simulating migrated and inverted seismic data by filtering a geologic model the simulation of migrated and inverted data is hampered by the high computational cost of generating 3d synthetic data followed by processes of migration and inversion for example simulating the migrated seismic signature of subtle stratigraphic traps demands the expensive exercise of 3d forward modeling followed by 3d migration of the synthetic seismograms this computational cost can be overcome using a strategy for simulating migrated and inverted data by filtering a geologic model with 3d spatial resolution and angle filters respectively a key property of the approach is this the geologic model that describes a target zone is decoupled from the macrovelocity model used to compute the filters the process enables a target orientedapproach by which a geologically detailed earth model describing a reservoir is adjusted without having to recalculate the filters because a spatial resolution filter combines the results of the modeling and migration operators the simulated images can be compared directly to a real migration image we decompose the spatial resolution filter into two parts and show that applying one of those parts produces output directly comparable to 1d inverted real data two dimensional synthetic examples that include seismic uncertainties demonstrate the usefulness of the approach results from a real data example show that horizontal smearing which is not simulated by the 1d convolution model result is essential to understand the seismic expression of the deformation related to sulfate dissolution and karst collapse

multiphase petrography of volcanic rocks using element maps a method applied to mount st helens 1980 2005 quantitative textural analyses including crystal size distributions csds provide insights into crystallisation kinetics of magmatic systems investigations of volcanic crystal textures often rely on greyscale variations on backscattered electron images to identify crystal phases which must then be thresholded and or traced manually a laborious task and investigations are typically restricted to a single crystal phase a method is presented that uses energy dispersive x ray element maps to generate textural data each pixel is identified as a crystal phase glass or vesicle according to relative chemical composition enabling concurrent acquisition of multiphase csd crystallinity and mineral mode data data processing is less time intensive for the operator but considerable instrument time is required to generate element maps the method is applied to 17 dacite samples from the 1980 1986 and 3 from the 2004 2005 eruptive periods of mount st helens volcano usa to provide quantitative insights into multiphase textural evolution all of the csds are curved and concave up in the standard csd plot with curvature increasing with plagioclase content to facilitate comparisons with previous studies csds for microlites 50 m length crystals are approximated as straight lines the line intercepts and slopes provide information on n 0 nucleation density and characteristic length or g the product of growth rate g and residence time respectively these parameters as well as the total groundmass crystallinity show distinct differences between explosive deposits from summer 1980 and post summer 1980 domes post summer 1980 microlite n 0 values are mostly at the lower end of the range of those measured for summer 1980 samples total groundmass crystallinities during summer 1980 are between 10 and 30 vol whereas post summer 1980 crystallinity increases to between 39 and 51 vol the range of n 0 values is similar to those previously published for mount st helens but g is consistently higher g of a may 1985 sample analysed in this study is approximately 2 m higher compared with previously published data for the same sample when processed using similar methodologies groundmass crystallinity data show similar trends to those previously published for the 1980 to 1986 eruption increasing sharply after summer 1980 then increasing more gradually during the dome building phase of the eruption the effects of varying l the apparent crystal size and crystal aspect ratio on resultant csds are also investigated whilst relative temporal variations in csds for a given dataset can be investigated absolute values from different studies cannot be compared unless methods of data acquisition and processing are exactly the same

sequence stratigraphy of source rocks applied to the study of the kim meridgian tithonian in the north west european shelf dorset uk yorkshire uk and boulonnais france abstract in dorset and yorkshire england the sedimentation of kimmeridgianfrithonian age mutabilis to pallasioides zones shows ordered organic sequences the distribution of the organic matter content per cent total organic carbon petroleum potential hydrogen indices is not random but occurs as widespread primary organic rich cycles nested within each other these organic rich cycles with thicknesses of about 0 5 m show regular variations in organic carbon contents reaching a maximum value midway through the cycle they formed in response to widespread phenomena and can be correlated over long distances the cycles were deposited in marine environments mainly below the storm wave base they show little sedimentological evidence of sea level fluctuation either transgression or regression in the boulonnais france a more proximal setting the comparable strata show a greater lithological contrast and depositional environments corresponding to bathymetric changes are more easily determined a comparison of the distribution of organic matter through the sequence dated by ammonites in the three areas studied shows a good correlation between the distal dorset and yorkshire and the proximal boulonnais areas the main result of the biostratigraphic revision in the boulonnais france concerns the argiles de ch tillon which can be subdivided into two members these belong to the autissiodorensis zone autissiodorensis subzone and the gigas elegans zone respectively thus the kim meridgian tithonian boundary is located within this formation transgression does not appear to be the main factor determining the accumulation of autochthonous organic matter type ii not every major transgressive facies change seen in the kimmeridgian tithonian of the boulonnais is characterized by an enrichment in organic matter in the basinal area good source rocks with high petroleum potentials result from a conjunction between the physiography the transgression and the climate this last causes the variations in primary productivity which produce the organic rich cycles transgressions act mostly to reveal the climatic variations they are a necessary condition for the accumulation of the autochthonous organic matter but they are not sufficient by themselves as demonstrated by the transgressions in the autissiodorensis and elegans zones in the first instance the strata are depleted in organic matter in both the distal and proximal areas in the second instance type ii organic matter accumulated in both distal and proximal environments the vertical fluctuations in the total organic carbon contents the types of organic matter and the petroleum potentials of the organic rich cycles determine the oil potentials of transgressive sequences in sedimentary basins

vesiculation and microlite crystallization induced by decompression a case study of the 1991 1995 mt unzen eruption japan isothermal decompression experiments were performed to simulate magma ascent at unzen volcano from the depths of magma storage to shallow crustal levels corresponding to pressure decrease from 300 to 50mpa a partially crystallized synthetic rhyodacitic magma representing equilibrium conditions at 8508c and 300mpa was used as a starting material this has a composition identical to the groundmass of unzen rocks erupted in 1991 1995 decompression rates were varied from 0 0002 to 20mpa s experiments conducted with decompression rates 0 1mpa s 1 were decompressed continuously a multi step decompression approach was used at decompression rates 0 1mpa s the experiments were fluid saturated either containing only water as a fluid component h2o bearing or containing a water and carbon dioxide mixture h2o co2 initial mole fraction of h2o in the fluid 0 6 the experimental products of the h2o bearing experiments consist of amphibole pyroxenes oxides and glass plagioclase microlites nucleated and grew only in experiments with the two lowest decompression rates of 0 0005 and 0 0002mpa s the length of those plagioclases is up to 200 250 mm which is consistent with the size of plagioclase microlites observed in the natural samples the experimental products of the h2o co2 bearing system are composed of pyroxenes oxides glass and plagioclase plagioclase microlites in the h2o co2 system were already present in the starting assemblage and grew to a maximum size of 80 mm equilibrium concentrations of water in the residual glasses at the final pressure of 50mpa are reached at decompression rates 1mpa s 1 for the h2o co2 bearing system and 0 1mpa s 1 for the h2o bearing system the bubble number density bnd values range from 10 to 10 mm 3 in the h2o bearing system and from 10 4 6 to 10 mm 3 in the h2o co2 bearing systems in both systems bnd values decrease with decreasing decompression rate from 20 to 0 01mpa s and increase with decreasing decompression rates50 01mpa s which is interpreted to reflect predominant bubble growth and bubble nucleation respectively the onset of crystallization observed from changes in the chemical composition of the residual melt occurs at decompression rates 50 1mpa s at the lowest decompression rate 0 0002mpa s the chemical composition of the residual melt in the h2o co2 bearing system becomes similar to the natural matrix glass composition there is no significant variation of the microlite number density mnd value as a function of the decompression rate the mnd values for plagioclases only range from 10 to 10 mm whereas the mnd values for the other phases range from 10 to 10 mm our experimental mndpl values are in the range of those from natural samples 10 10 mm we show that the size of microlites nucleating and crystallizing during decompression plagioclase in our experimental dataset is useful to constrain magma ascent rates at the onset of the crystallization of the corresponding phase based on the size of plagioclase microlites and on the composition of the residual melts the average magma ascent rates of unzen magmas in the pressure range 200 to 50mpa is estimated to be 10 50 m h

field and seismic images of sharp based shoreface deposits implications for sequence stratigraphic analysis abstract sharp based shoreface sandstones are of considerable interest because of their potential as hydrocarbon reservoirs and because they play an important role in the stratigraphic analysis of basin fills the sharp based shoreface sandstones studied herein are upper jurassic kimmeridgian tithonian and exposed along the coastal cliffs of the dover strait in northwestern france these series consist of tens of meter thick alternations of sandstones bodies and organic rich shales that can be correlated for over 30 km along coastal cliff exposures and tied to high resolution ca 1 m of sediment marine seismic profiles obtained several hundred meters offshore the units described here comprise two sharp based sandstone bodies each is composed of a basal progradational set of shoreface parasequences overlain by a progradational aggradational shoreface succession each sharp based sand body lies on a marine regressive surface of erosion and is truncated by a marine transgressive surface of erosion which in turn is overlain by a thin retrogradational ravinement lag or coarse grained planar laminated bedset the two progradational packages are separated by a third surface a subaerial exposure surface that is interpreted as a sequence boundary two distinct types of seismic units referred to as type a and type b have been identified in the study area seismic unit a has conformable upper and lower boundaries and parallel aggradational configurations seismic unit b is characterized by downlap and toplap boundaries and simple or compound sigmoid and oblique tangential progradational configurations a single sharp based shoreface sandstone body makes up the type b unit and typically consists of two compound superimposed progradational sets b1 b2 the lowermost set b1 corresponds in the field to the progradational set sensu stricto whereas b2 corresponds to a progradational aggradational set b1 and b2 are separated in outcrop by a sequence boundary these observations led us to reevaluate the sequence stratigraphic interpretation of sharp based shoreface sandstones it is proposed here that complete single sharp based shoreface sandstones bodies can be separated into two different systems tracts 1 a progradational set b1 seismic body at the base which corresponds to the forced regressive wedge systems tracts frwst of hunt and tucker 1992 and 2 a progradational aggradational set b2 at the top above the sequence boundary which corresponds to the lowstand systems tract lst of posamentier et al 1992 a complete sharp based shoreface sandstone body is bounded below the frwst by a regressive surface of marine erosion caused by the downward shift of wave base and by a transgressive surface of marine erosion or ravinement surface at the top of the lst

