depositional processes and stratigraphy of fluvially dominated lacustrine deltas mississippi delta plain abstract a geomorphic and stratigraphic investigation of lacustrine delta deposits in the atchafalaya basin louisiana revealed that lacustrine delta formation is rapid and cyclic in nature during the holocene thin coarse grained regionally extensive fluvially dominated lacustrine deltas filled interdistributary basins in the transition zone between the alluvial valley and the marine delta plain of the mississippi river one delta lake fausse pointe delta prograded 6 5 km partially filling the lake and covering more than 29 km2 in area in twelve years depositional processes in lake fausse pointe ranged from suspension settling of mud and organic matter during low sediment input to traction deposition of sand during floods hyperpycnal flow conditions set up by the introdu tion of sediment laden river water into the freshwater lake induced underflows that scoured the lake bottom and deposited upward coarsening lobes the low relief of the mississippi basin a constant large volume of fine grained sediment supply and prevalent fluvial processes have formed fluvially dominated lacustrine deltas that differ sedimentologically and stratigraphically from gilbert type and brackish water lacustrine deltas parallel laminated prodelta mud rippled to cross laminated delta front silty sand and very finegrained to medium grained distributary mouth bar sand are characteristic of rapidly deposited sediment whereas rooted and burrowed sediments signify periods of minimal deposition in a fluvially dominated setting delta geometry and sediment distribution patterns are controlled by river mouth processes basin shape and bathymetry thickest sand accumulations occur in linear dip elongate distributary m uth bar and natural levee lobes that are separated laterally by mud filled channels and interdistributary troughs lacustrine delta deposition is driven by basin subsidence regional downwarping and sediment compaction and the concomitant development of distributary channels in the interdistributary basins numerous lacustrine deltaic wedges each bounded by rooted backswamp clay are preserved multilaterally in atchafalaya basin sediments although lacustrine deltaic deposits constitute much of the basin s sedimentary fill each individual delta sequence records depositional events of only 100 years duration these deltaic deposits represent basin filling aggradational episodes that preceded the formation of marine delta complexes such as the maringouin teche la fourche and atchafalaya deltas of the mississippi river

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

the influence of pore pressure and confining pressure on dynamic elastic properties of berea sandstone compressional and shear wave velocities of watersaturated berea sandstone have been measured as functions of confining and pore pressures to 2 kbar the velocities measured by the pulse transmission technique were obtained at selected pressures for the purpose of evaluating the relative importance of confining pressure and pore pressure on elastic wave velocities and derived dynamic elastic constants changes in berea sandstone velocities resulting from changes in confining pressure are not exactly canceled by equivalent changes in pore pressure for properties that involve significant bulk compression compressional wave velocities and bulk modulus an incremental change in pore pressure does not entirely cancel a similar change in confining pressure on the other hand it is shown that a pore pressure increment more than cancels an equivalent change in confining pressure for properties that depend significantly on rigidity shear wave velocity and poisson s ratio this behavior as well as observed

geochemistry of the lublin formation from the lublin coal basin implications for weathering intensity palaeoclimate and provenance abstract the lublin formation upper westphalian a and westphalian b is the main coal bearing series of the lublin coal basin lcb so far few geochemical studies of the carboniferous of the lcb have been performed and there is almost no data on the geochemistry of this series this paper presents geochemical data for 118 samples from the lublin formation from the central part of the lcb major oxide concentrations al2o3 sio2 fe2o3 p2o5 k2o mgo cao na2o k2o mno tio2 cr2o3 ba were obtained using an x ray fluorescence spectrometry trace and major elements zr th sc la u cu sr rb ni fe mn ca mg k na were analysed using inductively coupled plasma mass spectrometry concentrations of the major and trace elements showed significant diversity especially in the westphalian b deposits the chemical index of alteration plagioclase index of alternation and weathering index of parker values as well as the rb sr sr cu c and th u ratios of the studied samples suggest a high degree of chemical weathering of the source rocks and a prevailing warm humid climate with some arid episodes based on indicators such as al2o3 tio2 tio2 zr and la th it is suggested that all the studied samples from the lublin formation of the lcb were derived from felsic to intermediate igneous rocks while the th sc ratio suggests a mixed source for these sediments

the application of sequence stratigraphy to upper carboniferous fluvio deltaic strata of the onshore uk and ireland implications for the southern north sea stratigraphical correlations and fades interpretations of upper carboniferous fluvio deltaic strata have been based traditionally on cyclothems bound by marine flooding surfaces marine bands the recent recognition of major regionally extensive erosional unconformities exxon style sequence boundaries within selected cyclothems questions their validity as units of genetically related strata u sing examples from the carboniferous of the onshore uk and ireland we present sedimentological criteria for the recognition of sequence boundaries placing particular emphasis on the regional context of these surfaces sequence boundaries comprise widespread deeply eroded surfaces at the base of major fluvial sandstone complexes and laterally equivalent palaeosols developed on interfluves at the margins of the fluvial complexes these sequence boundaries define units of genetically related strata sequences which contain other key surfaces of time stratigraphic significance including marine bands and regionally extensive coals the recognition of key surfaces enables the construction of a high resolution stratigraphic framework within which coeval facies relationships can be interpreted sequence boundaries can be correlated between individual basins in the onshore uk by reference to their position in relation to a particular marine band for example the sequence boundary at the base of the farewell rock in the south wales basin can be correlated with that at the base of the rough rock in the pennine basin northern england since both these sandstone bodies are directly overlain by the subcrenatum marine band interbasinal correlations of this nature imply that potential fluvial sandstone reservoirs within major incised valley fills in the upper carboniferous strata of the southern north sea can be predicted by correlation with the onshore uk the stratigraphical framework can be extended and tested using core and well log data particularly spectral gamma ray data which are able to identify key sequence stratigraphic surfaces

stratigraphy and sequence stratigraphy of the moscovian in the donets basin new results are presented on the stratigraphy based on fusulinids and palynomorphs and the sequence stratigraphy of the moscovian in the donets basin they have been developed by comparison of our observations on cross sections near artemovsk and the published coal mine logs of artemovsk geological survey the moscovian of the donets basin is equivalent to the uppermost westphalian b and the westphalian c and d of western europe in the donets basin the moscovian forms a second order sequence as in the moscow basin that can be subdivided into four third order sequences subdivided into fourth order sequences the upper bashkirian shows two fourth order sequences the vereian exhibits two fourth order sequences the kashirian shows four fourth order sequences the podolskian offers eight fourth order sequences the myatchkovian presents four fourth order sequences these sequences begin with an erosive base and show a succession of elementary sequences with fluvial sandstone coal seam limestone and deltaic facies the fluvial sandstone corresponds with an aggradation period the coal and the limestone with a transgressive period and the deltaic facies with a progradation period a decrease of the sandstone thickness and an increase of the marine deposits that are transgressive and regressive upwards are observed from the base to the top of sequences these fourth order sequences present a higher spatial amplitude than the third order sequence and obscure these sequences the second order sequence equivalent to the moscovian shows a lowstand system tract with more fluvial sandstone in the lower part of the vereian a transgressive system tract in the upper part of the vereian tsinskaya and kashirian a maximum flooding period during the podolskian and lower part of the myatchkovian with more marine facies and a highstand system tract in the upper part of the myatchkovian with more lagoonal and swampy palaeoenvironments the sequences are controlled by the regional tectonic subsidence in the graben and the uplift of the horsts and or by eustasy with either a plate tectonic or a glacial origin other investigations particularly radiometric dating will be useful for solving this problem

