sediment dispersal and quantitative stratigraphic architecture across an ancient shelf two large 200 to 300 km near continuous outcrop transects and extensive well log data ca 2800 wells allow analysis of sedimentological characteristics and stratigraphic architecture across a large area ca 60 000 km2 of the latest santonian to middle campanian shelf along the western margin of the western interior seaway in eastern utah and western colorado usa genetically linked depositional systems are mapped at high chronostratigraphic resolution ca 0 1 to 0 5 ma within their sequence stratigraphic context in the lower part of the studied interval sediment was dispersed via wave dominated deltaic systems with a compound clinoform geomorphology in which an inner wave dominated shoreface clinoform was separated by a muddy subaqueous topset from an outer clinoform containing sand poor gravity flow deposits these strata are characterized by relatively steep net regressive shoreline trajectories 0 1 with concave landward geometries narrow nearshore belts of storm reworked sandstones 2 to 22 km wide offshore mudstone belts 250 km and relatively high sediment accumulation rates ca 0 27 mm year 1 the middle and upper parts of the studied interval also contain wave dominated shorefaces but coeval offshore mudstones enclose abundant isolated tide influenced sandstones that were transported sub parallel to the regional palaeoshoreline by basinal hydrodynamic tidal circulation these strata are characterized by relatively shallow net regressive shoreline trajectories 190 km and relatively low sediment accumulation rates ca 0 11 mm year 1 the change in shelfal sediment dispersal and stratigraphic architecture from i compound clinoform deltas characterized by across shelf sediment transport to ii wave dominated shorelines with isolated tide influenced sandbodies characterized by along shelf sediment transport is interpreted as reflecting increased interaction with the hydrodynamic regime in the seaway as successive shelfal depositional systems advanced out of a sheltered embayment utah bight this advance was driven by a decreasing tectonic subsidence rate which also suppressed autogenic controls on stratigraphic architecture

tectonic control of nested sequence architecture in the castlegate sandstone upper cretaceous book cliffs utah abstract the castlegate sandstone at its type section price canyon near price utah encompasses a single stratigraphic sequence spanning approximately 5 m y it includes a sandstone member corresponding to a lowstand systems tract consisting of braided fluvial sheet sandstones and a mudstone member in which shales are more abundant and some evidence of tidal influence is present this is the transgressive to highstand systems tract from near trail canyon eastward the mudstone member passes laterally into the sego sandstone and neslen formation a succession of at least six higher frequency sequences of fluvial estuarine origin the buck tongue a marine shale unit separating the castlegate sandstone and the sego sandstone east of green river is erosionally truncated below the sego sand tone northwest of trail canyon we suggest that the origin of the sequences is related to flexural loading and intraplate stress on two time scales eustasy cannot be ruled out but there is no independent evidence for this process the main 5 m y sequence reflects regional tectonism with the sandstone member developing at a time of slow subsidence and the mudstone member reflecting a higher long term subsidence rate the higher order sequences nested within the third order sequence east of trail canyon are interpreted as a basinal response to episodes of crustal shortening on a 105 yr time scale this study amplifies the model of posamentier and allen 1993a in which ramp type foreland basins are divided into areas of rapid and slow subsidence zones a and b we postulate that these zones migrated asinward and landward in response to variations in long term subsidence rate an effect not predicted in the original model and can be mapped by reference to the distribution of type 1 sequence boundaries in the higher order sequences differences in sequence architecture east and west of trail canyon may have been amplified by differences in crustal rheology the sequence architecture changes at the boundary of the underlying paleozoic paradox basin a zone of nw se oriented folds faults and salt diapirs which we suspect were reactivated by cretaceous tectonism the high frequency sequences are within the area of the paradox basin an area that may have been more prone to vertical structural movements in response to intraplate stresses incipient uplift of laramide structures may also have modified fluvial patterns and controlled the orientation of incised valleys on several of the sequence boundaries

