prerift and synrift sedimentation during early fault segmentation of a tertiary carbonate platform indonesia abstract eocene carbonate deposits of the barru area sulawesi indonesia provide a rare insight into sedimentation prior to and during propagation of normal faults to the surface three main successions late prerift latest prerift earliest synrift and synrift are characterised by distinctive facies associations and sequence development shallow water foraminiferal shoals and intervening lower energy depositional environments occurred during the late prerift in areas which latter formed footwall highs and hangingwall depocentres respectively during the latest prerift earliest synrift shallow water shelves deepened laterally into slope environments in developing hangingwall depocentres in both these sequences sections in developing hangingwall areas are thickest deepen up section and thin laterally towards growing footwall highs active faulting resulted in rapid drowning of hangingwall depocentres and massive reworking of material derived from collapse of the platform margin and adjacent shallow water emergent footwall highs differential subsidence controlling water depths and accommodation space types of carbonate producers and active faulting were the main factors affecting depositional environments and facies distributions carbonate producers are extremely sensitive indicators of depositional water depth and energy hence rapid lateral and vertical facies variations in the barru area provide quantifiable insight into environmental changes prior to and during active faulting

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

energetics of winter troughs entering south america abstract the energetics and behavior of midtropospheric troughs over the southern hemisphere and their relationship with south america surface cyclogenesis were studied during the winters of 1999 2003 all surface cyclogenesis situations over uruguay and adjacent areas associated with 500 hpa troughs were analyzed the atmospheric circulation associated with type b and type c cyclones form the basis for two composites composite b with 25 cases and composite c with 13 cases the results showed that the midtropospheric troughs were more intense in composite c than in composite b before the surface cyclogenesis and that the opposite occurred during the surface cyclogenesis the baroclinic conversion was dominant in both composites in composite b the ageostrophic flux convergence afc contributed positively to the intensification of the surface cyclone since it imported energy into the area before the cyclogenesis started but in composite c the afc served as a sink because it exported energy based

age and significance of sequence boundaries on jurassic and early cretaceous rifted continental margins the age and significance of sequence boundaries on jurassic to early cretaceous rifted continental margins in three ocean basins have been documented the margins are the santos basin in the south atlantic the grand banks in the north atlantic and the beaufort sea in the arctic ocean large industry data bases were used for the interpretation of each area megasequence boundaries separate the major phases of basin evolution for example syn rift and post rift boundaries developed with an average periodicity of 49 m y sequence boundaries define the component parts of each megasequence and developed with a modal periodicity of 10 15 m y out of 27 total boundary ages most 16 are developed on just one margin only two possible age ranges overlap on all three margins ighty percent of the megasequence boundaries and 50 of the sequence boundaries show a direct causal connection with coeval faulting and or folding the rest of the boundaries appear as unstructured surfaces separating transgressive and or regressive sedimentary wedges and are interpreted to result from changes in the rate of basin subsidence sediment input and long term eustatic sea level these data do not support theories advocating synchronous worldwide boundary development resulting from periodic short term falls in global eustatic sea level only in like basins of the same age with identical subsidence and sediment input rates are boundaries likely to develop synchronously hence the concept of global synchroneity of sequence boundary development may well be an illusion creat d by the similarity in age of the majority of basins studied as a result of this study it seems wise discard the global approach to basin analysis

palaeoclimate of the late jurassic of portugal comparison with the western united states investigation of the palaeoclimatic conditions associated with upper jurassic strata in portugal and comparison with published palaeoclimate reconstructions of the upper jurassic morrison formation in western north america provide important insights into the conditions that allowed two of the richest terrestrial faunas of this period to flourish geochemical analyses and observations of palaeosol morphology in the informally named upper jurassic lourinhaformation of western portugal indicate warm and wet palaeoclimatic conditions with strongly seasonal precipitation patterns palaeosol profiles are dominated by carbonate accumulations and abundant shrink swell vertic features that are both indicative of seasonal variation in moisture availability the d 18 osmow and ddsmow values of phyllosilicates sampled from palaeosol profiles range from 22ae4 to 22ae7 and 53ae0 to 37ae3 respectively these isotope values correspond to temperatures of formation between 32 c and 39 c 3 with an average of 36 c which suggest surface temperatures between 27 c and 34 c average 31 c on average these surface temperature estimates are 1 c higher than the highest summer temperatures modelled for late jurassic iberia using general circulation models elemental analysis of matrix material from palaeosol b horizons provides proxy chemical index of alteration minus potassium estimates of mean annual precipitation ranging from 766 to 1394 mm year with an average of approximately 1100 mm year palaeoclimatic conditions during deposition of the lourinhaformation are broadly similar to those inferred for the morrison formation except somewhat wetter seasonal variation in moisture availability does not seem to have negatively impacted the ability of these environments to support rich and relatively abundant faunas the similar climate between these two late jurassic terrestrial ecosystems is probably one of the factors which explains the similarity of their vertebrate faunas

geochemical characterization of oils and their correlation with jurassic source rocks from the lusitanian basin portugal abstract seeking to identify the oils groups accumulated in the jurassic of the lusitanian basin and the source rock of each group stable carbon isotope and gas chromatography coupled with mass spectrometry analyses were performed in oils and oil shows from the main discoveries and on representative organic extracts from the potential source rocks selected based on previous works and data obtained by total organic carbon and rock eval pyrolysis techniques the geochemical comparison between the oils and between the oils and the organic extracts allowed the identification of three oil groups whose differences depend on their source rocks oils generated at the coimbra formation lower upper sinemurian and accumulated in the same formation and in the agua de madeiros formation upper sinemurian lower pliensbachian in the northern sector of the basin oils originated from the top of the cabacos formation middle oxfordian and accumulated in the montejunto middle upper oxfordian and abadia lower upper kimmeridgian formations in the central and southern sectors of the basin and oil generated and accumulated at the base of the montejunto formation in the central sector of the basin the geochemical correlations between the oils and the organic extracts allowed the identification of the source rocks of the different accumulations of the jurassic succession allowing further guidance to the petroleum exploration in the lusitanian basin

