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

patterns of early post depositional and burial cementation in distal shallow marine sandstones upper cretaceous kenilworth member book cliffs utah usa there is a limited understanding of the spatial linkage between cementation processes in shoreface coastal plain successions and those operating in distal offshore successions to address this an integrated sedimentological sequence stratigraphic and diagenetic study was undertaken on a distal shallow marine succession the upper cretaceous kenilworth member book cliffs utah usa laterally extensive carbonate cement is the most volumetrically significant diagenetic feature it constitutes up to 55 vol of the distal lower shoreface sandstone and sandy siltstone units beneath major flooding surfaces during rising relative sea level major flooding events resulted in low sedimentation which extended residence time of sediments in early diagenetic zones and promoted enhanced cementation beneath these boundaries carbonate for early calcite cements was probably derived from sulphate reduction marine water and oxidation of organic matter stable isotopic composition of later ankerite 18o 11 9 to 6 0 vdpb 13c 4 5 to 0 3 vdpb suggests precipitation during progressive burial c 1 7 to 3 4 km 72 to 122 c from evolved marine fluids the carbonate and other mineralizing solutes were derived increasingly with burial from decarboxylation of organic matter and clay mineral transformations in adjacent siltstones and shales these interbedded overlying and underlying facies provided an important source of mineralizing solutes that influenced the extent of pervasive cementation during burial the combination of stratigraphic and lithofacies control resulted in laterally extensive cements that differ to shoreface successions although are similar in form to those described for many offshore mudstone dominated successions limited early concretionary ferroan dolomite beneath the expression of the sequence boundary and some flooding surfaces however suggests cementation by meteoric fluids at times of relative sea level lowstand similar processes have been demonstrated in more proximal successions in the book cliffs

shelf construction in a foreland basin storm beds shelf sandbodies and shelf slope depositional sequences in the upper cretaceous mesaverde group book cliffs utah the upper cretaceous campanian kenilworth member of the blackhawk formation mesaverde group is part of a series of strand plain sandstones that intertongue with and overstep the shelfal shales of the western interior basin of north america analysis of this section at a combination of small sedimentological and large stratigraphical scales reveals the dynamics of progradation of a shelf slope sequence into a subsiding foreland basin four major lithofacies are present in the upper mancos and kenilworth beds of the book cliffs a lag sandstone and channel fill shale lithofacies constitutes the thin basal transgressive sequence which rests on a marine erosion surface it was deposited in an outer shelf environment shale interbedded sandstone and shale and amalgamated sandstone lithofacies were deposited over the transgressive lag sandstone lithofacies as a wave dominated delta and its flanking strand plains prograded seaward analysis of grain size and primary structures in kenilworth beds indicates that there are four basic strata types which combine to build the observed lithofacies the fine to very fine grained graded strata of the interbedded facies are tempestites deposited out of suspension by alongshelf storm flows geostrophic flows there is no need to call on cross shelf turbidity currents density underflows to explain their presence very fine to fine grained hummocky strata are likewise suspension deposits created by waning storm flows but were deposited under conditions of more intense wave agitation on the middle shoreface cross strata sets in this region are bed load deposits that accumulated on the upper shore face in the surf zone lag strata are multi event bed load deposits that are the product of prolonged storm winnowing they occur on transgressive surfaces while the graded beds are tempestites in the strict sense all four classes of strata are storm deposits the distribution of strata types and their palaeocurrent orientations suggests a model of the kenilworth transport system driven by downwelling coastal storm flows and probably by a northeasterly alongshore pressure gradient the stratification patterns shift systematically from upper shoreface to lower shoreface and inner shelf lithofacies partly because of a reduction in fluid power expenditure with increasing water depth but also because of progressive sorting which resulted in a decrease in grain size in the sediment load delivered to successive downstream environments the kenilworth member and an isolated outlier the hatch mesa lentil constitute a delta prodelta shelf depositional system their rhythmically bedded lenticular sandstone and shale successions are a prodelta shelf facies and may be prodelta plume deposits major upper cretaceous sandstone tongues in the book cliffs are underlain by erosional surfaces like that beneath the blackhawk formation which extend for many tens of kilometres into the mancos shale these surfaces are the boundaries of upper cretaceous depositional sequences the sequences are large scale genetic stratigraphic units they result from the arranging of facies into depositional systems the depositional systems are in turn stacked in repeating arrays which constitute the depositional sequences the anatomy of these foreland basin sequences differs