variscan deformation along the teisseyre tornquist zone in se poland thick skinned structural inheritance or thin skinned thrusting abstract recently acquired seismic reflection data provide better insight in the structural style of extensive sedimentary series overlying the sw slope of the east european craton eec in poland the two main seismic datasets the polcrust 01 profile and polandspan survey yielded contrasting thick and thin skinned structural models for the same structural units in se poland we reattempt an interpretation of the polcrust 01 profile using techniques of cross section balancing and restoration aided by 2d forward seismic modelling an outcome is the thin skinned structural model is this solution relies on a continuous top of the eec crystalline basement well represented in the seismic data as well as on fragmentary yet conclusive seismic geometries in shallow depth intervals proving the ediacaran palaeozoic series to be thrust and folded a variscan late carboniferous compressional regime is consequently invoked to explain thin skinned structuring of the pre permian sedimentary pile and 20 km of calculated shortening we demonstrate an ambiguous nature of the top basement irregularities previously used as indicators of basement rooted vertical faulting the tilt and abrupt increase of the top basement taper under the thin skinned belt are attributed to pre ordovician tectonic processes operating along the sw margin of the eec post rift subsidence and or flexural loading giving rise to a broken foreland plate are invoked

evolution of atchafalaya lacustrine deltas south central louisiana abstract the entrenched pleistocene holocene mississippi alluvial valley was cut during the last low sea level stand and alluviation of the entrenched valley occurred during the holocene sea level rise regional gulf coast structures salt domes and faults have strongly influenced the morphology of the valley valley paleotopography has controlled depositional patterns and locations of major river courses as well as partially isolated large interdistributary basins within the alluvial deltaic plain interdistributary basin formation is further enhanced by distributary channel progradation switching and abandonment in conjunction with compactional subsidence of the alluvial plain surface geomorphology and sediment cores from the atchafalaya basin louisiana revealed that this basin has alternately accumulated fine grained organic rich sediments and terrigenous clastic dominated meander belt and lacustrine deposits basin subsidence and the presence of an active distributary channel in the basin are major determinants of the lithology of the sedimentary fill prograding lacustrine deltas of the atchafalaya river are the primary mechanism for filling the atchafalaya basin these upward coarsening deltas are relatively thin 3 m but are areally extensive tens to hundreds of kilometers and because they occur so frequently during the infilling process they account for a significant volume of the basin sequence the atchafalaya basin sequence documents lacustrine deltaic episodes dating from the early holocene maringouin and teche deltas to the present atchafalaya delta continued development of the atchafalaya river will rework portions of the backswamp and lacustrine deposits into meander belt deposits upon complete filling of the atchafalaya basin sediment will mostly bypass the basin and become deposited in the marine delta in atchafalaya bay

late palaeozoic environmental changes an introduction the idea of this volume arose from our proposal to the palaeoclimatic session held at the european geosciences union general assembly 2011 conference in vienna austria although the original scope was broader the included contributions focus on palaeoenvironmental changes during the late palaeozoic late palaeozoic history is especially important in that it records an increase of tectonics diastrophism frequent sea level fluctuations and climatic changes all finally leading to the most geocratic time of earth s history with the formation of the supercontinent pangaea this volume includes a number of articles that discuss the fossil record around the late palaeozoic ice age and its decline during the carboniferous with its unusual plant proliferation soon after when the hottest and driest period in earth s history in the permian caused the development of huge sand seas on the land finally a biotic event the largest mass extinction in earth history at the permian triassic transition ends the palaeozoic world this volume addresses two key issues the palaeoclimate and depositional cycles both of which have a strong impact on the record of palaeoenvironmental changes and the understanding of environmental perturbations the vigorous current debate on the future climate of the globe inevitably increases our interest in past climates from a geological perspective climatic perturbations occurred many times before humans were on the planet climate varies on several timescales depends on many high order factors including tectonic uplift and the orbital wandering of the earth and as a result it changes through time consequently palaeoclimatic reconstructions are growing in their importance as they enable us to use the past as a key to the future the earth s system experiences various cycles of very different origin scale frequency amplitude phase and basic level from a geological perspective the cyclicity appears unidirectional like brownian motion however in the past the complex interaction of these cycles has led to catastrophic changes in earth s systems such as those during the late palaeozoic when palaeoclimatic and geotectonic cycles coincided these cycles are also influencing our lives and will do so in our future so their impact needs to be understood the geological archives record both the climatic and cyclic phenomena on local to regional scales including in the late palaeozoic as documented in this volume understanding these records will improve our predictions about climate phenomena in the future they also show that the present climatic perturbations are insignificant from a geological point of view changes in the late palaeozoic earth system are illustrated in this volume by case studies of fossil records from north and south america east and south asia south africa and australia and as regional reviews section one the methods include palaeoenvironmental analysis including palaeobiological sedimentological stratigraphic sequence stratigraphy palaeomagnetic and geochemical methods they describe various environmental settings from palaeodeserts through marine associated giant salt pans to shallow to deep marine records the articles report new data from less known study areas provide up to date data ordering and expand our knowledge of the evolution of marine and terrestrial environments climatic changes and biotic events in late palaeozoic time this special publication is divided into five chapters the first comprising articles focused on the broad descriptive character of late carboniferous to early triassic palaeoclimatic changes and stratigraphy with the latest part of this period in europe i e zechstein subsequent articles include more detailed studies of the geological periods grouped into the latest devonian to early carboniferous section two late carboniferous to early permian section three middle to late permian section four and finally the permian triassic transition section five a brief synopsis of individual papers is given below wopfner 2012 reviews westphalian early triassic palaeoclimatic conditions between samfrau comprising the southern margins of south america and south africa extending via antarctica