velocity profile of a sand cloud blowing over a gravel surface particle dynamic analyzer pda measurement technology was used to study the turbulent characteristics and the variation with height of the mean horizontal in the downwind direction and vertical in the upward direction particle velocity of a sand cloud blowing over a gravel surface the results show that the mean horizontal particle velocity of the cloud increases with height while the mean vertical velocity decreases with height the variation of the mean horizontal velocity with height is to some extent similar to the wind profile that increases logarithmically with height in the turbulent boundary layer the variation of the mean vertical velocity with height is much more complex than that of the mean horizontal velocity the increase of the resultant mean velocity with height can be expressed by a modified power function particle turbulence in the downwind direction decreases with height while that in the vertical direction is complex for fine sands 0 2 0 3 mm and 0 3 0 4 mm there is a tendency for the particle turbulence to increase with height in the very near surface layer 4 mm the movement of blown sand particles is very complex due to the rebound of particles on the bed and the interparticle collisions in the air wind starts to accelerate particle movement about 4 mm from the surface the initial rebound on the bed and the interparticle collisions in the air have a profound effect on particle movement below that height where particle concentration is very high and wind velocity is very low

a characteristic life cycle of upper tropospheric cyclogenetic precursors during the experiment on rapidly intensifying cyclones over the atlantic erica abstract this paper documents a characteristic life cycle of upper tropospheric precursors to surface cyclogenesis observed during the field phase of the experiment on rapidly intensifying cyclones over the atlantic erica december 1988 february 1989 this life cycle begins with the development of an elongated region of lower dynamic tropopause that forms in association with an intensifying midtropospheric jet front over central north america the elongated disturbance subsequently compacts into a more circular configuration prior to crossing the east coast of north america and frequently is associated with rapid surface cyclogenesis offshore a representative example of the life cycle outlined above is documented through a detailed case study of the upper precursor associated with the second erica intensive observation period iop 2 cyclone emphasis is placed upon i description of the tropopause structure and evolution during the upper precursor life cycle ii diagnosis of mechanisms leading to t

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

an experimental study of wind abrasion rocks were abraded by a sand laden air jet in the laboratory to examine the quantitative relationships between wind abrasion and wind velocity quantity and grain size of windblown sand particles and physical properties of the target rocks the results of 101 runs are expressed by an experimental equation with dimensionless constant which indicates that the rate of abrasion is directly related to the kinetic energy of the sand projectiles and inversely proportional to the compressive strength of the target rocks a tentative extension of the experimental equation to field condition leads to an equation for the wind abrasion in fields an application of the latter equation to the natural settings is preliminarily examined by comparing it with sharp s 1964 field experiments and a plausible result is obtained

upscale effects of deep convection during the north american monsoon abstractthe ability of deep monsoon convection to influence the larger scale circulation over north america is investigated for a 6 day long case study during the 2006 north american monsoon results from rossby wave ray tracing and numerical simulations using the advanced research weather research and forecasting model indicate that north american monsoon convection provides a source region for stationary rossby waves two wave trains are seen in the numerical model simulations with behaviors that agree well with expectations from theory and ray tracing the shorter and faster moving wave train moves eastward from the source region in mexico and reaches the western atlantic within 4 days the longer and slower moving wave train travels northeastward and reaches the coastal new england region within 6 days an upstream tail of anticyclonic vorticity extends westward from the source region into the central pacific ocean the monsoon convection appears to help cut off the low level anticyclonic flow by deve

northern hemisphere 500 hpa trough merger and fracture a climatology and case study abstract the results of an objective climatology of 500hpa trough merger defined as the amalgamation of two initially separate vorticity maxima and trough fracture defined as the splitting of a single vorticity center into two separate vorticity centers are presented for the northern hemisphere the data source is the gridded national meteorological center nmc now the national centers for environmental prediction analyses available on cd rom on the nmc operational octagonal grid 381 km resolution at 60 n for the period september 1957 to may 1989 a total of 2152 3053 merger fracture events are identified merger and fracture events tend to occur preferentially in the band of middle latitude westerlies merger events exhibit a tendency to avoid major mountainous regions and show a somewhat higher frequency of occurrence downstream of these regions fracture events cluster somewhat over eastern ocean basins the southwestern united states and northwestern africa while also avoiding major mount

diachronous evolution of late jurassic cretaceous continental rifting in the northeast atlantic west iberian margin 1 regional 2 d seismic reflection profiles outcrop and borehole data are used to characterize the evolution of deep offshore sedimentary basins in southwest iberia alentejo basin the interpreted data indicate the bulk of late jurassic earliest cretaceous subsidence occurred in the present day continental slope area as shown by 1 significant thickening of synrift strata basinward from a slope bounding fault system sfs west of which the total thickness of sediment can reach more than 9 0 km and 2 relatively thin mesozoic strata east of the sfs where thickening of synrift units against principal faults is limited five principal regressive events and their basal unconformities reflect tectonic uplift and relative emersion in proximal basins which were located on the rift shoulder to subsiding tilt blocks west of the sfs these regressive events are correlated with major rift related events occurring on the deeper margin direct comparisons with the peniche basin of northwest iberia reveal that significant portions of the iberian lower plate margin were uplifted and eroded during the last stages of continental rifting this process was repeated at different times and in different areas as the locus of rifting and continental breakup migrated northward as a result two distinct rift axes are recognized in west iberia a first axis extending from the porto basin to the alentejo basin and a second axis located on the outer proximal margin north of 38 30n in addition the sfs delimited 1 prograding deposits of cretaceous paleogene age and 2 late cenozoic deposits draping the modern continental slope these latter facts demonstrate that on lower plate passive margins the relative position of the continental slope is established during the final rifting episode s preceding continental breakup

