quantitative seismostratigraphic inversion of a prograding delta from seismic data quantitative stratigraphy predicts the geometry of geologic strata and their petrophysical properties based on mathematical models of geological processes and parameters which affect the formation and evolution of geologic strata such processes include erosion sediment transport and deposition quantitative stratigraphic inversion estimates the process parameters from a priori data by systematic modeling until the predictions are compatible with the observations in the case of quantitative seismostratigraphic inversion the a priori data are predominantly of the seismic kind to evaluate feasibility we designed a preliminary algorithm which we applied in a prograding delta environment we found that by fixing the sediment influx rate subaerial transport rate and the initial topography we were able to reproduce the basic features of the delta with only three to five parameters which included subaqueous transport rate and its depth dependent decay rate base level and sediment source location and spatial extent

microearthquakes beneath median valley of mid atlantic ridge near 23 n tomography and tectonics data from a microearthquake experiment in the median valley of the mid atlantic ridge near 23 n in 1982 are used to measure earthquake source parameters to determine the laterally heterogeneous seismic velocity structure across the inner floor and to develop a kinematic tectonic model for this portion of the median valley fifty three microearthquakes occurred over a 10 day period beneath the median valley inner floor and eastern rift mountains twenty of 23 well located inner floor epicenters define a line of activity about 17 km long having a strike of n25 e and located near an along axis depression some 300 400 m deeper than surrounding regions earthquakes with well resolved hypocenters generally have focal depths of 4 8 km beneath the seafloor of both the inner floor and the rift mountains the hypocentral locations are robust with respect to plausible lateral variations in seismic velocity structure composite fault plane solutions for inner floor events indicate normal faulting on planes dipping at angles near 45 normal faulting mechanisms although poorly constrained are also indicated for the rift mountain microearthquakes seismic moments approximate fault dimensions and average stress drops for the largest events recorded are 1019 1020 dyn cm 200 400 m and 1 70 bars respectively a twodimensional tomographic inversion of p wave travel time residuals from microearthquakes and local shots indicates a well resolved lateral heterogeneity in crustal velocity structure across the median valley inner floor p wave velocities at 1 5 km depth within a zone less than 10 km wide beneath the central inner floor are lower by several percent than in surrounding regions the most likely explanation for the low velocities is that the region is the site of the most recent local magmatic injection and remains pervasively fractured as a result of rapid hydrothermal quenching of the newly emplaced crustal column by this view the seismic velocity structure at the ridge axis evolves probably by the sealing of cracks and pores within the first few hundred thousand years of crustal accretion consideration of the detailed sea beam bathymetry in this region of the inner floor the characteristics of large earthquakes that the region has experienced during the past 25 years and the results of the microearthquake and tomography analysis suggests that this section of the median valley has been undergoing continued horizontal extension and block faulting without significant crustal injection of magma for at least the past 104 years

do seismic reflections necessarily have chronostratigraphic significance many seismic reflections from within sedimentary successions are thought to be generated along stratal surfaces because those surfaces are laterally continuous and have marked acoustic impedance contrasts as stratal surfaces are isochronous those reflections are then also taken as being chronostratigraphically significant in contrast seismic reflections are thought not to be generated along the boundaries of lithostratigraphic units because those boundaries are discontinuous and gradational nevertheless synthetic seismic analysis shows that seismic reflections should in many circumstances be expected to follow lithostratigraphic unit boundaries not stratal surfaces as these lithostratigraphic unit boundaries will generally be diachronous seismic reflections from within sedimentary successions should evidently not be treated as necessarily having chronostratigraphic significance

large scale alluvial architecture and correlation in a triassic pebbly braided river system lower wolfville formation fundy basin nova scotia canada abstract determining what the controls are on the large scale 10 km horizontal architecture of coarse grained fluvial deposits is important for understanding subsurface fluid distribution and extraction from these important aquifers and hydrocarbon reservoirs this contribution describes the architecture of coarse grained fluvial sediments from an almost continuous lateral profile 27 km long by 115 m high in the upper triassic wolfville formation fundy basin nova scotia the lateral extent and quality of exposure allows development of a high resolution correlation scheme and definition of architectural elements the lower wolfville formation lithofacies composed of breccias conglomerates sandstones mudstones and paleosols comprises alluvial fan fluvial and ephemeral lake margin facies associations alluvial fan deposits form 15 of the studied section and are developed locally between the overlying fluvial facies and the unconformity with carboniferous strata where they infill remnant topography the succession is dominated 80 by pebbly sandstones deposited as part of a gravelly braided fluvial system and ends abruptly with a thin ephemeral lake margin facies association 5 the large scale architecture and sedimentology of the pebbly sandstone succession is documented with particular attention focussed on bounding surfaces and stacking patterns in the fluvial facies association two scales of development of erosion surface and cycles can be recognized the s surfaces can be correlated across the profile 27 km and show evidence of up to 10 m of erosion a significant facies or grain size change onlap and association with mature calcic paleosols the e surfaces can be correlated between 5 and 17 km display erosion of the regional extent of the e and s surfaces indicate that the gravelly fluvial system has a large scale sheet like geometry which comprises a series of stacked erosion dominated multi story bodies high resolution architectural elements are poorly defined in this coarse fluvial system and make it difficult to constrain the scale of the depositional system an individual high resolution cycle records braid plain development and is interpreted as a multi story channel belt the braid plain width is estimated at 19 km but the width of individual active channels is unknown the sediments were deposited in a proximal fluvial setting disconnected from marine influences we interpret the high resolution cycles and bounding e surfaces to record a progressive decrease in runoff and fluvial transport capacity indicative of a drying upward climatically driven signal the origin of the s surface bounded packages is more difficult to determine a variety of mechanisms are considered including changes in discharge driven by climatic fluctuations changes in stream power related to drainage capture within the source area and tectonic tilting an important aspect of the study is that the s surfaces can be identified and correlated for 27 km and provide an example of a robust high resolution correlation framework in coarse grained braided fluvial deposits that could be applied elsewhere in contrast the e surfaces do not display any significant changes in facies or grain size across them such that many of the smaller scale cycles could potentially be miscorrelated

seismostratigraphic inversion appraisal ambiguity and uncertainty geologic process models predict the geometry of geologic strata and their petrophysical properties based on mathematical models of geological processes that affect the formation and evolution of geologic strata such processes include erosion sediment transport and deposition the resulting forward model is typically nonlinear given observations and a misfit measure one may attempt inversion of these models to estimate process parameters that yield compatible predictions for seismostratigraphic inversion seismic data are used as observations we tested such an algorithm in a prograding delta environment to examine the effect of using different seismic attributes as observations and thus different choices of misfit measures the first measure based on the degree of parallelism between seismic reflectors and modeled geologic strata demonstrated a trade off between geologic time and the sediment influx rate used to parameterize the model a second misfit measure used unwrapped seismic instantaneous phase as a crude proxy to relative geologic time which regularized the model parameters then last we combined the two measures to take advantage of their individual characteristics for most of these inversion experiments we obtained results that capture the geometry of the geologic strata as observed on the seismic data with the exception of the depositional time rate trade off where the same strata can be obtained in a shorter geologic interval when rates are increased we found the inversion to be surprisingly stable with a unique cluster of acceptable parameters despite the nonlinearity of the geologic forward model

volumetric flattening an interpretation tool volumetric flattening is a novel method for automatically flattening 3d seismic cubes that converts seismic volumes to volumes of horizon slices with little or no effort an interpreter can scan over the resulting horizon slices to see channels and other geologic features as they were laid down furthermore the flattening transformation captures the shapes of all horizons in the cube this transformation leads naturally to numerous interpretation applications ranging from isopach analysis to stratigraphic attributes this algorithm is currently able to reconstruct across nearly vertical faults and incorporate hard constraints such as manual picks and well ties in summary this data driven method exploits the computer s ability to honor all of the data in all three dimensions to remap the data to a more geologically intuitive format