shallow marine sedimentary processes in the late devonian catskill sea new york state shallow marine strata of the upper devonian west falls group in south central new york comprise centimetre to decimetre thick sheetlike to lenticular beds of sandstone and siltstone interbedded with mudstone unidirectional current scour marks and tool marks occur on the basal erosion surfaces of the sandstones their internal structures are hummocky cross strata of various styles planar laminae and wave ripple cross laminae with characteristic vertical and lateral transitions among them vertical burrows of the skolithos ichnofacies dominate upper portions of sandstone beds whereas mudstones and silt stones contain mainly horizontal burrows of the cruziana ichnofacies transported and in situ shelly fossils occur throughout in places concentrated in coquinite lenses large scale 15 to 30 in bedding sequences are characterized by upward thickening and coarsening of sandstone beds increase in amalgamated hummocky cross strata coquinites plant debris and bivalves followed by abrupt fining and thinning of beds the depositional environment is interpreted as a shallow marine shelf episodically influenced by intense tropical storms hurricanes individual sandstone beds were deposited by spatially decelerating combined flows where an initially strong offshore directed flow component decreased in time relative to the oscillatory flow component large scale bedding sequences reflect changes in storm combined current intensity and deposition rate strong eustatic control is unlikely and there is no evidence of changing wave climate instead these sequences may be associated with delta lobe progradation and or offshore bar development

eustatic and hydrodynamic controls on the architecture of a deep shelf sand bank celtic sea the architecture of a tidal sand bank in the south eastern celtic sea was examined using very high resolution seismic surveys the bank comprises four depositional units the lowest unit 1 is characterized by gently dipping 1 8 strata that strike parallel to the length of the bank unit 1 is erosionally overlain by unit 2 which forms the bulk of the bank this unit consists of stacked sets of downcurrent dipping 7 12 master bedding formed by climbing sinuouscrested tidal dunes that are up to 20 m high these deposits are locally incised by an anastomosed channel network unit 3 that may represent a buried swatchway system the upper part of the bank comprises wave related deposits that are mainly preserved on the bank flanks unit 4 the outer bank surface is erosional the bank is believed to have formed during the last postglacial sea level rise the facies evolution from unit 1 to unit 3 indicates an upward increase in tidal energy mainly characterized by the thickening of dune cross bed sets in unit 2 the majority of bank growth is inferred to have occurred in water depths of the order of 60 m this evolution was controlled by relative sea level rise which is likely to have caused an episode of tidal resonance with associated strong tidal currents that were responsible for the incision of the deep cross cutting channels of unit 3 the transition to wavedominated sedimentation in unit 4 is related to the decay of resonance with continued sea level rise

ichnofabrics and geometric configurations of ophiomorpha within a sequence stratigraphic framework an example from the upper cretaceous us western interior ichnofabric in the upper cretaceous sego sandstone and anchor mine tongue of east central utah can be differentiated into two components 1 discrete ophiomorpha and 2 mottling and other trace fossils the ichnofabric index method was employed to evaluate spatial variability of the ichnofabrics within depositional sequences and component systems tracts indices were logged for amount of bioturbation caused solely by ophiomorpha oii and that represented by all other biogenic features bii values of oii 1 are more pervasive in lowstand systems tracts compared to transgressive systems tracts this is consistent with the predominance of marginal and nearshore marine sand dominated settings that are characteristic of lowstands which are favourable habitats for colonization by ophiomorpha producers ichnofabric index values vary both vertically and laterally within any given systems tract reflecting differences in physical and biological parameters operating in the palaeoenvironment these parameters include the total number and behaviours of organisms occupying the substrate as well as substrate texture and grain size and rates of sedimentation the architectural style of ophiomorpha was examined within five depositional facies shelf storm deposit lower shoreface shoreface and estuarine inclinations of individual burrow elements were approximated relative to bedding planes categorized as either vertical inclined or horizontal and then plotted on ternary diagrams based on the types of facies present these results suggest that variations in the geometric configurations of ophiomorpha are controlled primarily by physical energy levels and the rate and nature of sedimentation results of this study have broad implications for understanding the physical factors affecting facies variability within sequences and systems tracts when coupled with sedimentologic data recognition of variations in the distribution of ichnofabrics and architectural style of ophiomorpha can provide additional information useful for characterizing depositional environments and therefore could be integrated with other basin analysis techniques to test and refine sequence stratigraphic interpretations