the 1995 1998 eruption of the soufriere hills volcano montserrat wi eruption of the soufriere hills volcano began on 18 july 1995 after three years of elevated seismic activity four months of increasingly vigorous phreatic activity culminated in mid november 1995 with the initiation of dome growth growth rates increased unevenly through early march 1996 with fluctuations on time scales from hours to months since march 1996 gravitational collapse of the unstable dome flank has affected an ever increasing area with pyroclastic flows surges and ashfalls major collapse of the eastern flank on 17 september 1996 resulted in a sub plinian explosive eruption later that day by february 1997 the dome had outgrown the confines of the crater and begun to spill into the surrounding valleys a large collapse on 25 june 1997 caused pyroclastic flows and surges on the northern flanks and resulted in the only deaths of the eruption in august september and october 1997 vulcanian explosions followed further collapses on the western and northern flanks the largest event of the eruption occurred on 26 december 1997 with failure of the southwestern flank of the volcano producing a debris avalanche and large dome collapse pyroclastic flows dome growth ceased in early march 1998 but residual volcanic activity has continued and consists of ash venting mild explosions and dome collapse pyroclastic flows

crystal size distribution in magmatic rocks proposition of a synthetic theoretical model the crystal size distribution csd corresponds to the number of crystals of a mineral per unit volume within a series of defined size intervals many crystal size distributions in igneous systems are straight lines when plotted on the classical diagram of ln population density versus size other common csds are concave down on such graphs for the low size values the effect of growth rate on csds seems to be small and nucleation apparently increases exponentially with time although magmatic systems are always multiphase only a few csd studies deal with several phases on the basis of the few available published examples it seems that the parallelism defined as y spacing constancy of the normalized csds i e where the crystal lengths are normalized to the greatest length for each phase is a common feature in igneous systems the aim of our modelling is to propose a mathematical framework to unify the csd typology to explain the common occurrence of straight lines on the classical csd diagram and the y spacing constancy of the normalized csds for multiphase rocks and also to provide a convenient tool to easily test petrogenetic scenarios through efficient computer simulations the bulk balance modelling is based on a square matrix having for coefficients the number of nuclei of one phase by the crystallized volume of another phase this interaction matrix is the mainspring of our csd modelling which requires straightforward assumptions about the uniformity of crystal shape and growth 1 at each time every crystal of a phase has the same shape and 2 the one dimensional growth rate of a crystal is independent of its size consequently the values of the normalized csd are linked together by means of an integral equation for the most part the behaviour of the csds theoretically obtained with a constant matrix may also be observed in computer simulations of more general cases this extended approach makes feasible the application of the model to natural cases concave down shapes for the lowest size are classically interpreted as a consequence of the ending of crystallization by roughly taking into account crystal interactions during the growth process through the concept of mean clutter we successfully simulate such concave down csds

storm induced concentration of sulfurized marine origin organic matter as a possible mechanism in the formation of petroleum source rock abstract black shales though laminated are not systematically synonymous with quiet conditions of deposition a number of papers report about black shales yielding sedimentary structures echoing relatively high hydrodynamic conditions here we examine two sedimentary sequences pertaining to the late jurassic argiles de ch tillon formation of the boulonnais area northernmost france each of them including a meter thick black shale horizon the two laminated black shales contain sulfurized i e organic s rich organic matter reaching a maximum of 9 however some differences set the two black shales apart the lower one was deposited under calm suboxic to anoxic bottom water conditions the classic way the upper black shale was deposited under oxic agitated bottom water conditions not compatible with stable sulfidic conditions required for organic matter sulfurization the upper black shale experienced hydrodynamically induced concentration of sulfurized recalcitrant organic matter of marine origin the sulfurized organic matter could be preserved and quantitatively accumulated owing to its non putrescible nature leading to the formation of a potential hydrocarbon source rock the association of pyrite inclusions with sulfurized organic matter probably modified the hydrodynamic behavior of organic particles the storm induced remobilization and concentration of sulfurized organic matter implies that the sulfurization factory operated in proximal shallow environments such as estuaries mud flats or mangrove environments such a model is in agreement with findings from modern coastal shelf environments notably mangroves and fully transposable to many other sedimentary situations of any geological time period

fuzzy models for analysis of rock mass displacements due to underground mining in mountainous areas the displacement and deformations of rock mass due to underground mining has often resulted in major disasters throughout the world frequently inflicting heavy losses of life and damage to property and these disasters have motivated the development of rock mass mechanics the prediction of displacement of rock mass and their surface effects is an important problem of the rock mass mechanics in the excavation activities especially the coal and metal mining in mountainous areas based on results of the statistical analysis of a large amount of measured data in mining engineering the fundamental fuzzy model of displacements and deformations of rock mass is established by using the theory of fuzzy probability measures the theories of both two and three dimensional problems are developed and applied to the analysis of engineering problems in excavation and underground mining in mountainous areas the agreement of the theoretical results with the field measurements shows that our model is satisfactory and the formulae obtained are valid and thus can be effectively used for predicting the displacements and deformations and the safety evaluation of the buildings on the ground

controls on acoustic properties of upper jurassic siliciclastic rocks boulonnais northern france more than 200 plugs from outcrop and a nearby borehole in a carbonaceous siliciclastic interval of late jurassic kimmeridgian to tithonian age were quantitatively analyzed for texture mineralogy and acoustic properties our primary goal was to study the effect of clay fraction smaller than 8 m silt sand fraction larger than 8 m and carbonate on the acoustic properties the quantitative nature and volume of the data made it possible to observe four dimensional relationships in contoured ternary diagrams primary control on the acoustic properties is exerted by porosity but the trend of this relationship significantly deviates from popular velocity transforms the contribution of clay silt sand and carbonate particular material and cement explains the remaining variation in acoustic properties although no clear linear thresholds are defined a general trend is that clay and carbonate content have opposite and overlapping effects on acoustic properties the influence of clay content progressively increases with decreasing carbonate content and visa versa with increasing carbonate content the variation of acoustic velocity at a given porosity value increases to nearly twice of that in the clay dominated sediment traditional classification boundaries are present but strongly overprinted by this interplay between clay and carbonate this study may have important implications for porosity and lithofacies prediction from wireline logs in similar mixtures of sediment in addition the quantitative character of the textural and mineralogical data may provide a direct link from acoustic properties to the primary depositional system and sequence stratigraphy

temporal development of prograding beach shoreface deposits the holocene of kujukuri coastal plain eastern japan abstract prograding beach foreshore deposits with a basal ravinement bed are recognized from detailed ams 14c dating and grain size analyses of holocene deposits of the kujukuri coastal plain facing the pacific coast of japan the holocene deposits are about 20 m thick and consist of an upward shoaling beach foreshore succession that has a basal unconformity overlain by a thin layer of relatively coarse sand the unconformity is a downlap surface which originated from a ravinement surface the overall succession was formed by a prograding beach foreshore system during the highstand in sea level of the last 6000 years poorly preserved fossil shells enclosed in the thin layer of coarse sand at the base of the succession date from the transgressive stage in sea level before 6000 cal yr bp grain size distribution patterns are polymodal in the basal sand layer and unimodal in the remainder of the succession modal classes of the basal part are fine 3 3 2 6 medium 2 3 1 8 and coarse 1 2 1 0 the fine mode and the unimodal grain sizes define an overall upward coarsening trend which correlates with the upward shoaling succession in contrast the medium and coarse modes are restricted to the basal sand and are interpreted as related to the ravinement process the thin basal sand layer an admixture of these modal classes is interpreted as a type of ravinement deposit preserved during sea level highstand no transgressive deposit was preserved on the ravinement surface because sediment supply was so small that the sediment on this surface experienced thorough reworking by storm waves

comparison between high resolution seismic and sequence stratigraphic approaches applied to the upper jurassic deposits of the dover strait area northern france abstract this study is an attempt to interpret very high resolution seismic data usually devoted to shallow marine surveys in terms of very high resolution seismic and sequence stratigraphy at the scale of the reservoir seismic data are compared with outcrop based observations in order to discuss the geometrical relationships between rock bodies and the nature of the seismic reflections in terms of seismic facies related to type lithologies two high resolution seismic surveys using a sparker were performed in the dover strait area some 100s of metres away from the boulonnais coastal cliffs the aim was to look to the 130 m thick mixed siliciclastic carbonate deposits of upper jurassic age kimmeridgian tithonian cropping out at the sea floor and to compare them to the coastal cliffs exposures the 100 m apart seismic profiles exhibit a 100 m deep penetration and 1 m in vertical resolution upper 30 ms part of the profiles four seismic facies are recognised on the seismic profiles they comprise ten seismic units which can be grouped into three broad families group 1 has a parallel aggradational reflection configuration and conformable boundaries which may correspond to the transgressive and highstand systems tracts the seismic facies exhibit either a high continuity high amplitude corresponding to clayey mudstone lithologies of the mid ramp environment or a high continuity low amplitude corresponding to shaly lithologies of the outer ramp environment group 2 has a sigmoid progradational reflection configuration bounded at the base by a downlap surface and at the top by a toplap surface these boundaries correspond respectively in the field to a marine regressive surface of erosion and a marine transgressive surface of erosion the seismic facies is cross layered and exhibits a moderate continuity low to moderate amplitude and moderate frequency group 2 corresponds to the bioclastic sand prone facies of the inner ramp environment it is interpreted as lowstand sharp based shorefaces group 3 exhibits a progradational complex to chaotic configuration it lies on an erosional unconformity with paleogullies the seismic facies shows discontinuous reflections with moderate amplitude and high to moderate frequency it corresponds in the field to cross bedded sandstones in channel fill arrangements of fluvial origin wealdian deposits marking the top of the section the different systems tracts sequence boundaries and depositional sequences identified onshore can be recognised as well on the seismic profiles but the comparison demonstrates that seismic data complement the onshore sequence stratigraphic analysis by providing the geometrical relationships between systems tracts onlap downlap toplap that cannot be observed onshore the maximum flooding surfaces however present no specific seismic signature on such a low angle ramp profile it can only be identified precisely in the field which also help to relate lithologies to seismic facies this study represents one of the first attempts to interpret very high resolution seismic data at the outcrop scale it will be improved again in the future by the collection of impedance logs and synthetic seismic traces from cored sections on the coastal cliffs for comparison with the seismic data