loss of provenance information through subsurface diagenesis in plio pleistocene sandstones northern gulf of mexico abstract subsurface alteration of plagioclase potassium feldspar and a variety of nonopaque heavy minerals has substantially modified the detrital composition of plio pleistocene sediments in the northern gulf of mexico albitization of plagioclase and dissolution of unstable grains are the two principal mechanisms of grain alteration grain alteration increases progressively with depth and has taken place without the influence of significant amounts of meteoric fluids the degree to which strictly subsurface grain alteration has affected these young sediments suggests that grain assemblages in older rocks should be viewed most skeptically with regard to their state of preservation

the effects of transport and weathering on heavy minerals from the cascade river new zealand abstract the effects of transport and weathering processes on heavy mineral suites have been assessed by examining suites from the cascade martyr river system westland new zealand and its associated beach these rivers drain a predominantly ultramafic source that supplies a large amount of unstable minerals including forsteritic olivine enstatite diopside actinolite tremolite and ti rich brown amphibole the weathering processes at outcrop which take place in a wet temperate climate have not caused a significant decrease in mineral diversity the only variations in mineralogy that are detectable in the river samples reflect slight variations in catchment lithologies suggesting that weathering processes on the floodplain have not affected heavy mineral suites during transit this indicates that most coarse sediment movement takes place during floods and that coarse sediment does not reside for extensive periods on the floodplain the suites found in the river sands do not differ appreciably from those in the beach indicating that longshore drift does not introduce extraneous sediment to the cascade detritus as it enters the beach furthermore mechanical abrasion processes on the beach have not caused any significant decline in abundance of any of the constituent minerals even of olivine one of the most mechanically unstable heavy minerals therefore neither mechanical abrasion nor weathering has had a marked effect on the heavy mineral suites in the cascade martyr river system

least squares horizons with local slopes and multigrid correlations most seismic horizon extraction methods are based on seismic local reflection slopes that locally follow seismic structural features however these methods often fail to correctly track horizons across discontinuities such faults and noise because the local slopes can only correctly follow laterally continuous reflections in addition seismic amplitude or phase information is not used in these methods to compute horizons that follow consistent phase e g peaks or troughs to solve these problems we propose a novel method to compute horizons that globally fit both local slopes and multi grid correlations of seismic traces in this method we first estimate local reflection slopes by using structure tensors and compute laterally multi grid slopes by using dynamic time warping to correlate seismic traces within multiple laterally coarse grids these coarse grid slopes can correctly correlate reflections that may be significantly dislocated by faults or other discontinuous structures we then compute a

diagenesis provenance and reservoir quality of triassic tagi sandstones from ourhoud field berkine ghadames basin algeria the triassic tagi trias argilo greseux inferieur fluvial sandstones are the main oil reservoirs in the berkine basin algeria nonetheless their provenance and diagenesis and their impact on reservoir quality are virtually unknown samples from the ourhoud field representing the lower middle and upper tagi subunits were studied using a combination of petrographic mineralogical and geochemical techniques the lower tagi sandstones have an average framework composition of q98 3f0 6r1 1 and 95 of the quartz grains are monocrystalline by contrast the middle upper tagi sandstones have an average framework composition of q88 3f9 8r1 9 and 79 7 of the quartz grains are monocrystalline the lower tagi quartz arenites derived from paleozoic siliciclastic rocks whereas the middle upper tagi subarkoses originated mainly from metamorphic terrains this change in provenance is a potential criterion for correlation within the tagi also this change has contributed to the significantly different diagenetic paths followed by the lower tagi quartz arenites and the middle upper tagi subarkoses grain coating illitic clays are abundant in the lower tagi where they exert a critical control on reservoir quality these clays are interpreted as pedogenic and or infiltrated in origin and to have had in part smectitic precursors shallow burial fe dolomite cementation was favored in the downthrown block of the field bounding fault where it contributed to the poor reservoir quality magnesite siderite cements are multiphase the earliest generation is composed of fe rich magnesite that precipitated during shallow burial from hypersaline fluids with high mg ca ratios probably refluxed residual brines associated with the liassic evaporites later magnesite siderite generations precipitated during deeper burial from waters with progressively higher fe mg ratios authigenic vermicular kaolin largely consists of dickite that replaced previously formed kaolinite dickitization was followed by late stage illitization related to the dissolution of detrital and authigenic k feldspar quartz the most abundant cement was mainly sourced by the pressure or clay induced dissolution of detrital quartz and is a critical factor controlling the reservoir quality overall quartz cement is more abundant in the lower tagi than in the middle upper tagi and this increase correlates with a decrease in average porosity within the lower tagi quartz cement abundance is stratigraphically very variable which is in part related to facies controlled variations in grain coating clay resulting in major vertical variations in reservoir quality anhydrite and barite cements postdate quartz overgrowth the sulfate necessary for their formation was likely sourced by deep subsurface dissolution of late triassic liassic evaporites

effects of sandstone provenance on reservoir quality preservation in the deep subsurface experimental modelling of deep water sand in the gulf of mexico deep water turbidite sandstone reservoirs in the gulf of mexico have been sourced from a variety of provenance terrains as a result the framework composition of each reservoir in the basin varies widely including volcanic rich litharenite oligocene vicksburg feldspathicrich lithic arkose oligocene frio metamorphic rich feldspathic litharenite palaeogene wilcox lithic poor quartzarenite miocene quartz rich sublitharenite cretaceous and quartzand feldspar rich subarkose norphlet provenance driven differences in composition have a complex but critical influence on how each of these reservoirs responds to burial induced changes in depth fluid pressure effective stress and temperature a combination of petromod and touchstone modelling programs are used in this study to simulate the influence of provenance on compaction and cementation of the main reservoir types in the gulf of mexico for example modelling results predict that at higher levels of thermal exposure some lithic rich sands although more ductile and highly compacted will experience less quartz cementation than less ductile quartz rich sands thereby preserving a higher range of porosity and permeability furthermore modelling results predict that temperature effective stress depth windows for optimal reservoir quality preservation vary widely depending on sandstone provenance the evaluation of sandstone grain composition and subsequent interpretation of sand provenance has proven to be a useful methodology for oil and gas exploration for many years specific applications of provenance studies are varied and have included the following assistance in the interpretation of basin evolution and tectonic setting dickinson 1985 help in discriminating sandstone petrofacies and source areas ingersoll 1990 interpretation of relief and climate of source areas folk 1980 help with the interpretation of palaeo drainage and sediment dispersal patterns lowe et al 2011 and help with improving stratigraphic correlation morton hurst 1995 recent workers have used provenance as a means of discriminating potential areas of basins with higher reservoir quality potential vincent et al 2010 2013 provenance reconstruction has also become a critical step in selecting the most appropriate analogues for predictive reservoir quality modelling using diagenetic modelling software such as exemplarw lander walderhaug 1999 and touchstone lander et al 2008 what has not been reported as yet is the degree to which provenance affects predictive modelling results with this in mind we pose a question could provenance related differences in sandstone composition within a single basin be large enough to significantly affect predictive modelling results this study is intended to address that question by comparing a variety of sandstone compositions across a wide range of simulated burial histories specifically sandstone compositions representing the mesozoic through tertiary gulf of mexico reservoirs of the deep water basin are used in a series of test cases this basin provides a natural laboratory for testing the effects of provenance on reservoir quality prediction and the findings from this study are intended to be used for global application provenance and reservoir quality modelling provenance transport distance climate and depositional setting all affect the initial detrital composition and to some extent the textural attributes of sandstone reservoirs at the onset of burial depositional texture and composition greatly control the rate and style of compaction and other diagenetic processes that occur during burial specific subsurface processes that are affected by initial sand composition include the following 1 mechanical compaction 2 chemical compaction 3 dissolution of unstable minerals 4 precipitation of quartz cement 5 precipitation of other cements e g carbonates zeolites sulphates from scott r a smyth h r morton a c richardson n eds 2014 sediment provenance studies in hydrocarbon exploration and production geological society london special publications 386 27 47 first published online september 12 2013 http dx doi org 10 1144 sp386 17 the geological society of london 2014 publishing disclaimer www geolsoc org uk pub ethics at conocophillips on august 28 2014 http sp lyellcollection org downloaded from