depositional facies of high energy beach to offshore sequence comparison with low energy sequence a study of the nearshore zone and continental shelf of a high energy coast was made in the ventura port hueneme area of california during the summer of 1974 to investigate depositional facies characteristics and compare them with similar facies from a low energy coastal setting analysis of box cores can cores and vibracores permits recognition of three principal zones 1 nearshore facies backshore to 9 m water depth made up primarily of parallel ripple and cross bedded clean sand bioturbation is only locally significant 2 transition facies 9 to 18 m water depth a zone of fine sand and silty sand characterized by an increase in biogenic over physical sedimentary structures that are commonly preserved as laminated to burrowed beds wave ripple bedding and parallel lamination are important structures in this facies 3 offshore facies 18 m water depth sandy silt is the primary texture and bioturbation is the dominant sedimentary structure remnant parallel lamination is the only physical sedimentary structure present comparison of the results of this study with a previous description of a low energy beach to offshore sequence at sapelo island georgia indicates that the two areas do not differ greatly in their facies or overall vertical sequence of sedimentary structures the principal difference is in the thickness of the three facies the california facies are significantly thicker than their georgia counterparts this difference is in direct response to the role of higher wave energy on the california coast

sedimentological characterization of the sego sandstone nw colorado usa a new scheme to recognize ancient flood tidal delta deposits and implications for reservoir potential marginal marine deposits are typically excellent hydrocarbon reservoirs around the world certain depositional environments may provide natural selective physical processes that produce better reservoir rocks than others depending on associated energy hydraulic regime etc with this paper we present new detailed sedimentological petrographic and grain size data of ancient flood tidal delta deposits that provide means to characterize this environment in the ancient as well as to determine reservoir characteristics in this study we compare grain size grain and cement composition and the ratio of pore space to cement from thin sections between tidal shoreface and flood tidal delta facies of the sego sandstone in northwest colorado the intent of this comparison is to provide an evaluation of different physical processes and the degree of diagenesis related to different environments to better understand the relative controls on reservoir characteristics we find that flood tidal deltas show a statistically larger average grain size than either shoreface or other tidal facies also flood tidal deltas have a smaller ratio of pore space to cement shoreface facies have a larger ratio of pore space to cement overall than that of flood tidal delta or other tidal facies we propose that this may be due to chemistry and higher weathering rates in the backbay environment in contrast to the shoreface environment where higher mechanical reworking may lead to selective removal of chemically unstable minerals to test this hypothesis we conducted statistical analyses of these petrophysical and grain size characteristics our results show that flood tidal deltas are characterized by clean upper fine grained cross bedded sandstone that is well sorted and subrounded to rounded with a majority of landward paleocurrent directions and a presence of tidal bundles mud drapes and reactivation surfaces