accommodation and sediment supply controls on clastic parasequences a meta analysis this study combines data from many published case studies to undertake a quantitative characterization of clastic parasequences with the aim to determine how accommodation sediment supply and autogenic sediment storage dynamics are recorded in their sedimentary architecture and stacking patterns results of this study are used to critically evaluate the validity of paradigms and models that are routinely used to explain and predict trends in the anatomy and arrangement of parasequences data on 957 parasequences from 62 case studies of clastic shallow water successions were coded in a relational database which includes outcrop and subsurface datasets of ancient and quaternary examples these units cover the preserved records of both river dominated deltas and wave dominated coasts representing shoreline transits over a breadth of timescales likely of both local and regional extent the role of extant accommodation rates of creation of accommodation and rates of sediment supply in determining parasequence architecture is assessed through analysis of relationships between i proxies of these variables at different scales rates of aggradation and progradation facies belt shoreline trajectories systems tract type parasequence set stacking patterns parasequence progradation angle and stratigraphic rise size of feeder rivers and ii parameters that describe the geometry and stacking style of parasequences and associated shallow water sand bodies statistical analyses of database outputs indicate which proxies of accommodation sediment supply and accommodation sediment supply ratio are significant as predictors of parasequence architecture and allow for interpretations of the importance of allogenic and autogenic factors the principal results of this study reveal the following i parasequence thickness varies as a function of water depth accommodation generation and erosional truncation and these variations are also reflected across types of systems tracts and parasequence sets ii the dip length of parasequence sand bodies demonstrates scaling with measures of accommodation sediment supply ratio at multiple scales partly in relation to the possible effect of sediment supply on progradation rates iii in systems tracts stratigraphic trends in parasequence stacking due to autogenic mechanisms or to acceleration or deceleration in relative sea level fluctuations are not revealed quantitatively iv some association is seen between the abundance of deltaic or river dominated parasequences and progradational stacking v positive but modest correlation is observed between measures of river system size and the dip length of shallow marine parasequence sand bodies the resulting insights can be applied to guide sequence stratigraphic interpretations of the rock record and the characterization of sub seismic stratigraphic architectures of subsurface successions

high resolution facies analyses of mudstones implications for paleoenvironmental and sequence stratigraphic interpretations of offshore ancient mud dominated successions abstract the extent of lithofacies variability in fine grained sedimentary rocks is very poorly known in comparison to that present in coarser grained clastic and carbonate successions the absence of this information means that sediments present on continental shelves are rarely considered as integrated systems because fine grained facies such as shales are mostly excluded from sophisticated regional facies models to shed light upon lithofacies and grain size in shale dominated successions so that they can be incorporated into shelf wide depositional models the blackhawk formation of the mancos shale campanian age exposed in the book cliffs utah was investigated using combined field whole rock geochemical optical and electron optical methods these sediments show systematic grain size variations are intensely bioturbated and composed predominantly of detrital clays mainly dioctahedral micas quartz and feldspar with minor pyrite and organic matter they are organized into very thin 10 mm upward fining genetic beds they exhibit both systematic lateral 103 m scale and vertical 10 2 to 100 m scales lithofacies variability preferentially cemented units occur close to sequence boundaries unconformities these cemented units typically contain a very different detrital assemblage including significant quantities of chlorite from the rest of the succession and are located close to levels where there are marked stacking pattern discontinuities overall lithofacies variability is interpreted in terms of deposition occurring on an oxic continental shelf with the coarser grained facies being deposited in proximal settings offshore transition zone in contrast to the finer grained units that were deposited in more distal environments offshore zone storms are interpreted to have been the dominant mechanism dispersing the sediment once deposited the surface layers of the sediment were intensely reworked by burrowing organisms preferential preservation of ichnogenera from mid and lower tiers suggest that the depositional environment was energetic and erosion commonly removed the surface sediment layers prior to deposition of thin 10 2 m storm beds the larger scale 100 m upward coarsening units that are composed of stacked beds are interpreted to be parasequences preferential cementation at levels where large scale stacking patterns change is interpreted to occur at horizons where there were breaks in sediment accumulation and bacterial metabolic processes were able to supply sufficient solutes to fill uncompacted pore space with cement the presence of a very different detrital assemblage in these units suggests that winnowing occurred despite their relatively innocuous appearance in the field these surfaces are likely to be significant bypass surfaces over which sediment was delivered to the deeper parts of the basin during times of relative lowstand of sea level

recommendations for a uniform chronostratigraphic designation system for phanerozoic depositional sequences many published sequence stratigraphic frameworks lack a systematic and consistent designation for both depositional sequences and key surfaces despite the original goal to provide a fully integrated stratigraphic architecture including diagnostic age information based on a system in use for more than 10 yr at exxonmobil we recommend methodologies for a chronostratigraphic designation system cds using more uniform and robust sequence stratigraphic designations after objectively defining important physical stratigraphic surfaces biostratigraphic and other age constraining information is used to designate surfaces and the packages of rocks they bound this leads to the establishment of a sequence chronostratigraphic framework for a local area of investigation outcrop section field region or basin only after demonstrating clear well documented ties to phanerozoic global coastal onlaps or cycle charts are these sequences and associated surfaces considered as global entities and designated as such higher frequency sequences and surfaces are also accommodated in this cds alternative designations for areas with limited or poor quality chronostratigraphic information are also discussed the cds has proven to have great use in all phanerozoic strata different tectonic settings and depositional environments especially when chronostratigraphic age constraints are robust we have used this system at regional and basinal scales in many geographic locations to help reduce uncertainty in identifying and correlating reservoirs sources and seal rocks predicting the local distribution and quality of reservoirs as well as seals within a producing field and near field wildcats is also facilitated by this system this system has demonstrated use in the correlation of outcrop sections within a basin or between basins rigorous use of the cds proposed here will permit meaningful regional and or interbasinal correlation that is difficult to carry out with the diverse systems currently in use this uniform designation scheme will also facilitate communication within a company and between institutions as well as among academic investigators

