base level buffers and buttresses a model for upstream versus downstream control on fluvial geometry and architecture within sequences abstract the effects of downstream base level control on fluvial architecture and geometry are well explored in several broadly similar sequence stratigraphic models cretaceous dakota group strata u s western interior have characteristics reflecting combined downstream and upstream base level controls that these models cannot address particularly three layers of amalgamated channel belt sandstone within this group thicken and are continuous for distances 300 km along dip that stretch the reasonable lengths for which these models are intended to apply as well architecture in up dip reaches records repeated valley scale cut and fill cycles this contrasts with equivalent strata down dip which record channel scale lateral migration with no such valley scale cycles apparent we here introduce the concept of buffers and buttresses to address these observations we assume that river longitudinal profiles are each anchored down dip to some physical barrier e g the sea strand etc that we refer to as a buttress buttress shift is considered the primary downstream control on base level profiles extrapolated up dip from the buttress over any modeled duration of buttress shift can range widely because of high frequency variability in upstream base level controls e g discharge etc all these potential profiles however are bounded above by the profile of highest possible aggradation and below by the profile of maximum possible incision these upper and lower profiles are buffers and they envelop the available fluvial preservation space thickness of the buffer zone is determined by variability in upstream controls and should increase up dip to the limit of downstream profile dominance dakota valley scale surfaces record repeated cut and fill cycles driven by up dip controls and are confined between thick stable buffers equivalent strata down dip record lateral reworking within a thinner channel scale buffer zone that was positioned by downstream controls regression exposed slopes similar to the buffer zone thus buffers were stable for long distances and durations this prompted dip extensive lateral reworking of strata into upstream valley scale and downstream channel scale sheets buffers and buttresses provide a broadly applicable model for fluvial preservation that captures upstream vs downstream base level controls on geometry and architecture the model lends general insights into dip oriented variations in fluvial architecture production of sheet vs lens geometry total preservation volumes for fluvial systems and variations in these factors related to contrasting climatic conditions and basin physiography the model can be amended to existing sequence stratigraphic approaches in order to capture dip oriented variations in sequence architecture

facies and facies architecture of paleogene floodplain deposits willwood formation bighorn basin wyoming usa abstract paleogene deposits of the willwood formation were analyzed in two areas of the bighorn basin to provide a better understanding of the facies and facies arrangement of floodplain deposits and the various processes that influence floodplain construction and facies variability despite similar facies and facies organization floodplain deposits in the two areas differ in grain size hydromorphy and maturity of the paleosols and scale and organization of ribbon sandstones in the avulsion deposits these differences appear to be controlled by basin position of the study areas and differences in avulsion between the areas two kinds of cumulative floodplain paleosols red and purple paleosols formed on overbank deposits the red paleosols were better drained and formed on less clay rich parent material intense mottling and iron oxide nodules indicate that the purple paleosols which formed on more clay rich parent material were poorly drained the grain size differences reflect basin position in particular distance from a local sediment source avulsion deposits are volumetrically important comprising about half of the floodplain deposits in both areas the avulsion deposits resemble the stage iii splays described by smith et al 1989 smith n d cross ia dufficy j p clough s r 1989 anatomy of an avulsion sedimentology 36 1 24 in terms of characteristics of their ribbon sandstones and the presence of thin sheet sandstones or siltstones paleosols that formed on the fine grained facies show morphologic differences interpreted as developmental differences and attributed to differing rates of avulsion in the two study areas this study shows that avulsion belt paleosols provide a key to understanding avulsion rate in the stratigraphic record other differences between the willwood avulsion deposits in the two areas and between these ancient deposits and the modern avulsion deposits described by smith et al may reflect 1 problems in clearly recognizing ancient avulsion deposits in the field and 2 sampling bias resulting from the areally restricted view provided by the stratigraphic record of an areally extensive modern depositional feature at the same time because exposures are three dimensional the willwood strata reveal aspects of the facies and facies arrangement of avulsion belts not readily observed in the modern ones

recognition and importance of amalgamated sandy meander belts in the continental rock record meandering fluvial channels and their meander belts are common in modern continental sedimentary basins yet compose a minor constituent of the reported fluvial rock record here we document exhumed amalgamated meander belt deposits from the upper jurassic morrison formation utah united states the size of the amalgamated meander belt 9000 km2 is significantly larger than any documented previously and comparable in size to those from modern sedimentary basins we describe a representative outcrop of sandy point bar deposits that shows features considered characteristic of both braided and meandering fluvial systems lateral accretion sets compose 5 of the outcrop area yet point bar morphology is clearly visible in plan view we suggest that difficulties in the identification of sandy amalgamated meander belt deposits indicate that they have gone largely unrecognized in the rock record their recognition has important implications for basin scale reconstructions of fluvial systems and interpretation of tectonic setting

basin wide magnetostratigraphic framework for the bighorn basin wyoming new paleomagnetic data from six different sections in the bighorn basin are combined with previously published results to construct a basin wide magnetostratigraphic framework geomagnetic polarity reversals between chrons c26r c26n c25r c25n c24r and c24n have been identifi ed among multiple stratigraphic sections in different parts of the basin using the new magnetostratigraphic framework paleontological paleobotanical and isotopic information from these varied locations in the basin can now be correlated and compared to similar records from elsewhere in the world these new data resolve previous uncertainty concerning the timing of an important episode of faunal turnover known as biohorizon b which is slightly below the chron c24r c24n boundary close to the position of the elmo isotope excursion in marine records backstripping analysis using these new magnetostratigraphic data helps defi ne the time transgressive onset of basin formation and shows the different subsidence histories of the northern and southern parts of the basin

two dimensional geostatistical modeling and prediction of the fracture system in the albala granitic pluton sw iberian massif spain abstract we use a fracture index distribution method of geostatistical modelling and prediction to characterize quantitatively the fracture system in two dimensions 2d in the mina ratones area located in the albala granitic pluton sw iberian massif the fracture index fi is a quantitative estimate of the fracture density in discrete domains to validate the results of geostatistical modeling a detailed structural map of the area was also made on a scale of 1 1000 the resulting grids expressed as pixel maps describe the continuous value of the fi in 2d for the whole mina ratones area based on the modelled distribution of the fi and their correlation with mapped faults we distinguish two structural domains in the studied area elongated bands of fracture zones with high fi values and romboidal blocks located between them with low fi values the separation between both domains is gradual though a threshold value of the fi that separate both structural domains is not clearly defined the fracture zones generally present fi 1 and the individualized blocks fi

ichnofossils of the alluvial willwood formation lower eocene bighorn basin northwest wyoming u s a abstract the ichnofossil assemblage of the lower eocene willwood formation consists of at least nine distinct endichnia that are preserved in full relief four forms three ichnogenera and four ichnospecies are new and represent fodinichnia and domichnia of oligochaete worms an insect or spider an unknown vertebrate probably a mammal and domichnia of an unidentified organism other potential trace makers of the ichnofauna include insects mollusks and decapods in contrast to an egyptian oligocene fluvial ichnofauna produced largely by animals that burrowed in stream channel deposits the willwood assemblage is principally of flood plain origin though the ichnofauna occurs in a variety of paleosol types most of the fossils are restricted in distribution to specific sediment and soil types and within paleosols to specific identifiable horizons this attribute will make them valuable indiced of paleoenvironment once they are better known in other ancient alluvial sequences the environment suggested by the willwood trace fossils damp but not wet soils with fluctuating water tables is consistent with the warm temperate to subtropical possibly monsoonal conditions that are interpreted for the willwood formation by independent evidence of body fossils and paleopedology