estimation of surface roughness and stone cover in burnt soils using sar images abstract in many quartzitic slopes in the nw of the iberian peninsula there is a high topsoil stoniness which produces a random surface roughness the surface roughness is one of the control parameters in the signal of synthetic aperture radar sar images in this work we test the use of the sar images for distinguishing and mapping areas with different surface roughness which in this study correspond with areas with different surface stoniness in accordance with the geographic location the relief of the study area and the aims of the project jers and envisat sar images were used the images are characterized by the high view angles between 33 and 42 alternating polarization hh hv vv vh data and ascending and descending passes in order to describe the soil roughness various measuring methods were applied in plot parcels direct measurements of height of clasts and laser scanning and different roughness models were tested the results show that there are relation between sar signal dn and the soil roughness classes dn a b and the b parameter is correlated with the roughness the best fit between roughness model and sar data was found for mean standard deviation rms height of clasts once verified that the correlation between sar signal and surface roughness exists the envisat images were classified into three successive surface roughness classes in order to facilitate the classification principal components analysis were carried out over all polarization bands and the object oriented classification was applied to validate the accuracy of the sar images classification we elaborated by photointerpretation a surface condition map for an area of 10 700 ha the sar classification and photointerpreted map were compared for three classes surface without stones surface with stones low and medium stoniness and total cover of loose clasts the overall coincidence between the maps is about 70 besides large areas located in the northwest of the iberian peninsula suffer soil degradation caused by wildfires and the increase of surface stoniness is one of the effects described in the postfire erosion the influence of wildfires and the associated erosion is particularly important on quartzitic slopes partially covered by coarse grain supported deposits like the ones considered in this study the available data for the area of study suggest the high correlation between the different classes of surface roughness and stoniness obtained from sar imagery and the gradual different status of postfire soil erosion

the role of catastrophic geomorphic events in central appalachian landscape evolution abstract catastrophic geomorphic events are taken as those that are large sudden and rare on human timescales in the nonglaciated low seismicity central appalachians these are dominantly floods and landslides evaluation of the role of catastrophic events in landscape evolution includes assessment of their contributions to denudation and formation of prominent landscape features and how they vary through space and time tropical storm paths and topographic barriers at the blue ridge and allegheny front create significant climatic variability across the appalachians for moderate floods the influence of basin geology is apparent in modifying severity of flooding but for the most extreme events flood discharges relate mainly to rainfall characteristics such as intensity duration storm size and location landslide susceptibility relates more directly to geologic controls that determine what intensity and duration of rainfall will trigger slope instability large floods and landslides are not necessarily effective in producing prominent geomorphic features large historic floods in the piedmont have been minimally effective in producing prominent and persistent geomorphic features in contrast smaller floods in the valley and ridge produced erosional and depositional features that probably will require thousands of years to efface scars and deposits of debris slide avalanches triggered on sandstone ridges recover slowly and persist much longer than scars and deposits of smaller landslides triggered on finer grained regolith even though the smaller landslides may have eroded greater aggregate volume the surficial stratigraphic record can be used to extend the spatial and temporal limits of our knowledge of catastrophic events many prominent alluvial and colluvial landforms in the central appalachians are composed of sediments that were deposited by processes similar to those observed in historic catastrophic events available stratigraphic evidence shows two scales of temporal variation one related to quaternary climate changes and a more recent higher frequency variation due to rare events during the holocene in much of the central appalachians landforms related to quaternary climate changes persist as the most prominent features despite the modifying effects of late holocene catastrophic events

the application of 137cs to post fire erosion in north west spain abstract wildfires are a frequent occurrence in the cantabrian mountain range in north west spain causing erosion and soil degradation with the aim of measuring this erosion 43 soil cores were taken from four slopes with different degrees of fire frequency and 137 cs concentration the four slopes are located in the same geographical area they have a quartzitic substrate with slopes of between 20 and 30 and share the same type of soil elevation and orientation however vegetation cover is different as a result of the action of fire maps of the area showing the burnt areas over the period 1984 to 2004 remote sensing data confirm the effects that fire has had soil cores were taken from transects on each slope and three reference samples were also taken from a high plateau in order to establish a reference value for 137 cs inventory soil redistribution rates erosion and deposit for the slopes could thus be calculated according to whether 137 cs inventory was higher or lower than the reference value the values obtained show that 137 cs inventory is lower for the slopes with shrubby vegetation than for the reference samples and its distribution indicates higher erosion rates for the upper slope samples mean erosion rates obtained for these slopes were 6 75 t ha 1 year 1 and 6 6 t ha 1 year 1 these data are compared with erosion rates for 137 cs obtained in areas with different climates and patterns of land use 137 cs redistribution was not found on slopes with tree cover suggesting that surface erosion has not occurred or at least not during the time period for which 137 cs can be measured 137 cs distribution was compared with the distribution of other variables and topographical indices distance from the hilltop accumulated flow slope curvature and cti the application of 137 cs in studies of post fire erosion is relatively novelty and it a useful technique in post fire erosion studies over long timescales and for study sites larger than point and plot scales

uncertainties in quantitative time lapse seismic analysis most seismic time lapse studies so far have been of a qualitative nature identification of areas with minor or no seismic changes has been used to plan new infill drilling targets increased accuracy in seismic acquisition methods in both conventional streamer surveys and newer methods such as multicomponent sea bed seismic and permanent sensors opens possibilities for the next step quantitative time lapse analysis quantitative methods here mean the estimation of for instance a change in fluid saturation from 20 water to 90 water or the estimation of a pore pressure change of 5 mpa explicit expressions for the uncertainties associated with estimated changes in for instance reservoir pressure and fluid saturation are derived these formulae can be used to compare relative uncertainties between estimated parameters as well as to identify the critical factors in various estimation techniques the importance of accurate rock physics input as well as that of highly repeatable time lapse seismic data is emphasized furthermore uncertainty analysis can be used to find optimal weight factors when the same parameter e g saturation change is estimated by two or three different techniques

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

analysis of time lapse travel time and amplitude changes to assess reservoir compartmentalization fluid depletion within a compacting reservoir can lead to significant stress and strain changes and potentially severe geomechanical issues both inside and outside the reservoir we extend previous research of time lapse seismic interpretation by incorporating synthetic near offset and full offset common midpoint reflection data using anisotropic ray tracing to investigate uncertainties in time lapse seismic observations the time lapse seismic simulations use dynamic elasticity models built from hydro geomechanical simulation output and a stress dependent rock physics model the reservoir model is a conceptual two fault graben reservoir where we allow the fault fluid flow transmissibility to vary from high to low to simulate non compartmentalized and compartmentalized reservoirs respectively the results indicate time lapse seismic amplitude changes and travel time shifts can be used to qualitatively identify reservoir compartmentalization due to the high repeatability and good quality of the time lapse synthetic dataset the estimated travel time shifts and amplitude changes for near offset data match the true model subsurface changes with minimal errors a 1d velocity strain relation was used to estimate the vertical velocity change for the reservoir bottom interface by applying zero offset time shifts from both the near offset and full offset measurements for near offset data the estimated p wave velocity changes were within 10 of the true value however for full offset data time lapse attributes are quantitatively reliable using standard time lapse seismic methods when an updated velocity model is used rather than the baseline model

