra de santa helena formation and passes upward into peritidal carbonates of the lagoa do jacare formation these sedimentary successions encompass suites of retrogradational aggradational and progradational lower rank cycles and are bounded by erosional surfaces regional seismic interpretation well data and the available literature indicate that most of these deposits and their correlatives are continuous over most of the sete lagoas basement high showing remarkable variations within the studied forebulge grabens our analysis demonstrates that the depositional architecture of sequence 1 and sequence 2 marks the interplay of successive episodes of tectonically driven forebulge uplift and regional eustatic and climatic changes the latter are mainly recorded by the lower second order sequence sequence 1 which contains typical sedimentary features deposited in the aftermath of an important glaciation affecting lower latitudes during the late neoproterozoic an additional local accommodation control is restricted to the forebulge grabens and is associated with episodic and local subsidence pulses as indicated by lower to higher rank cycles it has been responsible for the deposition of thicker transgressive to early regressive successions a few gravitational flow deposits and the development of the deltaic to shallow marine carbonate cycles of sequence 2 the overall stratigraphic architecture of the studied successions suggests that several basin mechanisms operating during the phanerozoic were also present in the late neoproterozoic the close association between organic rich post glacial shales potential reservoir facies and rift related migration paths and hydrocarbon traps indicate that forebulge grabens represent important elements to consider in hydrocarbon exploration campaigns

hardened subtidal stromatolites bahamas hardened high relief stromatolites have been discovered along the margins of some bahamian platforms they occur in high energy tidal oolitic sand environments in waters ranging in depth from about 1 to 5 meters physical stress produced by actively migrating bed forms of oolitic sand appears to exclude grazing gastropods and subsequent community successions permitting stromatolite growth

veracity of neoproterozoic negative c isotope values the termination of the shuram negative excursion abstract there is widespread interest in the neoproterozoic period of the earth s history 1000 to 542 ma because of unprecedented 13 c fluctuations to 1000 m succession of stratigraphically complex sedimentary rocks deposited during tens of millions of years in contrast phanerozoic large negative c isotope excursions have been interpreted as the result of diagenetic fluid mixing during carbonate stabilization and burial and are less enigmatic due to the excellent biostratigraphic control on their timing and duration the ediacaran nafun group of oman part of the huqf supergroup spanning the cryogenian early cambrian contains a large 13 c negative excursion the shuram excursion reaching values as negative as 12 at the base of the shuram formation a steady recovery to positive values occurs over the entire shuram and half through the overlying buah formation suggesting a duration on the order of tens of my based on trace metal chemostratigraphic and sedimentological analyses the carbon isotope record obtained from the buah formation of northern oman indicates a systematic and reproducible shift of 13 c values from 6 to 1 in 1 a demonstrably diagenetic altered carbonate cemented siliciclastic facies and 2 a least diagenetically altered stromatolitic facies the identical reproducible isotopic pattern in these time equivalent sections combined to the presence of exceptionally preserved 18 o values around 2 to 1 associated with the most negative 13 c values rules out isotopic resetting by diagenetic fluids as a mechanism to explain these values it is concluded that it is possible to retain depositional 13 c values in demonstrably diagenetically altered carbonates this raises the issue of the ability to recognize diagenetic alteration of c isotopic values in neoproterozoic rocks where a robust time frame to support reproducibility is not available the results of this study provide strong support to a non diagenetic origin of the negative shuram c isotope excursion believed to be the most profound in terms of amplitude and duration in the earth s history

the dinantian stratigraphy of the east midlands a seismostratigraphic approach six tectonically controlled seismic sequences have been identified in the dinantian succession of the widmerpool gulf east midlands and they have also been recognized in outcrop sections in derbyshire and the bowland basin these correlations are made possible by integrating and calibrating sequence boundaries with the biostratigraphical evidence from foraminifers conodonts and palynomorphs and relating these to the tectonostratigraphical evolution of the basin it is suggested that the current chronostratigraphical stages of the dinantian do not always reflect major regional stratigraphical events and that the seismic sequence stratigraphy erected herein may provide a more applicable chronostratigraphical subdivision of the dinantian of the east midlands and northern england

ripple marks in quartz arenites of the hurwitz group northwest territories canada evidence for sedimentation in a vast early proterozoic shallow fresh water lake abstract supermature quartz arenites of the whiterock member deposited in the early proterozoic intracratonic hurwitz basin have a maximum thickness of 400 m and a minimum areal extent of 100 000 km2 the unit is unusual in that it is virtually devoid of other rock types and displays sedimentary structures that consist almost entirely of short spaced ripple marks and parallel stratification both formed by oscillatory flow the ripples have spacings that are consistently small average

understanding carbonate ramp dynamics using δ13c profiles examples from the neoproterozoic buah formation of oman the late neoproterozoic buah formation nafun group oman is a carbonate unit outcropping in the jabal akhdar and huqf areas it is composed mostly of shallow water carbonates deposited on a distally steepened carbonate ramp correlation of two 13c isotope shifts shows that in the jabal akhdar ramp differentiation into fast and slow subsiding areas was followed by lateral progradation in the huqf area however a uniform scenario of upward shallowing of the facies and lateral progradation is demonstrated by chemostratigraphic timelines cross cutting the facies belts the chemostratigraphic profiles show that the buah formation was deposited during sea level highstand conditions and that ramp differentiation was due to synsedimentary tectonics high resolution correlation of 13c profiles from the same lithostratigraphic unit whether precambrian or phanerozoic in age lacking biostratigraphic data can shed light on carbonate systems dynamics tectonic vs eustatic controls on depositional sequences and basin subsidence