a crystal size distribution study of the kiglapait layered mafic intrusion labrador canada evidence for textural coarsening crystal size distributions csd of plagioclase olivine and clinopyroxene from the kiglapait intrusion labrador were measured for a series of 13 samples spanning most of the exposed intrusion all csds lack small crystals and are slightly curved to the right concave up all csds of a mineral sweep out a fan as expected where there is relatively little variation in phase proportion csd dispersion can be replicated using the communicating neighbours model of textural coarsening ostwald ripening most of the textural variation in the intrusion is the result of variable degrees of coarsening it is proposed that coarsening occurred in the outer part of the crystallisation boundary layer where release of latent heat and changes in the intercumulus liquid composition resulted in a reduction in undercooling suppression of nucleation and coarsening particularly coarse grained areas reflect focusing of circulating magmatic fluids during coarsening the effects of crystal settling were not observed in the csds even within single well developed layers they were probably concealed by the pervasive textural coarsening csds do not suggest that mechanical compaction has played an important role in the formation of texture although it is very likely to have occurred however samples from the lower part of the intrusion show textural evidence of pressure solution compaction

quartz silt in mudrocks as a key to sequence stratigraphy kimmeridge clay formation late jurassic wessex basin uk sequence stratigraphic interpretation of mudrocks is often carried out using proxy indicators for grain size or by consideration of other aspects of lithology thought to relate to sea level change such as organic matter content an alternative stratigraphic analysis based on direct estimation of quartz silt content was carried out on a major late jurassic mudrock and oil source rock the kimmeridge clay formation of the wessex basin dorset uk the new data generated by backscatter sem x ray and image analysis show decametrescale stratigraphic patterns that are incompatible with many previous sequence stratigraphic interpretations based on gamma ray logs or visual lithofacies and biofacies description correlation with a basin margin section in the boulonnais northern france indicates that silt rich intervals in basinal facies are coeval within the limits of biostratigraphic resolution with shallow water sand rich packages on the margin variation in silt content in the kimmeridge clay therefore appears to be a record of relative sea level change of at least regional extent it is suggested that analysis of silt content offers the most reliable basis for generation of a regional sequence stratigraphy in basinal mudrocks a revised relative sea level curve for the wessex basin kimmeridgian and early tithonian is presented based on this premise

mineral lamination development in layered gabbros of the british palaeogene igneous province a combined anisotropy of magnetic susceptibility quantitative textural and mineral chemistry study mineral lamination development in layered gabbros of the british palaeogene igneous province a combined anistotropy of magnetic susceptibility textural and mineral chemistry study

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization crystal size distributions csds measured in metamorphic rocks yield quantitative information about crystal nucleation and growth rates growth times and the degree of overstepping t of reactions during metamorphism csds are described through use of a population density function n dn dl where n is the cumulative number of crystals per unit volume and l is a linear crystal size plots of ln n vs l for olivine pyroxene and magnetite in high temperature 1000 c basalt hornfelses from the isle of skye define linear arrays indicating continuous nucleation and growth of crystals during metamorphism using the slope and intercept of these linear plots in conjunction with growth rate estimates we infer minimum mineral growth times of less than 100 years at t 10 c and nucleation rates between 10 4 and 10 1 cm3 s garnet and magnetite in regionally metamorphosed pelitic schists from south central maine have csds which are bell shaped we interpret this form to be the result of two processes 1 initial continuous nucleation and growth of crystals and 2 later loss of small crystals due to annealing the large crystals in regional metamorphic rocks retain the original size frequency distribution and may be used to obtain quantitative information on the original conditions of crystal nucleation and growth the extent of annealing increases with increasing metamorphic grade and could be used to estimate the duration of annealing conditions if the value of a rate constant were known finally the different forms of crystal size distributions directly reflect differences in the thermal histories of regional vs contact metamorphosed rocks because contact metamorphism involves high temperatures for short durations resulting csds are linear and unaffected by annealing similar to those produced by crystallization from a melt because regional metamorphism involves prolonged cooling from high temperatures primary linear csds are later modified by annealing to bell shapes

environmental cycles in the late jurassic northwest european epeiric basin interaction with atmospheric and hydrospheric circulations abstract despite the large size and the heterogeneity of the northwest european late jurassic kimmeridgian lower tithonian epeiric basin the sedimentary environment was rather uniform in general deposition of mudstones and the microlaminated organic rich sediments took place under low oxic to anoxic conditions detailed environmental analysis clearly points to a seasonal alternation of aerobic with anaerobic conditions in substrate and bottom water resulting in one year life cycles in the benthic environment the widespread uniformity of facies and the seasonal alternation in the oxygen budget of the benthic environments are best explained by a summer to winter change in the atmospheric circulation of the northern hemisphere this change strongly influenced the oceanographic situation in the northwestern european epeiric basin superposed on this one year cyclicity three more hierarchical levels of cycles are stratigraphically recorded they reflect a complex history of orbital forced and non orbital forced climatic changes and or eustatic sea level fluctuations in the late jurassic

between beds and sequences stratigraphic organization at intermediate scales in the quaternary of the virginia coast usa stratigraphy presupposes a hierarchy of scales of spatial organization supplemented at the small scale end by sedimentological concepts beds bed sets and bed cosets and at larger spatial scales by sequence stratigraphic concepts systems tracts parasequences sequences between these two end members are intermediate sclae bodies described as lithofacies or simply facies a more restricted concept granulometric facies can be described in terms of horizontal grain size gradients facies change and cvclic vertical grain size gradients stratification assemblages of facies so defined also called depositional systems are not random loot occur in a limited suite of patterns such assemblages may be linked to two classes of bounding surfaces a source diastem the immediate source of the sediment and a surface of closure if preserved between which is sandwiched a transgressive or regressive basinward fining facies succession systems bounding surfaces are notably more continuous than internal gradational facies boundaries by thus restricting the definition of a facies assemblage depositional system it is possible to describe the quaternary of the virginia coast wish as few as 12 systems depositional systems in the quaternary of the virginia coast are allometric in that any system can be derived from any other by plastic expansion of one or more facies relative to another or by simple symmetry operations self similarity prevails across this intermediate scale of stratigraphic organization facies assemblages depositional systems consist of event beds which themselves have erosional basal boundaries and internal successions of microfacies at larger spatial so ales depositional systems are repeated either autocyclic repetitions forced by processes within the basin of deposition or allocyclic repetitions as parasequences and high frequency sequences in the virginia quaternary systems architecture is compatible with sequence architecture and nests conformably within its framework but analysis of systems architecture reveals rules beyond those governing sequence architecture

crystallization and textural evolution of a closed system magma chamber insights from a crystal size distribution study of the lilloise layered intrusion east greenland the recognition that postcumulus processes significantly modify primary textures in layered mafic intrusions has thrown into question many early observations on which classical crystallization theories are based petrographic observations combined with quantitative textural analysis of samples from various stratigraphic levels of the lilloise intrusion east greenland demonstrate that postcumulus textural modification of cumulates formed during the solidification of a closed system magma chamber may be detected crystal size distribution csd measurements of lilloise cumulates and the resulting csd profiles are compared to predicted theoretical closed system csd profiles similarities between the measured csd profiles and published predicted csd profiles support lilloise magma evolving in a closed system chamber and indicate that primary crystallization processes can be distinguished using quantitative textural techniques textural coarsening driven by syn magmatic deformation is suggested to be the dominant postcumulus process affecting csd plot morphology csd slope values and profiles plot shapes remain relatively constant for a given liquidus mineral particularly olivine and clinopyroxene so that the number of phases on the liquidus at any one time affects mineral modal abundances as a result csds generally exhibit overall smaller grainsizes and progressively lower nucleation densities at higher levels in the intrusion

sequence analytical approach to the upper kimmeridgian lower tithonian storm dominated ramp deposits of the boulonnais northern france a landward time equivalent to offshore marine source rocks an interdisciplinary approach based on high resolution physical stratigraphy biostratigraphy organic matter analysis and clay mineralogy has been applied to the mixed siliciclastic carbonate kimmeridgian tithonian deposits of the boulonnais north western france these rocks are the age equivalents of some of the offshore marine source rocks of the north sea and were deposited in an overall storm dominated homoclinal ramp setting which may represent one of the most shore proximal sediments of this age cropping out in north western europe comparison with data from the yorkshire dorset lorraine and aquitaine areas allows the discrimination of three major transgressive regressive sediment packages with disconformities of interregional extent 1 from the baylei zone to top eudoxus zone 2 from the autissiodorensis zone to base scitulus zone 3 from the upper scitulus zone to the pectinatus zone the lower two regionally correlative disconformities correspond to the sequence boundaries at the top of the eudoxus zone and the top of the autissiodorensis zone formed by high frequency relative sea level variations during the periods of maximum transgression of the platform the latter disconformity the p1 nodule bed reflects a major tectonically induced reorganization of the north west european intrashelf sedimentary basin characterized by a shift in both the location of the main depocentre and the sources of sediment production

a refined technique for measuring crystal size distributions in thin section log normal size distributions are of the form n noe l where n number density l crystal length and is a constant a method for measuring three dimensional log normal crystal or grain size distributions csds in thin section has been deduced from computer experiments in which 2d sections were cut through assemblages of 3d solids the size ranges and distributions studied were appropriate for igneous microphenocryst to megacryst populations conversion from 2d to 3d is based on an exact correction for spheres of uniform diameter cumulate numbers of polygons with length l n2d are converted to n3d by the equation ln n3d ln n2d l s ln l s the number density is then obtained as n dn dl the parameters s and correct the measured lengths and no no number density at l 0 respectively and are functions of crystal shape the parameter is a weak function of the degree of spatial orientation of the crystals highly symmetrical shapes such as cubes octahedra and elongated prisms can be accurately measured when randomly oriented however rectangular solids with a b c cannot be accurately measured because they produce bimodal length distributions in cross section strongly oriented textures trachytic or lineated can be accurately measured regardless of crystal shape new csd data from alkaline rocks and a kimberlite give examples of csds modified by megacryst retention xenocryst addition phenocryst accumulation and groundmass nucleation