no change in fluvial style across a sequence boundary cretaceous blackhawk and castlegate formations of central utah u s a nonmarine sequence stratigraphic models are based largely on studies of fluvial units in the cretaceous western interior of north america including the blackhawk and castlegate formations of central utah these models suggest that fluvial units should show a transition from mudstone prone isolated meander belt deposits of the transgressive and highstand systems tract into amalgamated braided stream sandstones of the lowstand systems tract these mudstone rich fluvial strata are largely assumed rather than documented to represent the deposits of isolated meander belt deposits despite recent work that suggests that there is no simple relationship between the proportion of preserved floodplain mud and fluvial style there are numerous studies documenting the braided character of the sandstone rich castlegate formation but there are no corresponding studies that document the internal fluvial facies architecture within the blackhawk formation to support the interpretation that the blackhawk comprises the deposits of a meandering stream system we test the validity of the sequence stratigraphic model by comparing dimensions and styles of associated bar and channel deposits as well as cross stratal thicknesses between the blackhawk and castlegate formations along salina canyon in utah data compiled from 24 measured sections and 6 photomosaics show that the blackhawk formation comprises isolated sandy channel belt sheet sandstones 5 8 m thick contained within thick floodplain mudstones whereas the castlegate formation consists of about 80 m of amalgamated sandy channel belt sheets 4 7 m thick with only minor mudstone the average height of cross sets is 13 cm in the castlegate formation and 14 cm in the blackhawk formation and formative dune height is estimated to be 38 cm for the castlegate formation and 45 cm for the blackhawk formation average bar accretion thicknesses are 2 m in both the blackhawk and castlegate formations corresponding water depths are estimated to be 2 5 4 1 m for the blackhawk and 2 3 3 8 m for the castlegate the correlation of master bedding planes in the blackhawk formation shows overlapping lens shaped bar deposits and channel fills bar tops appear to dip in several directions indicating both lateral and downstream accretion of mid channel braid bars while there is some indication that castlegate rivers were slightly shallower the differences do not suggest a major change in fluvial style across the sequence boundary both are braided the lack of change in scale of channels also is not compatible with a hypothesized increase in aridity between the blackhawk and the castlegate the difference in fluvial architecture between the two formations is interpreted to reflect changes in accommodation that were likely tectonic in origin this supports that idea that preservation of thick successions of fine grained overbank material is not a function of the plan view channel geometry

the aguablanca ni cu pge deposit sw spainossa morena zone lat 37 57 n long 6 11 w

environmental signal propagation in sedimentary systems across timescales abstract earth surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales the geomorphic and stratigraphic products of this source to sink sediment transfer record signals of external environmental forcings as well as internal or autogenic dynamics of the sedimentary system here we evaluate environmental signal propagation across sediment routing systems with emphasis on sediment supply qs as the carrier of up system forcings we review experimental numerical and natural examples of source to sink sediment routing and signal propagation during three timescales 1 historic which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries 2 centuries to several millions of years referred to as intermediate timescale and 3 deep time we discuss issues related to autogenic dynamics of sediment transport transient storage and release that can introduce noise lags and or completely mask signals of external environmental forcings we provide a set of conceptual and practical tools for evaluating sediment supply within a source to sink context which can inform interpretations of signals from the sedimentary record these tools include stratigraphic and sediment routing system characterization sediment budgets geochronology detrital mineral analysis e g thermochronology comparative analog approaches and modeling techniques to measure calculate or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment routing systems

autogenic erosional surfaces in fluvio deltaic stratigraphy from floods avulsions and backwater hydrodynamics erosional surfaces set the architecture of fluvio deltaic stratigraphy and they have classically been interpreted in terms of changes in boundary conditions such as climate tectonics and base level allogenic forces intrinsic dynamics of sedimentary systems autogenic dynamics can also create a rich stratigraphic architecture and a major knowledge gap exists in parsing the relative roles of autogenic versus allogenic processes emerging theoretical and experimental work suggests that backwater hydrodynamics play an important role in driving transient channel incision in river deltas even those experiencing net aggradation here we identify and quantify two autogenic mechanisms that produce broad erosional surfaces in fluvio deltaic stratigraphy namely floods and avulsions using a simple mass balance model for single threaded delta channel systems we show that flood induced scours begin near the shoreline and avulsion induced scours begin at the avulsion site and both propagate upstream over a distance that scales with the backwater length bed slope and bed grain size we also develop scaling relationships for the maximum scour depths arising from these mechanisms which are functions of characteristic flow depth and formative flood variability we test our theoretical predictions using a flume experiment of river delta evolution governed by persistent backwater hydrodynamics under constant relative sea level results indicate that autogenic dynamics of backwater mediated deltas under conditions of constant base level can result in stratigraphic surfaces and shoreline trajectories similar to those often interpreted to represent multiple sea level cycles our work provides a quantitative framework to decouple autogenic and allogenic controls on erosional surfaces preserved in fluvio deltaic stratigraphy