giant subtidal stromatolites forming in normal salinity waters we report here the discovery of giant lithified subtidal columnar stromatolites 2 m high growing in 7 8 m of clear oceanic water in current swept channels between the exuma islands on the eastern bahama bank they grow by trapping ooid and pelletal carbonate sand and synsedimentary precipitation of carbonate cement within a field of giant megaripples the discovery is important to geologists and biologists because similar organo sedimentary structures built by a combination of cementation and the trapping of sediment by microbes were the dominant fossil types during the precambrian stromatolites are thought to have been responsible for the production of free oxygen and thus the evolution of animal life1 2 until the discovery of small lithified subtidal columnar stromatolites in the bahamas3 the only subtidal marine examples known to be living while undergoing lithification were in the hypersaline waters of hamelin pool at shark bay western australia4 7 shark bay stromatolites range from intertidal to the shallow subtidal with the larger columns reaching 1 m in height the shark bay stromatolites have strongly influenced geological interpretation by analogy many ancient stromatolites have been considered to have grown in intertidal and or hypersaline conditions8 although hypersalinity was not a necessity for growth during the precambrian because grazing metazoan life had not then evolved

fine grained agglutinated elongate columnar stromatolites tieling formation ca 1420 ma north china the mesoproterozoic tieling formation near jixian northern china contains thick beds of vertically branched laterally elongate columnar stromatolites carbonate mud is the primary component of both the stromatolites and their intervening matrix its abundance is attributed to water column whiting precipitation stimulated by cyanobacterial photosynthesis neomorphic microspar gives the stromatolites a streaky microfabric and small mud flakes are common in the matrix the columns consist of low relief mainly non enveloping laminae that show erosive truncation and well defined repetitive lamination in plan view the columns form disjunct elongate ridges 10 cm wide separated by narrow matrix filled runnels the stromatolite surfaces were initially cohesive rather than rigid and prone to scour and are interpreted as current aligned microbial mats that trapped carbonate mud the pervasive ridge runnel system suggests scale dependent biophysical feedback between i carbonate mud supply ii current duration strength and direction and iii growth and trapping by prolific mat growth together these factors determined the size morphology and arrangement of the stromatolite columns and their laminae as well as their branching patterns alignment and ridge runnel spacing ridge runnel surfaces resemble ripple mark patterns but whether currents were parallel and or normal to stromatolite alignment remains unclear the formation and preservation of tieling columns required plentiful supply of carbonate mud mat building microbes well adapted to cope with this abundant sediment and absence of both significant early lithification and bioturbation these factors were time limited and tieling stromatolites closely resemble coeval examples in the belt purcell supergroup of laurentia the dynamic interactions between mat growth currents and sediment supply that determined the shape of tieling columns contributed to the morphotypical diversity that characterizes mid late proterozoic branched stromatolites this article is protected by copyright all rights reserved

structural style of buried ediacaran basins in saudi arabia on seismic reflection data abstract several isolated ediacaran basins subcrop phanerozoic strata in saudi arabia the structural styles of these subcropping basins are reviewed here based on interpretation of 2d and 3d seismic reflection data and comparison with arabian shield outcrops the basins are distinguished by layered seismic reflectors that are interpreted as sedimentary and volcanic strata due to limited well penetrations these packages cannot be directly dated but a relative chronology is established anchored by constraints from the arabian shield and regional studies most of the basins are bound by extensional faults and the basin fills show growth architectures and angular unconformities the bounding faults trend broadly north south and are interpreted to be late to post orogenic reactivations of oceanic terrane margins based on their structural characteristics in comparison with sub basins exposed on the shield the basin fills are correlated with the ediacaran jibalah group an equivalent of the omani nafun group these sub basins experienced inversion and exhumation prior to ongoing volcanism and unconformable deposition of late ediacaran to earliest cambrian kurayshah group sediments the kurayshah group is disconformably overlain by the widespread tayma group siliciclastics this disconformity correlates to the angudan unconformity in oman the kurayshah group includes a late ediacaran stratovolcano over 40 km in diameter in the eastern basins evaporitic structural styles indicate the presence of hormuz ara evaporites with local igneous intrusions that correlate at least in part to the kurayshah group the tayma group infills significant accommodation space variations and was affected by ongoing but declining differential subsidence and reactivation of the underlying basin bounding faults