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

on the periodicity and magnitude of late carboniferous glacio eustatie sea level changes data from sedimentary cycles in basins from northern england the appalachians and midcontinent us afford an insight into periodicities and controls of late carboniferous glacio eustatic sea level changes lithofacies with identifiable palaeobathymetry are used to assess the magnitude of sea level change in the pennine basin of northern england the method yields a minimum value of 42m walsh power spectral analysis is employed to resolve periodicities of about 120ka within the pennine basin of northern england 212 140 and 93 ka within the midcontinent us succession and 109 84 67 63 ka within the appalachian basin within the pennine basin periodicities and magnitudes are found to be independent of their position within the basin thus any tectonism can be assumed to have had a negligible effect on the transgressions a simplified modelled climatic curve is derived from milankovitch parameters and pleistocene 18 o data this is used in a basin fill model that simulates the thermally subsiding pennine basin the resulting distribution of marine deposits is seen to depend upon both the steady regional subsidence and the magnitude and extent of glacio eustatic transgressions

the petrophysical basis for shallow water flow prediction using multicomponent seismic data physical properties of shallow water flow swf sands differ from most reservoir and seal rocks studied for petroleum purposes these materials exist near the transition zone between rocks and sediments our investigations the subject of this article suggest that physical properties of swf sands are amenable to a prediction methodology that uses high resolution multicomponent seismic data swf sands are a primary hazard to deepwater drilling operations in the gulf of mexico they have the potential to result in well failures and significant discharges of subsurface fluids into the ocean however at present most operators make only a modest attempt to identify swf before drilling they drill through these hazards and mitigate any resulting damage at significant expense if one is encountered this is not rare according to a report from fugro geoservices approximately 70 of all deepwater wells have experienced swf a method for predrill delineation of sands that are close to failure and thus likely to exhibit swf would be advantageous in selecting optimal drilling locations and in developing cost effective well plans the current method of identifying swf involves predrill hazard studies utilizing conventional and high resolution seismic data to identify zones that might produce swf however the high incidence of swf mitigation events in deepwater wells shows that existing techniques do not provide adequate resolution or accuracy at present no robust seismic method exists for accurately identifying and characterizing swf operators do not have the option to avoid the hazard instead of mitigating the problem after it has started a new method is required that will permit operators to identify the hazard before the well is drilled using seismic data for accurate understanding of the physical properties and deformational behavior of swf sands is essential to characterization prediction and interpretation of these stratigraphic units to date very few core and

time and the persistence of alluvium river engineering fluvial geomorphology and mining sediment in california abstract river managers need to understand fluvial systems as they change through time many river systems are presently in a state of flux as a result of substantial anthropogenic changes to water and sediment regimes and channel hydraulics yet historical approaches to understanding river systems rarely receive adequate attention because historical methodologies are not conducive to the application of quantitative analysis while there is limited precision in most historical reconstructions the information derived from these studies constrains other interpretations and is essential to a full understanding of the behavior of fluvial systems geomorphology provides a perspective on river systems in which time at various scales is interwoven into practical and theoretical aspects of scientific inquiry thus geomorphology is important to our understanding of not only physical systems but also fundamental concepts of time this study examines channel morphological changes in the bear and american basins brought about by two episodes of sedimentation from hydraulic gold mining the primary event was the production of more than 1 billion m3 of sediment throughout the northern sierra nevada from 1853 to 1884 which caused aggradation in many channels across the sierra foothills and sacramento valley assumptions by both engineers and geomorphologists that morphologic responses to this event were ephemeral that sediment loads have returned to previous levels and that deposits have stabilized are not borne out by field and historical data in the sacramento valley a secondary sedimentation event not previously studied was the production of at least 24 million m3 of sediment during a period of licensed mining from 1893 to 1953 this episode of sedimentation has been largely overlooked as a geomorphic hydrologic or water quality event yet channel morphologic responses in phase with mining during this period are demonstrated systematic changes in stage discharge relationships reflect channel morphological changes that are relevant to flood risk assessments stability of engineering structures on floodplains and geomorphic interpretations

late yeadonian upper sandstone group incised valley supply and depositional systems in the south wales peripheral foreland basin implications for the evolution of the culm basin and for the silesian hydrocarbon plays of onshore and offshore uk abstract the upper sandstone group of south wales has previously been interpreted as a simple nnw sse trending incised valley that was filled during the late yeadonian namurian g1b data presented in this study indicate a far more complex scenario the group is well developed in the pembrokeshire sub basin but it is absent from the main part of the south wales basin located to the east of the penlan axis the principal source area for sediment flux was the forebulge of the basin located to the north in lower palaeozoic foreland strata variscan flexural uplift of this source area and an accompanying rapid high magnitude fall in sea level produced a very high sediment budget thus during the late yeadonian lowstand of sea level massive amounts of sediment were being generated and transported via an incised valley system across the western part of the south wales peripheral foreland basin the location and orientation of the incised supply system and its related interfluves were controlled by intrabasinal synsedimentary variscan structures many of which were reactivated caledonian extensional faults during the succeeding sea level rise the incised valley was filled initially by fluvio deltaic sands and later by estuarine argillaceous sediments the implications of this combined tectonic sedimentological high resolution sequence stratigraphic model for the evolution of the late namurian crackington formation turbidites of the culm basin are discussed examples of silesian incised valley fill sandstone reservoirs developed in the east midlands oilfield and the southern gas basin are briefly summarised and their spatial and temporal distributions are appraised data generated from these case studies are assessed in terms of their use for the modelling of incised valley fill sequences in foreland basins and other tectonic settings

sequence of deformation at the front of an orogen lublin basin case study poland abstract we provide a detailed description of a late carboniferous fold and thrust belt in the lublin basin based on seismic lines including new high resolution acquisitions and legacy borehole and gravimetric data a series of regional cross sections integrate results of the joint seismic borehole gravimetric interpretation cross section restoration provides estimates of the minimum incremental and total shortening and reveals its along strike variations the lublin basin straddles a leading edge of the variscan orogen and its undeformed foreland therefore it experienced only a minor deformation it preserves a fossilized record of early phases of shortening seismic scale divergent intra formational thrusts and folds in horizontal strata that were later passively rotated by subsequent folds developed above a regional decollement lateral variations of deformation styles from displacement of the entire basin with little internal deformation to dispersion of shortening by numerous contractional structures is attributed to along strike changes in lithology and thickness of the silurian detachment horizon lateral change of detachment strength is quantified using the critical wedge theory our observations deliver a new perspective on factors controlling the localization of incipient structures their differentiation as a function of detachment strength and interplay between folding and thrusting along a leading edge of an organic system