energetics and dynamics associated with two typical mobile trough pathways over east asia in boreal winter two dominant types of east asian mobile trough eamt are identified by a novel mobile trough detection algorithm the two major eamts likely pass through to the north and the south of lake baikal in this study both of synoptic and planetary time scales influences on east asia are studied for synoptic scale southern path of mobile trough shows a higher rate of intensification that of northern path southern path has stronger impact on southeast asia temperature fluctuation because of more southern pathway and stronger magnitude of wave train but duration of fluctuation is shorter in southern due to the downstream development for planetary scale the northern path shows a large warm anomaly over southeast asia and a cold anomaly over northeast asia which is associated with the northward shift of the jet stream the southern path shows a cold anomaly over east asia due to a northwesterly anomaly the forcing of high frequency eddy on low frequency eddy is estimated in terms of momentum and energy the reinforcement of high frequency eddy flux on low frequency variation can be observed in northern path but not in southern path the energy difference for two paths is also caused by the variations of barotropic and baroclinic conversion the energy tendency of interaction between two frequency eddies is only responsible for sustention of energy anomaly over southwestern japan

height profile of the mean velocity of an aeolian saltating cloud wind tunnel measurements by particle image velocimetry abstract the velocity of saltating particles is an important parameter in studying the aeolian sand movement we used particle image velocimetry to measure the variation with height of the mean particle velocity of a saltating cloud over a loose sand surface in a wind tunnel the results suggest that both the horizontal and vertical particle velocities fit the gaussian distribution well and that the mean particle velocity of a saltating cloud varies with wind velocity particle size and the height above bed the mean horizontal velocity is mainly the result of acceleration by the wind and increases with an increase in friction wind velocity but decreases with an increase in grain size because greater wind velocity causes more acceleration and finer particles are more easily accelerated at a given wind velocity it also increases with an increase in height by a power function in agreement with previous results obtained by other methods such as the high speed multi flash photographic method and particle dynamics analyzer pda reflecting first the increase in wind velocity with height through the boundary layer and second the longer trajectory particle path length increases with height and affords a longer time for acceleration by the wind an empirical model relating the mean horizontal particle velocity and height friction wind velocity as well as particle size is developed the ratio of the mean horizontal particle velocity to the clean wind velocity at the same height increases with height but decreases with grain size the magnitude of mean vertical velocity is much less one or two orders less compared with the mean horizontal velocity the average movement in the vertical direction of a saltating cloud is upward the mean vertical velocity is positive although the upward velocity of a saltating particle should decrease with height due to gravity the mean vertical upward velocity the average of both ascending and descending particles generally shows a tendency to increase with height it seems that at higher elevations the data are more and more dominated by the high flyers the underlying mechanism for the mean vertical velocity distribution patterns needs to be clarified by further study

extensional tectonics and stratigraphy of hibernia oil field grand banks newfoundland the tectonic evolution of the grand banks involved several episodes of rifting and sequential development of the continental margin the dominant period of rifting and basin formation in the central grand banks was late callovian to aptian extensional failure of the central grand banks crust probably occurred along a shear zone that dipped gently to the west listric normal basin forming faults merge at depth with this detachment system the listric murre fault soles at 26 km 16 mi creating the very deep jeanne d arc basin cross basin transfer faults accommodated different amounts and rates of extension and resulted in the conspicuous offset pattern and funnel shaped geometry of the jeanne d arc basin the hibernia oil field is associated with one of these structural salients the stratigraphy of the jeanne d arc basin and the hibernia oil field is a direct response to this tectonic and structural framework large scale unconformity bounded sequences correspond to major plate reorganizations and zipper type opening of the atlantic ocean smaller scale adjustments to episodic extension are expressed in multiple stacking of depositional sequences the broad scale evolution of the synrift succession involved the early deposition of limestones and oil prone shales about 10 12 m y later rifting climaxed resulting in floods of coarse terrestrial material from the rift shoulders the characteristics of these depositional systems reflect a pervasive structural control affecting the distribution of facies tracts dip slip movement on basin bounding faults and c oss basin transfer fault trends were equally important a profound structural modification of the hibernia structure occurred in late barremian time when a major detachment developed within the basin fill this structural modification and associated antithetic and synthetic faulting in the hanging wall largely controlled reservoir distribution and the maturation migration and trapping of hydrocarbons

a diagnostic study of jet streaks kinematic signatures and relationship to coherent tropopause disturbances abstract a diagnostic study is conducted of the kinematics and evolution of upper level jet streaks representative of three of the four phases in the shapiro conceptual model of a jet streak progressing through a synoptic scale baroclinic wave over north america the three phases selected for consideration apply to those segments of the wave pattern where jet streaks are relatively straight the 1200 utc 2 december 1991 case trough over ridge considers a strong jet streak located over eastern north america and constitutes the bulk of the study the other two cases which also concern jet streaks over north america are from 0000 utc 11 november 1995 northwesterly flow and 0000 utc 28 october 1995 southwesterly flow kinematic signatures consistent with the classic four quadrant conceptual model for a straight jet streak are evident in all three cases although flow curvature and thermal advection lead to significant departures from this conceptual model the position of the jet streak within the s