parameters controlling sonic velocities in a mixed carbonate siliciclastics permian shelf margin upper san andres formation last chance canyon new mexico we have measured the acoustic properties and mineralogic composition of 48 rock specimens from mixed carbonate siliciclastic outcrops of the permian upper san andres formation in last chance canyon new mexico the goals were 1 identify and model the parameters controlling the sonic velocities 2 assess the influence of postburial diagenesis on the acoustic velocities the variation in sonic velocity in the 0 to 25 porosity range is primarily controlled by porosity and secondly by the ratio of carbonate siliciclastic material linear multivariate fitting resulted in a velocity porosity carbonate content transform that accurately predicts sonic velocity at different effective stresses the slope of the velocity porosity transform steepens with increasing carbonate content which may be explained by the higher velocity of carbonate minerals another reason may be the property of carbonate minerals to form more perfect intercrystalline boundaries that improve the transmission properties of acoustic waves and are less sensitive to changes in effective stress the velocity ratio vp vs is an excellent tool to discriminate between predominantly calcitic lithologies ratio between 1 8 and 1 95 and predominantly dolomitic and quartz rich lithologies ratio between 1 65 and 1 8 gardner s experimental curve overestimates and the velocity porosity transforms by wyllie and raymer underestimate the observed sonic velocities probably because they do not account for variations in texture carbonate mineralogy and pore geometry petrographic observations show that postburial diagenesis is minor and does not seem to significantly affect porosity therefore the outcrop data set can be regarded as a proxy for the subsurface analog these findings underline the significantly more complex acoustic behavior in mixed carbonate siliciclastic sedimentary rocks than in pure siliciclastics where mineralogic composition explains most of the observed relationships between porosity and sonic velocity

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

three magmatic components in the 1973 eruption of eldfell volcano iceland evidence from plagioclase crystal size distribution csd and geochemistry abstract the 1973 eruption of eldfell volcano iceland appears to have been a short simple event but textural and geochemical evidence suggest that it may have had three different magmatic components the first erupted fissure magmas were chemically evolved rich in plagioclase 18 and had shallow straight crystal size distribution csd curves the early lavas were less evolved chemically had lower plagioclase contents 13 and steeper slightly concave up csds the late lavas were chemically similar to the early lavas but even richer in plagioclase than the initial magmas 24 and had the steepest csds there was no chemical evidence for plagioclase fractionation but compositional diversity could be produced by clinopyroxene fractionation which must have occurred at depth we propose that the eruption started with old coarsened ostwald ripened magma left over from a previous eruption possibly that which produced surtsey island ten years earlier the early flows may be mixtures of small amounts of this old magma with a new low crystallinity uncoarsened magma or a completely new magma the late flows are another new magma from depth chemically similar to the early flows but which has grown plagioclase under increasing saturation undercooling perhaps during its ascent all three magmatic components may have originated from the same parent but had varying degrees of clinopyroxene fractionation plagioclase nucleation and growth and coarsening

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

modelling holocene stratigraphy and depocentre migration of the volga delta due to caspian sea level change the volga system is sensitive to allogenic control due to its low on and offshore gradient similar to 5 cm km in sequence stratigraphy little attention has been paid to the effects of sea level change in these ramp margin fluvio deltaic settings the high frequency sea level changes of the caspian basin have considerable amplitude up to 18 m over the holocene time span which is usually considered as the lower boundary of fifth order cycles a process response model aquatellus has been used to investigate fluvio deltaic response to sea level fluctuation calibration of the model with measured data over the last century comprising a full 3 m sea level cycle showed plausible progradation and sedimentation rates the numerical modelling showed that sea level changes forced the holocene volga delta to migrate similar to 200 km over the caspian plain leaving only thin laterally extensive deposits the frequent depocentre shifts add a whole new perspective to the ongoing discussion about the impact of sea level changes along the longitudinal profile the periods during which significant deposition occurred coincide with the times that migration distances were relatively low thicker progradational wedges have been deposited at these time intervals at similar to 9000 8000 similar to 7400 6700 similar to 5200 3700 and similar to 2400 900 years bp c 14 dated deposits in the lower delta plain area corroborate the model output remarkably this is both in highstand and lowstand conditions the low gradient makes wave effects insignificant and tides are nonexistent so that the fluvial deposits are hardly reworked and no shoreface facies or maximum flooding surface develop the volga delta response indicates that sequence stratigraphic concepts are not scale independent in low gradient settings and that short term high frequency sea level changes have a far reaching impact on the stratigraphy c 2002 elsevier science b v all rights reserved

acoustic properties of ancient shallow marine carbonates effects of depositional environments and diagenetic processes middle jurassic paris basin france abstract examination of petrophysical properties acoustic velocity porosity permeability and density and petrographical characteristics texture facies composition and diagenesis of more than 250 core plugs from the middle jurassic carbonates of the eastern paris basin provides insights into the parameters controlling acoustic velocities in relatively low porosity carbonate rocks 20 the pore type observations reveal distinct acoustic velocities in samples with intergranular macropores and samples with micropores in subhedral micrite such that velocities in microporous mudstone wackestone lagoonal deposits are greater than in macroporous grainstone shoal samples at a given porosity range 15 20 the standard wyllie and raymer transforms fit very well with the linear regression between acoustic velocity and porosity from mudstone or lagoonal facies marls and fine grained deposits interpreted as lagoonal facies include statistically significant correlation r 0 9 between velocity and porosity however the data suggest that the wide scatter in velocity porosity relationship from grainstones are not the result of different sorting grain size pore type dolomite content or clay content instead early cementation greatly influences acoustic properties during diagenesis and are interpreted to account for the high variability of velocities over a given porosity range specifically at a given porosity acoustic velocities in compacted grainstone that did not undergo early cementation are higher than in early cemented grainstone petrographic observations suggest that early cementation limits mechanical compaction creating a heterogeneous medium from the earliest stages of diagenesis non touching grains preservation of intergranular macropores that are partially to totally filled by later blocky calcite cement the abundant interfaces between micritized ooids early cement fringes and blocky calcites in grainstones may induce significant wave attenuation as a result the standard time average equations fail to predict the effect of diagenetic features such as early cementation on sonic velocity conversely an absence of early cementation favors mechanical compaction grain to grain contact and suturing the result is a homogeneous micritized grain supported network that may facilitate wave propagation through demonstration of the key role of early cementation in the explanation of variability in acoustic properties the results of this study illustrate the complicated factors influencing velocity transforms in carbonates wyllie and raymer i e classical tools for predicting reservoir properties these insights on the interpretation of vp and the refinement of velocity porosity transforms in grainstone units may be broadly applicable to enhancing seismic based exploration in carbonate successions

geochemistry of early carbonate cements in the cardium formation central alberta abstract authigenic minerals and diagenetic textures in the marine conglomerates and sandstones of the cretaceous cardium formation in the northeast pembina area preserve a complex sequence of diagenetic events textural relationships observed in thin section and under the scanning electron microscope were used to determine the relative timing of diagenetic events in these marine sediments paragenetic sequences are similar for the conglomerate sandstone and siderite nodules in the enclosing shales extensive cementation by siderite and calcite occurred early in the diagenetic history before any significant compaction the geometry and distribution of lithofacies in the cardium may have influenced the diagenesis and internal stratigraphy of the conglomerate overlying shale matrix conglomerate may have trapped upward migrating fluids increased in buoyancy by dissolved co2 produced by decay of organic matter in the enclosing shales these fluids could have infiltrated the upper portion of open matrix conglomerate causing cementation petrographic evidence shows alternating precipitation of siderite and pyrite implying fluctuating activities of dissolved carbonate and hydrogen sulfide probably caused by bacterially mediated processes during early diagenesis early sequences of siderite and pyrite precipitation can be related to zones of iron reduction sulfate reduction and possibly decarboxylation during diagenesis carbon and oxygen isotopic data indicate a systematic change in the isotopic compositions of calcite and siderite from 25 to 3013c and 018o for cements early in the paragenetic sequence to 0 to 513c and 15 18o for cements which are interpreted to occur later in the paragenetic sequence this observation is consiste t with the influence of meteoric water on later stages of cement deposition in the cardium a unit considered to be marine and deposited well offshore on a shallow marine shelf the intrusion of meteoric water far offshore may be related to changes in sea level many variables must be accounted for but it is feasible using the estimated regional dip of the cardium at the time of deposition 0 005 for a 1 m drop in sea level to push the freshwater seawater interface seaward on the order of 100 km

black shales on the basin margin a model based on examples from the upper jurassic of the boulonnais northern france abstract organic rich shales were deposited during two phases of relative sea level rise in the kimmeridgian late jurassic basin margin sections of the boulonnais n france pyrite framboid analysis indicates that bottom waters were euxinic during substantial periods of organic rich shale formation and th u ratios and degree of pyritisation of fe suggest severe oxygen restriction whilst palaeoecological and sedimentological evidence suggests that seafloor oxygenation events were frequent interbedded hummocky cross stratified sandstones indicate deposition above storm wave base correlation of lateral facies changes reveals that the black shales record deposition beneath a nearshore zone of oxygen poor waters that contracted in lateral extent during parasequence formation the boulonnais black shales are similar to other varieties of transgressive black shale in that they are developed upon surfaces of marine starvation but they differ in that they pass down dip into better oxygenated facies they are therefore classified as transgressive nearshore tn black shales that do not record the feather edge of basinal conditions deposition is interpreted to have occurred beneath a small volume of sub thermocline bottom waters that were readily de oxygenated whilst anoxia was less readily developed in more offshore settings due to the greater volume of sub thermocline water why such conditions should pertain only during initial stages of base level rise remains obscure