lower eocene alluvial paleosols willwood formation northwest wyoming u s a and their significance for paleoecology paleoclimatology and basin analysis abstract the lower eocene willwood formation of northwest wyoming is a 700 m thick accumulation of alluvial floodplain and channel mudstones and sandstones nearly all of which show paleopedogenic modifications pedogenesis of willwood sandstones is indicated by taproot and vertebrate and invertebrate bioturbation early local cementation by calcium carbonate and thin illuviation cutans on clastic grains pedogenesis in willwood mudstones is indicated by plant bioturbation insect and other invertebrate burrow casts and lebensspuren free iron aluminum and manganese mobilization including hydromorphic gleying sesquioxide and calcareous glaebule formation in lower parts of the solum presence of clay rich and organic carbon rich zones and well differentiated epipedons and albic and spodic horizons probable a horizons are also locally well developed occurrence of variegated paleosol units in thick floodplain mudstone deposits and their association with thin lenticular and unconnected fluvial sandstones in the willwood formation of the central and southeast bighorn basin suggest that these soils formed during times of rapid sediment accumulation the tabular geometry and lateral persistence of soil units as well as the absence of catenization indicate that willwood floodplains were broad and essentially featureless all willwood paleosols were developed on alluvial parent materials and are complex in that b horizons of younger paleosols were commonly superimposed upon and mask properties of suspected a and b horizons of the next older paleosols the soils appear to be wet varieties of the spodosol and entisol groups aquods and ferrods and aquents respectively though thick superposed and less mottled red purple and yellow paleosols resemble some ultisols most willwood paleosols resemble warm temperate to subtropical alluvial soils that form today under alternating wet and dry conditions and or fluctuating water tables the up section decrease in frequency of gley mottles increase in numerical proportion and thickness of red versus orange coloration and increase in abundance of calcrete glaebules indicate better drained soils and probably drier climate in late willwood time this drying is believed to be related to creation of rain shadows and spacing of rainfall but not necessarily decrease in absolute rainfall due to progressive tectonic structural elevation of the mountainous margins of the bighorn basin

the influence of stratigraphy and facies distribution on reservoir quality and production performance in the triassic skagerrak formation of the uk and norwegian central north sea acknowledgements funding information the triassic phase 2 consortium members bp total jx nippon cairn energy are gratefully acknowledged for their support of this work all reviewers are thanked for their comments and additions which undoubtedly improved the manuscript

alluvial response to differential subsidence sedimentological analysis aided by remote sensing willwood formation eocene bighorn basin wyoming usa a colour landsat thematic mapper image was used to identify and to map on a regional scale alluvial facies in the lower eocene willwood formation each facies covers a distinct geographical area of several hundred square kilometres in the bighorn basin of wyoming usa comparison of the image with laboratory spectra from willwood formation rocks and field exposures shows that the image provides information regarding the colour of mudstones their relative abundances and the relative abundance of sandstones facies were further characterized from field study and published descriptions on the basis of sandbody geometry the types of nodules present in the mudstones and the abundance and geometry of carbonaceous mudstones this information helps to interpret the fluvial environments represented and types of alluvial palaeosols found in the willwood formation four facies have been distinguished the first facies is dominated by sheet sandbodies associated with immature palaeosols the sheets mark the locations of major channels which tend to occur in topographic lows the second facies is characterized by more mature moderately drained soils that required relatively lengthy periods of non deposition facies three and four dominantly consist of drab mudstones and abundant carbonaceous units both formed in poorly drained areas although minor red mudstones demonstrate that drainage conditions periodically improved in facies three facies four underwent prolonged saturation the geographical facies distribution suggests that east west faults previously mapped in the bighorn mountains extend westward into the bighorn basin and were active during early eocene time the lithological heterogeneity of the willwood formation rocks is attributed to warping associated with movement along these basement controlled faults fault activity created topographic gradients which influenced the position of major channel systems and helped produce variable drainage conditions that affected eocene soil development

abrasion set limits on himalayan gravel flux rivers sourced in the himalayan mountain range carry some of the largest sediment loads on the planet yet coarse gravel in these rivers vanishes within approximately 10 40 kilometres on entering the ganga plain the part of the north indian river plain containing the ganges river understanding the fate of gravel is important for forecasting the response of rivers to large influxes of sediment triggered by earthquakes or storms rapid increase in gravel flux and subsequent channel bed aggradation that is sediment deposition by a river following the 1999 chi chi and 2008 wenchuan earthquakes reduced channel capacity and increased flood inundation here we present an analysis of fan geometry sediment grain size and lithology in the ganga basin we find that the gravel fluxes from rivers draining the central himalayan mountains with upstream catchment areas ranging from about 350 to 50 000 square kilometres are comparable our results show that abrasion of gravel during fluvial transport can explain this observation most of the gravel sourced more than 100 kilometres upstream is converted into sand by the time it reaches the ganga plain these findings indicate that earthquake induced sediment pulses sourced from the greater himalayas such as that following the 2015 gorkha earthquake are unlikely to drive increased gravel aggradation at the mountain front instead we suggest that the sediment influx should result in an elevated sand flux leading to distinct patterns of aggradation and flood risk in the densely populated low relief ganga plain

the okavango fan and the classification of subaerial fan systems abstract controversy exists over the classification of fluvially formed subaerial fans authors either restrict alluvial fans to debris flow dominated types or extend the spectrum to fans dominated by braided rivers the okavango fan provides an end member which extends this spectrum to fans dominated by meandering and low sinuosity rivers the fan is a large 150 km radial axis shallowly sloping 0 00036 highly vegetated subaerial fan which can be subdivided into four subenvironments these are 1 the entry corridor or panhandle characterized by single and anastomosing meander belts 2 the upper fan characterized by meander belts diverging from the fan apex comprising peat confined meandering channels with interchannel swamps forming thick peats 3 the middle fan with highly confined single and anastomosing low sinuosity rivers and less common prograding meander belts whose channels are confined by thick peats with however little chance of peat preservation and 4 the lower fan in which annual floods from relatively unconfined channels spread over the fan surface and interact with pre existing aeolian and lacustrine deposits with the recognition of this new fan type the spectrum of subaerial fan types can be expressed in terms of 1 debris flow dominated fans of which the death valley fans are a member 2 braided river dominated fans of which the kosi fan is a member and 3 low sinuosity meandering losimean river dominated fans of which the okavango fan is a member this spectrum can be expressed in terms of variation in slope maximum size and percentage of surface vegetation but crucial to the evolution of the various fan types is variation in the flashy to continuous nature of the discharge and the degree of channel confinement evident on the fan surface comparable ancient examples of the three fan types are recognizable many of which provide intermediates between the ideal end members debris flow dominated and braid dominated fan types are known from throughout earth history however the losimean fan type because of its reliance on confining vegetation may only have developed after the devonian period the spectrum of subaerial fan types can be expressed on a triangular field of variation with the vertices defined by the relative importance of the processes which shaped a particular fan system be they debris flows processes associated with braided rivers or processes associated with meandering and low sinuosity rivers