a marine late jurassic syn rift succession in the lusitanian basin western portugal tectonic significance of stratigraphic signature abstract in the lusitanian basin which is located along the western iberian margin rapid subsidence in the oxfordian tithonian resulted from extension related to the opening of the north atlantic in the santa cruz area located in the western part of the lusitanian basin the kimmeridgian syn rift marine abadia formation and the overlying alluvial kimmeridgian tithonian praia da amoreira member of the lourinha formation were deposited in the middle part of the hangingwall dip slope of a larger half graben that constitutes the turcifal subbasin the marine part of the succession consists of base of slope and lower slope mudstones and sandy turbidites middle slope mudstones upper slope to shelfal shoreline mudstones and sandstones and fan deltaic deposits two intermediate scale fining to coarsening fucu units are present in the marine strata the lower fucu unit represents a normal base of slope lower slope to upper slope shoaling upward succession the unit reflects the progradation of a hangingwall shelfal ramp and infilling of an inherited rift bathymetry during a period of relative tectonic quiescence the upper fucu unit represents an intermediate scale deepening shoaling upward or backstepping forestepping sequence which is related to a single rift event the backstepping segment was deposited during a period of increasing basinal subsidence and basin floor tilt rates the early syn rotational stage it consists of submarine channel fill incised into slumped upper slope sediments and adjacent overbank deposits the backstepping segment terminates with a clay prone marine interval with abundant soft sediment deformation features which represent a period of maximum sea level stand during the rotational climax the overlying forestepping segment consists of a shoaling upward slope to fan deltaic succession which terminates with alluvial deposits it represents an interval with decreasing basinal subsidence and basin floor tilt rates and renewed overbalance of sediment supply which led to a regression during the late syn rotational stage in medial reaches of the hangingwall dip slope periods of increasing to decreasing rift activity are recorded by a backstepping forestepping package or a threefold sandstone mudstone sandstone lithosome motif the formation of smaller scale units superimposed on the intermediate scale fucu syn rotational motif were controlled predominantly by minor fault controlled subsidence events or higher frequency faulting events

upper level frontogenesis associated with the birth of mobile troughs in northwesterly flow previous studies have shown that 500 hpa mobile trough births or genesis occur preferentially in northwesterly flow during upper level frontogenesis and that cold advection assists in and is a product of mobile trough intensification this study focuses on the synoptic environments and thermal advection patterns of upperlevel fronts associated with mobile trough births in northwesterly flow a climatology of 186 such events derived from an earlier study by sanders shows that most births tend to occur within uniform or diffluent flow and that most tend to be associated with relatively weaker 500 hpa thermal advection most mobile trough births in diffluence however tend to be associated with increasing 500 hpa cold advection typically indicated by a cyclonic rotation of isentropes whereas most mobile trough births in confluence tend to be associated with weaker 500 hpa thermal advection two cases of upper level frontogenesis associated with mobile trough genesis one in diffluence and one in confluence are compared to determine the processes acting to produce the differing thermal advection patterns at 500 hpa a thermal advection tendency equation is developed and shows that the magnitude of the temperature advection can be changed by accelerating the advecting wind speed or by changing the temperature gradient i e vector frontogenesis the latter can be accomplished either by changing the magnitude of the temperature gradient the frontogenetical component fn also known as scalar frontogenesis or by rotating the direction of the temperature gradient relative to the flow the rotational component fs the dominant processes acting on fn for the diffluence and confluence cases are tilting and deformation frontogenesis respectively the dominant process acting on fs for the diffluence case is rotation of the isentropes due to the vorticity term whereas rotation of the isentropes due to the vorticity and tilting terms are both important for the confluence case the rotational component of frontogenesis is cyclonic downstream of the vorticity maximum for both cases favoring increasing cold advection downstream of the vorticity maximum for both cases the rate of rotation of the isentropes at a point due to horizontal advection is large and that due to vertical advection is negligible since advection can only transport the existing isentrope angle and cannot change the isentrope angle the rotational component of frontogenesis normalized by the temperature gradient is the only term that can increase the isentrope angle following the flow this term dominates in the diffluence case but is small in the confluence case this diagnosis suggests the following reasoning in diffluent flow the vorticity associated with the incipient trough is compacted into a more circular shape and intensifies the potent vorticity maximum leads to robust isentrope rotation in confluent flow however the vorticity is deformed into an elongated maximum inhibiting both strong isentrope rotation and increasing cold advection thus the rotational frontogenesis component explains the rotation of the isentropes that is responsible for the differing thermal advection patterns diagnosis of these cases supports the results from the climatology indicating a strong relationship between the synoptic environment and the upper tropospheric thermal advection pattern nevertheless current conceptual models of upper level frontogenesis do not fully explain the variety of these features in the real atmosphere in particular mobile trough genesis and its associated upper level frontogenesis can occur in weak 500 hpa thermaladvection patterns in contrast to the confluence and cold advection that have been previously identified as important to upper level frontal intensification this result provides further support for the possibility that generation and intensification of mobile troughs can occur by barotropic processes