anatomy of a cyclically packaged mesoproterozoic carbonate ramp in northern canada abstract carbonates in the upper member of the mesoproterozoic victor bay formation are dominated by lime mud and packaged in cycles of 20 50 m these thicknesses exceed those of classic shallowing upward cycles by almost a factor of 10 stratigraphic and sedimentological evidence suggests high amplitude high frequency glacio eustatic cyclicity and thus a cool global climate ca 1 2 ga the victor bay ramp is one of several late proterozoic carbonate platforms where the proportions of lime mud carbonate grains and microbialites are more typical of younger phanerozoic successions which followed the global waning of stromatolites facies distribution in the study area is compatible with deposition on a low energy microtidal distally steepened ramp outer ramp facies are hemipelagic lime mudstone shale carbonaceous rhythmite and debrites mid ramp facies are molar tooth limestone tempestite with microspar intraclast lags in a marine environment where stromatolitic and oolitic facies were otherwise rare large stromatolitic reefs developed at the mid ramp coeval with inner ramp facies of microspar grainstone intertidal dolomitic microbial laminite and supratidal evaporitic red shale deep subtidal outer ramp cycles occur in the southwestern part of the study area black dolomitic shale at the base is overlain by ribbon nodular and carbonaceous carbonate facies all of which exhibit signs of synsedimentary disruption cycles in the northeast are shallow subtidal and peritidal in character shallow subtidal cycles consist of basal deep water facies and an upper layer of subtidal molar tooth limestone tempestite interbedded with microspar calcarenite facies peritidal cycles are identical to shallow subtidal cycles except that they contain a cap of dolomitic tidal flat microbial laminite and rarely of red shale sabkha facies or of sandy polymictic conglomerate a transect along the wall of a valley extending 8 5 km perpendicular to depositional strike reveals progradation of inner ramp tidal flats over outer and mid ramp facies during shoaling the maximum basinward progradation of peritidal facies coincides with a zone of slope failure that may have promoted the development of the stromatolitic reefs the sea level history of the victor bay formation is represented by three hectometre scale sequences an initial flooding event resulted in deposition of the lower victor bay shale member upper member carbonate cycles were then deposited during highstand mid ramp slumping was followed by late highstand reef development the second sequence began with development of an inner ramp lowstand unconformity and a thick mid ramp lowstand wedge a second transgression promoted a more modest phase of reef development at the mid ramp and shallow water deposition continued inboard a third and final transgressive episode eventually led to flooding of the backstepping ramp overall consistent cycle thickness and absence of truncated cycles as well as the high rate and amount of creation of accommodation space suggest that the periodicity and amplitude of sea level fluctuation were relatively uniform and point to a eustatic rather than tectonic mechanism of relative sea level change high amplitude high frequency eustatic sea level change is characteristic of icehouse worlds in which short term large scale sea level fluctuations accompany rapidly changing ice volumes affected by milankovitch orbital forcing packaging of cyclic upper victor bay carbonates therefore supports the hypothesis of a late mesoproterozoic glacial period as proposed by previous workers

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

a vortex based perspective of eastern pacific tropical cyclone formation tropical cyclone formation over the eastern pacific during 2005 and 2006 was examined using primarily global operational analyses from the national centers for environmental prediction this paper represents a vortex view of genesis adding to previous work on tropical cyclone formation associated with tropical waves between 1 july and 30 september during 2005 and 2006 vortices at 900 hpa were tracked and vortex following diagnostic quantities were computed vortices were more abundant during periods of an enhanced hadley circulation with monsoon westerlies around 10 n in the lower troposphere this zonally confined hadley circulation was significantly stronger during the genesis of developing vortices developing vortices were stronger at the outset with a deeper potential vorticity maximum compared to nondeveloping vortices this implies that developing disturbances were selected early on by favorable synoptic scale features the characteristic time mean reversal of the meridional gradient of absolute vorticity in the lower troposphere was found to nearly vanish when the aggregate contribution of strong vortices was removed from the time mean vorticity this finding implies that it is difficult to unambiguously attribute development to a preexisting enhancement of vorticity on the synoptic scale the time mean enhancement of cyclonic vorticity primarily results from the accumulated effect of vortices it is suggested that horizontal deformation in the background state helps distinguish developing vortices from nondevelopers and also biases the latitude of development poleward of the climatological itcz axis

50 myr recovery from the largest negative δ13c excursion in the ediacaran ocean sedimentary rocks deposited during the ediacaran period 630 542 ma contain carbonates whose carbon isotopic ratios show a marked negative excursion consisting of a precipitous drop from 5 to 12 followed by a sub linear recovery to positive 13c values isotopic ages u pb and thermal subsidence modelling are combined to constrain the excursion in time and indicate an onset at 600 ma and duration of recovery of approximately 50 myr the excursion is widely recognized in oman and has potential correlatives in ediacaran strata elsewhere and may thus represent a characteristic feature of the ediacaran period the amplitude of this carbon isotope excursion far exceeds those of other neoproterozoic anomalies the isotopic trend of negative excursion and long term recovery spanned at least one short lived glacial episode at 580 ma but appears unrelated to glaciation which indicates that negative anomalies in the neoproterozoic marine carbon isotope record are not directly or uniquely linked to ice ages

calibrating the coevolution of ediacaran life and environment the rise of animals occurred during an interval of earth history that witnessed dynamic marine redox conditions potentially rapid plate motions and uniquely large perturbations to global biogeochemical cycles the largest of these perturbations the shuram carbon isotope excursion has been invoked as a driving mechanism for ediacaran environmental change possibly linked with evolutionary innovation or extinction however there are a number of controversies surrounding the shuram including its timing duration and role in the concomitant biological and biogeochemical upheavals here we present radioisotopic dates bracketing the shuram on two separate paleocontinents our results are consistent with a global and synchronous event between 574 0 4 7 and 567 3 3 0 ma these dates support the interpretation that the shuram is a primary and synchronous event postdating the gaskiers glaciation in addition our re os ages suggest that the appearance of ediacaran macrofossils in northwestern canada is identical within uncertainty to similar macrofossils from the conception group of newfoundland highlighting the coeval appearance of macroscopic metazoans across two paleocontinents our temporal framework for the terminal proterozoic is a critical step for testing hypotheses related to extreme carbon isotope excursions and their role in the evolution of complex life

convective contribution to the genesis of hurricane ophelia 2005 abstract the convection occurring in the tropical depression that became hurricane ophelia 2005 was investigated just prior to tropical storm formation doppler radar showed a deep wide intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail the updraft of the cell was 10 km wide 17 km deep had updrafts of 10 20 m s 1 throughout its mid to upper levels and contained a cyclonic vorticity maximum the massive convective updraft was maintained by strong positive buoyancy which was maximum at about the 10 km level probably aided by latent heat of freezing evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft the convective updraft was fed by a layer of strong inflow that was several kilometers deep wind induced turbulence just above the ocean surface enriched the equi