modification of heavy mineral assemblages in english coversands by acid pedochemical weathering summary weathering of non opaque heavy minerals in five english soil profiles developed in texturally homogeneous late devensian coversands has been investigated by spline interpolation of detailed mineral counts values for d90 90 mineral depletion derived from the splines suggest a depletion sequence that is generally applicable to moderately acid weathering of sediments apatite olivines amphiboles pyroxenes epidotes garnets more resistant minerals weathered minerals form three groups each of which is eliminated in an almost discrete stage weathering is accompanied by a characteristic developmental sequence of surface textures weathering rates of most of the silicate minerals are probably determined mainly by their fe2 contents effective surface areas and soil ph considerable variations in the depth and severity of weathering between profiles may reflect differences in vegetation histories heavy mineral weathering is related to soil chemistry to examine its implications for podzol genesis

domain transform a tool for imaging and interpreting geomorphology and stratigraphy in seismic volumes the presence of complex structure on seismic data often makes it difficult to recognize and interpret depositional systems in the volume a number of techniques under the broad topic of chronostratigraphy have been developed in recent years to address this problem and enable more complete imaging and interpretation of seismic geomorphology and stratigraphy a domain transform dt is an interpretation guided process designed to remove some or all structural deformation from a seismic volume it improves the imaging of paleo depositional systems by creating a volume that consists of approximations of paleo depositional surfaces such volumes are ideal for imaging analysis and interpretation of seismic geomorphology and stratigraphy

synthetic heavy mineral stratigraphy applications and limitations abstract a multi disciplinary study of the dominantly fluvial lower triassic otter sandstone formation east devon uk is presented the approach integrates a variety of methods including sedimentology conventional heavy mineral analysis single grain microprobe analysis and elemental whole rock geochemistry icp aes and icp ms a species level conventional heavy mineral study is compared to a whole rock geochemical analysis for the corresponding samples to investigate whether or not heavy mineral compositions can be discriminated from elemental whole rock data the comparison provides sufficient evidence that the absolute and relative abundance of some of the heavy minerals apatite iron titanium oxides monazite and zircon can be discriminated geochemically the established element mineral relationships are used to construct both synthetic heavy mineral assemblages and synthetic heavy mineral index values from the geochemical data which show considerable similarity to those of the conventional heavy mineral analysis the presented synthetic heavy mineral logs display intraformational packages that enable subdivision of this barren continental succession furthermore the observed subdivision is correlatable over a considerable distance when extended into the offshore wessex basin the chemical approach unquestionably lacks the sensitivity of conventional heavy mineral analysis however by comparison it is rapid this novel approach demonstrates that synthetic heavy mineral stratigraphy based as here on a well constrained stratotype has considerable potential for creating high resolution correlations in both outcrops and the subsurface and may be of significant value to people working with reservoir characterisation

accurate relative earthquake hypocenters reveal structure of the burma subduction zone the burma arc links the himalaya to the andaman sumatra trench and comprehension of the geological features in the region is vital to understand the active tectonic processes in the area subduction on the sumatra trench produced the devastating 2004 sumatra earthquake m w 9 0 but the mechanisms accommodating relative india sundaland motion in burma are still unknown previous seismological studies of the area use only earthquake catalog hypocenters so structural details of subducted material remain poorly understood here accurate relative hypocenters for 81 earthquakes are estimated using first arrivals picked from regional and teleseismic recordings depth determination is improved using measured travel time differences between p onsets and depth phases pp and sp the results clearly illustrate a slab 21 25 n dipping 25 at 40 80 km deep 40 at 80 120 km deep and 60 at 120 160 km deep and its strike follows the indo burman ranges at latitudes 25 n earthquakes become more shallow and a diffuse picture of hypocenters with an east west lateral discontinuity at depth is observed indicating lateral deformation of the slab previous studies suggest there is a transition at 90 km deep from shallower strike slip earthquakes to deeper thrust type events here accurate depth estimates combined with confirmation of two global centroid moment tensor solutions using body wave modeling shows that thrust and strike slip earthquakes both occur deeper than 100 km in the burma arc

heavy mineral assemblages in sandstone intrusions panoche giant injection complex california u s a excellent exposure from part of the panoche giant injection complex in the san joaquin valley is used to examine provenance characteristics of sandstone intrusions with respect to two parent sandstone units that are known to feed the sand injection complex the succession is part of the upper mesozoic to lower tertiary great valley group and was deposited in a deepwater part of an evolving deep water forearc basin the section examined is mudstone dominated and the sand injection is constrained to have occurred in the danian sandstones in the dosados member moreno fm are identified as the main parent unit on the basis of total heavy mineral assemblage compositions and varietal studies of selected minerals tourmaline garnet titanite apatite and zircon fluidized sand is emplaced in turbulent flow conditions creating high velocity inter grain collisions evidence of comminution and diminution of minerals that are less hard than quartz is documented using indices for the relative hardness tah and durability tad of heavy minerals preferential settling of high density zircon relative to lower density tourmaline produces density controlled variations of zircon tourmaline upward through the injection complex heavy mineral dissolution occurred in the most permeable sandstone intrusions and is believed to record the effects of mid eocene deep weathering when subtropical climate prevailed in the study area detrital heavy mineral assemblages which are dominated by titanite and garnet record erosion of the sierran metamorphic terrane with mafic and alkaline plutonic rocks zircon with u pb ages of c 140 160 ma and c 90 110 ma consistent with earlier independent analyses record erosion of sierran granitoids on the paleo seafloor enrichment of ca amphibole and epidote is indicative of sierran provenance concurrent with sand extrusion the presence of na amphibole in the uhalde sandstone supports earlier work that suggested sediment input from obducted seafloor to the west

horizon volumes with interpreted constraints abstracthorizons are geologically significant surfaces that can be extracted from seismic images color coding of horizons based on amplitude or other attributes can help reveal ancient sedimentary environments and structural features extracted horizons are also used for building structure models and stratigraphic interpretations we propose two methods for constructing seismic horizons aligned with reflectors in a 3d seismic image the first method generates horizons one at a time the second method generates an entire volume of horizons at once by first computing a relative geologic time volume from seismic normal vectors rather than gradually building a horizon by extending one or more seed points to a surface along seismic reflectors both of our methods generate whole horizons at once by solving partial differential equations derived from seismic normal vectors the most significant new aspect of both methods is the ability to specify perhaps interactively during interpretation a small number of

building 3d subsurface models conforming to seismic structural and stratigraphic features abstractsubsurface modeling from seismic and borehole data is important for reservoir prediction geophysical exploration and production a reasonable model should honor borehole rock properties and conform to seismic structural and stratigraphic features such a subsurface model can be difficult to build in cases complicated by faults and unconformities automatic and semiautomatic methods have been proposed to build subsurface models from seismic and borehole data however seismic structural and stratigraphic features and borehole measurements are not fully used in most methods i have developed a workflow to fully use seismic and borehole data to build subsurface models that honor borehole measurements and conform to seismic horizons faults unconformities and stratigraphic features such as channels in this workflow i first automatically remove the faulting and folding in seismic and borehole data and map them into an unfaulted and flattened space in which seismic reflectors and borehole measure