discrimination of local and global effects on upper mississippian stratigraphy illinois basin u s a abstract interpretive cross sections based on detailed descriptions of 33 outcrops and cores are used to better understand the relative effects of tectonics eustasy tides and climate on upper mississippian middle chesterian stratigraphy in the tectonically active tide dominated illinois basin the cross sections show that five mixed carbonate siliciclastic high frequency sequences in the bethel through glen dean formations can be correlated around the outcrop belt through areas with very different subsidence histories the sequence boundaries are marked by paleosols and incised valleys and can be correlated basin wide within a framework of distinctive marker beds because of its updip position lowstand systems tracts are not preserved in the illinois basin the transgressive systems tracts generally consist of one or two parasequences that are typically composed of tidally influenced quartz sandstone filling incised valleys at the base overlain by open marine skeletal limestone shallow marine shale and heterolithic siliciclastic tidal flat deposits the maximum flooding surface mfs for the sequences is picked at the base of the deepest water limestone facies highstand systems tracts are composed of 1 to 6 regressive parasequences that consist of basal offshore skeletal limestone capped by laterally extensive shale and heterolithic siliciclastic tidal flat facies the basin wide extent of the sequence boundaries and maximum flooding surfaces across tectonic highs and lows suggests that the sequences were produced by eustatic sea level changes rather than local tectonics or autogenic processes the sequences were likely produced by moderate to high amplitude 30 100 m fourth order 400 ky glacio eustatic sea level changes driven by the transition from the greenhouse conditions of the early mississippian to the icehouse conditions of the late paleozoic the lateral extent and frequency of component parasequences suggests that they were likely produced by fifth order sea level changes 10 100 ky the sequences may be bundled into third order composite sequences but the third order signal is obscured by the magnitude of the fourth order sea level changes a feature typical of ice house stratigraphies the sequences can be used as time slices to identify spatial and temporal variations in differential subsidence between the cincinnati arch and the more rapidly subsiding basin interior episodes of high and low differential subsidence occurred every two to three sequences these subsidence variations had a major impact on lithofacies distribution and onlap and offlap geometries in sequences and parasequences the occurrence of some widespread seismically disturbed beds suggests that active faulting occurred during deposition normal faulting appears to have occurred during periods of high differential subsidence and reverse faulting during periods of low differential subsidence differential subsidence and related normal and reverse faulting may have occurred in response to phases of thrust loading and quiescence in the appalachian orogenic belt to the east even in this tectonically active setting however it is the eustatic signal that generates basin wide mappable stratigraphic sequences

nature and timing of late mississippian to mid pennsylvanian glacio eustatic sea level changes of the pennine basin uk the pennine basin of northern england contains a comparatively complete serpukhovian moscovian succession characterized by high resolution ammonoid zonation and cyclic paralic sedimentation two new isotope dilution thermal ionization mass spectrometry zircon ages from a bentonite deposited during the arnsbergian mid serpukhovian regional substage and tonstein of earliest bolsovian early moscovian regional substage have been determined the weighted mean 206 pb 238 u ages of 328 34 0 55 and 314 37 0 53 ma total uncertainty respectively require modification of the time scale for the western europe regional chronostratigraphy the areal extent of acme ammonoid facies is used as a proxy for the magnitude of 47 discrete flooding events incised valleys major sequence boundaries are used as a proxy for the magnitude of sea level falls the frequency of these events in the light of the new radiometric dating indicates the following 1 there is temporal coincidence between major glaciations in gondwana and phases of increased frequency of sequence boundaries in the pennine basin 2 high amplitude flooding surfaces have an average frequency of c 400 ka 3 average cycle durations during the pendleian early arnsbergian and chokierian bolsovian of c 111 and c 150 ka respectively reflect short duration eccentricities 4 multiple flooding surfaces with the same ammonoid assemblages may equate with sub 100 ka precession or obliquity frequencies supplementary material u pb method description and data procedure for the calculation of the areal extent of marine bands and tables showing a full listing of biostratigraphical data used in the study are available at www geolsoc org uk sup18505

the devonian and carboniferous of the moscow syneclise russian platform stratigraphy and sea level changes abstract the moscow syneclise is a vast sedimentary basin located in the centre of the east european platform the palaeozoic sequence of this syneclise and especially its devonian carboniferous part is most suitable for sea level fluctuation analysis the devonian and carboniferous sediments consist mainly of shallow marine carbonates containing several minor terrigenous intervals they attain total thicknesses of up to 1 5 km the modern stratigraphic scale includes 33 regional stages for the devonian and 32 for the carboniferous correlation of this scale with global scales is supported by conodont miospore and foraminifera zonations the new calibrated devonian and carboniferous relative sea level curves for the moscow syneclise reflect late eifelian mid frasnian early tournaisian late visean early serpukhovian and moscovian gzhelian transgressions several of these sea level changes which are particularly evident on the margins of the moscow syneclise originated in response to differential tectonic movements of the voronezh anteclise and the tokmovo uplift as well as to vertical oscillations of the entire east european craton

riverbank stability analysis ii applications bank retreat occurs by a combination of lateral erosion by the flow and mass failure under gravity a new analysis of bank erosion and failure is developed using a critical shear stress concept to account for lateral erosion and a slope stability criterion for mass failure in this paper we apply the analysis to two problems of bank retreat often encountered by practicing engineers dealing with alluvial channels the first application is to the prediction of degradation downstream of a dam for the case in which bed lowering causes bank instability we show that rapid bank retreat can occur once the threshold height for mass failure of the banks is reached this supplies sediment to the flow tends to limit the depth of degradation and drives complex response downstream the second application is to the modeling of flow in channel bends and the prediction of the equilibrium cross section we show that scour depth at the outer bank may be limited by the critical bank height if scouring causes the outer

modeling scour and deposition in ephemeral channels after wildfire the area burned by wildfire in the states of arizona and new mexico in the southwestern us has been increasing in recent years in many cases high severity burns have caused dramatic increases in runoff and sediment yield from burned watersheds this paper describes the potential and limitations of the hec6t sediment transport model to describe changes in channel scour and deposition following the cerro grande fire near los alamos new mexico following the fire pueblo canyon near los alamos was subject to a peak flow two orders of magnitudes higher than any discharge in the 7 year period of record and twice the initial post fire estimate of the 100 year event hec6t requires that the limits of scour and deposition on a cross section be specified prior to application this was achieved by using geomorphologic principles predicted post burn hydrology and longterm estimates of channel change derived from air photos to estimate post fire channel widths because significant quantities of silt and clay were present in the runoff erosion shear stress and erosion rate parameters for cohesive sediments had to be obtained experimentally after a sensitivity analysis an optimization routine was used to estimate the optimal model parameter values for sensitive parameters hec6t was able to accurately model the change in cumulative sediment volume change derived from airborne laser swath mapping alsm often called lidar taken before and after the large post fire event one discrepancy between the hec6t model prediction and the alsm estimated change was that the alsm estimated change showed the greatest amount of deposition in a portion of the canyon with increasing slope which the hec6t model did not predict