crystal sizes in evolving silicic magma chambers crystal size distributions csds of quartz and zircon phenocrysts in individual pumice clasts from several voluminous ash flow tuffs provide a quenched snapshot view of conditions in preclimactic magma chambers a common feature of these csds is a concave down lognormal shape in contrast to the reported linear csds in more mafic systems this feature is interpreted to be a general result of surface controlled size dependent growth by a layer nucleation in silicic magmas at low supersaturation specific csds may be important for interpreting nucleation and crystal growth conditions and mechanisms in magmas erupted as large ash flow tuffs and smaller volume volcanic units and for fingerprinting different magma batches layers in products of the same eruption

verification of ideal semi logarithmic lognormal or fractal crystal size distributions from 2d datasets crystal size distributions can follow any function provided the total crystal content is less than 100 however many theories suggest that they approximate a number of ideal distribution models the most widely adopted model for igneous rocks produces a straight line on a classic csd diagram of ln population density versus size lognormal by size distributions have been proposed for igneous and metamorphic rocks and materials that crystallise at low temperatures lognormal models are difficult to prove with simple linear frequency histograms or on a classic csd diagram instead it is better to use a normalized cumulative distribution function diagram which gives a straight line for lognormal distributions similarly fractal size distributions can best be verified simply by using a bi logarithmic diagram statistical measures can be used to invalidate a null hypothesis but with much caution for real data especially those derived from two dimensional measurements and with a limited range in sizes these methods are applied to csds of plagioclase in three igneous rock samples to illustrate the pitfalls of model fitting a simple nomenclature is proposed for ideal csd shapes

sedimentological petrophysical and seismic characterization of an upper jurassic shoreface dominated shelf margin the boulonnais northern france abstract the integration of high resolution 25 cm vertical spacing and continuous quantitative data on grain size carbonate content porosity density and p wave velocity from outcrop borehole and core over 1000 samples and a real seismic section allows a calibration of seismic sequence stratigraphic principles this approach has been tested in the boulonnais along the english channel coast in northern france on a succession of upper jurassic sharp based shoreface deposits embedded in offshore marine shales statistical analyses of grain size distributions allow a characterization of hydrodynamic conditions and depositional processes affecting low inclination shelf margins and create a framework for identifying locations of preferential and enhanced carbonate cementation which exerts primary control on reservoir and acoustic properties stratigraphic surfaces and systems tracts are quantified for physical properties and results in a quantitative mechanical sequence stratigraphic model the combination of this model with seismic wavelets and a contrast between this synthetic and a real seismic section shows that key bounding sequence stratigraphic surfaces are in fact discontinuous reflectors because stratal relationships of sharp based shoreface deposits are subtle physical contrasts are generally stratabound and the deposits are typically not very thick the geological recordings of sea level falls and potential reservoirs are easily overlooked or go unseen in seismic sequence stratigraphic analyses by defining key diagnostic seismic criteria for sharp based shoreface deposits this study contributes to the understanding of processes controlling sedimentary fills of epicontinental basins

carbonate cementation in a sequence stratigraphic framework upper cretaceous sandstones book cliffs utah colorado abstract three macroscopic diagenetic features can be recognized in the sandstones of the upper cretaceous desert member of the blackhawk formation and castlegate sandstone of the mesaverde group exposed in the book cliffs utah each of which have distinctive form geometry and stratigraphic distribution diagenetic alterations are 1 leached zones whitecaps up to 10 m thick beneath coal beds 2 large up to 8 m concretionary carbonate cemented bodies in amalgamated shoreface and thin fluvial sandstones and 3 thin up to 2 m laterally extensive carbonate cemented horizons beneath major marine flooding surfaces each feature has distinct petrographic and geochemical signatures and formed through discrete diagenetic processes large isolated carbonate cemented bodies are composed of ferroan dolomite most of which precipitated during early diagenesis field and petrographic data coupled with stable isotope data early cements 13c 2 5 to 3 4o oo vpdb 18o 7 8 to 12 0o oo vpdb 87sr 86sr 0 7078 later cements 13c 3 1 to 5 7o oo vpdb 18o 12 0 to 15 1o oo vpdb 87sr 86sr 0 7093 suggest precipitation from meteoric fluids input into sediments during times of relative sea level fall the source of carbonate for the dolomite cement was dissolution of detrital dolomite from beneath coals by organic acids and subsequent mobilization by meteoric fluids carbonate precipitation in laterally extensive cement horizons appears to have started as a result of hiatus in sediment accumulation during marine flooding events relative sea level rise cement precipitation in these horizons continued through sediment burial as a result of organic matter oxidation reactions in overlying organic rich mudstones the results of this study show a link between sedimentation related to changes in relative sea level and diagenesis leading to the potential for the development of process based predictive models of early diagenesis in depositional successions

iron availability as a dominant control on the primary composition and diagenetic overprint of organic matter rich rocks iron is known to stimulate surface ocean productivity as well as intervene with bacterially mediated processes of organic matter remineralization during early diagenesis in this paper we examine the influence of iron supply on the geochemistry trace metals 34s organic matter of sedimentary rocks deposited in a clastic dominated marine ramp environment to this end we studied two late jurassic formations of the boulonnais area north france both formations were deposited under quite similar conditions but they differ in the reactive iron supply they received only one of the two formations was affected by the particulate iron shuttle process our results indicate that 1 the iron shuttle may be recorded through concomitant enrichments in p mo as and sb 2 a limited reactive iron supply will allow the sulfurization of organic matter even in a context of moderate productivity thus sulfurization can be a factor favoring a noticeable accumulation of organic matter iron may thus be an important agent in the c cycle

test of the concepts of sequence stratigraphy in the kimmeridgian late jurassic of england and northern france abstract three distinct models are available for the prediction of sediment accumulation patterns the sequence stratigraphic models of both galloway 1989 and exxon are derived from passive margins whereas the model of einsele 1985 is based on marginal sedimentation in epicontinental seas the models are tested on the marine mudrocks and minor sandstones of the kimmeridgian epicontinental seas of england and northern france a total of ten hiatus bounded sedimentary packages sequences can be delimited and aspects of both the exxon and galloway models are applicable however only a few of the sequence boundaries correspond to the eustatic sea level chart of haq et al 1989 the sequence boundaries appear to be caused by falls in a base level controlled by a storm wave base and the transgressive regressive cycles appear symmetrical as predicted by the einsele model in both the exxon and galloway models condensed sections are predicted to form in distal basin settings beyond the reach of terrigenous sediments but they are not developed in the relatively small kimmeridgian half grabens which were infilled with non progradational packages of sediment thus the basin centres such as the kimmeridge bay type locality contain the thickest and most complete sequences

the parasequence definition are transgressive deposits inadequately addressed abstract in only a few decades sequence stratigraphy has become one of the cornerstones of modern stratigraphy although the sequence is the principal stratigraphic unit parasequences are the fundamental composite building blocks by definition parasequences are typically upward shoaling successions that are bounded by flooding surfaces that form in response to relatively rapid rises of relative sea level in that definition little provision is made for significant transgressive deposition during the time of flooding but transgressive deposits do exist in the geological record because these deposits lie above the flooding surface and derive much of their sediment from transgressive erosion of the underlying progradational succession should the parasequence boundary not be moved from the u derlying flooding surface upward to the top of the transgressive unit by doing so the underlying progradational unit and the overlying transgressive unit would constitute one complete regressive transgressive succession nonetheless although appealing the typical inability to easily accurately and consistently identify the uppermost surface of the transgressive unit makes it an untenable surface for stratigraphic purposes as suggested by earlier workers therefore the flooding surface a readily identifiable surface that caps the progradational package and consistently underlies transgressive deposits is the most appropriate surface to bound the parasequence in any event to ignore transgressive deposits is to ignore an important component of the geological record a record that not only provides insight into transgressive depositional processes but also is one that can be economically important as a result transgressive deposits need to be included in the parasequence definition possibly only implicitly but certainly not explicitly excluded furthermore the notion that sequences typically indicate progradational deposition excludes examples where upward fining transgressive deposits related to upward deepening are present and lie below the upward shoaling progradational part of the same parasequence

a flower like glomerophyric diorite porphyry from central china constraints on the unusual texture abstract an unusual texture with plagioclase phenocrysts clustered as flower like glomerocrysts has been discovered in the wulong diorite porphyry at the southern margin of north china craton the rock consists mainly of plagioclase and amphibole with the former as dominant phenocryst two groups of the plagioclase phenocrysts have been distinguished flower like glomerocrysts fg type and single isolated phenocrysts sp type chemical compositions of both fg and sp type plagioclases are similar in anorthite contents an35 45 which are slightly higher than the matrix an25 35 calculation of the plagioclase crystallization time based on crystal size distribution csd program shows that the fg type crystals have been formed within a longer timescale 226 2782 years than the sp type crystals 98 1910 years the concave down csds and lack of small crystals for fg type plagioclases suggest that coarsening may have been involved in contrast a concave up csd within the size of 3 10 mm plagioclase indicating that a rejuvenation kinetic process after coarsening a possible formation history for the unusual flower like plagioclase glomerocrysts was proposed as follows 1 initial nucleation and growth of single crystals in a confined environment 2 ascent of early crystals with magma upwelling and radial coarsening at the roof layer of magma chamber 3 remobilization of dense crystal mush and final emplacement at shallow level of crust 4 rapid cooling and extensive nucleation and growth of matrix 5 post magmatic alteration and metamorphism it is likely that the morphologic diversity of plagioclase glomerocrysts are largely influenced by variation of undercooling degrees the second step is the most important for the formation of the flower like glomerophyric texture which requires an environments of relatively low undercooling degree