a relationship between alluvial backswamps and avulsion cycles an example from the willwood formation of the bighorn basin wyoming abstract stratigraphically limited intervals from the lower eocene willwood formation contain laterally extensive carbonaceous shales and ribbon sandstone networks associated with channel avulsion we present data from one such interval that documents the avulsion sequence vertical sections measured along the outcrop of this interval are similar and comprise a basal carbonaceous shale overlain by fine grained deposits on which weakly developed hydromorphic paleosols formed the paleosols enclose and are locally incised by ribbon sandstones some of which cut down to and partly through the carbonaceous shale the ribbons have width thickness ratios between 3 and 13 some ribbons cluster at a particular stratigraphic level which together with paleocurrent trends suggests that they formed channel networks sections are capped by yellow brown paleosols showing moderate pedogenic development we suggest that the carbonaceous shales developed in low lying topogeneous swamps in distal portions of the floodplain far from the trunk channel such a location set limits on the sediment that they received the mudrocks with weakly developed paleosols and associated ribbon sandstones are interpreted as crevasse splay complexes resulting from avulsion of the trunk river the ribbon sandstones represent ancient feeder channels of the avulsion complex the rapid influx of avulsion deposits appears to have been crucial to preserving the organic material and this study reveals an important and as yet uncharacterized link between trunk channel processes and the accumulation of organic rich deposits in distal alluvial swamps similar deposits are found in other stratigraphic units in the rocky mountain region and the development of these and other organic rich deposits should be reassessed in terms of channel avulsion

imaging low velocity anomalies with the aid of seismic tomography abstract theoretical considerations snell s law suggest that low velocity fanomalies are undersampled and therefore should be poorly resolved by inversion schemes based on ray tracing methods a synthetic study considering a 40 20 m low velocity anomaly 300 m s placed at the center of a 400 50 m block with gradient background velocity model from 3000 m s at the surface to 4000 m s at the base indicates that the low ray density in ray tracing coverage diagrams of tomographic inversion studies can be used as evidence for the existence of low velocity anomalies combined normal incidence seismic reflection images and the velocity models obtained by tomographic inversions of first arrival travel times form an efficient scheme to resolve low velocity anomalies such as fracture zones furthermore the velocity models derived from tomographic inversions are used in a wave equation datuming algorithm to account for statics caused by a strongly laterally variable shallow surface weathering layer and provide seismic reflection images of fracture zones low velocity anomaly within a granitic pluton

late cretaceous fluvial megafan and axial river systems in the southern cordilleran foreland basin drip tank member of straight cliffs formation and adjacent strata southern utah u s a abstract the upper cretaceous lower campanian drip tank member of the straight cliffs formation in the grand staircase region of southern utah is an upward coarsening sandstone rich low sinuosity fluvial deposit in the cordilleran foreland basin the drip tank member thins from 75 m to 30 m eastward across the basin foredeep approximately parallel to its dominant eastward sediment dispersal direction and thins southward along the foredeep to as little as 17 m near its southern outcrop extent along modern cliff lines it overlies and underlies mudstone rich fluvial strata of the john henry member of the straight cliffs formation and lower member of the wahweap formation respectively both of which were deposited by northeast flowing rivers the john henry drip tank contact lies in an interfingering progradational stratigraphic transition from medium grained lenticular sandstone bodies to tabular coarse grained amalgamated sandstone bodies the contact with the overlying wahweap formation is locally a prominent surface of erosion or sediment reworking sandstone petrography and detrital zircon age populations of the strata indicate detrital sources in basement south of the foreland basin thrust sheets to the west and magmatic arc rocks to the southwest the uppermost part of the john henry member contains as much as 10 feldspar and abundant 1 84 1 60 ga detrital zircons derived from yavapai mazatzal basement rocks in the mogollon highlands the drip tank member ranges from quartzarenite to chert bearing sublitharenite with grenville 1 2 1 1 ga neoproterozoic and early paleozoic detrital zircons derived from proterozoic through jurassic strata exposed in the sevier orogenic belt lower member wahweap litharenites contain abundant thrust belt derived detrital carbonate grains absent from compositionally mature drip tank sandstones as well as a broad range of zircon ages the drip tank member constitutes deposits of a sand rich fluvial megafan or distributive fluvial system that displaced a subjacent but partly time equivalent axial fluvial system eastward as the megafan driven in part by seasonally high discharge fed by monsoonal precipitation prograded across the basin foredeep a thick amalgamated fan axis succession present in northern exposures contrasts with a thinner fan flank succession in southern localities tabular sixth order lithosomes each containing channels on the order of 7 m deep define three individual fluvial fans or fan lobes in the megafan system younger wahweap fluvial channels eroded uppermost drip tank deposits of the fan axis and fan flank transverse fan progradation across the foredeep recorded falling accommodation sediment supply in an aggradational to progradational systems tract erosion and reworking of the upper fan surface record decreased accommodation sediment bypass and erosion prior to reoccupation of the foredeep by the wahweap axial fluvial system the upper contact of the drip tank member is thus the primary sequence boundary in this multi component fluvial system and the lower wahweap represents transitional systems tract deposits accumulated as accommodation sediment supply increased

quantification of a distributive fluvial system the salt wash dfs of the morrison formation sw u s a abstract recent analysis of modern aggradational continental sedimentary basins reveals that sedimentation patterns are dominated by distributive fluvial systems dfss the salt wash member of the late jurassic morrison formation has previously been described as a fan shaped fluvial system this study characterizes facies variations across the salt wash dfs to quantitatively test predicted trends in conceptual dfs models notable proximal to distal trends include a change in total thickness of the fluvial succession from 174 m to 40 m and an average grain size from coarse sand to silt while the percentage of sand decreased from 70 in the proximal region to 8 in the distal region the proportion of amalgamated channel belt deposits decreased from 67 to 0 while floodplain facies and lacustrine deposits increase 38 to 94 and 0 1 to 7 respectively a downstream decrease in average channel belt thickness 15 m to 3 8 m from thickest to thinnest and average story thickness 7 7 m to 2 3 m from thickest to thinnest is also recorded significant downstream changes in deposit architecture were also noted with proximal regions dominated by stacked channel belt deposits with a high degree of amalgamation distal deposits are dominated by floodplain muds and sheet sandstones and sparse ribbon channels with little to no amalgamation of channel deposits this study provides quantified information for an ancient dfss with the aim of providing a dataset that can be used for objective comparison between different dfss as well as providing numerical data to aid resource exploration and modelling efforts