tectonics and seismic sequence stratigraphy a two day meeting convened by graham williams university of keele and angela dobb mobil north sea ltd was held at the geological society in london on 6 and 7 february 1991 the aim of the meeting was to address the problems of the interaction between eustacy sediment supply rate and tectonics in seismically imaged basin sequences the meeting discussed the importance of tectonics in generating recognizable sequence boundaries on both a regional and local scale it was felt that eustacy as the dominant factor in controlling basin stratigraphy has been overplayed in the past there were 190 participants at the conference representing the oil industry and academia some 21 oral presentations were given covering theoretical aspects of sequence stratigraphy numerical modelling and field analogues case histories from europe north america africa and the uk were presented basin scale numerical modelling in the simplest case stratigraphy in extensional basins and passive margins may be subdivided into pre syn and post rift sequences representing stratigraphic fill related to a single rifting event a widely recognized unconformity or megasequence boundary between syn and post rift sequences is referred to as the breakup unconformity numerical modelling on a basin scale in extensional regimes has been carried out by m j newall and n j kusznir shell research liverpool who concentrated on the post rift subsidence history and palaeobathymetric evolution of snorre magnus and other areas of the northern north sea basin subsidence resulting from thermal effects compaction and sediment loading has been numerically modelled using flexural

an observational study of fronts and frontal mergers over the continental united states abstract the stormscale operational and research meteorology fronts experiment systems tests storm fest field program was carried out over the central united states to investigate the structure and dynamics of fronts and their attendant precipitation systems adjacent to complex topography and to evaluate new observing networks and analysis techniques for mesoscale research and weather forecasting this study presents the analysis of data taken between 8 and 10 march 1992 which was the most active period of storm fest this three day observing period was characterized by the passage of an extratropical cyclone and related fronts the synoptic scale conditions related to the cyclone and frontal evolutions are described multiple frontal zones i e pacific and arctic cold fronts quasi stationary polar front dryline maritime warm front and associated regions of precipitation are documented and their origins and interactions are explored these features both well defined and subtle were observed wi

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

the role of synoptic scale flow during tropical cyclogenesis over the north atlantic ocean abstract the synoptic scale flow during tropical cyclogenesis and cyclolysis over the north atlantic ocean is investigated using compositing methods genesis and lysis are defined using the national hurricane center nhc now known as the tropical prediction center best track data genesis lysis occurs when nhc first last identifies and tracks a tropical depression in the final best track dataset storm centered composites are created with the analysis of the tropical oceanic lower level atoll 900 hpa and 200 hpa winds for june november produced by nhc for the years 1975 93 results show that significant regional differences exist in 200 hpa flow during genesis across the atlantic basin composites of genesis in the western part of the basin show a 200 hpa trough ridge located to the west east of the atoll disturbance in the eastern half of the basin composites of genesis show a sprawling 200 hpa ridge centered northeast of the atoll disturbance the major axis of this elliptically shaped 20

sediment slides and turbidity currents on the laurentian fan sidescan sonar investigations near the epicenter of the 1929 grand banks earthquake the epicenter area of the 1929 grand banks earthquake on the continental slope south of newfoundland has been investigated using sea marc i a deeply towed midrange sidescan sonar with a 4 5 khz subbottom profiler shallow slides pass downslope into debris flows on the muddy continental slope east of the epicenter at the head of the eastern valley of the laurentian fan west of the epicenter arcuate slide scars cut undisturbed upper slope sediment and lead downslope to a lineated erosional seabed at a water depth of about 1600 m this erosional seabed passes into extensive fields of 100 m wavelength gravel waves situated on the broad irregular valley floor the gravel waves become better developed downslope and extend at least to water depths of 3000 m all these morphological features appear fresh on the sidescan sonograms suggesting that they date from the 1929 earthquake event and the distribution of slides corresponds to the area of instantaneous cable breaks in 1929 the upper limit of erosion on valley walls suggests that the 1929 turbidity current was less than 300 m thick timing of cable breaks downfan suggests that flow velocities were sufficient to rework gravel deposits into large bedforms during waning flow stages over elevated areas of the valley floor similar cross bedded coarse sands and gravels are common in ancient channel deposits

seismic and sedimentologic features of oxfordian kimmeridgian syn rift sediments on the eastern margin of the lusitanian basin following deposition of widespread middle oxfordian lacustrine carbonates and evaporites the lusitanian basin was differentiated into a number of sub basins the arruda sub basin is a half graben basin situated some 30 km north of lisbon it accumulated over 2 5 km of kimmeridgian siliciclastic sediments and is bounded to the east by the vila franca de xira fault zone carbonate deposition persisted over horsts along the fault zone from the oxfordian to the early kimmeridgian and in places to the late kimmeridgian and shows a pronounced west east facies zonation with higher energy framestones and grainstones accumulating along the exposed western margins seismic data indicate a major gap between the horst blocks that acted as a conduit through which basement derived siliciclastics were fed westwards into the sub basin to form a submarine fan system the presence of large blocks of framestone carbonates encased in siliciclastics indicates that carbonate sedimentation occurred in abandoned parts of the fan system the rapid changes of sediment thicknesses and facies types along the eastern margin of the arruda sub basin are indicative of contemporaneous strike slip movements

geoheritage and advanced training for the oil industry the lusitanian basin case study portugal the lusitanian basin central portugal is a recurring subject of study within different disciplines of earth sciences mainly because of the excellent stratigraphical and paleontological records as well as the world class quality of outcropping elements of petroleum systems and salt tectonics geometries in fact in the lusitanian basin three global stratigraphic references were defined for the jurassic system the toarcian global stratotype section and point gssp the bajocian gssp and the bathonian auxiliary stratigraphic section and point but the sedimentary record of the lusitanian basin includes a set of geosites that provide favorable conditions for educational activities in the frame of the portuguese educational system which are increasingly being sought for the development of advanced training activities in the context of the hydrocarbon exploration models this paper presents the main reasons that attract this particular public which includes geospecialists and geoexperts to the lusitanian basin outcrops as well as the geosites that are currently visited for advanced training purposes by different oil companies as such the geological heritage of the lusitanian basin represents a paradigmatic example of the relevance of enlarging the traditional vision that confines technical applications of geoconservation to scientific research education and geotourism the last of which is considered in the sense of an activity intended exclusively for geoamateurs and or people who are either unaware of or interested in learning about geological issues