spatial and temporal evolution of coastal depositional systems and regional depositional process regimes campanian western interior seaway u s a abstract this paper provides a critical review and regional synthesis of late cretaceous shallow marine deposits along part of the western margin of the western interior seaway of north america which contains the most extensively documented outcrop based studies of siliciclastic coastal depositional systems in the world the results of this synthesis are presented in the form of paleogeographic maps covering present day new mexico utah colorado and wyoming usa for five timeslices in the campanian these maps are used to evaluate the spatial and temporal evolution of regional depositional process regimes along a large 1000 m stretch of coastline the evolution of regional depositional process regimes is linked to tectonic and paleoceanographic controls on the western interior seaway which enables the results of this synthesis to be applied to prediction of depositional process regimes in other less intensively studied basins six gross depositional environments have been mapped for each timeslice 1 alluvial to coastal plain sandstones 2 coastal plain coals mudstones and sandstones 3 shoreline sandstones 4 marine mudstones 5 gravity flow siltstones and sandstones and 6 marine marls and chalk shoreline sandstones in each timeslice are interpreted in further detail using documented evidence for the three principal classes of depositional process wave tidal and fluvial and published reconstructions of coastal morphology which is widely considered to reflect depositional process regime based on these interpretations shoreline sandstones are assigned to five categories of depositional process regime 1 regressive wave dominated shorefaces and delta fronts 2 regressive river dominated delta fronts 3 regressive mixed tide and wave influenced delta fronts 4 regressive tide dominated delta fronts and 5 transgressive barrier islands back barrier lagoons and estuaries the accuracy of and uncertainty in classification of depositional process regime are critically evaluated additionally stratal thickness and sediment routing pathways have been interpreted in order to assess the impact of tectonic and paleoceanographic controls on spatial and temporal changes in all of the evaluated shallow marine successions thin tide influenced intervals were deposited in back barrier and lagoon systems associated with net transgressive shorefaces and estuaries however it is notable that all preserved tide dominated and tide influenced regressive deltaic systems are located along the northern margin of the utah bight a tectonically related embayment that had a pronounced expression during the middle campanian the southern margin of the embayment and coastlines to the north are conspicuously more wave dominated which supports their exposure to a larger wave fetch in contrast the northern margin of the embayment was relatively wave protected it is concluded that tidal range was amplified due to resonance of the principal semidiurnal tide in the strongly embayed geometry of the middle campanian utah bight

facies architecture and sequentiality of nearshore and shelf sandbodies haystack mountains formation wyoming usa the haystack mountains formation campanian mesaverde group us western interior basin wyoming contains a series of shallow marine sandbodies extending tens of kilometres out from a basin margin the study succession around 200 m thick is composed of eight major sandstone tongues bolten ranch o brien spring seminoe 1 2 3 4 hatfield 1 and 2 members each partially encased within marine shale intervals the formation is sequential at several scales at the largest scale the whole succession presents an aggradational to basinward stepping stacking pattern of the sandstone tongues at a lower level each tongue member is characterized internally by two different types of lithosome the first represents shoreface progradation with hummocky cross strata passing up to swaley and trough cross stratified sandstones this lithosome is erosively truncated at its top in most cases and has a general sheet like geometry along strike whereas down dip it displays a series of sharp bounded clinothems the latter sometimes indicate a downward as well as a basinward shift through time as suggested by the occurrence of coarser and or shallower facies at a lower level in the shoreface profile the second type of lithosome is sheet or wedge like and sharply overlies the shoreface deposits the lithosome consists of laterally widespread units of planar tabular to trough cross bedded medium sandstones passing laterally in a dip direction into bioturbated sandstones the lower part of this lithosome is progradational becoming retrogradational into the overlying shales the facies within the cross bedded lithosome suggest a tidally dominated delta front to estuarine depositional setting the two types of lithosome are not related genetically the erosion surface separating the two lithosomes is a sequence boundary separating forced regressive relative sea level fall shoreface deposits from lowstand to transgressive early relative sea level rise cross bedded deposits the uppermost part of the cross stratified lithosome shows a landward stepping of component parasequences and is abruptly blanketed by open marine shales the most widespread cross bedded lithosomes are apparently best developed in the lowermost members of the haystack mountains formation i e in the aggradational part of the large scale progradational succession in the uppermost highly progradational sandstone tongues the shoaling upward shoreface lithosome dominates whereas the cross bedded lithosome occurs in narrow lensoid belts or is absent the middle portion of the succession shows intermediate characteristics the vertical variation in geometry thickness and progradational extent of successive cross bedded lithosomes results from greater confinement of the incised nearshore systems both in space landward direction and in time from the aggradation to the progradation architecture the latter is a consequence of a decreasing rate of accommodation creation through time