origin of anorthosite by textural coarsening quantitative measurements of a natural sequence of textural development the textures of plagioclase crystals within large olivine oikocrysts preserve the sequence of the formation of anorthosite such textures have been quantified in a troctolite anorthosite from the proterozoic lac st jean anorthosite complex canada crystal size distributions csds indicate that initially plagioclase nucleated and grew in an introduction environment of linearly increasing undercooling producing a straight the textures of plutonic rocks are one of their most line csd during this phase latent heat of crystallization was striking aspects but they have been little used to elucidate largely removed by circulation of magma through the porous crystal petrological processes as compared with chemical and mush by about 25 solidification the crystallinity was such that isotopic methods where used discussion has tended it reduced but did not eliminate the circulation of magma resulting to be qualitative in contrast to quantitative chemical in the retention of more latent heat within the crystal pile the methods hence reducing the weight of this approach temperature rose until it was buvered by the solution of plagioclase indeed it is not possible to verify physical models if close to the liquidus temperature of plagioclase nucleation of quantitative data are not available quantitative textural plagioclase was inhibited and conditions were suitable for textural studies of volcanic rocks are becoming more common coarsening of both plagioclase and olivine to occur ostwald and these methods are applied here to the development ripening in this process small crystals were resorbed whereas of anorthosite larger crystals grew from both material recycled by the resorption of quantitative textural studies of plutonic rocks really crystals smaller than the critical size and new material brought in started with jackson s studies of the stillwater complex by the circulating magmatic fluid the results of this process resemble in 1961 jackson 1961 he measured crystal size disthose of high temperature metasomatism but there is no necessity for tributions but did not record the area that he measured a magmatic fluid with a diverent composition the shapes of the hence his data cannot be completely compared with plagioclase csds fit better the communicating neighbours equation of modern data his pioneering work was not really followed textural coarsening rather than the classic lifshitz slyozov wagner up and since then most studies have looked only at equation as do other examples drawn from the literature if olivine average or typical crystal sizes these data are much started to nucleate at a higher temperature than plagioclase then less revealing of petrological processes than crystal size during the textural coarsening phase olivine would have been more distributions partly because they only give one parameter undercooled than plagioclase and would have had a higher maximum for each sample the few existing studies of crystal size growth rate in these conditions olivine would coarsen more rapidly distributions in plutonic rocks have not treated than plagioclase and engulf it hence the order of crystallization plagioclase determined from the textures would be the reverse of the order of one problem especially pertinent to quantitative texfirst nucleation of the two phases from equilibrium phase diagrams tural studies is the way that many igneous petrologists maintenance of the temperature near the plagioclase liquidus may look at rocks they commonly try to reconstruct how a rock has formed by examining the final fully crystallized also inhibit the nucleation and growth of other phases

seismic models of a shelf margin depositional sequence upper san andres formation last chance canyon new mexico abstract the seismic resolution of stratal geometries and facies distributions observed in san andres formation permian outcrops in last chance canyon guadalupe mountains new mexico is studied by seismic modeling of a published detailed stratigraphic cross section the outcrops in last chance canyon are composed of two fourth order depositional sequences an aggrading carbonate bank upper san andres 3 usa3 followed by a strongly progradational offlapping mixed carbonate siliciclastic succession upper san andres 4 usa4 each sequence comprises a number of subsidiary high frequency sequences fifth order two alternative impedance models were used model a in which all facies transitions are reflecting boundaries and model b in which only time significant surfaces act as reflectors and lateral facies transitions are represented by horizontal velocity gradients the vertical incidence modeling technique was used to compute perfectly migrated time and depth sections with different frequencies using a low frequency wavelet 25 hz the sequence boundary separating the two fourth order cycles usa3 and usa4 is poorly imaged instead one is tempted to incorrectly interpret an onlap pattern generated by a high frequency cycle within usa4 as this major sequence boundary in addition the 25 hz runs show toplap and downlap lap out patterns in an overly oblique fashion obscuring true asymptotic stratal relationships both at 35 hz and 50 hz profiles based on model b image the genetic structure of both usa3 and usa4 relatively well at 50 hz model a incorrectly shows a transition from a ramp to a rimmed margin within usa4 the 35 hz models are qualitatively compared with a published exxon production research co seismic line located approximately 50 km along depositional str ke to the northeast model a shows an unexpected good match with the exxon seismic line whereas model b comes much closer to the depositional anatomy observed in outcrop our results show that the resolution of stratal geometries and facies distributions in last chance canyon is strongly related to carbonate sandstone alternations and the way impedance contrasts at carbonate sandstone transitions are represented

time average equation revisited expressions that relate velocity to porosity and to pore fluid compressibility are among the most important deliverables of rock physics such relations are used often as additional controls for inferring porosity from well logs as well as in situ indicators of pore fluid type the oldest and most popular is the wyllie et al 1956 equation p s f where p is the measured traveltime of a p wave s is the traveltime expected in the solid phase material and f is the traveltime expected in the pore fluid it follows from equation 1 that 1vp 1 vps vpf where is porosity vp is the measured p wave velocity and vps and vpf are the p wave velocities in the solid and in the pore fluid phases respectively

evaluation of a wide range laser diffraction grain size analyser for use with sediments the qualities of a laser diffraction grain size analyser the coulter ls 100 range claimed by the manufacturer 0 4 900 mum in a single measurement are evaluated on sediments of fluvial and lacustrine origin accuracy and resolution of measurement on standard latex spheres are excellent reproducibility of the results on natural sediments appears to be satisfactory but the method underestimates the fraction of clay particles with an efficiency of detection 36 70 proportional to the clay content determined from pipette analysis this efficiency is somewhat higher than those reported from other instruments of the same generation comparison of the coulter ls 100 with other sizing techniques shows good agreement with the sieving method but some differences appear with the electroresistance particle technique median and mean size values measured by the coulter counter ta1 are systematically lower than those obtained by the coulter ls 100 analyses show good correlation with those of a malvern laser particle analyser but a discrepancy appears with very fine silt and clay sized sediments the coulter ls 100 detects a higher clay content than that measured with the malvern laser sizer 2600 except when precise measurements of clay content are needed the coulter ls 100 produces precise and accurate results in size ranges required for geological and environmental studies

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

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

variations in petrophysical properties along a mixed siliciclastic carbonate ramp upper jurassic ricla ne spain abstract a multi scale petrophysical study was performed on an upper jurassic siliciclastic carbonate ramp system near the village of ricla spain a combination of textural field observations thin section and grain size analysis chemical mineralogical thermo gravimetric analysis and physical porosity gamma ray and velocity measurements properties was used to capture the heterogeneity of this mixed sedimentary system subsequently synthetic seismic sections with varying resolution were created to show the characteristics of the internal ramp structures the translation from the measured petrophysical properties to a synthetic seismic section helps to better understand subsurface seismic although upscaling problems are a recurring issue the homogeneity of the samples and the continuity of the outcrop and facies reduce the number of uncertainties acoustic properties are generally controlled by the amount and type of pore spaces due to the low porosities the ramp geometry is characterized by an overall lateral homogeneity and vertical heterogeneity textural sedimentological and stratigraphic transitions in the outcrop are related to the defined facies each has its own unique mineralogical signature amplitude variations in the synthetic seismic profile are primarily caused by changes in mineral composition thus facies transitions

calcite cemented concretions in cretaceous sandstone wyoming and utah u s a abstract spheroidal cannon ball calcite cemented concretions some of gigantic size were studied from three cretaceous shelf sandstone units ferron frontier and second frontier the concretions have diameters between 2 cm and 6 m those larger than 40 cm in diameter in the ferron and frontier have septarian structure rare concretions in the second frontier with cone in cone also have septaria the pattern of carbon and oxygen isotopic data and intergranular volume igv data across concretions indicate that concretion growth was complex not all concretions grew progressively from their centers toward their edges in many concretions displacive fascicular optic high mg calcite foc precipitated simultaneously throughout the concretions pervasive growth pattern although the earliest cementation was concentrated in and near their centers remaining pores were subsequently filled by poikilotopic calcite of lower mg content displacive foc cement in the bodies of concretions and in cone in cone structure and the large igv values indicate that these carbonate phases formed at burial depths no greater than tens of meters igv values indicate that spar cement continued to depths of at least 50 m and possibly deeper the association of organic matter and microbial structures or microbial byproducts with displacive foc and cone in cone calcite raises the possibility that biogenic processes were responsible for the apparently rapid growth of the displacive calcite the oxygen isotope composition of pore waters was fairly uniform in the range of 18o of 4 to 6 smow during 80 of concretion growth but became even more depleted in 18o during the last stage of growth and during septarian fracture filling ranging into values as depleted as 14 smow 13c in calcite is negative 4 to 18 v pdb but variable reflecting a range of microbial processes under both oxidizing and reducing conditions earlier calcites fall mostly in the range of 10 to 16 v pdb relatively later calcite in veins and on concretion margins is more enriched in 13c fe and mn concentrations in calcites have a rough positive correlation with higher 13c values the concentration of mg derived from seawater and altered volcanic rock fragments covaries positively with the degree of meteoric influence lower mg contents correlate positively with relatively depleted 18o values 87sr 86sr values are typical of sr derived from coeval seawater or marine skeletal debris growth of concretions 4 to 6 m in diameter apparently in 5 my requires some spatial localization of growth sites by a self organization process and probably a large supply of carbonate shells in the original sediment elongation of larger concretions in the plane of bedding suggests that advective rather than diffusive supply of cement components dominated late in concretion growth history concretions formed close to the tops of parasequence boundaries

a genetic link between synsedimentary tectonics expelled fluids microbial sulfate reduction and cone in cone structures abstract the late jurassic tithonian marlstones of the boulonnais area english channel france contains diagenetic carbonate beds and nodules some nodules exhibit cone in cone structures on their lower face we studied such nodules using various techniques of imaging and chemical major and trace elements and isotopic analyses ccarb corg o and s stable isotopes we interpret the cone in cone to be the end product of carbonate nodule formation during early diagenesis the diagenetic carbonate precipitation was induced by microbial activity bacteria and archeae fueled by upward migrating fluids fluid expulsion was itself triggered by synsedimentary fault movements under such circumstances cone in cone structures can form during early diagenesis as the result of bacterially mediated sulfate reduction possibly coupled to sulfate dependent anaerobic oxidation of methane this genetical scheme may be transposed to many other settings