on the effect of mid air collisions on aeolian saltation the effect of mid air collisions on aeolian saltation is investigated using concentration profiles and grain velocities predicted by a numerical saltation model the probability of a mid air collision is found to be greater at high wind speeds it is also found that mid air collisions tend to reduce the number of grain bed impacts and thus reduce the number of ejecta near the bed this in turn reduces the intensity of mid air collisions it is suggested that this feed back mechanism significantly influences transport rates at high wind speeds

tectono stratigraphic signature of multiphased rifting on divergent margins deep offshore southwest iberia north atlantic 1 regional 2d multichannel seismic borehole dredge and outcrop data together with burial models for strata in southwest iberia are used to investigate the tectono stratigraphic signature of multiphased rifting on divergent margins our burial model reveals that mesozoic extension occurred during three main phases each comprising distinct subsidence pulses separated by short lived periods of crustal uplift the importance of the three phases varies across discrete sectors of the margin each one revealing similar depositional architectures and associated tectonic systems tracts 1 the rift initiation phase characterized by incipient subsidence and overall aggradation progradation over a basal unconformity 2 the rift climax phase which marks maxima of tectonic subsidence and is characterized by retrogradation progradation and 3 the late rift phase recording the progradational infill of the basin and the effects of eustasy the rift initiation systems tracts comprise sinemurian and late callovian early oxfordian strata marine units in the pliensbachian and late oxfordian kimmeridgian represent the rift climax phase a period marked by the development of maximum flooding surfaces late rift deposits were identified in the rhaetian hettangian toarcian bathonian and kimmeridgian berriasian the results of this work are important to the economic exploration of deep offshore rift basins as they reveal that sequence stratigraphy can be used to predict sedimentary facies distribution in more distal segments of such basins significantly this work recognizes that multiple tectonic stratigraphic rift cycles can occur on deep offshore rift basins from the onset of rift related extension until continental break up a character that contrast to what is known from deep sea drilling data from the distal margin of northwest iberia

submarine sand dunes and sedimentary environments in oceanographer canyon abstract observations from research submersibles in the northern part of oceanographer canyon reveal the presence of an extensive field of large sand dunes on the canyon floor the dunes are medium to coarse sand are oriented across the axis and the largest of them are as high as 3 m and have wavelengths up to 15 m their asymmetry grain size and height suggest that they are formed by axial currents flowing up and downcanyon and that the largest dunes require flows of at least 70 cm sec shelf sand low in silt and clay content is transported by currents down and along the canyon walls onto the canyon floor as the sand enters the canyon it is mixed with immobile gravel deposits on the canyon rim lower on the walls the sand is mixed with silt and clay burrowed by organisms from the se iconsolidated sandy silt that underlies the canyon walls and floor upon reaching the canyon floor the sand is sculpted into bed forms by currents and the fines are winnowed out and transported out of the canyon at present the shelf and canyon walls are being eroded by bottom currents and burrowing organisms whereas the canyon floor is covered by mobile sand that moves both up and down the axis in this part of the canyon

the deposits internal structure and geometry in six alluvial fan fan delta bodies devonian norway a study in the significance of bedding sequence in conglomerates discussion and reply

traction carpet stratification in turbidites fact or fiction abstract the spaced stratification that characterizes some thick deep water sandstones consists of a stack of layers 5 10 cm thick that are inversely graded at their base and structureless at their top these layers have been attributed to deposition from a succession of collapsed inertia layers traction carpets prior to collapse each layer was believed to have been maintained by shear from the overriding turbidity current this depositional model is based on the mistaken assumption that the distribution of shear stress in such a traction carpet is indistinguishable from the distribution of shear stress in a grain flow on a steep slope instead shear stress in an externally sheared traction carpet should be approximately constant from the top to the base of the layer and deposition sho ld be a gradual process leaving no record of sequentially active inertia layers inertia layers that do form under large turbidity currents are probably never as thick as 5 10 cm based on available data from shear cell experiments instead inertia layers are probably about 1 cm thick similar to the thickness of the inversely graded basal part of each layer in field examples of spaced stratification the rest of each inversely graded stratum probably forms due to rapid fallout from suspension the basal inversely graded 1 cm is believed to record strong shear that may accompany impingement on the bed of large turbulent eddies hence spaced stratification may not be a structure produced beneath steady flows but may record strong y fluctuating hydrodynamic conditions and vigorous burst sweep cycles in large turbidity currents

synoptic scale environments of predecessor rain events occurring east of the rocky mountains in association with atlantic basin tropical cyclones abstractthe synoptic scale environments of predecessor rain events pres occurring to the east of the rocky mountains in association with atlantic basin tropical cyclones tcs are examined pres that occurred during 1988 2010 are subjectively classified based upon the synoptic scale upper level flow configuration within which the pre develops with a focus on the following 1 the position of the jet streak relative to the tc 2 the position of the jet streak relative to trough and ridge axes and 3 the positions of trough and ridge axes relative to the pre and to the tc three categories were identified from this classification procedure jet in ridge southwesterly jet and downstream confluence pre relative composite analysis for each category reveals that consistent with previous studies pres typically occur near a low level baroclinic zone beneath the equatorward entrance region of an upper level jet streak and in the presence of a stream of water vapor from a tc despite these common