dolomitization on an evaporitic paleoproterozoic ramp widespread synsedimentary dolomite in the denault formation labrador trough canada abstract the denault formation 2 1 1 9 ga crops out in the labrador trough northeastern quebec and western labrador rocks surrounding the town of schefferville quebec contain textural characteristics consistent with deposition on the middle and outer portions of a storm influenced shallow ramp mid ramp facies consist of intraclastic grainstones with hummocky cross stratification hcs swaley cross stratification scs current ripples and graded event beds further outboard grainstones grade into deeper water laminites that are composed of even mm scale couplets of flat lying organic and dolomudstone laminae scours within the laminites suggest periodic storm activity laminites gradually grade into outer ramp deep water shales an isolated eastern stromatolitic buildup is separated from these ramp facies by 50 km present day this succession can be interpreted as the remnant of a near continuous margin or may simply represent an isolated accumulation that developed on a pre existing topographic high the presence of gypsum pseudomorphs in all lithofacies indicates that the denault margin was restricted and evaporitic four paragenetic stages are recognized in the diagenetic evolution of the denault formation 1 carbonate deposition contemporaneous marine cementation authigenic gypsum growth and precipitation of authigenic chert 2 synsedimentary mimetic dolomite precipitation 3 pore rimming and pore occluding shallow burial dolomite cement and 4 fabric destructive sutured anhedral burial dolomite gypsum crystals occur in all lithofacies form the nuclei of interstitial dolomite rhombs average 10 m in length and often display swallowtail twinning paleoproterozoic ocean water had very low concentrations of dissolved sulfate and evaporation in restricted settings would have been required to form gypsum formation of microcrystalline gypsum across this restricted ramp facilitated dolomite precipitation by increasing pore water mg ca ratios and lowering its dissolved sulfate concentrations such an interpretation may explain why there is an abundance of synsedimentary dolostone in the precambrian and the relative paucity of phanerozoic analogs

use of spot 5 and ikonos imagery for mapping biocenoses in a tunisian coastal lagoon mediterranean sea mapping marine biocenoses is an efficient method for providing useful data for the management and conservation of mediterranean lagoons fused images from two satellites spot 5 and ikonos were tested as management tools for identifying specific ecosystems in the el bibane lagoon situated in southern tunisia near the libyan border the objectives of this study were to provide a precise map of the entire el bibane lagoon using fused images from spot 5 and to compare fused images from spot 5 and ikonos over a test area after applying a supervised classification pixels are automatically classified in four classes low seagrass cover high seagrass cover superficial mobile sediments and deep mobile sediments the maps of the lagoon revealed and confirmed an extremely wide distribution of seagrass meadows within the lagoon essentially cymodocea nodosa 19 546 ha and a large area of mobile sediments more or less parallel to the shore 3 697 ha a direct comparison of overall accuracy between spot 5 over the entire area spot 5 over the test area and ikonos over the test area revealed that these tools provided accurate mapping of the lagoon environment 83 25 85 91 and 73 41 accuracy respectively the spot 5 images provided greater overall accuracy than the ikonos image but did not take into account the heterogeneous spatial structure of the seagrasses and sediments present in the lagoon environment although ikonos imagery provided lower overall accuracy than spot 5 it proved a very useful tool for the mapping of heterogeneous structures as it enabled the patchiness of formations to be better taken into account the use of spot 5 and ikonos fused images appears to be very promising for completing the mapping of lagoons in other regions and countries of the mediterranean sea

cloudina microbial reef resilience to substrate instability in a cadomian retro arc basin of the iberian peninsula abstract the navalpino anticline of the central iberian zone provides a unique case study of well exposed late ediacaran reefs drone images show their spatial arrangement as tens of shelly microbial patch biohermal and complex reefs encased in a dominantly shaly succession the latter was deposited on a perturbed block platform located in a cadomian retro arc basin fringing west gondwana reefs display the traditional core flank inter reef subdivision and developed on generally low energy clear water substrates between normal and storm wave base cores consist of millimetre sized irregular mesoclots of dense microbial microsparite locally interrupted by laminated stromatolitic fabrics containing abundant sinotubulites and cloudina shells the last with upright preservation basement breakdown perturbations related to fissuring hydrothermal influence and slope apron breccia deposition led to nucleation and development of patch reefs on unstable substrates their ecological succession is characterized by stabilization pioneer to colonization phases the latter represented by cloudina shells preserved upright and encased in microbial crusts pointing to their active role as pioneer frame building taxa

a composite reference section for terminal proterozoic strata of southern namibia integrated sequence stratigraphic and chemostratigraphic data yield a framework for correlations of stratigraphic units in the terminal proterozoic to cambrian witvlei and nama groups of namibia coupled with precise u pb zircon age constraints these correlations make it possible to construct a composite reference section for use in calibrating terminal proterozoic chronostratigraphy the namibian reference section starts with two distinct glacial horizons and extends up to within 1 million years of the proterozoic cambrian boundary the two glacial horizons may represent each of two distinct varanger age glaciations better known from the north atlantic region from the higher of the two glacial horizons up the composite stratigraphy preserves one of the thickest and most complete available records of carbon isotope variability in post varanger terminal proterozoic seawater four carbon isotope chemostratigraphic intervals are recognized 1 a postglacial negative 13 c excursion npg interval 2 a rising interval pr interval of increasing positive delta 13 c values 3 a falling interval pf interval characterized by decreasing positive 13 c and culminating in near zero or negative values and 4 an interval of moderately positive relatively invariant 13 c values i interval that extends up to the unconformity that contains the proterozoic cambrian boundary each of these chemostratigraphic intervals can be recognized in widely separated correlative sections around the world by comparing sediment accumulation rate in the radiometrically calibrated namibian stratigraphy with sediment accumulation rates in correlative sections in arctic canada and oman a maximum age of 564 ma is estimated for the end of the younger varanger glaciation 25 m y younger than previous estimates