generic relationships in the mineral chemical stratigraphy of turbidite sandstones ratios of abundance of hydraulically and diagenetically equivalent heavy minerals apatite tourmaline garnet zircon from deep water sandstones of similar age and derived from the same overall source terrain have contrasting trends the differences are explained by contrasting sediment transport paths deep water sandstones with fluctuating heavy mineral ratios are inferred to be derived directly from alluvial basins bypassing any contemporaneous shallow marine shelf deep water sandstones with homogeneous heavy mineralogy are inferred to be fed by sediment that originally accumulated on shallow marine shelves but was subsequently mixed

geotime a 3d automatic tool for chronostratigraphic seismic interpretation and filtering chronostratigraphic seismic interpretation provides insight into basinal evolution because it maps the internal stratigraphic architecture this method has been widely used for well placement optimization and reservoir model building after many years of research at total a software tool called geotime has been developed for automatic chronostratigraphic analysis of seismic data particularly in complex geologic settings this tool first creates automatically from the seismic a 3d isogeologic time volume which highlights all stratigraphic surfaces then a 3d wheeler diagram volume is obtained by segmenting the seismic volume into different depositional or nondepositional packages this diagram provides better understanding of the spatial distribution of deposition through geologic time finally this tool can be used to automatically or semi automatically track chronostratigraphic surfaces

correlation of fluvial strata in the subsurface a review abstract correlation of ancient fluvial strata in the subsurface is challenging due to complex facies architectures and the lateral discontinuity of facies over short distances 10 km the complexity of the strata is due to the interplay of allogenic factors that determine the rate of creation of accommodation sediment supply and ultimately fluvial architectures on regional scales the application of commonly used stratigraphic techniques in such successions has allowed for improved regional correlations and an enhanced understanding of the evolution of basin fills lithostratigraphy biostratigraphy chemostratigraphy magnetostratigraphy event stratigraphy sequence stratigraphy pedostratigraphy chronostratigraphy in particular geochronology cyclostratigraphy and provenance stratigraphy are assessed outlining their benefits drawbacks and application using several case studies lithostratigraphy is highly discouraged as facies boundaries are often time transgressive on the contrary chemostratigraphy event stratigraphy and provenance stratigraphy show excellent potential for correlating ancient fluvial strata as key signatures can be recognized between different localities over distances greater than 25 km the character and thickness of paleosols can also greatly enhance both sequence stratigraphic and pedostratigraphic correlations the most promising correlation technique involves the use of chronostratigraphy in particular geochronology the high precision radiometric dating of tuffs or precisely dating the youngest zircon population in a sandstone sample using u pb ca tims when available provides a precise and independent way to correlate fluvially dominated strata unambiguously over large distances 100 km the integration of several techniques such as sequence stratigraphy in conjunction with pedostratigraphy is also recommended to construct a comprehensive stratigraphic framework for fluvially dominated successions the most appropriate correlation technique is dependent on several factors including budget the purpose and scope of the study and whether the data come from outcrops or the subsurface improved correlations will enhance our understanding of ancient fluvial systems and their resource potential

3 d seismic attributes using a semblance based coherency algorithm seismic coherency is a measure of lateral changes in the seismic response caused by variation in structure stratigraphy lithology porosity and the presence of hydrocarbons unlike shaded relief maps that allow 3 d visualization of faults and channels from horizon picks seismic coherency operates on the seismic data itself and is therefore unencumbered by interpreter or automatic picker biases we present a more robust multitrace semblance based coherency algorithm that allows us to analyze data of lesser quality than our original three trace cross correlation based algorithm this second generation semblance based coherency algorithm provides improved vertical resolution over our original zero mean crosscorrelation algorithm resulting in reduced mixing of overlying or underlying stratigraphic features in general we analyze stratigraphic features using as narrow a temporal analysis window as possible typically determined by the highest usable frequency in the input seismic data in the limit one may confidently apply our new semblance based algorithm to a one sample thick seismic volume extracted along a conventionally picked stratigraphic horizon corresponding to a peak or trough whose amplitudes lie sufficiently above the ambient seismic noise in contrast near vertical structural features such as faults are better enhanced when using a longer temporal analysis window corresponding to the lowest usable frequency in the input data the calculation of reflector dip azimuth throughout the data volume allows us to generalize the calculation of conventional complex trace attributes including envelope phase frequency and bandwidth to the calculation of complex reflector attributes generated by slant stacking the input data along the reflector dip within the coherency analysis window these more robust complex reflector attribute cubes can be combined with coherency and dip azimuth cubes using conventional geostatistical clustering and segmentation algorithms to provide an integrated multiattribute analysis

authigenic apatite in a fluvial sandstone sequence evidence for rare earth element mobility during diagenesis and a tool for diagenetic correlation abstract apatite grains in heavy mineral separates of samples from the statfjord formation triassic lower jurassic north sea exhibit variably corroded detrital cores and euhedral diagenetic overgrowths in the overlying marine deposits of the nansen formation apatite grains show no evidence of either corrosion or overgrowths compositions of detrital apatite in both formations are indistinguishable indicating that the source areas responsible for statfjord and nansen deposition included similar apatite bearing lithologies apatite corrosion in the statfjord formation is considered to be a response to leaching by acidic groundwaters during sediment storage on the fluvial floodplain any variations in the degree of corrosion that may have been generated by differences in floodplain residence time have been homogenized by sediment reworking laser ablation microprobe inductively coupled plasma mass spectrometry and wavelength dispersive electron microprobe analysis indicate that the authigenic apatite contains high abundances up to 3 5 total of the rare earth elements ree implying a degree of ree mobilization during diagenesis ree profiles nasc normalized for the authigenic apatites are convex upwards with enrichment of the mree the ree are considered to have been derived from dissolution of other ree bearing heavy minerals e g garnet during alluvial storage with possible contributions from dissolved feldspars which may account for slight positive eu anomalies and rees adsorbed onto clay surfaces ree mobilization was probably enhanced by fluoride and or phosphate complexes although organic complexing related to pedogenic processes is also a possibility through the statfjord formation authigenic apatite displays subtle variations in major element minor element and trace element chemistry which may find application as a tool for diagenetic correlation

the application of fission track analysis to the dating of barren sequences examples from red beds in scotland and thailand in continental red beds facies which often contain little or no organic material for biostratigraphic dating fission track ft analysis of detrital zircon crystals represents one method by which a maximum stratigraphic age may be determined in addition ft analysis of detrital apatite provides a means of palaeotemperature estimation especially in areas where there is insufficient or unsuitable organic matter for vitrinite reflectance two examples of the application of ft analysis to the solution of stratigraphic problems in red bed sequences are described from scotland and thailand from authors

stratal slicing benefits and challenges in the petroleum industry seismic interpretation meth odology varies according to a subject s scale in basinal to field scale hundreds of meters the goal is to map gross stratigraphic and structural features that are associated with petroleum systems including stratigraphy and depositional history hydrocarbon generation migration and entrapment seismic stratigraphy and sequence stratigraphy are common tools for this purpose at the reservoir scale meters to tens of meters the goal becomes characterizing distribution and physical properties related to volumetrics and production in a reservoir system in this task details are crucial seismic lithology and inversion seismic geomorphology and sedimentology and attribute analysis are some of the tools developed for this purpose