avulsion deposits in lower eocene alluvial rocks bighorn basin wyoming abstract eocene alluvial rocks in the northern bighorn basin can be subdivided into three major kinds fine grained deposits on which cumulative paleosols developed lithologically heterogeneous packages associated with immature paleosols and major sheet sandstone bodies the heterogeneous packages which alternate vertically with the cumulative paleosols are dominated by fine grained deposits and also contain ribbon sandstone bodies and thin 1 m sheet sandstone bodies most ribbon sandstones are less than 3 m thick and are more common in the middle and upper parts of the packages cut and fill deposits with fine grained fills are locally important because the lithologic packages are readily apparent in the field because of the immature or simple paleosols developed on the fine grain d facies they are referred to as simple paleosol packages the major sheet sandstones were deposited by meandering trunk rivers and locally overlie and truncate the other deposits contrary to classical models of meandering streams only a portion of the fine grained rocks in the study area were deposited by overbank flooding of a trunk channel on the basis of their stratigraphic position and few ribbon sandstones the upper parts of some simple paleosol packages are interpreted as ancient levee deposits associated with a trunk channel farther from the trunk channel overbank floods deposited alluvium on which the cumulative paleosols formed the greater parts of the simple paleosol packages including their fine grained deposits were deposited rapidly during channel avulsion ribbon sandstone bodies represent ancient splay channels on the avulsion belt simple paleosol packages in the willwood formation support the contention of smith et al 1989 that n many meandering river systems a significant portion of the fine grained deposits were deposited as the trunk channel avulsed deposits that resemble the simple paleosol packages may provide a means of recognizing avulsion episodes in other alluvial sequences

analysis of fluvial architecture in the blackhawk formation wasatch plateau utah u s a using large 3d photorealistic models abstract there are numerous allocyclic and autocyclic factors which influence fluvial sandbody geometry unraveling the relative importance of such factors is challenging because fluvial systems can migrate and avulse across significant distances on the floodplain so that collecting datasets that cover a large enough area with sufficient detail is difficult this problem has been addressed by acquiring an oblique helicopter mounted lidar survey over 16 km of exposed sections from cretaceous coastal plain deposits cropping out in the wasatch plateau of east central utah the exposures of the blackhawk formation occur in steep cliffs which are continuous for several tens of kilometers and have been previously inaccessible for study the recorded lidar data were used to build detailed photorealistic models virtual outcrops from which quantitative dimensional data on fluvial architectural elements mostly sandstone channel bodies were collected those channelized bodies show significant variation in width and thickness 26 of the sandbodies were identified as being multistory channel bodies with a thickness of 9 1 m 4 67 m 1 and a width of 142 6 m 180 7 m which are significantly larger than the measured single story sandbodies 5 9 m and 96 9 m respectively 50 of all sandbodies have aspect ratios smaller 13 1 and the highest values reach 78 1 the spatial constraint of the 397 fluvial sandbodies enabled the recognition of a series of vertical trends within the dataset these trends include a subtle upward increase in width and thickness of both the mean and maximum values this is coupled with a general upward decrease in the number of sandbodies and results in a broadly constant channel to overbank ratio a clear correlation between wider channels with increased distance to the shoreline could also be documented these observations can be explained by considering the entire blackhawk formation as the deposits of a large distributive fluvial system in this model the key control on channel architecture is the distance to the shoreline contrasting with previous interpretations of the blackhawk depositional system in which the rate of accommodation creation in the coastal plain was thought to be the key control on channel geometry and stacking patterns

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

multi scale classification of fluvial architecture an example from the palaeocene eocene bighorn basin wyoming this work was supported by phase 2 of the fluvial systems research group bp bg chevron conocophillips and total mgms thanks the sao paulo research foundation fapesp 2014 13937 3 the authors also wish to thank numerous residents of the bighorn basin for their kind hospitality and access to land we also thank john howell for discussions on fluvial geometries and nomenclature and isobel buchanan and alistair swan for assistance in the field comments from reviewers andrew miall luca colombera and an anonymous reviewer greatly improved this manuscript

tectonic control on facies distribution of the camp rice and palomas formations pliocene pleistocene in the southern rio grande rift the pliocene pleistocene camp rice and palomas formations in the rio grande rift of southern new mexico provide an excellent test of the role of basin symmetry in the distribution of piedmont and axial fluvial facies in the asymmetrical palomas and northern mesilla basins the axial fluvial facies is characterized by multistory channel sands and sandstones and is concentrated near the locus of maximum subsidence within a few kilometers of the footwall scarp fanglomerate derived from the footwall uplift extends only a few kilometers or less from the footwall scarp whereas alluvial fan and alluvial flat conglomerate sand and mudstone deposited on the hanging wall dip slope occupy a much wider outcrop belt in the symmetrical hatch rincon basin the axial fluvial facies extends to within a few kilometers of both the northern and southern basin margins and has a much higher percentage of fine grained overbank deposits some of which contain calcareous paleosols in all three basins a tongue of fanglomerate as much as 30 m thick prograded over the axial fluvial facies near the end of camp rice and palomas deposition the distribution of facies of the camp rice and palomas formations supports previously published models that predict a two stage history of asymmetrically subsiding basins during tectonically active periods axial river channels preferentially avulse into the topographically lowest area of the alluvial plain which is directly above the axis of maximum subsidence during the postorogenic stage when erosion rate exceeds subsidence rate coarse transverse dispersed sediment progrades toward the center of the basin

alluvial response to the paleocene eocene thermal maximum climatic event polecat bench wyoming u s a abstract the stratigraphic interval spanning the paleocene eocene thermal maximum in the northern bighorn basin wyoming shows changes in the alluvial record that can be tied to a high resolution climate record the complexity and stratigraphic spacing of paleosols change through the study section comparison to the climate record reconstructed from paleosols indicates the changes correspond to paleocene eocene thermal maximum climatic fluctuations in particular the middle of the section contains thick welded paleosols and thin avulsion deposits that link to times of well drained floodplains and lower mean annual precipitation stratigraphic intervals below and above the main part of the paleocene eocene thermal maximum interval correspond to times of less well drained floodplains and higher mean annual precipitation these strata contain thinner paleosols and thick avulsion deposits differences in paleosol complexity and spacing suggest that sediment flux to the depositional site varied in response to precipitation fluctuations associated with the paleocene eocene thermal maximum welded paleosols and thin avulsion deposits indicate reduced floodplain accretion during deposition of the middle of the paleocene eocene thermal maximum intervals with widely spaced paleosols indicate more rapid accretion we hypothesize that drier episodes associated with warming caused reduced vegetation in source areas and promoted erosion and increased sediment yield because precipitation was reduced much of that sediment was stored in upstream reaches of the fluvial system rather than moving to the depositional basin welded paleosols formed because of diminished sediment supply to the basin with a return to wetter conditions during the recovery phase of the paleocene eocene thermal maximum upstream water flux increased stored sediment moved to the basin and vertically spaced thinner paleosols developed the results demonstrate how vertical sections of alluvial paleosols can provide information on how climate fluctuated through time and how the fluvial system responded to climate change

river systems and their sediment flux indo gangetic plains northern bihar india river systems of part of the himalayan foreland northern bihar plains india are described in terms of their channel morphology hydrology and suspended sediment characteristics a simple classification of the river systems based mainly on the source area characteristics is proposed i mountain fed ii foothills fed iii plains fed and iv mixed fed rivers distinct differences are noted between these classes of river systems most rivers show evidence of channel movement mainly by avulsion but cut offs also occur locally the mountain fed rivers are characterized by very high discharge and low suspended sediment concentration and the plains fed rivers have relatively low discharge and high suspended sediment concentration the foothill fed rivers have moderate values of discharge and suspended sediment concentration the mountain fed rivers have built megafans of large extent whereas the foothills fed and plains fed rivers have formed muddy interfan areas semi quantitative estimates of water and sediment flux suggest that about 99 9 of the mass transfer into the plains is water with the remaining 0 1 being sediment and that 10 s of the latter 0 01 of the total is retained in the basin the remainder being transferred to the bengal fan