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

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

tectonic control on coarse grained foreland basin sequences an example from the cordilleran foreland basin utah newly released reflection seismic and borehole data combined with sedimentological provenance and biostratigraphic data from upper cretaceous paleocene strata in the proximal part of the cordilleran foreland basin system in utah establish the nature of tectonic controls on stratigraphic sequences in the proximal to distal foreland basin during campanian time coarse grained sand and gravel were derived from the internally shortening charleston nebo salient of the sevier thrust belt a rapid regional campanian progradational event in the distal foreland basin 200 km from the thrust belt in 8 m y can be tied directly to active thrust generated growth structures and an influx of quartzose detritus derived from the charleston nebo salient eustatic sea level variation exerted a minimal role in sequence progradation

re evaluating the sedimentology and sequence stratigraphy of classic book cliffs outcrops at tusher and thompson canyons eastern utah usa applications to correlation modelling and prediction in similar nearshore terrestrial to shallow marine subsurface settings worldwide abstract the campanian book cliffs strata of eastern utah and western colorado has been used to develop test and refine sedimentological and stratigraphic ideas and models over the years including the principles and concepts of sequence stratigraphy book cliffs data sets are often used as outcrop analogues for similar subsurface settings worldwide thousands of geologists have visited the book cliffs including the archetypal desert member to lower castlegate sandstone outcrops at tusher and thompson canyons which are the focus of this study these localities regularly serve as representative field stops for teaching sequence stratigraphy recent work has begun to cast doubt on certain aspects of the conventional sequence stratigraphic interpretation of the desert castlegate interval hence re evaluation of these classic outcrops is warranted a progradational stack of shallow marine to nearshore terrestrial facies are observed at tusher canyon from bottom to top these include shelf mudstones lower shoreface to inner shelf heterolithics foreshore to upper shoreface sandstones cut by distributary and tidal estuarine channels coal bearing coastal plain mudstones with single storey fluvial sandstones amalgamated multi storey fluvial channel fills and a capping coastal plain mudstone package overlain by the marine mudstones of the buck tongue of the mancos shale a similar progradationally stacked facies succession is observed 30 km basinwards at thompson canyon with the exception of the proximal amalgamated fluvial sandstone package which is absent five of eleven desert member parasequences d1 to d5 are noted at tusher canyon while all eleven desert parasequences d1 to d11 and two of six castlegate parasequences c1 and c2 are identified at thompson canyon although parasequences and their flooding surfaces can be correlated between tusher and thompson canyons the discrete shoreface incised channels are only restricted to the proximal portions of each parasequence these channels mostly cut foreshore shoreface sandstones and are not continuously correlatable between tusher and thompson canyons re examination of these desert castlegate outcrops exemplifies the misfit with the conventional sequence stratigraphic model specifically the miscorrelation of the d5 and d11 shoreface incised channels over 60 m of deposits separate the d5 and d11 horizons along 30 km of dip oriented outcrop between tusher and thompson canyons contrary to earlier interpretations the shoreface incised channels in the desert castlegate are not nested within larger incised valley fills an alternative model showing temporal and spatial linkage between the nearshore terrestrial and laterally adjoining shallow marine facies is the best fit with the desert castlegate field observations selecting the appropriate correlation style has significant implications for the prediction of sand body continuity connectivity and distribution especially applications to subsurface data sets where visualization is limited and correlation uncertainties are high

sequential architecture in a fluvial succession sequence stratigraphy in the upper cretaceous mesaverde group prince canyon utah abstract five unconformity bounded sequences have been documented within a 1300 m thick succession of predominantly fluvial upper cretaceous and lower tertiary deposits in the price canyon area of the westernmost part of the book cliffs east central utah u s a this area experienced major tectonically induced changes in the paleogeography during deposition the earliest fluvial deposits in the study area were formed in a relatively simple foreland basin setting in front of the sevier orogenic belt and contain more marine influence than previously recorded following a gradual termination of thrusting sedimentation became increasingly controlled by uplift of the san rafael swell to the southeast our studies suggest that the fluvial systems in the upper part of the succession alternated bet een being confined within a valley open towards the north and being more directly eastward flowing on the basis of the observed sequences an idealized model of alluvial sequences whose internal architecture can be related to a fall rise fall cycle of the stratigraphic base level has been established upward or downward changes in the position of this base level dictate the creation and destruction of accommodation on the alluvial plain and therefore exert a direct control on the sequential architecture and sandstone body geometry of fluvial successions in our model the basal sequence boundary is overlain by an amalgamated fluvial sandstone sheet the sheet is succeeded by a fining upward more mudstone rich level with more isolated sandstone bodies and this level may culminate in a marine or lacustrine transgression the upper part of the sequence may show a coarsening upward trend heralding the next phase of base level fall and sequence boundary generation use of the suggested model has the potential to refine existing lithostratigraphic schemes and given the higher resolution and more detailed correlation may significantly improve paleogeographic reconstructions and aid in prediction of potentially hydrocarbon bearing reservoirs a revised and refined lithostratigraphy has been established on the basis of alluvial sequence analysis the lower half of the succession forms the youngest part of a major eastward prograding clastic tongue the mesaverde group and is campanian we divide this part into the blackhawk castlegate and price river formations the rest of the succession is maastrichtian to paleocene and is referred to the north horn formation this formation was deposited in an intermontane setting