feature and duration of metre scale sequences in a storm dominated carbonate ramp setting kimmeridgian northeastern spain abstract metre scale sequences may result from the combined effects of allocyclic and autocyclic processes which are closely inter related the carbonate ramp that developed northwest of the iberian basin during the late kimmeridgian was affected by northwestward migrating cyclones marl limestone alternations that settled in mid ramp environments contain abundant mm to cm thick coarse grained accumulations that have been related to these events the aim of this paper is to determine the impact of storm induced processes on the metre scale sequence features four sections r3 r4 r6 and r7 which are 5 to 7 m in thickness were studied bed by bed along a 4 km long outcrop which shows the transition between the shallow and the relatively deep realms of the middle ramp metre scale sequences were defined and correlated along this outcrop according to the detailed microfacies analysis of host fine grained deposits palynofacies and sequence stratigraphic analyses and carbon and oxygen isotope measurements the evolution through time of sedimentary features such as the size of quartz grains and the relative abundance of grains other than quartz i e muscovite bivalve ooid and intraclast does not correlate from one section to the other suggesting that the finest as well as the coarsest sediment was reworked in these storm dominated environments small and medium scale sequences are defined according to changes in alternation marly interbed and limestone bed thickness and correlated from one section to the other because of the effects of storms on sediment distribution and preservation sequence boundaries coincide with thin alternations and marly interbeds in the most proximal sections i e r3 r4 while they correspond to thin alternations and limestone beds in the most distal sections i e r6 r7 field observations and palynofacies analyses confirm this sequence stratigraphic analysis the excursions in carbon and oxygen isotope values are consistent with the lithological correlations but in themselves are not conclusive marl limestone alternations and small and medium scale sequences are hierarchically stacked suggesting an orbital control on sedimentation with alternations lasting 20 kyr small scale sequences 100 kyr and medium scale sequences 400 kyr as biostratigraphic analyses and spectral analysis are not the most appropriate tools to validate this time calibration in such a short interval and highly dynamic system an alternative approach is developed which is based on the quantification of the rates of sediment accumulation preservation and sea level rise

stratigraphy and sedimentology of the great oolite group in the humbly grove oilfield hampshire abstract the main reservoir of the humbly grove oilfield comprises variably dolomitic grainstones and packstones representing the bathonian great oolite group the bathonian sequence commences in lower fuller s earth claystones which coarsen upwards into oncolitic claystones and skeletal packstones probably equivalent to the fuller s earth rock above is a variable succession of wackestones and thin packstones which have a distinctive sandstone at their base this sequence is named here the hester s copse formation the succeeding great oolite limestone is predominantly oolitic and cross bedded on a variety of scales it exhibits both coarsening and fining sequences which have locally well developed capping hardgrounds and burrowed horizons the great oolite limestone is subdivided into three members the lowest the humbly grove member and the highest the herriard member begin with massive shoal oolite deposition but each then pass upward into more interbedded sequences representing a more transgressive environment the middle member the hoddington is a thin but widely correlatable wackestone the overlying forest marble commences abruptly in claystones but there is an upward increase in both the incidence and thickness of discrete oolitic limestones both the great oolite limestone and forest marble were affected by early fresh water dissolution and cementation in addition to the localized development of submarine cements the top of the great oolite group is represented by the cornbrash the lower cornbrash is a thin micritic limestone while the upper cornbrash is a calcareous claystone which passes upwards into the kellaways clay the bathonian sequence overlies the dolomitic limestones of the inferior oolite the lower fuller s earth claystones being interpreted as a basinal marine mudstone sequence marking a substantial deepening and transgressive phase at the opening of the bathonian these mudstones shoal upwards into the quiet but photic water deposits of the fuller s earth rock the hester s copse formation represents the temporary development of wave dominated terrigenous shoreface and lagoonal conditions renewed transgression established a high energy tide dominated carbonate shelf upon which the great oolite limestone was deposited as a series of shoal oolites channels tidal deltas and spill overs periodic exposure of the carbonate sand bodies led to the production of early dissolutional and cementation fabrics that post date and largely obliterate submarine cements the forest marble opened with a further phase of deepening and the temporary establishment of muddy facies subsequently discrete tide dominated ridges and linear channelized oolitic sands prograded into the area the latest bathonian is marked by subsidence of the carbonate ramp to the south of the london platform the cornbrash kellaways clay sequence accumulating under progressively deepening waters

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

an investigation of composite dropsonde profiles for developing and nondeveloping tropical waves during the 2010 predict field campaign abstractcomposite dropsonde profiles are analyzed for developing and nondeveloping tropical waves in an attempt to improve the understanding of tropical cyclogenesis these tropical waves were sampled by 25 reconnaissance missions during the 2010 pre depression investigation of cloud systems in the tropics predict field campaign comparisons are made between mean profiles of temperature mixing ratio relative humidity radial and tangential winds relative vorticity and virtual convective available potential energy cape for genesis and nongenesis cases genesis soundings are further analyzed in temporal progression to investigate whether significant changes in the thermodynamic or wind fields occur during the transition from tropical wave to tropical cyclone significant results include the development of positive temperature anomalies from 500 to 200 hpa 2 days prior to genesis in developing waves this is not observed in the nongenesis mean progressive mesoscale moistening of the column is observe