spillover models for axial rivers in regions of continental extension the rio mimbres and rio grande in the southern rio grande rift usa the pliocene early pleistocene history of the ancestral rio grande and quaternary history of the rio mimbres in the southern rio grande rift new mexico illustrate how axial rivers may alternately spill into and subsequently abandon extensional basins three types of spillover basins are recognized based on the angle at which the axial river enters the basin and whether it descends the hanging wall dip slope or footwall scarp to reach the basin floor in the mimbres basin type the axial river enters and flows through the spillover basin nearly parallel to the footwall scarp resulting in a narrow belt of basin axis parallel channel sand bodies located near the footwall scarp in contrast an axial river may enter a spillover basin at a high angle to its axis either descending the hanging wall dip slope columbus basin type or footwall scarp tularosa basin type and construct a fluvial fan consisting of radiating distributary channels orientated nearly perpendicular to the basin axis faulting exerts significant control on river spillover by creating the topographic gaps through which the axial river moves and by terminating spillover by subsequently uplifting or tilting the gap spillover may also be autocyclic in origin as a result of aggradation to the level of a pre existing gap headward erosion creating and or intersecting a gap or simple river avulsion upstream of a gap predicting facies architecture in the three types of spillover basins is critical to successful subsurface exploration for hydrocarbon reservoirs groundwater aquifers or placer mineral deposits

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

paleogeographic and paleotectonic setting of laramide sedimentary basins in the central rocky mountain region in the rocky mountain region between central montana and central new mexico sedimentologically isolated nonmarine basins were produced by basement deformation during the laramide orogeny within the area formerly occupied by a broad late cretaceous foreland basin in which laterally continuous marine facies had accumulated previously laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere laramide basins include perimeter basins along the cratonic periphery of the arcuate laramide province axial basins along a north south intramontane trend and ponded basins located farther west closer to the overthrust belt twelve specific stratigraphic and sedimentologic criteria for the onset duration and termination of laramide deformation allow the chronology of basin development to be inferred independently for each basin maastrichtian initiation of laramide deformation was approximately synchronous throughout the laramide province but termination of laramide deformation was systematically diachronous from north to south between early and late eocene time widespread eocene erosion surfaces truncate syntectonic laramide sequences and are overlain by largely volcanic and volcaniclastic post laramide strata of eocene age in the north and oligocene age in the south fluvial depositional systems draining toward the great plains were dominant in perimeter and axial basins but ponded basins were occupied at times by large lakes that served as regional sediment traps paleocene drainages from ponded basins also led eastward toward the continental interior but partly interconnected lakes that developed within several ponded basins by mid eocene time were either closed hydrologically or else they drained westward into the tyee paleoriver of the pacific northwest

stratigraphic architecture of an experimental basin with interacting drainages abstract the stratigraphic architecture of intracontinental rift basins is defined by a dynamic relationship between depositional processes associated with the basin floor and flanking tributary streams the resulting depositional belts are sensitive to a variety of factors including basin geometry subsidence rate and sediment discharge the experimental earthscape run in 2006 xes06 examined the development of fluvial morphology and alluvial architecture as a function of subsidence and sediment flux in an experimental basin based on the form of a simple half graben sediments from tributary drainages were introduced into the axial stream through toe cutting and realignment of transverse drainage courses to parallel the prevailing axial flow direction transverse sediment contributions to the axial stream were almost equally apportioned over a wide range of sediment discharges tested in the experiments sediment tracers showed a larger contribution of footwall derived sediment into the axial belt probably due to more frequent and aggressive toe cutting by axial streams changes in the axial transverse deposit boundary to external forcing by subsidence and sediment discharge and relatively rapid intrastage stabilization of the depositional belts resembles the large scale self organization observed in moving boundaries that define the morphology of fluviodeltaic systems basin sedimentation was matched to subsidence in order to maintain a constant base level which made the location and width of the axial belt sensitive to the relative sediment fluxes from the transverse systems rather than the axis of maximum subsidence the asymmetrical subsidence pattern and the transverse fan morphology influenced the preservation of sedimentary sequences stage bounding stratigraphic lacunae were well preserved in the hanging wall succession providing a reliable record of basin development

recognition of interfluve sequence boundaries integrating paleopedology and sequence stratigraphy in shallow marine and coastal plain strata sequence boundaries are easily recognized at the base of incised valley fills between valleys however it is more difficult to recognize sequence boundaries where they are expressed as interfluve paleosols we suggest that interfluve paleosols can be most reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure color and degree of rooting and 3 micromorphological features such as bioturbation fabric clay coatings ferruginous features and siderite and barite only micromorphology permits recognition of temporal changes in drainage surface stability and protracted pauses in sedimentation that typify these surfaces this three part approach has been successfully employed to identify interfluve sequence bounding paleosols in the cenomanian dunvegan formation in alberta and british columbia canada

fluvial morphology and sediment flux steering of axial transverse boundaries in an experimental basin abstract the distinction between depositional belts associated with the basin axis and flanking piedmont streams is a fundamental attribute of the stratigraphic architecture of intracontinental rift basins spatiotemporal distributions of these lithofacies associations are sensitive to a combination of factors including basin geometry subsidence rate and sediment discharge however most studies have focused on one or two controls and one depositional component axial or tributary of the basin fill succession a new perspective on how these depositional belts develop under simple but precisely controlled boundary conditions of steady subsidence sediment flux and water discharge is achieved through the creation of an experimental stratigraphic succession the experimental earthscape run in 2006 xes06 focused on the geomorphic evolution of sedimentary successions within an asymmetrically subsiding basin analogous to a simple half graben containing four interacting supply points of sediment and water under the imposed conditions the experimental system self organized into an axial stream flanked by transverse fans imposition of various combinations of longitudinal and lateral sediment flux showed that the locations and widths of the axial and transverse systems were strongly controlled by relative sediment fluxes flux steering and less influenced by the location of the subsidence maximum and subsidence rate the axial drainage was dominated by transversely sourced sediment through toe cutting of the transverse fans except during the highest axial sediment discharges footwall fans persisted even under conditions of very large axial sediment discharge aided by topographic inheritance of the steeper transverse depositional slopes

high resolution reflection seismics applied to detection of groundwater resources in glacial deposits sweden a large proportion of sweden s ground water resources is contained in sand gravel glaciofluvial deposits that overlie precambrian crystalline basement and are covered by clay the depth to the sand gravel deposits varies from near surface to about 100 m and their thickness is generally 10 20 m traditionally due to logistics short refraction seismic profiles and penetration tests have been used to localize the sand gravel deposits below the clay and to determine their thickness however when the overlying clay deposits are thick or the glacial deposits show significant 2 d structure refracting waves may not penetrate into the sand gravel deposits or into the crystalline basement reflection seismic methods provide an alternative mapping method and a test profile was acquired over glacial deposits where the structure is well known standard processing shows in general excellent agreement between the seismic image and the structure determined from penetration tests