the castlegate sandstone of the book cliffs utah sequence stratigraphy paleogeography and tectonic controls abstract earlier stratigraphic work had predicted that at the type section of the castlegate formation the castle gate near price utah the unit consists of two sequences separated by a sequence boundary representing approximately one million years of unrecorded time although the type section is well exposed it consists of a monotonous succession of braided fluvial sandstones and no obvious boundary can be identified using facies criteria this is a good example of a cryptic sequence boundary petrographic data indicate however a significant change in detrital composition 20 m above the base of the section at a through going erosion surface that is therefore interpreted as the sequence boundary revised sequence correlations together with other petrographic data and regional paleocurrent patterns provide the basis for a model of the paleogeographic evolution of the area rocks assigned to the castlegate sandstone comprise two or possibly three sequences formed at times of slow regional subsidence erosional sequence boundaries and tilts in paleoslope between each sequence record thrust loading and unloading of the basin and the growing influence of intrabasinal upwarps movement of which was beginning to be affected by laramide movements toward the end of castlegate sedimentation

sedimentology of the rough rock a carboniferous braided river sheet sandstone in northern england the rough rock is a coarse grained fluvial sheet sandstone which outcrops across northern and central england it is interpreted as a braided river sandstone on the basis of sedimentary structures internal erosion and growth surfaces this study reveals that the rough rock represents more than a single phase of deposition and that internal erosion surfaces may indicate anabranch avulsions or more significant river avulsions detailed outcrop profiles are presented to try and distinguish the styles of deposition and the nature of internal bounding surfaces and channel geometry the rough rock formation contains a very large number of first and third order bedding contacts which represent the migration of dunes and channels respectively there are relatively few macroforms and bars preserved the lack of second order surfaces within many outcrops could indicate that bars in the rough rock rivers were very large and therefore cannot be resolved at the outcrop scale similarly the rivers which deposited the rough rock may have had such high width depth ratios that the dip of second order bounding surfaces are too low to be identified the large number of third order bounding surfaces indicates channel stacking which may have occurred in two ways 1 relocation of rivers in the same area over time or 2 anabranch avulsion within a braided river within a hierarchy of channels the problems associated with differentiating between these two mechanisms are discussed 1993 the geological society

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

channel planform as a non controlling factor in fluvial sedimentology the case of the squamish river floodplain british columbia abstract channel planform styles demonstrate a continuum of variability whereas end member situations may exhibit diagnostic sedimentologic characteristics non end member situations may be exceedingly difficult to reliably differentiate the relevance of channel planform based sedimentologic differentiation of fluvial depositional units has been questioned for some time e g jackson 1978 bridge 1985 brierley 1989a despite reservations outlined in these papers facies models and interpretations of depositional suites in the rock record continue to be applied in terms of channel planform style this paper describes a test of this principle in one particular depositional setting the squamish river in southwestern british columbia is a high energy gravel based river in a fjord setting in a 20 km reach this river displays a distinct downstream gradation in channel planform type from braided through wandering gravel bed to meandering assemblages of bedform scale facies units on bar surfaces in this river do not differ by planform type brierley 1989a rather facies associations relate directly to the pattern of morphostratigraphic units on bar surfaces brierley 1991a when analysed in floodplain exposures sediment sequences which are equivalent to morphostratigraphic units are termed elements these elements are defined in terms of their geometry bounding surface and sediment characteristics detailed analysis of floodplain deposits in the braided wandering gravel bed and meandering reaches of the squamish river demonstrates that just as assemblages of bedform scale facies cannot be differentiated by planform style neither can assemblages of floodplain elements indeed for the squamish river the type character and spatial association of these elements cannot be differentiated reliably at the channel planform scale this indicates the limited relevance of planform differentiation of sedimentary environments under transitional planform situations such as those of high energy gravel bed rivers in confined valleys in such situations sediment inventory at the element scale provides greater insight into mechanisms of floodplain evolution than can be provided by interpretation at either the channel bedform or channel planform scales