research note overpressure prediction from c wave seismic data abstract recently mode converted shear waves c waves have been shown to enable overpressure prediction in media where primary wave acquisition is inhibited by gas and fluid effects c wave moveout is analysed and a long standing relationship between differential stress and primary wave p wave velocity is modified and employed though pore pressure prediction based on c waves is supported by empirical evidence from laboratory and field experiments a theoretical justification has yet to be developed in this research note we provide a supporting algebra for the original relationship between pore pressure and c wave velocity

incision and morphologic evolution of an alluvial channel recovering from hydraulic mining sediment hydraulic gold mining in the sierra nevada california produced such a large volume of sediment from 1853 to 1884 that channels could not carry a substantial proportion of the delivered sediment the lower bear river aggraded as much as 5 m and underwent a major avulsion during the 1870s channel morphology continues to respond to these changes more than 100 years after the cessation of most hydraulic mining textures of mine tailings and older alluvium are contrasted and channel incision and channel shape changes from 1930 to 1985 are documented unlike the yuba and sacramento rivers the lower bear river had not returned to pre mining base levels by 1950 as sediment loads decreased nor were incision rates or morphological change governed by reduced sediment loads below dams built in 1928 and in the mid 1960s channel stability was due to resistance of a cohesive stratum on the channel bed an episode of channel down cutting was instigated by a moderately large flood in december 1955 that pierced the cohesive layer and was sustained through the 1970s by moderate magnitude floods the 1955 flood did not directly erode large volumes of sediment but it destabilized the channel allowing smaller floods to erode the channel at an accelerated rate episodic channel bed incision is contrasted to progressive morphologic changes cross section shape narrowed and deepened steadily from 1930 through the mid 1970s as the channel was superimposed onto cohesive older alluvium progressive deepening set up a positive feedback that ensured the ultimate penetration of the paved bed channel morphologic readjustment from the avulsion thus was both progressive and episodic

pore pressure detection sensitivities tested with time lapse seismic data in an exploration context pore pressure prediction from seismic data relies on the fact that seismic velocities depend on pore pressure conventional velocity analysis is a tool that may form the basis for obtaining interval velocities for this purpose however velocity analysis is inaccurate and in this paper we focus on the possibilities and limitations of using velocity analysis for pore pressure prediction a time lapse seismic data set from a segment that has undergone a pore pressure increase of 5 to 7 mpa between the two surveys is analyzed for velocity changes using detailed velocity analysis a synthetic time lapse survey is used to test the sensitivity of the velocity analysis with respect to noise the analysis shows that the pore pressure increase cannot be detected by conventional velocity analysis because the uncertainty is much greater than the expected velocity change for a reservoir of the given thickness and burial depth finally by applying amplitude variation with offset avo analysis to the same data we demonstrate that seismic amplitude analysis may yield more precise information about velocity changes than velocity analysis

siliciclastic and volcaniclastic influences on equatorial carbonates insights from the neogene of indonesia in active tectonic areas of humid equatorial regions nearshore shallow water environments are commonly sites of near continuous siliciclastic influx and or punctuated volcaniclastic input despite significant clastic influence neogene carbonates developed in se asia adjacent to major deltas or volcanic arcs and are comparable with modern mixed carbonate clastic deposits in the region research into delta front patch reefs from borneo and fore arc carbonate platform development from java is described and used to evaluate the effects of siliciclastic and volcaniclastic influx on regional carbonate sedimentation local changes in carbonate producing biota and sequence development regional carbonate development in areas of high siliciclastic or volcaniclastic input was influenced by the presence of antecedent highs changes in the amounts or rates of clastic input delta lobe switching or variations in volcanic activity energy regimes and relative sea level change a variety of carbonate producing organisms including larger benthic foraminifera some corals coralline algae echinoderms and molluscs could tolerate near continuous siliciclastic or volcaniclastic influx approximately equal to their own production rates these organisms adopted various strategies for coping with clastic input including a degree of mobility morphologies adapted to unstable substrate inhabitation or shedding sediment and shapes adapted to low light levels local carbonate production was also affected by energy regime clastic grain sizes and associated nutrient input clastic input influenced the inhabitable depth range for photoautotrophs the zonation of light dependent assemblages and the morphology and sequence development of mixed carbonate clastic successions this study provides data on the dynamic interactions between carbonate and non carbonate clastic sediments and when combined with information from comparable modern environments allows a better understanding of the effects of siliciclastic and volcaniclastic influx on carbonate production

quartz concentration as an index of sediment mixing hydraulic mine tailings in the sierra nevada california abstract hydraulic gold mining delivered large volumes of sediment to northern california stream channels from 1853 to 1884 distinctive quartz compositions of this sediment allow development of a sediment mixing index for determination of tailings concentrations in contemporaneous and reworked deposits this index reveals patterns of sediment mixing in the bear river california over the last 100 years a conceptual model summarizes the nature of sediment mixing in the bear river basin through time and space high terrace sediment compositions suggest that hydraulic mining sediment was diluted by about 22 other alluvium as it moved more than 60 km to the sacramento valley this substantial volume of other alluvium was introduced during the mining period by human activities in addition to hydraulic mining sediment compositions in modern low flow channels indicate that most channel reaches within the mining districts remain dominated by tailings due to sustained reworking of stored alluvium tailings are substantially diluted downstream in modern channel deposits however due to trapping of sediment by dams and local erosion of quarternary alluvium

measurements of erosion of undisturbed bottom sediments with depth a unique flume that measures the erosion of sediments at high shear stresses and with sediment depth has been designed constructed and used experiments in this flume sedflume can be done either with reconstructed sediments or with relatively undisturbed sediments from the field with either kind of sediment two different types of experiments can be conducted the first type determines the critical stress for erosion of the sediment as a function of depth while the second type determines the erosion rate of the sediment as a function of both shear stress and depth measurements of the erosion rates of sediments from the trenton channel of the detroit river in michigan and the lower fox river in wisconsin were made by use of sedflume at sediment depths up to 2 m representative results of these measurements are presented here these results demonstrate the capabilities of sedflume and also illustrate the large differences in erosion rates at different sites and the large variations in erosion rates with depth and as a function of shear stress