late cretaceous early eocene laramide uplift exhumation and basin subsidence in wyoming crustal responses to flat slab subduction low angle subduction of the farallon oceanic plate during the late cretaceous early eocene is generally considered as the main driver forming the high rocky mountains in wyoming and nearby areas how the deformation was transferred from mantle to upper crust over the great duration of deformation 40 myr is still debated here we reconstruct basin subsidence and compile paleoelevation thermochronology and provenance data to assess the timing magnitude and rates of rock uplift during the laramide deformation we reconstruct rock uplift as the sum of surface uplift and erosion constrained by combining paleoelevation and exhumation with regional stratigraphic thickness and chronostratigraphic information the amount and rate of rock uplift of individual laramide ranges was less than 2 4 4 8 km 0 21 0 32 mm yr during the early maastrichtian paleocene stage 1 and increased to more than 3 km 0 38 0 60 mm yr during the late paleocene early eocene stage 2 our quantitative constraints reveal a two stage development of the laramide deformation in wyoming and an increase of rock uplift during stage 2 associated with enhanced intermontane basin subsidence exhumation and uplift during stage 1 is consistent with eastward migration of cordilleran deformation associated with low angle subduction whereas the change in exhumation during stage 2 seems to follow a southwestward trend which requires an alternative explanation we here suggest that the increase of rock uplift rate during the late paleocene early eocene and the southwestward younging trend of uplift may be a response to the rollback and associated retreating delamination of the farallon oceanic slab

long hole destress blasting for rockburst control during deep underground coal mining abstract the lazy colliery in the ostrava karvina coalfield of the upper silesian coal basin adopted modern longwall technology for an underground extraction of coal seam no 504 this coal seam is located at a cover depth of around 700 m the seam thickness varied from 3 1 m to 5 0 m in the selected longwall panel two overlying coal seams nos 512 and 530 experienced mining at average heights of 58 m and 75 m respectively from the planned working horizon of the seam no 504 the proposed longwall panel was adversely situated below goaf edges of the workings in these two overlying extracted seams an analysis of the inter burden rock mass among these coal seams showed the presence of strong massive strata of sandstones and conglomerates with uniaxial compressive strength values between 70 mpa and 120 mpa the stress is measured at different mining stages by compact conical ended borehole monitoring ccbm a simple laboratory test of the coal sample found a high value of the ratio of the elastic deformation to the total deformation 0 8 indicating the energy storing characteristic prone to burst bump of the coal seam under the existing geo mining conditions of the site a suitable destress blasting long hole drilling and blasting design is adopted to pre fracture the identified competent strata from both gate roads in advance the total length of the panel could be extracted without any bump rockburst after the destress blasting the efficiency of the adopted destress blasting at the different mining stages is evaluated in terms seismic effect se which is calculated through the available seismic monitoring data and weight of the charged explosive a systematic adoption of the destress rock blasting led the 300 m long longwall panel to be smoothly extracted without any further rockbursts

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

effects of the shallow subsurface on upper crustal seismic reflection images abstract seismic imaging of the upper crust is strongly affected by the interactions of the seismic wavefield with the shallow subsurface in order to better understand these effects we have evaluated the seismic responses of a suite of canonical models of the upper crystalline crust and the near surface region our modelling is restricted to two dimensions but otherwise includes the full seismic wavefield notably the effects of attenuation and topographic variations along the free surface we find that s wave scattering is important in the upper crust and contributes significantly to the vertical component of the seismic reflection response the backscattered wavefield undergoes mode conversions when it interacts with the free surface even moderate topographic variations or velocity variations in the near surface region enhance these mode conversions and cause additional scattering much of the earth s surface is covered by thin layers of unconsolidated material or weathered bedrock with high attenuation and high velocity contrasts at the layer boundaries scattered and mode converted seismic energy gets trapped in these layers and thus interacts repeatedly with the free surface and its topography in analogy to large scale seismic resonance effects of sedimentary valley fills the level and duration of source generated noise depends heavily on the degree of attenuation in the shallow layers low attenuation causes high noise levels and vice versa in contrast the level of source generated noise is less sensitive to near surface layer thicknesses and velocity contrasts

paleohydrologic response to continental warming during the paleocene eocene thermal maximum bighorn basin wyoming abstract geologically rapid global warming occurred during the paleocene eocene thermal maximum petm 56 ma several studies have argued that important changes occurred in the hydrological cycle during the petm but results have been inconsistent ranging from global increases in humidity to drier conditions changes in paleosols during the petm in the southeastern bighorn basin document major drying during the body of the event paleosol changes also suggest transitional episodes of climate change that both preceded and followed the petm qualitative semi quantitative and fully quantitative analyses of a 70 m thick interval of paleosols provide a high resolution record of changes in soil moisture and precipitation those changes are compared to changes in temperature determined from 18o values of tooth enamel from the mammal coryphodon a distinct shift to drier soils occurred just prior to the petm a conclusion that is consistent with previous observations that warming began before the onset of the negative carbon isotope excursion associated with the petm paleosols show a progressive drying trend into the lower part of the petm and become even drier in the upper part of the body of the petm purple red paleosols that appear during the recovery phase of the petm indicate wetter soils although they are better drained than paleosols below the onset the purple red paleosols continue for 15 m above the recovery and indicate that wetter soil conditions persisted after the recovery it is not clear whether changes in the paleosols that preceded and followed the petm reflect global forcing factors like orbital cycles or release of carbon that lacks an isotopic label however such mechanisms would provide a unifying explanation for shifts seen in continental and marine environments

mudrock dominated fills formed in avulsion splay channels examples from the willwood formation wyoming mudrock dominated channel fills are common features of the fluvial palaeogene willwood formation of wyoming these fills are small on average 30 m wide and 3 m deep and they vary from simple plugs to more lithologically complex fills with internal scour surfaces some fills preserve plant material and others show pedogenic modification all fills are located within metre thick intervals of weakly pedogenically modified mudstones that surround ribbon sandstones the intervals have previously been attributed to channel avulsion the fine grained channel fills are interpreted as crevassesplay feeder channels within these avulsion deposits variation in fill type particularly the presence of pedogenic features appears to be related to floodplain drainage possible factors that influenced drainage were basin position of the fills and palaeogene climate fluctuations although the role of either is not unequivocal in general channel fills with sombre colours and preserved plant detritus indicating poorly drained conditions dominate locations that were proximal to the palaeogene basin axes fills that contain root traces red and yellow brown matrix colours and mottling which indicate pedogenic modification and episodic subaerial exposure of the sediment dominate locations that were more distal to the palaeogene basin axes eocene climate fluctuations particularly episodes of global warming may have been a secondary control on the kind of fill that developed mudrock dominated channel fills have not been described previously from ancient avulsion deposits their common presence in the willwood formation suggests that they are a typical component of avulsion belts and that similar channel fills in other stratigraphic units should be considered with regard to channel avulsion the variety of fills observed in the willwood formation indicates that avulsion belt channels can experience very different fill histories the descriptive details of fills provided here should help in their recognition elsewhere in addition the nature of the channel fill provides important information on ancient drainage conditions in the avulsion belt pedogenically modified channel fills have been recognized only rarely from the stratigraphic record their presence throughout the willwood formation suggests that they should exist in other alluvial successions and may have been overlooked previously they indicate that periods of sediment exposure alternated with episodic influxes of water and sediment in an active avulsion