quantitative analysis of the dimensions and distribution of channelized fluvial sandbodies within a large outcrop dataset upper cretaceous blackhawk formation wasatch plateau central utah u s a abstract conceptual and quantitative models of fluvial stratigraphy typically argue that alluvial architecture is driven by a combination of allogenic processes e g tectonic subsidence sea level sediment supply and autogenic behaviors e g avulsion we test these models via analysis of a large c 200 m thick by 100 km depositional strike extent alluvial to coastal plain succession that records shoreline progradation in response to decreasing tectonic subsidence late cretaceous blackhawk formation wasatch plateau central utah u s a oblique aerial photographs and architectural panels of six nearly linear nearly vertical cliff face windows were used to characterize the dimensions apparent widths thicknesses and spatial distributions of channelized fluvial sandbodies two statistical measures raster based lacunarity and point based l function are used to investigate whether the distribution of channelized sandbodies show significant regularity randomness or clustering over 490 channelized fluvial sandbodies are identified in the six cliff face windows from base to top of the blackhawk formation sandbodies broadly increase in width and decrease in overall abundance per unit area clustering of sandbodies occurs relatively frequently in lower coastal plain strata 50 km from the coeval shoreline a strong negative correlation between lacunarity and stratigraphic position is also observed such that a wider range and greater variety of spatial gaps occurs between sandbodies in lower coastal plain strata relative to upper coastal plain and alluvial strata comparison with numerical modeling studies of fluvial stratigraphic architecture implies the predominance of an avulsion generated pattern of sandbody distribution that includes an element of compensational stacking on the upper coastal plain and alluvial plain for a range of distances from the coeval shoreline c 40 130 km and tectonic subsidence rates c 40 700 m myr on the lower coastal plain 50 km from the coeval shoreline localized clustering of channelized sandbodies is interpreted to have formed by avulsion of deltaic distributary channels downstream of delta apex avulsion nodes possibly modulated by low amplitude 30 m sea level fluctuations

braided rivers perspectives and problems progress towards a fuller understanding of the dynamics and deposits of braided rivers demands an interdisciplinary approach to a host of unresolved problems although many advances have been made within recent years in interpreting the mechanics of flow transport of sediment and sedimentary architecture of braided rivers many key issues remain to be addressed in particular several areas demand attention the mechanisms of braid bar initiation confluence diffluence dynamics the nature of sedimentary facies over a range of grain sizes and the influence of flow stage and aggradational regime upon the depositional architecture over a range of channel scales this paper focuses upon these issues and highlights several areas of fruitful future interdisciplinary collaboration 1993 the geological society

sedimentary structures exposed in bar tops in the brahmaputra river bangladesh the brahmaputra river is one of the world s largest sand bed braided rivers with a channel belt up to 15 km wide a mean channel depth of 5 m and maximum scour depths of up to 40 m the recorded discharge varies by around 60 000 cumecs every year following the annual monsoon producing dramatic stage fluctuations with the water level falling between 7 and 8 m from bankfull to low flow stage in the dry season large areas of bar top and channel bed are exposed and low flow channels cut natural sections through bar tops exposing the internal stratification elements of upstream downstream and lateral accretion are identified although the high width depth ratio of channels up to 500 1 results in extremely low depositional dips on bed bounding surfaces within the accretionary elements vertical and lateral changes in sedimentary structures are ubiquitous and varied but some patterns can be discerned channel deposits are dominated by sinuous crested dunes and trough cross stratification upper stage plane bed lamination often with a very low angle depositional dip has been observed in beds up to 4 m thick and is generally found at the base of the exposed bar top sections trough cross stratification in bar tops occurs in sets from 0 1 m to 3 m thick with rapid vertical and lateral changes in set thickness very large sets of trough cross stratification 3 m thick do not occur in the bar top sections current ripple lamination is most abundant on the tops of bars with very high rates of climb associated with high rates of sediment deposition from these observations a generalised vertical sequence of bar top origin might include trough cross stratification overlain by upper stage plane bed lamination isolated sets of trough cross stratification truncated and capped by current ripple lamination this sequence which is considered to represent the deposits of a single flood may occur within the upstream downstream or lateral accretion elements however it should be noted that vertical and lateral changes in facies are extremely abundant with many changes in sedimentary structures and reactivation surfaces within each depositional episode

reevaluating dune scaling relations abstract in sand bedded rivers dunes dominate sediment transport and flow resistance dunes are also commonly preserved in fluvial deposits as cross stratified units that record their size shape and migration rates prediction of dune dimensions is therefore important for forecasting modern river channel dynamics as well as reconstructing past fluvial environments on earth and other planets predictions are often made by assuming that the formative flow depth h sets dune dimensions with height scaling as 1 6h and length as 5h yet there is a suite of other scaling relations that link dune dimensions to other variables like grain size transport stage and froude number here we present a new compilation of flow and dune dimension data to evaluate scaling relations the data reveal approximately two orders of magnitude variation in dune height and length at any given flow depth dune heights in shallow flows 2 5 m are often more symmetric have lower lee angles are relatively shorter in height than 1 6h and have a wider range of observed heights for a given depth none of the scaling relations predict the observations exceptionally well likely because of natural variability in dune dimensions and because they do not explicitly account for the apparent scaling break that occurs at 2 5 m we propose new simple depth scaling relations with added statistical uncertainty for the prediction of dune height and length from flow depth as well as flow depth from dune height we conclude that shallow and deep flow dunes exhibit different scaling due to a change in the dominant process controls as dunes get larger