sequence stratigraphy and correlation of late carboniferous and permian in the cis europe tethyan area north africa arabia china gondwanaland and the usa abstract sequence stratigraphy was used to correlate the depositional chronology during permo carboniferous time in various sedimentary basins of gondwanaland western europe eastern europe tethyan area north africa arabia china and north america during late carboniferous and permian eleven second order sequences sos were recognised throughout the whole area the sequence si is serpukhovian pp namurian a pp and chesterian the sequence sii is serpukhovian pp bashkirian pp namurian a pp b c westphalian a b pp and morrowan the sequence siii is late bashkirian moscovian westphalian b pp c d and atokan desmoinesian the sequence siv is kasimovian early stephanian and missourian the sequence sv is gzhelian orenburgian late stephanian and virgilian the sequence svi is asselian autunian and nealian the sequences svii ix are saxonian sakmarian artinskian kungurian and leonardian hessian cathedralian the sequences sx xi are guadalupian and lopingian depending on the regional setting different relationships exist between marine transgression and the respective effects of tectonics and of sea level changes in western europe effects of the glacial processes in gondwanaland are partly balanced by the late compression in the hercynian belt during moscovian eastern europe tethyan area north africa china and north america show a good correlation between glacial ice melting processes in gondwanaland and the intensity of the transgression which is increased by the westward progradation of the orogeny in urals and appalachians in arabia tunisia and tethyan area the impact of the neotethys opening is obvious from the artinskian and mainly during the late permian

relating 4d seismics to reservoir geomechanical changes using a discrete element approach a modified discrete element method is briefly introduced and used for modelling reservoir geomechanical response during fluid injection and depletion the modified approach works as a continuum method until some local failure is initiated after which it behaves like a discrete element method on a polygonal lattice the method is advantageous for modelling fracture developments in rocks it is applied here to synthetic models of two reservoirs taken from the north sea gullfaks and elginfranklin for gullfaks two cases of water injection were modelled one with low horizontal effective stress and the other with low vertical effective stress vertical fractures are developed in the first case whereas horizontal fractures are developed in the second case this would not have been seen using traditional methods based on 4d seismics data for the gullfaks field one may envision that horizontal fractures could have been formed the elgin franklin synthetic model is used to study various scenarios of changing stress field around the depleting reservoir based on 4d seismics data from this field one may see changes that could be interpreted in terms of possible fault reactivation

time lapse pre stack seismic data registration and inversion for co2 sequestration study at cranfield pre stack seismic data are indicative of subsurface elastic properties within the amplitude versus offset characteristic and can be used to detect elastic rock property changes caused by co2 injection we perform time lapse pre stack 3 d seismic data analysis for monitoring co2 sequestration at cranfield the time lapse amplitude differences of cranfield datasets are found entangled with time shifts to disentangle these two characters we apply a local correlation based warping method to register the time lapse pre stack datasets which can effectively separate the time shift from the time lapse seismic amplitude difference without changing the original amplitudes we demonstrate the effectiveness of our registration method by evaluating the inverted elastic properties these inverted time lapse elastic properties can be reliably used for monitoring co2 plumes

late palaeozoic strike slip tectonics versus oroclinal bending at the sw outskirts of baltica case of the variscan belt s eastern end in poland geophysical and geological data from the eastern sector of the central european variscan belt are presented and reviewed in the regional tectonic context matched filtering of isostatic gravity guided by results of spectral analysis along with other derivatives of gravity and magnetic fields reveal a dominant wnw ese trending pre permian structural grain in the external zones of the variscan belt in poland this trend is confirmed by regional distribution of dips in carboniferous and devonian strata that were penetrated by boreholes beneath permian mesozoic sediments based on these data two alternative concepts explaining the connection of the variscan belt and its ne foreland those of strike slip tectonics versus oroclinal bending are discussed the wnw ese structural trend in the variscan foreland is parallel to a set of major strike slip fault zones in the area including those of upper elbe intra sudetic odra dolsk and krakow lubliniec these faults are considered to convey a significant dextral displacement between laurussia and gondwana the revised position of the variscan deformation front shows a similar uninterrupted generally wnw ese trend up to the se border of poland which indicates an initial continuation of the variscan belt into the area of the present day western carpathians the geometry of the variscan deformation front along with the pattern of the variscan structural grain are inconsistent with the idea of an oroclinal loop affecting the external non metamorphic variscan belt however the data presented do not entirely rule out an oroclinal loop within the variscan internides the still possible options are 1 a semi oroclinal model postulating 90 bending of the variscan tectonostratigraphic zones into parallelism with the wnw ese strike slip faults or 2 an orocline limited only to the belt linking the wolsztyn high and moravo silesian non to weakly metamorphic fold and thrust belt regardless of the kinematic model preferred our data indicate that structural evolution of the polish variscides was concluded with the end carboniferous nne ssw shortening that resulted in the present day extent of the variscan deformation front

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

dynamic changes and processes in the mississippi river delta research in the modern delta of the mississippi river has revealed short term changes and processes that are of significant magnitude deltaic lobes each lobe covering an area of 30 000 sq km and having an average thickness of 35 km switch sites of deposition on an average of every 1 500 yr through short periods of geologic time this process results in a relatively thick accumulation of stacked deltaic cycles covering extremely large areas within a single delta lobe and operating on an even higher frequency are bay fills and overbank splays bay fills having areas of 250 sq km and thickness of 15 m require only 150 yr to accumulate four major events have taken place in the modern balize delta since 1838 overbank splays are much smaller covering areas of less than 2 sq km and having thicknesses of 3 m but are associated with high floods on the river at the river mouth continued progradation of the distributary channel can form distributary mouth sand bodies that have dimensions of 17 km long 8 km wide and a thickness of 80 m in a period of only 200 yr differential sedimentary loading at the river mouth results in formation of diapirs that display vertical movements in excess of 100 m in a period of 20 yr on the subaqueous delta platform sediment instabilities operate nearly continuously mass moving large quantities of shallow water deposits to deeper water environments via arcuate rotational slides and mudflow gullies and depositional lobes all of these changes and processes operate at differing spatial and temporal scales but all result in deposition of large volumes of sediment over extremely short periods of time