basin scale predictive models of alluvial architecture constraints from the palaeocene eocene bighorn basin wyoming usa this work was supported by phase 2 of the fluvial systems research group bp bg chevron conocophillips and total ae thanks the university of aberdeen for additional funding and mgms thanks the sao paulo research foundation fapesp 2014 13937 3 the authors also wish to thank numerous residents of the bighorn basin for their kind hospitality and access to land and isobel buchanan and alistair swan for assistance in the field the authors also thank reviewers luca colombera and sian davies vollum and ae christopher fielding for helpful comments on this manuscript

controls on synorogenic alluvial fan architecture beartooth conglomerate palaeocene wyoming and montana late palaeocene uplift of the beartooth range in northwestern wyoming and southwestern montana generated the beartooth conglomerate along the eastern and northeastern flanks of the range systematic unroofing sequences and intraformational unconformities folds and faults in the conglomerate attest to deposition during uplift along the eastern flank at least three ancient alluvial fan systems and a braidplain system can be distinguished on the bases of petrofacies and lithofacies the two southern fans consist of 700 m of sedimentary clast conglomerate and subordinate sandstone dominated by hyperconcentratedflow and stream flow facies the next fan to the north is dominated by plutonic and metamorphic clasts and contains abundant mud matrix supported debris flow facies as well as stream flow facies the northernmost depositional system consists of arkosic channellized fluvial conglomerate and sandstone overbank mudstone and crevasse splay sandstone units palaeocurrent data indicate eastward dispersal away from the beartooth range outstanding exposure of the beartooth conglomerate allows facies to be mapped on lateral photographic mosaics a seven fold hierarchy of bounding surfaces and enclosed lithosomes exists in the beartooth conglomerate first through fourth order surfaces are analogous to first through fourth order surfaces that recently have been documented in sandy fluvial facies with one exception sediment gravity flows are bounded by first order surfaces fifth order surfaces are either erosional e g lateral migration of fanhead trench or accretionary e g aggradation of fan surface during backfilling of trench and construction of lobes on lower fan during entrenchment on upper fan some fifth order surfaces coincide with intraformational angular unconformities and are thus the result of long term fanhead entrenchment following uplift of the upper part of the fan sixth order surfaces bound individual fan packages that are several hundred metres thick and 10 km2 in area the enclosed sixth order lithosomes are distinguishable in terms of petrofacies and lithofacies a single seventh order surface bounds the entire beartooth conglomerate lower order lithosomes are produced by intrinsic processes of fan construction fifth order lithosomes can be attributed to both extrinsic and intrinsic controls sixth and seventh order lithosomes are generated by extrinsic controls

fluvial systems in the siwalik miocene and wyoming paleogene abstract the 3 km thick miocene siwalik group himalayan foredeep in northern pakistan and the 2 km thick paleogene fort union willwood formations bighorn basin in wyoming both preserve long records of fluvial deposition adjacent to rising mountain belts depositional environments and associated habitats change across large basins along with changing physiography and with the location of different river systems that may have varied greatly in patterns of channel deposition and the drainage of adjacent floodplain areas deposits exposed in these two basins provide very different records of shifting paleoenvironments and patterns of basin filling these differences reflect distinct patterns and scales of depositional environments the nature of the exposures and the types of sedimentologic studies that have been carried out in each basin the siwalik group fills a basin that extended at least 1000 km along its axis and 150 250 km away from the mountain front comparison of siwalik deposits and modern drainages in the himalayan foredeep suggests the ancient siwalik basin was filled by large rivers that deposited low gradient sediment fans covering areas on the order of 1000 km 2 and by smaller intrafan rivers with more poorly drained floodplains despite the scale of these river systems relative to siwalik exposures in pakistan transitions between different systems have been recognized deposits of coeval river systems in the siwalik basin show pronounced differences in alluvial architecture the character of overbank deposits and the abundance and taphonomy of organic remains in contrast the bighorn basin in wyoming is a relatively small intermontane foreland basin extending 200 km along its axis and about 80 km across bighorn basin strata were deposited by a river that flowed south to north along the basin axis and by smaller rivers that flowed transverse to the basin axis much of this basin is exposed and thus it is possible to reconstruct changing patterns of deposition and environments through time in more detail than in the siwalik basin these patterns indicate changes in basin wide drainage conditions and environments through time but there are also important differences among coeval strata upsection shifts in environments and vertebrate faunas within both the siwalik and bighorn basins may reflect tectonic or climatic forcing but this comparison emphasizes the importance of recognizing deposits from different contemporaneous river systems before inferring such large scale controls on paleoecological change through time

chemostratigraphic implications of spatial variation in the paleocene eocene thermal maximum carbon isotope excursion se bighorn basin wyoming 1 the paleocene eocene thermal maximum petm is marked by a prominent negative carbon isotope excursion cie of 3 5 that has a characteristic rapid onset stable body and recovery to near pre cie isotopic composition although the cie is the major criterion for global correlation of the paleocene eocene boundary spatial variations in the position and shape of the cie have not been systematically evaluated we measured carbon isotope ratios of bulk organic matter 13corg and pedogenic carbonate 13ccarb at six petm sections across a 16 km transect in the se bighorn basin wyoming bed tracing and high resolution floral and faunal biostratigraphy allowed correlation of the sections independent of chemostratigraphy the onset of the cie in bulk organic matter at all six sections occurs within a single laterally extensive geosol the magnitude of the cie varies from 2 1 to 3 8 the absolute and relative stratigraphic thickness of the body of the cie in bulk organic matter varies significantly across the field area and underrepresents the thickness of the petm body by 30 80 the variations cannot be explained by basinal position and instead suggest that 13corg values were influenced by local factors such as reworking of older carbon the stratigraphic thickness and shape of the cie have been used to correlate sections estimate timing of biotic and climatic changes relative to the presumed carbon isotope composition of the atmosphere and calculate rates of environmental and biotic change localized controls on 13corg values place these inferences in question by influencing the apparent shape and duration of the cie

is the present the key to the past a global characterization of modern sedimentary basins the stratigraphic record is heavily biased because it is uniquely composed of sediments that were laid down in basins whereas the majority of the present and historic land surface of the planet is composed of areas that are in net long term erosion with no preservation potential global mapping and quantification of the distribution of currently active sedimentary basins suggest that only 16 of earth s terrestrial land surface is within sedimentary basins the remainder of the land is in upland areas that will not be represented in the future rock record furthermore 60 of the modern basin area has an arid climate as opposed to 27 of the land surface tectonic classification of modern basins indicates that intracratonic and foreland basins cover the greatest area whereas forearc extensional and strike slip basins are the least represented by area while this modern snapshot does not account for differences in subsidence rate or basin longevity the mapping and quantification of modern basins highlight the incompleteness of the stratigraphic record and the importance of caution when assuming the present is the key to the past