samarium neodymium isotope stratigraphy of the lunde and statfjord formations of snorre oil field northern north sea two sequences of fluviatile sediments from snorre oil field are investigated by the sm nd isotopic method the results illustrate distinctly different source areas for the upper triassic upper member of the lunde formation and for the lower jurassic statfjord formation the lunde formation has sm nd provenance ages mainly in the range 1500 to 1700 ma which is not diagnostic of a specific source area the statfjord formation has provenance ages in the range 1700 to 2150 ma this is old within the context of source areas in the hinterland of the northern north sea and provenance partly from the archaean lewisian shield to the northwest is suggested intensive sampling through the statfjord formation in one well illustrates that the provenance ages evolve systematically with time the pattern provides a detailed record of how source areas evolved during deposition of these strata the possibility is recognized of correlating changes or trends in provenance between wells the data also suggest that sm nd ratios and isotopic compositions of these rocks are not significantly fractionated between fine and coarse grained sediments by mechanical or diagenetic processes

active tectonics of the pamirs and karakorum the source parameters of moderate to large sized earthquakes and the spatial distribution of earthquake hypocenters are used to investigate the active tectonics and three dimensional configuration of the subducted lithosphere in the pamir karakorum intracontinental convergence zone the continental collision has resulted in intense deformation in the upper crust the deformation is distributed over a broad area and is absorbed by thrust and strike slip faulting along the northern margin of the pamirs where the deformation due to continental collision is most intense the northern pamir thrust and several major fault zones mark the present boundary most of the earthquakes that occurred in these fault zones are shallow crustal events with focal mechanism solutions correlated with the tectonic features of the region along the pamir front thrust faulting dominates while on the western and eastern edges of the pamirs the style of deformation is characterized by oblique thrusting with a component of strike slip motion thrust type events beneath the tadjik depression indicate that both the sedimentary rocks and the basement are involved in shortening right lateral strike slip motion is observed on the eastern edge of the pamirs where they border the tarim basin and in the talas fergana kun lun fault zone a southward dipping seismic zone beneath the pamirs and karakorum indicates that the asian lithosphere has been subducted along the pamir front to a depth of at least 200 km this interpretation is consistent with published geological and geophysical data focal mechanism solutions of some intermediate depth events beneath the pamirs show strike slip faulting with approximately n s horizontally oriented p axes indicating that nearly horizontal compression at the intermediate depth is the predominant mode of deformation a 90 km deep event beneath the karakorum is interpreted as occurring in the subducted asian lithosphere the fact that the p axis of this event is oriented parallel to the descending plate suggests downdip compression within the asian lithosphere the overall tectonics of the region is interpreted as a consequence of the underthrusting asian lithosphere being impinged upon by the shallow northward underthrusting indian lithosphere

effects of heterogeneity on earthquake location at isc abstract earthquake location at the international seismological centre is carried out by routine least squares analysis using jeffreys bullen travel times it is impossible to examine every earthquake in detail but when obvious discrepancies in location become apparent adjustments can be made by analysts usually in phase identification or the restraint of depth such discrepancies often result from inappropriateness of the jeffreys bullen model the effect is most apparent in subduction zones where it is often difficult to reconcile local and teleseismic observations and differences from the standard model can result in substantial mislocations large events located by steeply descending teleseismic phases may be only slightly misplaced with large residuals at close stations giving a true indication of velocity anomalies small events however are often significantly misplaced although giving small residuals at a few close stations these apparently well located events give compensating misinformation about velocities and location in other areas especially mid oceanic ridges difficulties in depth determination are likely to be related to deviations from a laterally homogeneous velocity model

an introduction to this special section chronostratigraphy in 1977 we saw the publication of aapg memoir 26 seismic stratigraphy applications to hydrocarbon exploration in this book peter vail and his colleagues in a series of papers introduced the industry to the concepts of seismic sequences the construction of chronostratigraphic charts and how the seismic data could be used to estimate the global rise and fall of sea level in this work they also showed how the shape of the reflections and their lapping relationships could be used to predict depositional environment which could be used to predict sediment type and facies

simultaneous travel time inversion for earthquake location and subduction zone structure in the central aleutian islands a combined location and velocity inversion technique is applied to travel time data from 151 well recorded central aleutian earthquakes the data include p and s wave arrivals at stations of a local network and p pp and sp wave arrivals at teleseismic stations after correction for crustal structure at the reflection points the depth phases pp and sp provide important constraints on subduction zone structure not ordinarily resolved by other types of data the structure is assumed to vary only across the arc and in depth it is parameterized with cubic splines by specifying the velocity at each point of a gridded arc cross section to avoid ray tracing it is assumed that the velocity part of the problem is linear preliminary results show that deep earthquakes apparently occur within a narrow downdip zone near the upper surface of the descending slab in contrast with previous studies which have located them within the presumably stronger and colder inner core of the slab a slab thickness of 80 100 km and a downdip length of about 400 km well below the deepest seismic activity are indicated the slab is characterized by seismic velocities as much as 11 higher than the surrounding mantle in its upper portions and 4 6 higher at depth a sharp velocity gradient and lower velocities occur directly beneath the volcanic arc near the top of the slab the slab anomaly appears to spread out and fall off very slowly with depth these are probably not real effects but consequences of the omission of three dimensional ray tracing

characteristics and evolution of the late permian source to sink system of the beisantai area in the eastern junggar basin nw china abstract many studies have focused on the tectonic evolution and sedimentary processes of the beisantai uplift nw china during the late permian however the sedimentary characteristics of the area are still not well documented due to a complex tectonic evolution of the uplift and the limited distribution of core data to understand the sedimentary evolution of this study area a source to sink system research is adopted first the research redefines the sequence stratigraphic framework of the late permian which corresponds to a complete third order sequence that can be further divided into a transgressive system tract tst and a regressive system tract rst then the integration of three dimensional 3d seismic reflection data well logs mud logs and core data provides new insights into the transportation and sedimentary processes within the source to sink system the different characteristics of the source area transfer system and sedimentary paleogeomorphology between the tst stage and rst stage ultimately led to significantly different sedimentary characteristics in the two stages in the tst stage the source to sink system exhibited a continued transgressive depositional characteristic that matched the sediment discharge evolution the steeper sedimentary paleogeomorphology enabled the development of large scale fan deltas with few beach bars during the rst stage the source to sink system had low sediment discharge and a smooth sedimentary paleogeomorphology the source to sink system was predominantly characterized by small scale beach bars with few fan deltas with the decreasing level of sediment discharge and continued smoothing of the sedimentary paleogeomorphology the beach bars expanded

the wheeler diagram flattening theory and time abstract wheeler diagrams are excellent tools to represent time stratigraphy these diagrams are produced by considering interpreted surfaces as snapshots of geologic times linked with transit cycles of the base level the base level defined in the nineteenth century can be regarded as an ultimate time reference for stratigraphic units the application of the base level concept to deep marine settings is a more recent development even though the same definition applies to all depositional environments flat timelines are also known as flattening theories can produce similar looking diagrams and have an edge that they operate in 3d however flattening of a dataset can be achieved with various techniques which are reviewed and the optimum algorithm which has a future application for hydrocarbon and research communities is improved to honor geological constraints such as faults and horizons a secondary aspect of the wheeler diagrams is the dual nature of geological timelines the diagrams are originally plotted on a relative geological time scale and no formal technique has yet been recommended for time calibration in this paper a nomogram approach is proposed to calibrate the timelines the representation of unconformities that are parallel to bedding planes is another important idea presented in this paper

stratal slice the next generation vail and his colleagues 1977a b laid a foundation for seismic chronostratigraphy by analyzing the relative rise of sea level indicated by coastal onlap these workers invented a novel way of converting a stratigraphic cross section in the depth or traveltime domain to a chronostratigraphic chart in the wheeler domain figure 1a and figure 1b with the widespread use of seismic data in the industry such conversion can now be achieved conveniently with the proper software at the basinal regional or prospect scale figure 1c and figure 1d