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

aspects of the structural evolution of the lusitanian basin in portugal and the shelf and slope area offshore portugal abstract the study provides a regional seismic interpretation and mapping of the mesozoic and cenozoic succession of the lusitanian basin and the shelf and slope area off portugal the seismic study is compared with previous studies of the lusitanian basin from the late triassic to the cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence the triassic rifting was concentrated in the central part of the lusitanian basin and in the southernmost part of the study area both as symmetrical grabens and half grabens the evolution of half grabens was particularly prominent in the south the triassic fault controlled subsidence ceased during the latest late triassic and was succeeded by regional subsidence during the early early jurassic hettangian when deposition of evaporites took place a second rift phase was initiated in the early jurassic most likely during the sinemurian pliensbachian this resulted in minor salt movements along the most prominent faults the second phase was concentrated to the area south of the nazare fault zone and resulted here in the accumulation of a thick sinemurian callovian succession following a major hiatus probably as a result of the opening of the central atlantic resumed deposition occurred during the late jurassic evidence for late jurassic fault controlled subsidence is widespread over the whole basin the pattern of late jurassic subsidence appears to change across the nazare fault zone north of the nazare fault fault controlled subsidence occurred mainly along nnw sse trending faults and to the south of this fault zone a nne ssw fault pattern seems to dominate the oxfordian rift phase is testified in onlapping of the oxfordian succession on salt pillows which formed in association with fault activity the fourth and final rift phase was in the latest late jurassic or earliest early cretaceous the jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones however only salt pillow development can be demonstrated the extensional tectonics ceased during the early cretaceous during most of the cretaceous regional subsidence occurred resulting in the deposition of a uniform lower and upper cretaceous succession marked inversion of former normal faults particularly along ne sw trending faults and development of salt diapirs occurred during the middle miocene probably followed by tectonic pulses during the late miocene to present the inversion was most prominent in the central and southern parts of the study area in between these two areas affected by structural inversion fault controlled subsidence resulted in the formation of the cenozoic lower tagus basin northwest of the nazare fault zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed the miocene compressional stress was mainly oriented nw se shifting to more n s in the southern part

a simple identification scheme for upper level troughs and its application to winter precipitation variability in northwest africa abstract a simple algorithm for the identification of upper level trough axes is introduced in contrast to the assumption of a basically circular geometry in many comparable routines found in the literature the presented identification scheme is based on the east west gradient in the 500 hpa geopotential height field accounting for the meridionally elongated troughs often found in the subtropics on the basis of the ncep ncar reanalysis data from 1958 to 1998 climatological aspects are discussed for the area 22 5 47 5 n 38 5 w 18 5 e for the period from 1977 to 1998 12 hourly precipitation reports from 37 stations in northwestern africa are used to investigate the influence of the identified troughs on winter precipitation it is demonstrated that more than 90 of the precipitation in this region can be assigned to nearby trough axes a comparison of rainy periods with the climatology reveals a significant enhancement of the occurrence of trough axes in a range of 10 15 longitude close to the re

aerodynamic entrainment threshold effects of boundary layer flow conditions experimental data are presented demonstrating the influence of boundary layer flow conditions on aerodynamic entrainment of grains in the absence of intersaltation collisions new methods are proposed for 1 the unambiguous determination of aerodynamic threshold for any grain population and 2 approximation of the probability density function pdf distributions of threshold shear velocity for aerodynamic entrainment in wind tunnel experiments the orderly spatial development of flow conditions within a developing boundary layer over the roughened surface of a flat plate constrains the aerodynamic threshold condition in terms of both mean and fluctuating values initial grain dislodgements and subsequent erosion from narrow strips of loose finely fractionated ballotini were recorded photographically as wind speed was increased boundary layer parameters including average threshold shear velocity u t were calculated using the momentum integral method direct observations show that sporadic oscillation of grains preceded dislodgement at slightly higher velocities most grains rolled over their neighbours before entering saltation initial entrainment in spatially semi organized flurries of 50 or more grains was followed by quiescent periods at airflow velocities close to threshold these observations provide strong circumstantial evidence linking both the nature and spatial pattern of initial grain motions to sweep events during the fluid bursting process for each grain fraction values of u t were found to span an unexpectedly wide range and to decrease downwind from the leading edge of the plate as turbulence intensity increased a probabilistic entrainment model is applied to the aerodynamic threshold condition so as to incorporate the effects of changing turbulent flow regimes over the plate analysis of strip erosion curves gives both an objective definition of the threshold condition and usable approximations of the pdf for u t required by the model and for future stochastic treatment of the threshold condition

architecture of shoreface to deep water systems in segmented rift systems evidence from the southern margin of the sogn graben northern north sea the spatial distribution of syn rift deposits and temporal evolution of sandy gravity flows in the context of rift segmentation are poorly constrained based on conventional core description well log analysis and 3d seismic interpretation this study focuses on the upper jurassic successions in the southern margin of the sogn graben northern north sea thirteen facies associations are classified in order to discuss the architecture of shoreface gravity driven submarine fans and basin plain deposits on the scale of centimeters to meters in the eastern part of the study area gamma ray log stacking patterns suggest that northeast southwest oriented shoreface successions underwent progradational to retrogradational deposition during the oxfordian age lithological description of conventional cores indicates that large submarine fan system formed by debris flow dominated channels and turbidity flow dominated lobe complexes covers a broad 22 20 km depositional area the entry of regional drainages and the location of sandy gravity flow deposits were controlled by first order rift segmentation whereas the route of submarine canyon feeder system and the orientation of submarine fan lobes were determined by second order rift segmentation thus both first order and second order rift segmentation should be considered when determining the sedimentary facies and depositional architecture of sandy gravity flow deposits in individual rift segments