quantitative characterization of architecture elements and their response to base level change in a sandy braided fluvial system at a mountain front abstract the rockcave member of the yungang formation middle jurassic in the datong basin china is a multistory sandstone that is interpreted as a sandy braided fluvial deposit based on grain size lithofacies and architectural elements the depositional setting was the mountain front of the datong basin which was tens of kilometers from the shoreline of a lacustrine basin during the middle jurassic the concept of base level is used to analyze the architectural elements of the braided system obtained from photographic mosaics and high resolution measurement of six outcrop sections from yungang rock cave grain size lithology and bounding surfaces together with scale and dimension parameters of the sedimentary structures in various architectural elements were used to quantitatively characterize each group of architectural elements and stratigraphic units width thickness values of trough crossbeds were found to be a fundamental component of the hydrodynamic regimes during base level rise the braided fluvial system developed large scale channel units bar units and overbank fills the relatively high proportion of bar units and overbank fills reflect processes operating during positive accommodation however during base level fall there are a high proportion of small scale channel units that reflect incision dominated processes such as channels with low w t values for trough crossbeds and less common overbank fines

the seismic interactions and spatiotemporal evolution of seismicity following the october 23 2011 m w 7 1 van eastern anatolia earthquake abstract we studied the mechanisms and spatiotemporal distribution of aftershocks of the mw 7 1 van earthquake in eastern turkey the van earthquake occurred on an e w trending thrust fault in a region under n s compression due to the convergence of the arabian plate toward eurasia we relocated the seismicity by combining catalogs from two agencies and studied the source mechanisms of the mw 3 5 5 6 aftershocks using regional body and surface waves in addition to the aftershocks with thrust mechanism on the mainshock fault we identified three clusters with strike slip activity two of the clusters are on the left lateral faults perpendicular to the mainshock fault and are located at the lateral termination of the co seismic rupture in each direction both western and eastern strike slip clusters were triggered within the first few hours following the mainshock they were initiated very close to the mainshock rupture plane and propagated away toward the south and north respectively these two dominantly strike slip zones are connected to the mainshock fault at a depth of 15 km and possibly determined the lateral extent of the 2011 rupture this system of two bounding left lateral faults with a thrust fault in between is overall consistent with the n s convergent tectonic regime in the region the complex geometry explains unexpected post seismic motion at a gps site and can be used to improve the post seismic slip estimate of the earthquake the third strike slip cluster with 17 days delay occurred on an e w trending right lateral fault and 40 km on the south of the mainshock the three activated faults have experienced coulomb stress increase due to co seismic rupture in addition most of the seismicity has occurred in regions that experienced coulomb stress increase

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

sequence stratigraphy and marine to nonmarine facies architecture of foreland basin strata book cliffs utah u s a the desert member of the blackhawk formation and the castlegate sandstone in the book cliffs of utah and colorado were analyzed to develop a model of sequence stratigraphy and facies architecture in foreland basins stratal architecture of these rocks is controlled by two regionally extensive surfaces of incision and subaerial exposure interpreted as major sequence boundaries and at least six surfaces of incision and subaerial exposure with more limited lateral extent interpreted as minor sequence boundaries each sequence boundary is a regionally correlatable single surface major sequence boundaries can be traced from marine into proximal alluvial plain environments sequence boundaries have different physical expressions depending upon where in the basin they are observed strata beneath sequence boundaries are unrelated to strata above and time lines cannot be carried across these boundaries flooding surfaces called parasequence or parasequence set boundaries also exert an important control on facies architecture based on parasequence stacking patterns position of sequence boundaries and facies associations the desert member and castlegate sandstone have been divided into sequences with durations of 200 000 to 300 000 yr there are an order of magnitude more sequences in this interval than are predicted by the global sea level chart of haq et al 1988 the major sequences have been divided into the following systems tracts or sequence sets 1 grassy highstand sequence set below the desert sequence boundary named for the grassy member of the blackhawk formation 2 desert lowstand transgressive and highstand systems tracts between the desert and castlegate sequence boundaries 3 castlegate lowstand sequence set resting on the castlegate sequence boundary and 4 castlegate transgressive systems tract parasequence stacking patterns suggest that the grassy highstand sequence set and the desert highstand systems tract were deposited during a relative rise in baselevel the grassy highstand sequence set is punctuated by minor relative falls in baselevel both of these stratal units contain thick