a sequence stratigraphic model for the lower coal measures upper carboniferous of the ruhr district north west germany upper carboniferous coal measures strata have been interpreted traditionally in terms of cyclothems bounded by marine flooding surfaces marine bands and coal seams correlation of such cyclothems in an extensive grid of closely spaced coal exploration boreholes provides a robust stratigraphic framework in which to study the lower coal measures namurian c westphalian a of the ruhr district north west germany three distinct types of cyclothem are recognized based on their bounding surfaces and internal facies architecture 1 type 1 cyclothems are bounded by marine bands each cyclothem comprises a thick 30 80 m regionally extensive coarsening upward delta front succession of interbedded shales siltstones and sandstones which may be deeply incised by a major fluvial sandstone complex the delta front succession is capped by a thin 5 km wide 20 40 m thick steep sided multistorey fluvial sandstone complexes erode deeply into and in some cases through these successions and are overlain by the coal seam defining the cyclothem top 3 type 3 cyclothems are bounded by regionally extensive coal seam groups characterized by numerous seam splits on a local 0 1 10 km scale intervening strata vary in thickness 15 60 m and are characterized by strong local facies variability root penetrated aggradational floodplain heteroliths pass laterally into single storey fluvial channel fill sandstones and coarsening upward shallow lake infill successions of interbedded shales siltstones and sandstones over distances of several hundred metres to a few kilometres narrow 2 km but thick 20 50 m multistorey fluvial sandstone complexes are rare but occur in a few type 3 cyclothems several cyclothems are observed to change character from type 1 to type 2 and from type 2 to type 3 up the regional palaeoslope consequently we envisage a model in which each cyclothem type represents a different palaeogeographic belt within the same idealized delta system subject to the same allogenic and autogenic controls on facies architecture type 1 cyclothems are dominated by deltaic shorelines deposited during a falling stage and lowstand of sea level type 2 cyclothems represent the coeval lower delta plain which was deeply eroded by incised valleys that fed the falling stage and lowstand deltas type 3 cyclothems comprise mainly upper delta plain deposits in which the allogenic sea level control was secondary to autogenic controls on facies architecture the marine bands widespread coals and coal seam groups that bound these three cyclothem types record abandonment of the delta system during periods of rapid sea level rise the model suggests that the extant cyclothem paradigm does not adequately describe the detailed facies architecture of lower coal measures strata instead these architectures may be better understood within a high resolution stratigraphic framework incorporating sequence stratigraphic key surfaces integrated with depositional models derived from analogous pleistocene holocene fluvio deltaic strata

the mid carboniferous eustatic event stratigraphic and paleontologic evidence from mid carboniferous namurian basin and shelf successions in widely scattered parts of the world indicates that a major eustatic event occurred about 330 ma the event began with a regression that is recorded in most shelf sequences the regression was followed by a brief transgression about 328 ma and the event ended with a transgression that flooded large shelf areas about 325 ma the mississippian pennsylvanian unconformity in north america is a well known product of this event but equally prominent and contemporaneous unconformity surfaces are also present in europe north africa and elsewhere the event is believed to have caused numerous extinctions and it resulted in marked fluctuations in faunal diversity 94 references 2 figures

shelf paralic and fluvial environments and eustatic sea level fluctuations in the origin of the tuscarora formation lower silurian of central pennsylvania abstract the tuscarora formation lower silurian of central pennsylvania owes its origin to a combination of tectonic eustatic and depositional events tuscarora deposition began at the beginning of the silurian period at the time of both glacioeustatic sea level rise and renewed tectonic elevation of the taconic source terrain braided alluvial systems transported coarse sediment northwestward to a wave dominated coast yet sea level rise was so rapid that the shoreline retrograded from western to eastern pennsylvania at the time of transgression shoreline characteristics varied from high energy beaches in central pennsylvania to estuaries along the south central border region of pennsylvania seaward of the shoreline sand was fashioned into shelf sand wave complexes analogous to moder shoreface connected sand ridges much of the tuscarora formation west of the susquehanna river accumulated in this shallow marine shelf environment later in the early silurian eustatic sea level fall resulted in progradation of lower energy coastal sand mud flats northwestward over the former shelf shortly before a subsequent sea level rise terminated tuscarora development with the return of the sea in which the rose hill formation was deposited the basis for these interpretations is the analysis of five major lithofacies in the exposed tuscarora formation of central pennsylvania the basal part of the tuscarora consists of two lithofacies of coastal origin the horizontally laminated lithofacies high energy beach and the pink transitional lithofacies estuary the main body of the tuscarora comprises the eastern cross laminated lithofacies braided fluvial and the western cross laminated lithofacies shelf sand wave complexes capping the tuscarora is the red skolithos burrowed lithofacies coastal sand mud flats

developing a post fire flood chronology and recurrence probability from alluvial stratigraphy in the buffalo creek watershed colorado usa stratigraphic and geomorphic evidence indicate floods that occur soon after forest fires have been intermittent but common events in many mountainous areas during the past several thousand years the magnitude and recurrence of these post fire flood events reflects the joint probability between the recurrence of fires and the recurrence of subsequent rainfall events of varying magnitude and intensity following the may 1996 buffalo creek colorado forest fire precipitation amounts and intensities that generated very little surface runoff outside of the burned area resulted in severe hillslope erosion floods and streambed sediment entrainment in the rugged severely burned 48 km 2 area these floods added sediment to many existing alluvial fans while simultaneously incising other fans and alluvial deposits incision of older fans revealed multiple sequences of fluvially transported sandy gravel that grade upward into charcoal rich loamy horizons we interpret these sequences to represent periods of high sediment transport and aggradation during floods followed by intervals of quiescence and relative stability in the watershed until a subsequent fire occurred an alluvial sequence near the mouth of a tributary draining a 0 82 km 2 area indicated several previous post fire flood cycles in the watershed dendrochronologic and radiocarbon ages of material in this deposit span approximately 2900 years and define three aggradational periods the three general aggradational periods are separated by intervals of approximately nine to ten centuries and reflect a millennium scale geomorphic response to a closely timed sequence of events severe and intense watershed scale stand replacing fires and subsequent rainstorms and flooding millennium scale aggradational units at the study site may have resulted from a scenario in which the initial runoff from the burned watershed transported and deposited large volumes of sediment on downstream alluvial surfaces and tributary fans subsequent storm runoff may have produced localized incision and channelization preventing additional vertical aggradation on the sampled alluvial deposit for several centuries two of the millennium scale aggradational periods at the study site consist of multiple gravel and loam sequences with similar radiocarbon ages these closely dated sequences may reflect a multidecade scale geomorphic response to more frequent but aerially limited and less severe fires followed by rainstorms of relatively common recurrence

estimation of thickness and velocity changes of injected carbon dioxide layers from prestack time lapse seismic data in this study we bring together the two main categories of time lapse seismic analysis amplitude analysis and time shift analysis to estimate simultaneously the changes in thickness and velocity of a 4d seismic anomaly the methodology is applied to time lapse seismic monitoring of carbon dioxide c o2 storage at sleipner field norway that shows significant 4d effects the 4d anomalies resulting from c o2 injection appear as a multilayer reflection pattern within the relatively shallow utsira sand this multireflective appearance within the sand layer is interpreted as c o2 layers trapped below thin shale layers because most of the c o2 layers are believed to be thin 0 20 m the interference between top and base of these layers needs to be taken into account in 4d seismic analysis by studying the reflected event from a horizon below the utsira sand we estimate 4d traveltime shifts caused by the presence of the c o2 layer above thishorizon we then combine these traveltime shifts with measur