stratigraphic organization of carbonate ramps and organic rich intrashelf basins natih formation middle cretaceous of northern oman the middle cretaceous carbonate deposits in the middle east are among the most productive oil bearing stratigraphic intervals in the world containing numerous giant fields in for instance the united arab emirates mauddud and mishrif formations iran sarvak formation and oman natih formation one of the main reasons for this concentration of hydrocarbons is a geological factor the coexistence of both reservoir facies and source rocks in the same depositional sequences due to the repeated creation of organic rich intrashelf basins this is demonstrated in a high resolution sequence stratigraphic study of the natih formation in oman which shows distinct and predictive patterns in the distribution and geometries of reservoir source rock and seal facies the sequence stratigraphic model presented here may serve as a reference for time equivalent deposits in the middle east the sedimentological analysis showed that the natih formation was formed by the alternation of two types of depositional systems 1 a flat bedded mixed carbonate clay ramp dominated by benthic foraminifera and 2 a carbonate dominated ramp bordering an intrashelf basin with abundant rudists in the mid ramp environment and organic rich basinal facies three fully developed third order sequences are distinguished showing a similar evolution of the depositional system with a mixed carbonate clay ramp system at the base followed by a carbonate dominated ramp system in the upper part variations occur on this pattern however depending on the relative influence of eustasy environmental factors and tectonism the late albiannearly cenomanian sequence i shows an evolution from a mixed flat ramp to a carbonate dominated ramp and organic rich intrashelf begin page 22 basin and sedimentation is predominantly controlled by eustatic sea level in the middle cenomanian sequence ii the evolution from a mixed ramp to a carbonate ramp is also observed but no intrashelf basin topography was developed in the studied area this may be due to the high influx of clay that influenced the environment in this sequence inhibiting the carbonate production probably in combination with the lack of sufficient creation of accommodation space the late cenomaniannearly turonian transgressive part of sequence iii shows a similar evolution to that observed in sequence i with the development of an organic rich intrashelf basin during highstand however a tectonically controlled sedimentation pattern is observed with the development of forced regressive wedges due to the flexural bulge of the foreland basin intrashelf basin formation occurred twice in the transgressive part of the third order depositional sequences of the natih formation our study shows that this is mainly the result of differential sedimentation rates that is the dynamics of the carbonate sedimentary system itself in response to rapid rises in relative sea level probably of eustatic origin tectonism was only a minor factor in the creation of the basin topography possibly through the creation of small initial relief the accumulation of the organic matter is not only a result of the creation of a sufficiently deep water column to guarantee dysaerobic conditions for its preservation the late albian and late cenomaniannearly turonian were also periods of generally favorable conditions worldwide for high organic matter productivity the time lines and stratigraphic architecture of the third order sequences presented here have an application potential at the scale of the arabian plate the general sedimentation pattern is predicted by our model but modifications due to different local conditions are likely to occur

a 600 million year carbonate clumped isotope record from the sultanate of oman carbonate clumped isotope thermometry is a promising technique that has the potential to help decode the significance of the variability of both physical and geochemical compositions of ancient carbonate rocks this study utilizes a 600 million year record of marine carbonate rocks from the subsurface and surface of the sultanate of oman to explore how burial and exhumation affected the carbonate clumped isotope thermometer samples span 6 km of burial depth and include calcite and dolomite mineralogies and a range of carbonate rock textures we find evidence for two broad patterns in the physical and geochemical behavior of carbonate rocks during burial the first group of carbonates yield water 18 o vsmow compositions slightly enriched or equal to an expected ice free seawater composition of 1 2 and display good to fair textural preservation suggesting that cementation and lithification occurred within tens of meters of the sediment water interface temperatures from the second group sit on the present day geotherm yield highly enriched water 18 o vsmow compositions and display fair to poor textural preservation we find no evidence for solid state reordering in paired analyses of calcites and dolomites our results contribute to a growing body of work that indicates that the seawater 18 o vsmow composition has not changed significantly over 600 myr and was not 6 in the ediacaran

the genesis of hurricane guillermo texmex analyses and a modeling study abstract the transformation of a mesoscale convective system into hurricane guillermo was captured by aircraft and doppler wind data during the tropical experiment in mexico the early phase of the system evolves in a way very similar to previously documented mesoscale convective systems with a midlevel mesocyclone developing in the stratiform precipitation region more unusually the cyclone extends to low altitudes a weak cyclone is discernable even in the 300 m altitude wind field after another day of evolution a small surface based warm core cyclone is observed to develop within the relatively cold air associated with the mesocyclone aloft this mesocyclone develops into a hurricane over the subsequent day a nonhydrostatic axisymmetric numerical model is used to explore the evolution of the initially cold core midlevel vortex into a tropical cyclone a mesoscale midlevel showerhead is switched on in an initially quiescent tropical atmosphere overlying a warm ocean surface evaporation of t

architecture and sedimentary evolution of the southwestern gissar carbonate platform uzbekistan during the middle late jurassic abstract sedimentological investigations have been carried out in the southwestern part of the gissar range uzbekistan in order to document the stratigraphic evolution of a vast middle upper jurassic carbonate platform developed on the northern margin of the amu darya basin two major sequences are distinguished based on their contrasting facies pattern platform configuration and carbon isotope signature 1 a callovian sequence and 2 an upper jurassic sequence potentially oxfordian to kimmeridgian in age a carbonate ramp with a double proximal distal polarity developed during the callovian sequence oo bioclastic grainstones were produced in two permanently agitated shallow water areas developing to the north and to the south patch and pinnacle reefs mainly built up close to the storm wave base passing distally to pellet and foraminiferal oncoid rich mid to outer ramp deposits the top of the callovian sequence is a regional discontinuity that could have formed by subaerial exposure of the platform this probable hiatus could record a major climatic change associated to the middle late jurassic transition the upper jurassic sequence consists of metre thick alternations of pellet algal pack to grainstones microbial oncoid floatstones ooid grainstones and mudstones which have likely accumulated in a vast lagoon protected by a large scale barrier reef observed south of the study area gypsum and anhydrite content gradually increased towards the top of the upper jurassic sequence ending up with a thick chicken wire gypsum accumulation recording the progradation of a large scale sabkha over the lagoon this phenomenon is related to a progressive aridification and restriction of the amu darya basin that could have begun during the middle late oxfordian and reached its climax during the tithonian with massive halite deposition comparable events occurred in jurassic platforms located along the tethyan margins pointing to regional and global controls on sedimentation