high resolution correlation of the upper cretaceous stratigraphy between the book cliffs and the western henry mountains syncline utah u s a abstract exposures of upper cretaceous strata in the book cliffs have played a key role in the formulation of modern sequence stratigraphic concepts and yet correlations with time equivalent strata in nearby regions remain uncertain resulting in an incomplete understanding of regional paleogeography this study presents detailed high resolution correlations of the upper cretaceous stratigraphy between the book cliffs the wasatch plateau and the western henry mountains syncline in utah with emphasis on the campanian interval two newly acquired measured vertical sections at coal canyon near green river in the book cliffs and blind trail in the henry mountains inform the correlations which also incorporate the substantial body of previous research correlations are further constrained by vertical and lateral facies stacking patterns and changes in sediment dispersal directions at discrete stratigraphic horizons derived from paleocurrent measurements much of the campanian succession can be characterized as a single low frequency third order depositional sequence within which are nested numerous high frequency sequences while it is not possible to correlate every high frequency sequence recognized in individual outcrop areas we define four intervals numbered 1 4 in ascending stratigraphic order that we correlate across the entire region interval 1 basal campanian is represented by initially deltaic and later wave dominated shoreface strata of the star point sandstone and equivalent basal muley canyon sandstone interval 2 lower campanian comprises coastal plain facies passing eastward into shallow marine strata of the lower blackhawk formation and equivalent muley canyon sandstone interval 3 lower to mid middle campanian comprises a thick aggradational stack of coastal plain fluvial strata that pass eastward into coastal and shallow marine facies blackhawk formation and equivalent masuk formation interval 4 overlying a major facies dislocation third order sequence boundary comprises amalgamated sheet fluvial deposits of the lower castlegate sandstone and equivalent tarantula mesa sandstone during the early to middle campanian the northern wasatch plateau and western henry mountains regions were along depositional strike with respect to one another the book cliffs near green river were located obliquely down depositional dip from the western henry mountains region during the campanian these new correlations and the improved understanding of paleogeography that derive from them have the potential to inform basin scale stratigraphic interpretations to a greater extent than has been hitherto possible

fourth order nonmarine to marine sequences middle castlegate formation book cliffs utah the lower part of the campanian castlegate formation one of the best known fluvial sheet sands of the western interior seaway combines with an overlying finer grained unit middle member of the castlegate formation to form an unconformity bounded third order stratigraphic sequence 3 m y duration this sequence contains a mappable muddy zone along the western book cliffs of utah now mapped as contiguous with the open marine parts of the succession buck tongue sego sandstone anchor mine tongue to the east the correlation within the middle castlegate has been refined and the nature of the link between tidally influenced fluvial strata in the west and marine strata in the east has been remapped five high frequency stratigraphic sequences all within the upper part of the larger third order sequence forming a thickness to 160 m have been mapped in the price area southeastward into the time equivalent marine succession near green river individual sequences probably 0 5 m y duration reflecting transgressive to regressive estuary infilling have an internal architecture in which fluvial and tidally influenced distributary channel belts pass up into muddy central basin sedimentary units to bayhead delta deposits and in some places up to more fluvial channel belts the key to the mapping of individual sequences is recognition of the muddy brackish water interval developed during maximum transgression of the time equivalent shoreline the two most proximal marine influenced sequences 2 and 3 are probably broadly time equivalent with the buck and anchor mine tongues to the east the analysis here contrary to recent suggestions shows that the marine sequences in the eastern book cliffs can be traced far into the time equivalent western fluvio estuarine succession

complex fluvial response to low gradients at maximum regression a genetic link between smooth sequence boundary morphology and architecture of overlying sheet sandstone abstract the mesa rica sandstone is an extensive fluvial sandstone sheet that is separated from underlying marine strata throughout northeastern new mexico by a regionally smooth and laterally continuous sequence bounding unconformity the mesa rica sandstone consists mostly of channel fill elements with lesser proportions of lateral accretion elements and almost everywhere is of the same thickness as the largest channel fills this broad sandstone sheet reflects deposition on a coastal plain by frequent avulsion and minor lateral migration of straight and low sinuosity streams under nearly stable base level conditions which are here attributed to rapid progradation of the adjacent mesa rica deltaic shoreline relative to change in relative sea level during maximum kiowa skull creek regressi n rapid deltaic shoreline progradation under such conditions caused seaward extension and gradient reduction in the adjacent mesa rica coastal plain overextension and resultant loss of power in mesa rica rivers crossing this coastal plain forced both stream straightening and storage of nontransportable coarser sediment in coastal plain channels because base level was stable mesa rica channels could aggrade only minimally and were forced to spread excess sediments mostly laterally by avulsion frequent avulsion and minor lateral migration of mesa rica channels under these conditions caused both regional scouring of a smooth sequence bounding unconformity and deposition of a sheet sandstone with minimal channel stacking the mesa rica sandstone and the sequence boundary that underlies it represent a distinctive genetic association of single story fluvial sheet sandstone and smooth sequence boundary morphology that is probably not unique to the lower cretaceous of northeastern new mexico such unincised sequence boundaries are also implied in conceptual models and flume experiments of previous authors