generating a relative geologic time volume by 3d graph cut phase unwrapping method with horizon and unconformity constraints abstractconstruction of a relative geologic time rgt volume is vital to seismic geomorphological and sedimentological interpretation seismic instantaneous phase unwrapping provides an excellent approach for generating an rgt volume although several 2d or 3d seismic phase unwrapping results have been published there is a clear need for discussions on concrete methods for seismic phase unwrapping we have developed the graph cut phase unwrapping method which performs well in the interferometric synthetic aperture radar image processing it has advantages of strong discontinuity preserving ability and high computing efficiency to make it suitable for 3d seismic phase unwrapping the method is improved by extending it from 2d to 3d and by introducing the seismic horizon and unconformity constraints the strong and continuous conformable seismic events which can be easily tracked by certain autopicking methods are introduced as horizon constraints for guiding the phase unwrapping to ensure a constant

frequency dependent relocation of the 1992 nicaragua slow earthquake an empirical green s function approach we present a two step empirical green s function analysis of the slow 1992 nicaragua earthquake mw 7 7 in the first step a narrow band cross correlation method recovers he relative source amplitude and phase delay spectra between the main shock and a suitable empirical green s function egf the analysis is performed at 2mhz intervals from 4 to 44mhz using first and second orbit fundamental mode rayleigh waves from the low frequency relative amplitudes we obtain the differences in mechanism and depth between the main shock and the egf and we present a method to correct for such differences in the second step we use the relative spectra to relocate the main shock relative to the egf position al a set of discrete frequencies in addition we invert the relative spectra for the relative source time functions using both a positivity and a smoothing constraint unlike standard egf deconvolution the spectral resolution achieved in our cross correlation method allows us to determine the conditions of validity of the egf approach from our analysis it appears that the centre of low frequency radiation 4 10 mhz during the slow 1 992 nicaragua earthquake is situated about 40 km trenchwards of the epicentre between 20 and 44 mhz centroids occupy intermediate positions between the low frequency points and the epicentre relative source time functions have an average duration of about 120 s they reveal a slow 1 km s1 smooth component of rupture with unilateral directivity towards the se along the trench axis a large amount of slip occurred at shallow depths at the interface between the subducted cocos plate and the caribbean plate in agreement with tsunami models of the event the low frequency radiation appears to originate from a zone devoid of teleseismic aftershocks this suggests that unusual frictional properties at the plate interface perhaps related to subducted sediments are responsible for the slow and smooth nature of the 1992 nicaragua earthquake

provenance of eolian sands in the ulan buh desert northwestern china revealed by heavy mineral assemblages abstract accurate identification of the provenance of eolian sand in deserts is essential to study sedimentation processes in the earth system exposed bedrock surrounding the desert has been regarded as the main source of eolian sand in some deserts of the world however few studies have focused on whether paleolacustrine deposits and bedrock outcrops in desert hinterlands are the main sources of eolian sand in this study we selected the ulan buh desert in northwestern china as the study area and a total of 99 samples were collected throughout the desert and nearby regions to study the provenance of the current eolian sand based on their heavy mineral assemblages and contents the results showed similar heavy mineral assemblages among the eolian sand the bedrock to the northwest of the desert and the paleolacustrine deposits and exposed bedrock in the desert hinterlands suggesting multiple provenance for the eolian sand in the ulan buh desert the sources of the eolian sand in the ulan buh desert include bedrock to the northwest gobi to the west and paleolacustrine deposits and exposed bedrock in the desert hinterlands helan mountains bedrock and yellow river fluvial deposits near the desert contribute little to the eolian sand moreover the paleolacustrine deposits and exposed bedrock in the desert hinterlands should not be neglected as the potential provenance of eolian sand in other studies this study enhances understanding the provenance of eolian sand in the deserts of northern china

3 d seismic imaging and seismic attribute analysis of genetic sequences deposited in low accommodation conditions a multidisciplinary team composed of stratigraphers petrophysicists reservoir engineers and geophysicists studied a portion of boonsville gas field in the fort worth basin of north central texas to determine how modern geophysical geological and engineering techniques could be combined to understand the mechanisms by which fluvio deltaic depositional processes create reservoir compartmentalization in a low to moderate accommodation basin an extensive database involving well logs cores production and pressure data from 200 plus wells 26 mi2 67km2 of 3 d seismic data vertical seismic profiles vsps and checkshots was assembled to support this investigation the reservoir system we studied was the bend conglomerate a productive series of gas reservoirs composed of middle pennsylvanian fluvio deltaic clastics 900 to 1300 ft 275 to 400 m thick in our project area we were particularly interested in this reservoir system because evidence suggested that many of the sequences in this stratigr

use of spectral gamma ray data to refine subsurface fluvial stratigraphy late cretaceous strata in the book cliffs utah usa high resolution sub seismic stratigraphic correlation in fluvial strata is extremely difficult using conventional subsurface core and wireline log data e g gamma ray neutron density sonic logs spectral gamma ray logs provide additional data on lithological composition that can aid identification of chronostratigraphic surfaces in a high resolution sequence stratigraphic correlation framework the application of spectral gamma ray data in constructing such a framework is demonstrated using data from exposures and the subsurface from the cretaceous non marine blackhawk formation and castlegate sandstone of the book cliffs area utah usa these strata provide an ideal test case for the use of spectral gamma ray data in fluvial stratigraphy because interpretations can be compared directly with a high resolution sequence stratigraphic framework from coeval shallow marine strata exposed nearby the stratigraphic abundance of coals and relatively uniform th k ratio which indicates uniform clay mineralogy in mudstone sections of the non marine blackhawk formation implies a humid subtropical climate throughout its deposition variations in facies architecture and stratigraphy are therefore interpreted to have been driven principally by fluctuations in relative sea level and hinterland tectonics fluvial and fluvio tidal sandstones within incised valleys which lie above erosional sequence boundaries have a highly variable spectral gamma ray character but locally are marked by distinctive heavy mineral lags and concentrations th consistently 3 ppm on the interfluves of incised valleys sequence boundaries are marked by palaeosols that locally have a distinctive leached potassium depleted character th k ratio 17 lateral variability in spectral gamma ray character of sequence boundaries is consistent with facies and sequence stratigraphic models of the non marine blackhawk formation and castlegate sandstone but sequence boundaries do not exhibit a clear diagnostic character in every location in addition high th k ratios of the type noted at interfluve palaeosols may be produced by potassium depletion beneath coal seams as a result of acid groundwater percolation during early diagenesis and by thorium enrichment in heavy mineral lags within foreshore sandstones these alternative interpretations can be eliminated if high th k ratios occur in intervals lacking coal seams and shallow marine sandstones respectively thus within the context of a sound understanding of detrital mineralogy diagenetic history facies and appropriate sequence stratigraphic models spectral gamma ray data allow sequence boundaries to be identified and correlated in non marine fluvial strata at least 80 km from the interpreted coeval shoreline