architecture of fluvial dominated valley fill deposits in the cretaceous fall river formation the fall river formation is a 45 m thick layer of fluvial dominated valley fills and shore zone strata deposited on the stable cratonic margin of the cretaceous western interior seaway fall river deposits in red canyon in the south west corner of south dakota usa expose a cross section of a 3 5 km wide valley fill sandstone and laterally adjacent marine deposits the marine deposits comprise three 10 m thick upward shoaling sequences each composed of multiple metres thick upward coarsening successions the lower two of these sequences are laterally cut by the valley fill sandstone and are capped by metres thick muddy palaeosols the upper sequence spans the top of the valley fill sandstone and is overlain by the skull creek shale the 30 m thick valley sandstone is partitioned into four distinct fills by major erosion surfaces and each of these fills contain many metres thick channel form bodies deposits in the lower parts of these fills are sheet like top truncated channel bodies whereas deposits in the upper parts of fills are upward concave laterally amalgamated channel bodies more completely preserved heterolithic channel bodies or wave deposited sheets each valley fill basal erosion surface records an episode of valley incision and relative sea level fall and the gradual progression from fluvial to more estuarine deposits upwards within each fill records relative sea level rise all fills are dominantly channel deposits and are capped by marine flooding surfaces the dominance of channel deposits the gradual change to more estuarine facies in the upper parts of fills and the location of flooding surfaces at valley fill tops all suggest that sediment supply initially kept pace with relative sea level rise and valleys filled during late marine lowstand and transgression not during subsequent highstands recently proposed facies models have focused on variations in the relative strength of tide wave and river currents as controls on valley fill deposits however relative rates of sediment supply and basin accommodation change and the shift in this ratio along the depositional profile during multiple scale cycles in relative sea level are equally important controls on the style of valley fill deposits

pleistocene macrotidal tide dominated estuary delta succession along the dong nai river southern vietnam abstract this paper focuses on the facies and sequence stratigraphic interpretation of a tide dominated incised valley system that is rare among geological records of the world for its completeness the subject is the middle upper pleistocene ba mieu and thu duc formations exposed along the dong nai river southern vietnam both the ba mieu and the thu duc formations are interpreted as a transgressive tide dominated estuary succession overlain by a highstand tide dominated delta succession the tide dominated estuary succession is generalized as follows in ascending order fluvial facies in landward portions tidal flat upward coarsening and thickening succession of marine sands with a tidal ravinement surface trs created by tidal scouring during transgression at the base and subtidal lag in seaward portions this tide dominated estuary is distinguished from wave dominated and wave and tide dominated estuaries by 1 the lack of a central basin lagoon tidal delta or bayhead delta facies 2 the widespread presence of marine sands 3 the presence of a subtidal lag and 4 the presence of an upper flow regime sand flat facies the tide dominated delta succession is generalized as follows in ascending order upward convex unit of marine sand and onlapping tidal flat deposits a thick upward fining succession of tidal flat salt marsh deposits and coarse fluvial deposits this delta is distinguished from an estuary as follows 1 it shows thick regional upward fining successions indicating shallowing whereas upward coarsening successions indicating deepening are recognized in an estuary a maximum flooding surface mxfs is recognized in the coarsest part of the succession in marine sand and tidal flat deposits 2 fluvial processes dominate the sediment supply in contrast to an estuary in which a thick marine sand body fed from marine sources is dominant 3 ebb tidal currents are dominant whereas flood tidal currents are dominant in an estuary key features of the incised valley system are 1 amplification of the incised valley geometry by tidal ravinement erosion 2 development of tidal channels filled with mud clasts in the estuary 3 a thick marine sand body in the estuary and 4 upward convex unit of marine sand and a thick tidal flat fluvial succession in the delta the ba mieu formation is recognized as depositional sequence sq 1 between sequence boundary sb 1 below and sb2 above sq1 consists of transgressive systems tract tst 1 and highstand systems tract hst 1 sq1 was formed by a transgression regression cycle during marine isotope stage mis 7 sb2 was formed by fluvial incision during the mis 6 lowstand and is amalgamated with the trs of mis 5 the thu duc formation is recognized as sq2 between sb2 below and sb3 above and it consists of tst2 and hst2 sq2 was formed by a major transgression regression cycle on which a lower rank cyclicity was superposed during mis 5 tst2 thins seaward as a result of tidal ravinement erosion the landward extent of marine environment in mis 5 is inferred to have been of greater scale than that in mis 7 from the distribution of the facies and the trs