simulation and interpretation of the genesis of tropical storm gert 2005 as part of the nasa tropical cloud systems and processes experiment abstract several hypotheses have been put forward for the mechanisms of generation of surface circulation associated with tropical cyclones this paper examines high resolution simulations of tropical storm gert 2005 which formed in the gulf of mexico during nasa s tropical cloud systems and processes experiment to investigate the development of low level circulation and its relationship to the precipitation evolution two simulations are examined one that better matches available observations but underpredicts the storm s minimum sea level pressure and a second one that somewhat overintensifies the storm but provides a set of simulations that encapsulates the overall genesis and development characteristics of the observed storm the roles of convective and stratiform precipitation processes within the mesoscale precipitation systems that formed gert are discussed during 21 25 july two episodes of convective system development occurred in each precipitation system evolution was characterized by i

diabatic divergence profiles in western pacific mesoscale convective systems abstract heating in the atmosphere can be expressed as diabatic divergence d which is nearly equal to the actual horizontal divergence in tropical convection high quality profile measurements from airborne doppler radar purls in ten mesoscale convective systems mcs observed during toga coare are examined and the mean profile is compared with rawinsonde array measurements young convective features have strong near surface convergence while older cells with better developed downdrafts and stratiform precipitation areas have their peak convergence aloft in the mean then surface flow is only weakly convergent or oven divergent so that the main convergence into mcss is deep and peaked aloft with a sharp melting convergence at 0 c divergence prevails above 10 km altitude but was undersampled by the radar unusual but well sampled observations in the purl dataset include a persistent widespread profile feature in one well sampled mcs a cyclone rainband oscillatory reverberations c

late precambrian cambrian sediments of huqf group sultanate of oman the huqf group is the oldest known sedimentary sequence overlying crystalline basement in the sultanate of oman it crops out on a broad regional high the huqf axis which forms a dominating structural element on the southeastern edge of the arabian peninsula subsurface and outcrop evidence within and outside of oman suggests that the sediments of the huqf group lie within the age span of late precambrian to early middle cambrian the huqf group is subdivided into five formations corresponding to an alternation of clastics abu mahara and shuram formations and carbonates khufai and buah formations deposited in essentially shallow marine to supratidal or fluviatile conditions and terminated by an evaporitic sequence ara formation evaporites are absent on the huqf axis but they are thickly developed to the west over a large part of southern and central oman where they acted as the major structure former of most of oman s oil fields and even locally pierced up to the surface in the subsurface the huqf group has been reached by the drill mainly in southern oman where its lithostratigraphy resembles that defined in the type area in central oman the oldest sediments exposed in the core of the oman mountains may be correlative with the huqf group regional correlations suggest that the predominantly carbonate evaporitic facies of the huqf group was widely distributed in late precambrian early cambrian time the huqf basin is tentatively considered part of a belt of evaporitic basins and intervening carbonate platforms which stretched across the pangea landmass from the indian subcontinent salt range of pakistan through south yemen oman and saudi arabia into the gulf states and iran hormuz series and carbonate platform north of the zagros

chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in earth history the neoproterozoic shuram formation nafun group oman abstract oman records in its neoproterozoic nafun group huqf supergroup an essentially complete carbonate rich ediacaran succession the nafun group overlies the presumed marinoan rift related fiq member ca 635 ma and ends just below the precambrian cambrian boundary 542 ma tectonic subsidence caused by thermal contraction following fiq aged rifting allowed the preservation of about 1 km of postrift stratigraphy with no major stratigraphic breaks the nafun group above the marinoan cap carbonate hadash formation represents two siliciclastic to carbonate grand cycles both initiated by significant transgressions these cycles comprise the masirah bay khufai formations and the shuram buah formations the khufai shuram boundary is associated with the start of a major carbon isotope perturbation the uppermost ramp carbonates of the khufai formation record a smooth decrease in 13c from about 4 to values around 0 followed by two descending steps across which values plunge to a nadir of 12 in the overlying red siltstones and shales interbedded with thin limestones of the shuram formation this fall in isotopic values is temporally rapid and coincident in both shallow and deep water sections in the time span of a single parasequence the 13c nadir is then followed by 50 million years of monotonic recovery the shuram shift represents the largest 13c inorganic carbon negative excursion in earth history although the snowball earth theory links periods of depleted carbon isotopic ratios with periods of global glaciation the non glaciated context of the shuram formation suggests that the causal relationship between global glaciation and negative carbon isotopic excursions is non unique although the precise mechanism driving this major perturbation of the carbon cycle remains enigmatic the long term remineralization of an isotopically depleted organic carbon reservoir in ocean water is a promising candidate