geochemical variability induced by entrainment sorting quantified signals for provenance analysis abstract a substantial part of the mineralogical and chemical heterogeneity of clay poor sands at the bed scale results from tractive redistribution of the grains in the bedload since coarse and light particles are more easily entrained than denser and smaller heavy minerals the latter commonly concentrate in grain scale lags that alternate with sand depleted in these minerals when sampled and analysed at the centimetre scale this primary heterogeneity translates into nice geochemical covariations between the minor trace elements that concentrate in some heavy minerals zr ti p cr v y ce among others regressing these variations allow us to derive two chemical fingerprints of the sand one records the proportions between some heavy minerals the other the average composition of framework grains i e a sand composition corrected from the contribution of heavy minerals both relate to provenance and allow different sand beds to be compared in appropriate spider diagrams the construction of these diagrams their potential use and their limitations are discussed using two contrasting examples continental channel sandstones from the ravenscar group middle jurassic yorkshire uk illustrate how these geochemical fingerprints vary from the local to the group scales and how robust they are against diagenetic overprint at ravenscar the zr vs ti v cr covariations record the presence of ti oxides and magnetite together with zircon and of volcanic lithoclasts at the deposition stage despite a high degree of diagenetic alteration overbank sandstones lateral to channels from the deep marine gres d annot formation eocene oligocene alps illustrates how apatite and monazite delivered by a dominantly granitic source generate covariations between zr and p y ce and th contents with characteristically steep slopes

application of multi seismic attributes analysis in the study of distributary channels abstract during the exploration of stratigraphic reservoirs the key to locating these reservoirs is to identify the sandstone distribution seismic data can be used to recognize large scale distributary channel sedimentary bodies however depiction of sedimentary bodies in small distributary channels using traditional interpretation data from seismic profiles is extremely difficult in the upper cretaceous first sandstone bed of the third member of the nenjiang formation called the nen 3 member for simplicity in the xb area of the southern songliao basin distributary channels are the main sedimentary facies the distributary channels migrate frequently therefore it is difficult to precisely depict the morphology of the channel and the distribution of sandstone in this study we investigated the deposition of distributary channels using equal scale formation plane seismic attributes such as post stack amplitude instantaneous amplitude and seismic waveform classification analyzed well logging data from target formations and mapped the distribution of distributary channels this study shows that seismic sedimentological study and stacking multiple attribute analysis can identify the distribution of distributary channels precisely and effectively the attributes of equal scale strata slices are evidently superior to those of time and horizon slices attribute extraction and selection of equal scale formation slices is an essential step the comprehensive selection of seismic attributes that show a good correlation to a single well can be used to clearly depict channel bodies the overlap of the 40 hz single frequency energy and the rms amplitude depicts the sedimentary characteristics and shapes of sandstone bodies in main channels as well as small scale distributary channels more clearly than a single attribute these attributes show that the first sandstone bed of the nen 3 member was from distributary channels with complex shapes the distributary channels cut across each other vertically and laterally it indicates that during the deposition of the nen 3 member in xb area the direction of the main channel is from north to south and the provenance could be from north and east the method of this paper may provide some helpful suggestions to the geologist using seismic attributes to undertake research on sedimentary environment at other places in the world

centroid depths of mid ocean ridge earthquakes dependence on spreading rate from inversions of teleseismic p and sh waveforms we have determined the source parameters of 50 large earthquakes that occurred during 1962 1983 on slowly spreading mid ocean ridges all events are characterized by predominantly normal faulting on planes that dip at approximately 45 and strike parallel to the local trend of the ridge axis centroid depths range from 1 to 6 km beneath the seafloor the p waves from these earthquakes show strong water column reverberations suggesting that fault rupture extended to the seafloor under the assumption that the centroid depth marks the mean depth of fault slip earthquake faulting extended to a depth of 2 10 km for these earthquakes the water depths inferred from the predominant periods of the water column reverberations constrain the epicenters of these earthquakes to lie within the relatively deep inner floor of the median valley the maximum centroid depths of ridge crest earthquakes decrease with increasing spreading rate and the maximum seismic moment may also decrease with increasing spreading rate these results indicate a general decrease with spreading rate in maximum thickness of the mechanically strong layer beneath the ridge axis region the concentration of large earthquakes within the deepest parts of the median valley and the depth extent of seismic faulting support lithospheric necking models for the origin of the median valley

predictive painting of 3d seismic volumes predictive painting is a numerical algorithm that spreads information in 3d volumes according to the local structure of seismic events the algorithm consists of two steps first local spatially variable inline and crossline slopes of seismic events are estimated by the plane wave destruction method next a seed trace is inserted in the volume and the information contained in that trace is spread inside the volume thus automatically painting the data space immediate applications of this technique include automatic horizon picking and flattening in applications to both prestack and poststack seismic data analysis synthetic and field data tests demonstrate the effectiveness of predictive painting

deciphering the late paleozoic to mesozoic tectono sedimentary evolution of the northern bohemian massif from detrital zircon geochronology and heavy mineral provenance from permian to late cretaceous the northern bohemian massif experienced a complex intra plate tectono sedimentary evolution involving development of at least four generations of sedimentary basins in different settings we examine this protracted evolution using stratigraphic changes in sediment provenance analyzed through heavy mineral assemblages and u pb detrital zircon geochronology by laser ablation icp ms in permian jurassic and late cretaceous successions the provenance data point to multiple temporally evolving sources ranging from local e g the west sudetic island through more distant from elsewhere in the bohemian massif to exotic likely derived from baltica the latter is interpreted as a trace of now completely eroded late jurassic to early cretaceous basin that once covered the lusatian lausitz block and received the baltica derived detritus from northerly fluvial and deltaic depositional systems we suggest that fill of this basin was recycled into the bohemian cretaceous basin during progressive unroofing of the west sudetic island a time slice reconstruction of the paleogeographic and tectono sedimentary evolution of the northern bohemian massif is then developed to show that periods of basin development and deposition early permian late early permian to early triassic middle jurassic early cretaceous and late cretaceous were interrupted by major depositional gaps middle triassic early jurassic mid cretaceous and post early campanian the mesozoic depositional episodes resulted from reactivation of major nw se strike slip fault zones due to stress transfer from the north atlantic rift during jurassic to early cretaceous overridden by the far field effect of convergence of iberia africa and europe during late cretaceous

correlation of sandstones using heavy minerals an example from the statfjord formation of the snorre field northern north sea correlation of sandstones using heavy minerals is dependent on the recognition and quantification of provenance sensitive parameters suitable criteria include ratios of minerals that have similar hydraulic and diagenetic behaviour and properties of populations of individual mineral species sandstones of the statfjord formation in the snorre field display marked variations in their heavy mineral assemblages although hydraulic and diagenetic processes have played some part in generating these variations major changes in the nature of the source material can be detected on the basis of heavy mineral ratio and varietal data these changes in sand provenance can be used to produce a detailed stratigraphic breakdown of the sequence and to correlate from well to well eleven heavy mineral zones have been recognised on the basis of variations in monazite zircon garnet zircon and rutile zircon ratios on the incoming of chloritoid and on the composition of garnet populations the marked changes in provenance result from the proximity of the depositional location to the hinterland and it is considered unlikely that the detailed correlation made in the snorre field area applies to statfjord sandstones in other parts of the northern north sea however there is evidence for some degree of allogenic control on the heavy mineral variations and therefore some events may have regional significance

the hydraulic equivalence of mica abstract settling experiments performed on silt to fine sand sized mica flakes with a holographic micro velocimeter revealed that mica is the hydraulic equivalent of quartz spheres having diameters a factor of 4 to 12 times smaller mica in the very fine to fine sand sizes has been traditionally used by sedimentologists to delineate areas of deposition or nondeposition and potential winnowing of fines and is here found to be the hydraulic equivalent of silt sized particles but not of clay experiments also showed that mica flakes tend to settle at orientations which are neither perpendicular nor parallel to the gravitational vector and tend to generally maintain their orientation throughout equations for the settling of a disc in lerman and others 1974 and that developed by komar and reimers 1978 are shown to be mathematically similar for the coarse silt to fine sand ranges of discs and are adequate predictors of settling rates of mica flakes a comparison of the hydraulic equivalency of quartz spheres to coarse silt through fine sand sized mica flakes is presented