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

constraining the degassing processes of popocatepetl volcano mexico a vesicle size distribution and glass geochemistry study abstract the explosive activity of popocatepetl volcano is a threat to the surrounding densely populated areas and it is therefore important to recognize indicators of change in eruptive style explosive to dome building within a short period of time in this study we present results of vesicle size distributions vsds and compositional analysis of matrix glass from juvenile clasts from five of the main plinian eruptions of popocatepetl ca 23 1 2 ka the 2001 small eruption during partial dome collapse and four eruptions during 1997 may 11th and june 14th 15th and 30th major element analysis of matrix glass wds epma allows the estimation of the depth from which the erupted magma went into disequilibrium between crystals and melt by calculating the equilibrium pressure using the quartz albite orthoclase ternary system of blundy and cashman 2001 quantitative interpretation of texture in juvenile pumice or scoria clasts via vsd analysis using csd software was used to link physical changes experienced by magma during ascent with conditions responsible for eruptions the extent and style of vesiculation in juvenile clasts is also related to eruption style and duration and has specifically allowed the recognition of changes in vesicular texture that represent variations from explosive to dome building activity mangan and sisson 2000 adams et al 2006 this study highlights a more complicated story in terms of magma storage than that previously accepted for the popocatepetl volcanic system and is an important contribution to ongoing research at the volcano

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

magma rheology variations in sheet intrusions of the ardnamurchan central complex scotland inferred from gabbro inclusion characteristics entrainment of xenoliths and their consequent assimilation are key processes in modifying the crystallization kinetics and magma dynamics of conduit systems here an integrated textural and mineral chemical study of the evolution of a suite of gabbroic inclusions within a set of sheet intrusions from the ardnamurchan central complex nw scotland is presented the key findings are as follows 1 the host magma sheets and inclusions are not cognate 2 there are microstructural and mineral chemical similarities between the gabbroic inclusions and the textures and mineralogy of the major hypersthene gabbro on ardnamurchan 3 orientations of magnetic fabrics within the host sheet groundmass and within the gabbroic inclusions are virtually identical field observations suggest that the inclusions were derived from the hypersthene gabbro and were entrained in a few laterally restricted magma segments that subsequently coalesced with inclusion free segments into continuous sheets using stokes law and adaptations thereof we calculate that the magma within the inclusion free segments behaved as a newtonian fluid with a potential settling velocity of50 028 m s in contrast the presence of gabbro inclusions probably modified the magma dynamics to bingham like behaviour we infer that this variation in the magma rheology of separate segments continued after coalescence and internally partitioned the magma sheet preventing lateral mixing and inclusion transport

magma dynamics beneath kameni volcano thera greece as revealed by crystal size and shape measurements size distributions of plagioclase crystals in series of recent porphyritic dacite lavas from kameni volcano greece can be modelled by mixing two populations of crystals each with overlapping linear crystal size distributions csd termed microlites and megacrysts the magmas bearing the microlites and megacrysts started to crystallise 6 13 and 24 96 years respectively before each eruption the dates of initiation of crystallisation of the megacrysts indicate that they are left overs of earlier injections of new magma into a shallow chamber some magma remains after each eruption and continues to crystallise new magma with few or no crystals is then introduced and the microlites crystallise from the mixed magma eruption followed 6 13 years after mixing such a model would suggest that some porphyritic magmas are products of a shallow magma chamber that is never completely emptied just topped up from time to time

the context of lowstand events in the kimmeridgian late jurassic sequence stratigraphic evolution of the wessex weald basin southern england abstract a depositional sequence stratigraphic framework for the kimmeridgian stage of the wessex weald basin southern england is applied in the investigation of the sedimentary and erosional response to proposed lowstand events this framework recognises 13 sequence boundaries km1 km13 and is based on the integrated assessment of geophysical sedimentological palaeontological and geochemical data changes in the nature and continuity of kimmeridgian unconformity surfaces record the effect of the reorganisation of the onshore basins in response to eustasy and tectonic movements during the earliest kimmeridgian the basin geometry was such that falls in relative sea level generated widespread unconformities associated lowstand events are recorded in marginal areas by a number of sand units derived from a variety of local sources a tectonically enhanced deepening event during the late early kimmeridgian eudoxus zone led to unconformities being confined in their distribution to the basin margins as sea level fell during the latest kimmeridgian a progressive reduction in the depositional area led to an amplification of the effects of lowstand processes at the basin margins where unconformity surfaces are amalgamated on the most positive areas these surfaces are overprinted by a major interregional hiatus the late cimmerian unconformity the timing and effects of kimmeridgian lowstand events were intimately linked to the tectonic evolution of the wessex weald basin thus at times when rates and amounts of eustatic change are small i e during greenhouse times the tectonic signature of a basin will be the primary signal recorded in sedimentary successions

filtering of depositional events and the completeness of sedimentary sequences the preservation of depositional events in sedimentary sequences is investigated using a monte carlo model in which sedimentation rates are constant and the magnitudes of the events follow a lognormal frequency distribution the model indicates that sedimentation processes act as a stationary low pass filter that preserves an amplitude distorted record of the depositional events imposed on the modern environment this low pass filter gives rise to two concepts of completeness of sedimentary sequences 1 preservation of time lines in sedimentary sequences or temporal completeness and 2 preservation of depositional events in sedimentary sequences or spatial completeness the model suggests that as sedimentation rate decreases 1 the number of time lines preserved decreases exponentially and the completeness of the record of depositional events decreases linearly and 2 low magnitude events are progressively eliminated from the record the latter characteristic of the model which arises because of the assumption of stationarity of the time series may be in conflict with observations from real sedimentary sequences a nonstationary component can be added to the model by taking into account other depositional variations that have been observed in modern environments

seismic model of a progradational carbonate platform picco di vallandro the dolomites northern italy we present a seismic model of a well exposed carbonate platform to basin transition from the triassic succession at picco di vallandro the dolomites northern italy the core of this model is a detailed lithologic cross section that represents 1500 m of stratigraphic section over a distance of 3 5 km the cross section is based on detailed measured sections photo interpretation and careful projection of surface mapping into the plane of section samples from the measured sections provide control on velocity and density distribution and these data were used to generate an impedance model from the cross section the impedance model was convolved with a zero phase 25 hz peak frequency wavelet to produce the seismic model the results illustrate how the platform to basin transition might be imaged by conventional seismic reflection data how the reflections relate to the distribution of lithology and through going geological surfaces and how constructive and destructive interference and seismic resolution combine to produce individual reflections the picco di vallandro section displays several scales of progradation and retrogradation ranging from stacked buildups that are several hundreds of meters thick to the interfingering of individual beds the seismic model displays this complexity with varying degrees of success the individual buildups are well imaged but as expected smaller features are not as clearly reproduced by the model intermediate scale sections that represent platform retrogradation are shown as surfaces of onlap in the seismic model but field work shows that the platform was still shedding sediment while retreating and that no simple onlap surface exists in the outcropping section a similar lack of stratigraphic resolution is shown by the model at the downlapping clinoforms which do not correspond to iscrete stratal surfaces but to the toe of slope position where major bedding units thin below seismic resolution smaller features such as the position of downslope terminations of carbonate breccia wedges are not resolved by the model toe of slope packages of limestone turbidites are represented only by reflection segments of higher amplitude the decreasing seismic resolution is caused by limited seismic bandwidths and by the effects of constructive and destructive interference interference has the largest effects at the complexly interfingering buildup to basin transition or at the most detailed part of our model an understanding of these types of seismic limitations and their controls is important as we try to extract more and more stratigraphic information from seismic data p

seismic models of a carbonate foreslope to basin transition picco di vallandro dolomite alps northern italy detailed geologic cross sections augmented by laboratory calibration of lithology and acoustic impedance have been used to produce synthetic reflection seismic sections of a carbonate foreslope to basin transition two areas from the picco di vallandro region of the dolomite alps were modeled a progradational section and a retrogradational backstepping section the resulting models show how these complex areas of strata interfingering might be displayed on conventional reflection seismic lines in the area of progradation rapid stratigraphic thinning below seismic detectibility coupled with abrupt impedance changes produces a reflection discontinuity between steeply dipping reflections of the foreslope and gently dipping parallel reflections of the basin section this apparent downlap surface marks the toe of slope for successive clinoforms but does not correspond to a discrete stratigraphic surface in the backstepping example similar stratigraphic thinning and impedance changes create an apparent onlap surface wavelet interference causes complications in both examples these models indicate how stratigraphic complexity can be simplified by the seismic reflection process and suggest that caution should be exercised when using seismic data to construct general models in areas of complex depositional geometries and rapidly changing facies

organic facies variation in the late kimmeridgian of the boulonnais area northernmost france recent studies of the upper kimmeridgian of the boulonnais area northernmost france have provided a sequence stratigraphical framework that is here used to help interpret variations in sedimentary organic matter om content and composition in response to fluctuations in relative sea level the organic facies are characterised using a combination of palynofacies bulk organic geochemistry toc rock eval pyrolysis and sulphur data and the particle size distribution of the total palynological residues the organic facies show a good correlation with the sequence stratigraphy exhibiting peak toc hi total s and sorg values in the lithofacies deposited around the two mfs the palynofacies in these intervals is characterised by a high content of fluorescent orange marine aom there is a strong correlation between the orange aom and the total and organic sulphur contents similar positive correlations between orange aom and organic sulphur have previously been observed in the distal organic rich sediments of the kimmeridge clay formation of dorset lateral time equivalents of the boulonnais facies but there the sulphur contents are lower indicating that organic sulphur content of orange aom is not fixed suggestive of preservation related parallel but not intrinsically related trends the s data can be used to estimate an apparent burial efficiency and hence the proportion of the primary productivity preserved this allows a rough estimate of palaeoproductivity model calculations suggest that for a sulphide retention of 30 70 and uncompacted sedimentation rate estimates in the range 5 10 cm ka the mean palaeoproductivity was in the range 52 175 gc m2 a up to 6 of which was preserved thus if the preservation is high as is the case for mfs the palaeoproductivity does not need to be above average for shelf waters to produce a given toc

quartz crystal size distribution of the ordovician millbrig k bentonite abstract crystal size distribution csd analysis has been applied to quartz crystals of the ordovician millbrig k bentonite which represents one of the largest known fallout ash deposits in the phanerozoic era to establish crystal growth histories and conditions in the magma chamber prior to eruption specific csds were examined for crystal growth conditions all millbrig samples exhibit lognormal concave down shapes in agreement with previously reported csds on large silicic systems but in contrast to more mafic systems characterized by linear csds concave down csds are possibly an intrinsic property of phenocryst growth in large volume silicic magmas as documented in the literature bindeman i n 2003 crystal sizes in evolving silicic magma chambers geology 31 367 370 quartz crystals of the millbrig must have been produced by surface controlled size dependent growth with a minor ostwald ripening component which could have easily changed to supply controlled growth due to a limited supply of nutrients as the crystals grew larger csds were also used to examine the possible origin of multiple ash beds in the millbrig these ash beds appear to be a product of a series of separate eruptions that represent separate magma layers or batches each with slightly different crystal growth conditions