alluvial fans and fluvial distributary systems oligo miocene northern spain contrasting processes and products sediments of alluvial fans and distributive fluvial sediments were deposited by contrasting processes during the oligo miocene in the north central ebro basin northern spain the coeval depositional systems can be separated on the basis of lithofacies criteria a number of localized deposits each covering only a few square kilometers and lying adjacent to the south pyrenean thrust front are made up of beds of poorly sorted conglomerate sandstone and mudstone that show a radial decrease in bed thickness and grain size these deposits are interpreted as the products of sheet flood events on alluvial fans that formed at the basin margin covering much larger areas of the basin several thousand square kilometers are conglomerate sandstone and mudstone as lensoid and irregular sheet bodies incised into thin bedded sheets of sandstone and mudstone these are interpreted as the deposits of fluvial systems that are considered to be distributary in form because the channel size and grain size of channel fill deposits decrease down paleoflow and because there is a radial pattern of paleocurrents at the distal margins the fluvial facies interdigitate with ephemeral lacustrine and alluvial plain deposits the deposits of the alluvial fans and the fluvial distributary systems are petrographically distinct reflecting separate source areas important components of the alluvial fan deposits are limestone clasts derived from the adjacent thrust front the deposits of the fluvial systems are mainly sand and subordinate gravel derived from rocks of the axial zone of the pyrenean mountain belt the deposits of these systems interdigitate and there are no transitional forms between the two within this stratigraphic package

geochronology and mammalian biostratigraphy of middle and upper paleocene continental strata bighorn basin wyoming the bighorn basin of northwestern wyoming preserves one of the most complete records of middle paleocene to lower eocene continental biota the geochronology of this important interval depends partly on numerical calibration of the geomagnetic polarity time scale gpts but the middle and late paleocene parts of the gpts have been poorly constrained radioisotopically a new volcanic ash from the northern bighorn basin provides the first radioisotopic age for upper middle paleocene strata upper selandian and is an important calibration point for the base of polarity chron c26n and the selandian thanetian stage boundary in the gpts sanidine from the ash has a weighted mean age of 59 00 0 30 2 ma based on twenty three 40 ar 39 ar bulk laser fusion analyses the ash corroborates the revised age estimate for the base of chron c26n in the most recent geomagnetic polarity time scale gpts 04 and confirms that c26n is older than depicted in the 1995 gpts we place paleocene mammalian biozones in the bighorn basin into a refined geochronologic framework these biozones are the primary basis for biostratigraphic correlation of middle and upper paleocene continental deposits in north america new paleomagnetic data provide synchronous tie points for correlation among three stratigraphic sections in the northern bighorn basin and to the gpts paleomagnetic correlation study of new fossil material review of known faunas and refined stratigra phy enable us to reevaluate several biozones we define three new zones based on first occurrences of taxa the phenacolemur ti 4b probathyopsis ti 5a revised and copecion cf 3 revised zones the phenacolemur zone includes some faunas previously placed in the plesiadapis churchilli and plesiadapis fodinatus zones ti 4 and ti 5a respectively the probathyopsis zone replaces the p fodinatus zone and the copecion zone replaces the phenacodus ectocion acme zone cf 3 seven of the biozones considered here are subdivisions of the tiffanian land mammalage thetiffanianwasoriginallytypifiedbythemasonpocketfaunainsouthwest ern colorado but it is now much better known from faunas in the northern bighorn basin biostratigraphic evidence and new paleomagnetic data from the bighorn basin indicate that mason pocket is considerably older than was previously recognized and occurs in chron c26r rather than c25r the geochronologic framework presented here helps to constrain the temporal ranges of species that occur in the middle and late tiffanian and it allows the bighorn basin record to be better compared to other faunal floral and paleoclimate records both regionally and globally

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

characterizing avulsion stratigraphy in ancient alluvial deposits guidelines for identifying ancient avulsion deposits were set forth by kraus and wells kraus m j wells t m 1999 recognizing avulsion deposits in the ancient stratigraphical record in smith n d rogers j eds fluvial sedimentology vi special publication of the international association of sedimentologists vol 28 pp 251 268 building on the study by smith et al smith n d cross t a dufficy j p clough s r 1989 anatomy of an avulsion sedimentology 36 1 23 of the modern saskatchewan river system cumberland marshes central canada and serve to characterize avulsion depositional sequences in the ancient willwood and fort union formations paleogene bighorn basin nw wyoming usa we recognize however that the model is not universally applicable to avulsion dominated successions specifically systems which lack defining heterolithic avulsion deposits set forth by kraus and wells kraus m j wells t m 1999 recognizing avulsion deposits in the ancient stratigraphical record in smith n d rogers j eds fluvial sedimentology vi special publication of the international association of sedimentologists vol 28 pp 251 268 observations in several fluvial intervals suggest that the avulsion stratigraphy outlined by kraus and wells kraus m j wells t m 1999 recognizing avulsion deposits in the ancient stratigraphical record in smith n d rogers j eds fluvial sedimentology vi special publication of the international association of sedimentologists vol 28 pp 251 268 represents one category of avulsion stratigraphy found in the rock record but does not capture the nature of avulsion deposits everywhere based on observations using measured sections outcrop photo panels and aerial photographs in the willwood formation eocene wyoming and ferris formation cretaceous paleogene wyoming we present two end member categories of avulsion stratigraphy in ancient deposits stratigraphically abrupt when a main paleochannel is stratigraphically juxtaposed directly atop floodplain overbank deposits and stratigraphically transitional where crevasse splays and other non floodplain overbank deposits stratigraphically precede a main paleochannel this characterization provides a broader more inclusive way to recognize and describe avulsion stratigraphy in ancient deposits and may be an important factor to consider when modeling connectivity in fluvial reservoirs furthermore our observations show that one type of avulsion channel stratigraphy may prevail over another within an ancient basin suggesting that system wide factors such as splay proneness or avulsion style i e aggradational incisional etc slingerland r smith n d 2004 river avulsions and their deposits annual review of earth and planetary sciences 32 257 285 may be primary controls on the type of avulsion stratigraphy deposited and preserved in ancient basin fills

evolution of the miocene sedimentary fill of the gediz graben sw turkey abstract the gediz graben is a continental extensional basin filled with miocene to recent sediments the evolution of the graben can be expressed in terms of two phases i miocene half graben phase and ii post miocene graben phase the miocene half graben phase was governed by the southern margin structure evolution of which significantly controlled the stratigraphic variability in the basin alluvial fluvial and lacustrine systems developed in the graben as a function of distance to the southern margin thus alluvial deposits with coarse grained facies dominate the southern margin and grade into finer fractions of fluvial and or lacustrine deposits to the north this depositional architecture repeated three times during the miocene and deposited alasehir caltilik and gediz formations these formations depict distinct thickness and grain size decrease from south to north to emphasize the half graben configuration for the favour of the southern margin the post miocene graben phase started with the faulting of the northern margin this resulted in relatively balanced partitioning of the subsidence between the two margins although the preceding asymmetry was inherited by the graben sediment influx became bipolar and alluvial fan systems developed along the both margins

calibrating 3d tomograms of a granitic pluton 1 first arrival time p waves from offset and azimuth variable vertical seismic reflection records are used to tomographically reconstruct the 3d p wave velocity structure around a 500 m deep vertical borehole comparisons with sonic and fracture index logs and core samples indicates that low velocity anomalies in the tomograms correlate with surface mapped fracture zones results also show that low velocity zones intersect the borehole in areas characterized by relatively low values for vp and vs determined from sonic logs these zones are characterized by poisson s ratio close to 0 3 which are indicative of altered or fractured rock and supported by the fracture index and core samples the high velocity anomalies intersect the well in areas characterized by low values of the fracture index and 0 25 or lower this suggests that the relatively high vp velocities are indicative of unfractured rock this study reveals that high resolution tomography produces results consistent with direct observations in a well sampled borehole