distal alluvial fan sediments from the upper jurassic of portugal controls on their cyclicity and channel formation the lusitanian basin of west central portugai is an iberian atlantic margin basin during a late jurassic rifting event a series of alluvial fans distributed coarse basement derived clastics southeastward from the western margin of the basin the distal part of this sequence which is about 140 m thick consists of heterolithic massive sandstone and massive mudrock facies arranged in crude fining upwards cycles 1 15 m thick these form discrete packets of sediment in a strongly aggrada tional sequence and are interpreted as the products of sheetflooding as the active area of sedimenta tion on the fan surface switched channelized flow was not necessarily an early feature of cycle development considerable fluctuations in discharge occurred and were probably related to climatic factors large quantities of tractional and suspended sediment were transported at high stages and were rapidly deposited as flows waned caliche soil profiles indicate a seasonal semi and climate however other features such as widespread soft sediment deformation the lack of desiccation structures and the absence of evaporites suggests that areas of active sedimentation often remained wet three fining upward megacycles are distinguished these indicate rapid advance of fan toes triggered by tectonic activity followed by gradual retreat

potential vorticity anomalies of the lowermost stratosphere a 10 yr winter climatology abstract inspection of the potential vorticity pv distribution on isentropic surfaces in the lowermost stratosphere reveals the ubiquitous presence of numerous subsynoptic positive pv anomalies to examine the space time characteristics of these anomalies a combined identification and tracking tool is developed that can catalog each individual anomaly s effective amplitude location overall spatial structure and movement from genesis to lysis a 10 yr winter climatology of such anomalies in the northern hemisphere is derived for the period 1991 2001 based upon the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 the climatology indicates that the anomalies are frequently evident above high topography and in a quasi annular band at about 70 n are long lived days to weeks and that their effective amplitude is typically 2 pv units pvu higher than that of the ambient environment in addition the derived climatologies and associated composites pose questions

numerical simulations of the genesis of hurricane diana 1984 part ii sensitivity of track and intensity prediction abstract the authors examine numerous simulations that probe the dynamics governing the intensification and track of tropical cyclone diana 1984 simulated in part i the development process is fundamentally dependent on a preexisting upper tropospheric trough ridge couplet this couplet focuses mesoscale vertical motion that in turn produces lower tropospheric potential vorticity pv anomalies which form the seed for the tropical storm removal of this trough ridge couplet from the initial conditions eliminates cyclogenesis the simulated rate of development of diana in the prehurricane phase depends principally on choices of cumulus parameterization boundary layer treatment sea surface temperature and grid spacing simulations with cumulus schemes that allow more grid scale precipitation on the 9 km grid exhibit unrealistic grid scale overturning and slower intensification primarily due to production of cyclonic vorticity anomalies at large radii use of an innermost nest with 3 km grid spacing

the depositional evolution of diapir and fault bounded rift basins examples from the lusitanian basin of west iberia new data on the evolution of rift basins is presented after analysing the late jurassic stratigraphy of the central lusitanian basin west iberia well outcrop and regional 2d seismic reflection profiles are used to investigate the differences in stratigraphic signature between diapir and fault bounded sub basins during the late jurassic syn rift phase surface rupturing in fault bounded sub basins resulted in the formation of tectonic scarps from which footwall derived gravity flows were sourced in contrast the diapir bounded bombarral alcobaca sub basin evolved as a distal bowl shaped depocentre with an axis located up to 10 km away from its basin margins low gradient marginal slopes developed in the bombarral alcobaca sub basin during the late jurassic rifting while growing salt pillows limited the vertical propagation of basement normal faults differences in tectonic evolution basin physiography and sediment input are the main factors responsible for the distinct sedimentary evolutions recorded in the study area 1 transverse footwall derived sediment fans predominant in fault bounded regions give place to axial southwards prograding fluvial to shallow marine units in the diapir bounded sub basins 2 growing salt pillows absent in the fault bounded sub basins formed barriers to and limited the development of transverse drainage systems

observed cyclone anticyclone tropopause vortex asymmetries relatively little is known about coherent vortices near the extratropical tropopause even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues through an objective census of observed tropopause vortices the authors test a hypothesis regarding vortex merger asymmetry where cyclone pairs are repelled and anticyclone pairs are attracted by divergent flow due to frontogenesis emphasis is placed on arctic vortices where jet stream influences are weaker in order to facilitate comparisons with earlier idealized numerical simulations results show that arctic cyclones are more numerous persistent and stronger than arctic anticyclones an average of 15 cyclonic vortices and 11 anticyclonic vortices are observed per month with maximum frequency of occurrence for cyclones anticyclones during winter summer there are are about 47 more cyclones than anticyclones that survive at least 4 days and for longer lifetimes 1 day survival probabilities are nearly constant at 65 for cyclones and 55 for anticyclones mean tropopause potential temperature amplitude is 13 k for cyclones and 11 k for anticyclones with cyclones exhibiting a greater tail toward larger values an analysis of close proximity vortex pairs reveals divergence between cyclones and convergence between anticyclones this result agrees qualitatively with previous idealized numerical simulations although it is unclear to what extent the divergent circulations regulate vortex asymmetries