reconstruction of depocenter evolution through time using relative stratigraphic thickness in this article we describe a new approach to seismic stratigraphic interpretation we build on the concept of the relative geologic time attribute introduced by stark 2004 to define a relative stratigraphic thickness attribute which can then be interpreted to reconstruct depocenter migration from seismic data the principles of seismic stratigraphy were established in the classic aapg memoir 26 at this time 1977 manual interpretation of 2d seismic was still typical in the e p industry simple truncation geometries such as onlap downlap and toplap were used to characterize sequence boundaries and flooding surfaces recent work continues to emphasize these 2d concepts for example using them in introductory sequence stratigraphic exercises the routine use of 3d seismic emerged in the 1980s and with it computer assisted interpretation the main focus of the industry was on large structural traps highly effective 3d structural interpretation workflows developed in the 1980s still form the core

relative geologic time age volumes relating every seismic sample to a geologically reasonable horizon the age volume described in this paper can significantly increase the amount of useful geologic information extracted from a seismic data volume this paper has three goals the first is to introduce and describe the relative geologic time volume referred to herein as either an rgt volume or an age volume every seismic sample in an age volume contains an estimate of the relative geologic time for that sample which automatically relates every sample to a geologic horizon the second goal is to discuss some of the applications and advantages of using a rgt volume to store and access seismic interpretation for example it can be used to sculpt a seismic volume along a desired horizon or view depositional changes as a function of geologic time the third goal is to describe two methods for generating such a volume the first employing standard interpretation techniques and the second relying on unwrapping instantaneous phase unwrapping the instantaneous phase is a new holistic approach to interpreting seismic data that can produce a very detailed seismic interpretation the goal of building and using an rgt volume is to extract significantly more geologic information from the seismic data than is available from conventional methods the rgt volume is both a way of storing and retrieving seismic horizons to generate such a volume each seismic sample needs to be assigned an estimate of relative geologic time which in essence connects it to a geologically reasonable horizon in normal sections these relative geologic time values will increase with depth or traveltime high gradients in the rgt volume could be indicative of faults unconformities fluid contacts or interpretation errors while a constant value surface in a rgt volume is a seismic horizon figure 1 contains a portion of the seismic data used to illustrate the

low temperature aqueous mobility of the rare earth elements during sandstone diagenesis abstract diagenetic francolite carbonate fluor apatite occurs as overgrowths on detrital apatite grains in sandstones from the lower jurassic statfjord formation of the north sea the francolite overgrowths are considerably more enriched in the rare earth elements up to 1 wt ce 2 o 3 sr and f than the detrital cores these elements were carried in aqueous solution probably in the form of complex ligands involving organically sourced carbon and halogens it is possible that reported aberrant neodymium isotope model ages within the statfjord formation are the result of mobilization and relative fractionation of sm and nd during diagenesis rather than a result of changes in provenance

diagenetic processes along a basin wide marker bed as a function of burial depth abstract the contessa megabed is a basin wide turbidite bed in the marnoso arenacea formation miocene of the northern apennines italy it has a mixed siliciclastic carbonatoclastic composition and was derived from the southern end of the elongate nw se trending periadriatic foreland basin heavy mineral contents of fifteen contessa samples taken across the whole outcrop area vary systematically zircon tourmaline rutile garnet chloritoid picotite and monazite are ubiquitous staurolite and to a lesser degree titanite are absent along the southwestern margin of the basin and become increasingly present toward the foreland to the northeast where the basin fill becomes progressively thinner other petrologic parameters of the contessa light mineral composition depict a similar geographic trend intrabasinal carbonate clasts are progressively more abundant northeastward toward the shallowest part of the basin whereas the relative percentage of sparite cement increases toward the southwest where the basin fill is thickest among the clay minerals mixed layer illit smectite is more abundant in the shallowest part of the basin and decreases progressively toward the deepest part of the basin petrologic parameters of mostly siliciclastic sandstone beds stratigraphically close to the contessa megabed and derived from the alps to the northwest non contessa samples depict similar trends in spite of their different provenance assuming that the respective compositions of the contessa and non contessa samples were initially homogeneous across the entire basin these areal differences in mineralogy are interpreted to result from varying degrees of diagenesis due to differential sedimentary tectonic load in the asymmetrical periadriatic basin provenance studies must consider this possibility to avoid erroneous reconstructions of sediment paleodispersal systems

detrital magnetite as a provenance indicator abstract detrital magnetite grains carry unique petrographic and chemical fingerprints that can be used in provenance research petrographic analysis of 2 941 detrital magnetite grains in holocene sands from felsic plutonic and volcanic intermediate volcanic mafic plutonic and volcanic and metamorphosed mafic ultramafic parent rocks has found that 58 are polymineralic polymineralic detrital magnetite grains are most common in sands derived from felsic volcanic mafic plutonic and metamorphosed mafic ultramafic parent rocks sands from felsic volcanic parent rocks are characterized by grains with composite or trellis type magnetite ilmenite intergrowths c c t 0 5 whereas sands from marie plutonic and metamorphosed mafic ultramafic parent rocks are characterized by grains with exsolved pleonaste or ulvospinel monomineralic homogeneous grains are characteristic of sands derived from felsic plutonic and intermediate volcanic sources sands from mafic volcanic sources are characterized by a 1 1 relationship between polymineralic grains with trellis or composite type magnetite ilmenite intergrowths c c t 0 5 and monomineralic grains a ternary plot with homogeneous grains grains with trellis or composite type magnetite ilmenite intergrowths and grains with exsolved pleonaste or ulvospinel as corners successfully grouped grains from these parent rocks into fields with minimum overlap electron probe microanalysis of 433 homogeneous grains identified the presence of a chemical fingerprint step wise discriminant function analysis found that tio2 mgo v2o3 and al2o3 could best discriminate between detrital magnetite grains from felsic plutonic and volcanic intermediate volcanic and mafic plutonic parent rocks within this control set detrital magnetite grains were correctly classified 98 of the time however grains from mafic volcanic and metamorphosed mafic ultramafic sources were not chemically distinct emphasizing the importance of integrating petrographic and chemical analyses in provenance research

three dimensional seismic velocity structure of the san francisco bay area seismic travel times from the northern california earthquake catalogue and from the 1991 bay area seismic imaging experiment basix refraction survey were used to obtain a three dimensional model of the seismic velocity structure of the san francisco bay area nonlinear tomography was used to simultaneously invert for both velocity and hypocenters the new hypocenter inversion algorithm uses finite difference travel times and is an extension of an existing velocity tomography algorithm numerous inversions were performed with different parameters to test the reliability of the resulting velocity model most hypocenters were relocated 12 km under the sacramento river delta 6 km beneath livermore valley 5 km beneath the santa clara valley and 4 km beneath eastern san pablo bay the great valley sequence east of san francisco bay is 4 6 km thick a relatively high velocity body exists in the upper 10 km beneath the sonoma volcanic field but no evidence for a large intrusion or magma chamber exists in the crust under the geysers or the clear lake volcanic center lateral velocity contrasts indicate that the major strike slip faults extend sub vertically beneath their surface locations through most of the crust strong lateral velocity contrasts of 0 3 0 6 km s are observed across the san andreas fault in the middle crust and across the hayward rogers creek calaveras and greenville faults at shallow depth weaker velocity contrasts 0 1 0 3 km s exist across the san andreas hayward and rogers creek faults at all other depths low spatial resolution evidence in the lower crust suggests that the top of high velocity mafic rocks gets deeper from west to east and may be offset under the major faults the data suggest that the major strike slip faults extend sub vertically through the middle and perhaps the lower crust and juxtapose differing lithology due to accumulated strike slip motion the extent and physical properties of the major geologic units as constrained by the model should be used to improve studies of seismicity strong ground motion and regional stress