an integrated and quantitative approach to petrophysical heterogeneity exploration in anything but the simplest of reservoirs is commonly more challenging because of the intrinsic variability in rock properties and geological characteristics that occur at all scales of observation and measurement this variability which often leads to a degree of unpredictability is commonly referred to as heterogeneity but rarely is this term defined although it is widely stated that heterogeneities are poorly understood researchers have started to investigate the quantification of various heterogeneities and the concept of heterogeneity as a scale dependent descriptor in reservoir characterization based on a comprehensive literature review we define heterogeneity as the variability of an individual or combination of properties within a specified space and or time and at a specified scale when investigating variability the type of heterogeneity should be defined in terms of grain e pore components and the presence or absence of any dominant features including sedimentological characteristics and fractures hierarchies of geologic heterogeneity can be used alongside an understanding of measurement principles and volumes of investigation to ensure we understand the variability in a dataset basic statistics can be used to characterise variability in a dataset in terms of the amplitude and frequency of variations present a better approach involves heterogeneity measures since these can provide a single value for quantifying the variability and provide the ability to compare this variability between different datasets tools measurements and reservoirs we use synthetic and subsurface datasets to investigate the application of the lorenz coefficient dykstraeparsons coefficient and the coefficient of variation to petrophysical data e testing assumptions and refining classifications of heterogeneity based on these measures 2015 the authors published by elsevier ltd this is an open access article under the cc by license

scale interactions during the formation of typhoon irving the development of typhoon irving is investigated using a variety of data including special research aircraft data from the tropical cyclone motion tcm 92 experiment objective analyses satellite data and traditional surface and sounding data the development process is treated as a dry adiabatic vortex dynamics problem and it is found that environmental and mesoscale dynamics mutually enhance each other in a cooperative interaction during cyclone formation synoptic scale interactions result in the evolution of the hostile environment toward more favorable conditions for storm development mesoscale interactions with the low level large scale circulations and with other midlevel mesoscale features result in development of vorticity in the midlevels and enhancement of the low level vorticity associated with the developing surface cyclone multiple developments of mesoscale convective systems after the storm reaches tropical depression strength suggests both an increase in low level confluence and a tendency toward recurrent development of associated mesoscale convective vortices this is observed in both aircraft data and satellite imagery where subsequent interactions including mergers with the low level tropical depression vortex are observed a contour dynamics experiment suggests that the movement of mesoscale convective systems in satellite imagery corresponds well to the movement of their associated midlevel vortices results from a simple baroclinic experiment show that the midlevel vortices affect the large scale low level circulation in two ways 1 initially interactions between midlevel vortices produce a combined vortex of greater depth 2 interaction between midlevel vortices and the low level circulation produces a development downward of the midlevel vorticity this strengthens the surface vortex and develops a more cohesive vortex that extends from the surface through the midtroposphere

the sedimentology of three tunisian lagoons abstract there are three major lagoons indenting the shoreline of tunisia the lake of bizerte on the north coast of tunisia is in the mediterranean climatic setting the lake of tunis 50 km to the south is in a semi arid climatic setting bahiret el bibane 450 km south of the lake of bizerte near the libyan border is in an arid climatic setting the summer salinities of the three lagoons reflect the climatic differences man has had an impact on the two northern lagoons the lake of bizerte outlet to the mediterranean has been deepened by dredging the lake of tunis has been altered through infilling by man an ongoing process construction of a diked ship channel and introduction of large amounts of raw sewage bahiret el bibane is relatively unaffected by the activities of man the sediments in the lake of bizerte are dominated by mud size clastics from intermittent streams draining farmland in addition there is an important biogenic component the most abundant sediment in the lake of tunis is an organic rich terrigenous mud derived from the adjacent drainage basin but biogenic productivity is high and forms a locally dominant sediment component calcareous worm reefs flourish because of the high nutrient content summer eutrophication is frequent the sediments of the semi restricted bahiret el bibane are dominated by biogenic fragments mostly mollusks but with an important wind transported detrital component the north to south changes in the character of the clastic sediments of the lake of bizerte and bahiret el bibane are mainly related to the source of the sediment which is largely controlled by climate the influence of man dominates sedimentation in the lake of tunis

the shuram and subsequent ediacaran carbon isotope excursions from southwest laurentia and implications for environmental stability during the metazoan radiation current understanding of secular changes in the carbon isotopic composition of mid to late ediacaran carbonates suggests a relatively long steady recovery of the global ocean from the shuram negative excursion followed by a smaller negative excursion at the precambrian cambrian boundary new radiometric stratigraphic and carbon isotope data from thick exposures of the upper johnnie formation in the panamint range of eastern california combined with data from carbonate rich facies of the stirling quartzite in the funeral mountains confirm an ediacaran age for these strata and provide a more complete record of isotopic variations during this time interval than previously determined from sw laurentia and other key sections around the globe a siltstone in the lower part of the johnnie formation yielded a detrital zircon grain with an age of 640 33 0 09 ma lowering the maximum radiometric age constraint on the johnnie formation by 400 m y consistent with an ediacaran age based on chemo and biostratigraphic data in contrast to previous c isotope compilations from this region which were generally based on relatively thin portions of the cordilleran miogeocline near its depositional hinge the more basinward exposures exhibit a recovery from values near 12 to 0 within the upper part of the johnnie formation details in the shape of the chemostratigraphic profile through the upper johnnie formation closely match those in profiles through the wonoka formation in south australia which lies above the basal ediacaran global stratotype section and point and the shuram buah interval in oman confirming temporal correlation and suggesting genesis through changes in the isotopic composition of the global ocean the shuram excursion in sw laurentia is followed by at least three smaller ediacaran to earliest cambrian isotopic excursions recorded within from oldest to youngest the uppermost johnnie formation the middle stirling quartzite and the lower wood canyon formation these data indicate that the negative excursion associated with the base of the cambrian is not a unique post shuram event and that post shuram pre cambrian animal evolution occurred in an environment of repeated large magnitude fluctuations in the carbon isotopic composition of the global ocean