sequence concepts at seismic and outcrop scale the distinction between physical and conceptual stratigraphic surfaces abstract the sequence stratigraphic terms maximum flooding surface and downlap surface as currently applied are ambiguous examples of these intra sequence surfaces are summarised from high frequency mid pleistocene sequences and from a cretaceous recent seismic megasequence both from new zealand at any one locality a mid pleistocene sequence contains up to four stratal discontinuities in ascending order the sequence boundary ravinement surface local flooding surface and downlap surface these physical surfaces which occur in outcrop are regionally diachronous and should be differentiated from theoretical isochronous horizons such as the time of maximum flooding horizon corresponding to maximum shoreline transgression and the time of peak eustatic or local relative sea level horizons corresponding to the highpoint of the eustatic and relative sea level cycles respectively in seismic studies the boundary between the transgressive and highstand systems tracts is usually located at the downlap surface on the basis of a major thermo tectonic sea level cycle in the canterbury basin it is shown that the downlap surface is not a single regional surface and that the change in slope associated with toes of successive prograding clinoforms rises in stratigraphic height basinwards the downlap surface therefore does not usually coincide with the maximum flooding horizon in plio pleistocene cyclothems a discrete unit the mid cycle shellbed straddles the contact between the transgressive and highstand systems tracts this unit might be classified within its own systems tract the condensed section systems tract csst alternatively the position of the boundary between the transgressive and highstand systems tracts can remain unspecified or unknowable

sequence stratigraphic distribution of diagenetic alterations in coal bearing paralic sandstones evidence from the rio bonito formation early permian southern brazil linking siliciclastic diagenesis to sequence stratigraphy allows a better understanding of the parameters controlling the spatial and temporal distribution of diagenetic alterations and hence of reservoir quality a study of the coal bearing alluvial deltaic estuarine and shallow marine sandstones of the rio bonito formation early permian parana basin southern brazil reveals that the distribution of diagenetic alterations and of related reservoir quality evolution can be constrained within a sequence stratigraphic framework calcite dolomite siderite kaolinite and pyrite cementation is consistently linked to sequence and parasequence boundaries transgressive and maximum flooding surfaces and is systematically distributed within lowstand transgressive and highstand systems tracts diagenesis of coal layers at parasequence boundaries has promoted the formation of stratabound calcite detectable in resistivity wire line logs concretionary pyrite and kaolinite and of silicate grain dissolution in sandstones located above and below these boundaries particularly in the transgressive systems tract meteoric water diagenesis caused grain dissolution and the formation of kaolinite in sandstones below sequence boundaries and in lowstand systems tract sandstones carbonate bioclasts and low sedimentation rates in lag deposits at parasequence boundaries transgressive and maximum flooding surfaces favoured the formation of grain rimming siderite the results of this study are relevant to the exploration of coal bed methane and other coal bearing reservoirs where it is crucial to unravel and predict the distribution and quality of reservoirs and compartments

unusual shoreface sedimentology in the upper jurassic of the boulonnais northern france abstract two upper jurassic sandstone formations the gres de chatillon and gres de la creche of the boulonnais of northern france record shoreline conditions on the eastern margin of a large epicontinental sea the wessex basin the interpreted range of bedforms is more diverse than has been recorded from other shorelines either ancient or modern the lower shoreface to transition zone was characterized by small lunate dunes oscillatory ripples mudstone drapes and discrete burrowed beds indicating the alternation of moderate currents oscillatory flow and prolonged quiescent intervals the shoreface itself was dominated by dunes that ranged in height from a few decimeters to more than a meter the larger sizes are twice the height of any shoreface bedforms previously described paleocu rent indicators within the shoreface deposits are highly variable from bed to bed and within individual cosets a feature that may indicate deposition on a barred shoreface evidence for tides is care occasional herringbone cross stratification in contrast to many other ancient shoreface sandstone units storms left little sedimentary record rare large shell gravel bars in the upper offshore zone although they generated numerous erosion surfaces in the lower shoreface the unusual aspects of the boulonnais sandstone units may relate in part to the particular paleogeographic location of the region an open embayment regardless this is a rare example of a fair weather wave dominated medium sand shoreline from the geological record

crystal size distribution of plagioclase and amphibole from soufriere hills volcano montserrat evidence for dynamic crystallization textural coarsening cycles the crystal size distributions csds of plagioclase and amphibole were determined from andesites of the soufriere hills volcano montserrat plagioclase occurs as separate crystals and as chadocrysts in large amphibole oikocrysts the chadocrysts represent an earlier stage of textural development preserved by growth of the oikocryst seventeen rock and eight chadocryst plagioclase csds are considered together as a series of samples of textural development all are curved concave up and coincident differing only in their maximum crystal size three amphibole csds have a similar shape and behaviour but at a different position from the plagioclase csds a dynamic model is proposed for the origin of textures in these rocks crystallization of plagioclase started following emplacement of andesite magma at a depth of at least 5km a steep straight csd developed by nucleation and growth this process was interrupted by the injection of mafic magma into the chamber or convective overturn of hotter magma the magma temperature rose until it was buffered initially by plagioclase solution and later by crystallization during this period textural coarsening ostwald ripening of plagioclase and amphibole occurred small crystals dissolved simultaneously with the growth of large crystals the csd became less steep and extended to larger crystal sizes early stages of this process are preserved in coarsened amphibole oikocrysts repetitions of this cycle generated the observed family of csds textural coarsening followed the communicating neighbours model hence each crystal has its own unique growth solution history without appealing to mixing of magmas that crystallized in different environments

modeling shore normal large scale coastal evolution abstract we present a model for the evolution of the shelf surface in response to marine sedimentary processes following morphodynamical theory the model presupposes a characteristic configuration of the shelf surface that in profile is a concave up exponential curve whose steeper inner limb is the shoreface the profile is seen as an equilibrium response to the variables of sedimentation the profile translates landward or seaward as sea level rises or falls but will do so in an state of dynamic equilibrium with the shape of the profile varying according to changes in 1 the rate of sea level change 2 the time averaged wave and bottom current conditions 3 the average allochthonous sediment supply rate and 4 the sediment grain size distribution the governing equations for the model include an equation for time averaged cross shore diabathic sediment flux and the sediment continuity equation p simulations of continental margin profiles show that profile adjustments affect mainly the coefficient of curvature of the profile an increase in the rate of sea level rise straightens the profile it decreases the slope of the shoreface but increases the shelf slope an increase in sediment input increases profile curvature the shoreface steepens while the shelf floor flattens an intensification of hydraulic climate straightens the profile in a manner similar to an increase in the sea level rise rate while an increase in grain size increases profile curvature as does an increase in sediment input

origin of lunar very high potassium vhk basalts a combination of endogenous and exogenous processes abstract very high potassium or vhk basalts have been described from the apollo 14 landing site at fra mauro on the lunar near side many of the known samples are clasts in polymict breccias with a few as new work completed on fourteen vhk basalts include crystal size distributions csds and in situ chemical analyses and element maps collected by electron probe microanalysis epma csds completed on three vhk basalt samples indicate that these basalts are not impact melts and represent endogenous melts of the lunar interior potassium k element maps reveal the spatial relationship between the k rich material and the basalt clasts with attached breccia matrix if present in situ epma analyses have identified two distinct types of k rich material k feldspar and k rich glass with these new data an additional mechanism for an exogenic petrogenesis of vhk basalts is proposed that involves the impact process vhk basalts can be divided into two groups based on density and viscosity vhk 1 basalts formed when a hot impact ejecta covered the granite felsite rich matrix material containing high al basalt clasts heat from the impact ejecta partially melted and possibly evaporated nearby k bearing materials which then infiltrated and contaminated the high al clasts vhk 2 basalts are consistent with the hypothesis of granite assimilation by a high al magma as seen in the higher abundances of network forming elements

origin of k feldspar megacrysts in rhyolites from the emeishan large igneous province southwest china abstract silicic rocks occur in the uppermost units of the longest volcanic succession 5000 m thick in the binchuan area of the permian emeishan flood basalt province of sw china they are predominantly rhyolites and to a lesser extent trachytes both containing potassium feldspar megacrysts as the dominant phenocryst phase up to approximately 20 mm in size these megacrysts contain domains of albite arranged in vein like networks likely formed by post magmatic alteration crystal size distributions csd suggest that these megacrysts grew in a stable magmatic system consistent with relatively uniform core to rim compositional k 2 o 14 16 wt and isotopic profiles 208 pb 206 pb ratios 2 06 2 08 0 005 both whole rock trace elements and pb isotope ratios of these silicic rocks are similar to the emeishan basalts suggesting a common source for both mafic and felsic units and a limited role of crustal melting in genesis of the felsic units major and trace element models further indicate that these rocks could not have formed exclusively by re melting of old crust or solidified basaltic rock but must have formed through crystal fractionation from the flood basalts or possibly partial melting of basaltic rock followed by fractional crystallization k feldspar bearing rhyolites are also observed in the last stages of other large igneous provinces we suggest that they represent final melt fractions and their appearance in the magmatic system coincides with waning of voluminous magmatic activities

stratigraphic control on laterally persistent cementation book cliffs utah field data from the upper cretaceous blackhawk formation in the book clitfs utah colorado demonstrate the presence of laterally extensive carbonate cements beneath major marine flooding surfaces the occurrence of firmgrounds compaction around concretions and high minus cement porosities indicate that cementation occurred during early diagenesis it is proposed that the early cementation associated with these marine flooding surfaces occurred as a result of reduced sediment accumulation rates or non depositional hiatuses linked to abrupt deepening during marine flooding these reduced sediment accumulation rates extended sediment residence time within early diagenetic zones leading to enhanced early cementation in shallow marine sandstones and mudstones