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

wintertime sea surface temperature fronts in the taiwan strait 1 we present wintertime variations and distributions of sea surface temperature sst fronts in the taiwan strait by applying an entropy based edge detection method to 10 year 1996 2005 satellite sst images with grid size of 0 01 from climatological monthly mean maps of sst gradient magnitude in winter we identify four significant sst fronts in the taiwan strait the mainland china coastal front is a long frontal band along the 50 m isobath near the chinese coast the sharp peng chang front appears along the peng hu channel and extends northward around the chang yuen ridge the taiwan bank front evolves in early winter as the winter progresses the front becomes broad and moves toward the chinese coast connecting to the mainland china coastal front the kuroshio front extends northeastward from the northeastern tip of taiwan with a semicircle shape curving along the 100 m isobath

sharp based tide dominated deltas of the sego sandstone book cliffs utah usa the lower part of the cretaceous sego sandstone member of the mancos shale in east central utah contains three 10 to 20 m thick layers of tide deposited sandstone arranged in a forward and then backward stepping stacking pattern each layer of tidal sandstone formed during an episode of shoreline regression and transgression and offshore wave influenced marine deposits separating these layers formed after subsequent shoreline transgression and marine ravinement detailed facies architecture studies of these deposits suggest sandstone layers formed on broad tide influenced river deltas during a time of fluctuating relative sea level shale dominated offshore marine deposits gradually shoal and become more sandstone rich upward to the base of a tidal sandstone layer the tidal sandstones have sharp erosional bases that formed as falling relative sea level allowed tides to scour offshore marine deposits the tidal sandstones were deposited as ebb migrating tidal bars aggraded on delta fronts most delta top deposits were stripped during transgression where the distal edge of a deltaic sandstone is exposed a sharp based stack of tidal bar deposits successively fines upward recording a landward shift in deposition after maximum lowstand where more proximal parts of a deltaic sandstone are exposed a sharp based upward coarsening succession of late highstand tidal bar deposits is locally cut by fluvial valleys or tide eroded estuaries formed during relative sea level lowstand or early stages of a subsequent transgression estuary fills are highly variable reflecting local depositional processes and variable rates of sediment supply along the coastline lateral juxtaposition of regressive deltaic deposits and incised transgressive estuarine fills produced marked facies changes in sandstone layers along strike estuarine fills cut into the forward stepped deltaic sandstone tend to be more deeply incised and richer in sandstone than those cut into the backward stepped deltaic sandstone tidal currents strongly influenced deposition during both forced regression and subsequent transgression of shorelines this contrasts with sandstones in similar basinal settings elsewhere which have been interpreted as tidally influenced only in transgressive parts of depositional successions

on the formation of sand banks of finite extent we consider a model where the fluid depth depends on both horizontal coordinates quasi steady depth uniform non divergent fluid flow is governed by inertial pressure and bottom frictional forces sand transport is proportional to the cube of the instantaneous current but augmented by a down slope component and by wind wave action and sand is conserved it is found that low parallel banks grow fastest so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate the inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump a small bump can evolve to an equilibrium bank typically after an initial rapid extension across the tidal currents provided that sand is sufficiently restricted and particularly if some wind wave action prevents growth up to the sea surface sand banks are likely to be in a late stage of evolution when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition the equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents or when sand is abundant

architecture and sequence stratigraphy of a late neogene incised valley at the shelf margin southern celtic sea abstract valleys on the outer celtic sea shelf were cut and filled during the late pliocene early pleistocene the kaiser valley is one of several valleys forming an anastomosed network the main valley directed 20 azimuth true n is 50 m deep and 10 km wide it is connected to the parallel dompaire and parsons valleys by several 120 140 directed incisions of lesser width and depth analyzed by mean of very high resolution seismic data the kaiser valley is interpreted as containing a compound fill consisting of eight erosionally based depositional sequences a typical sequence comprises two facies 1 fluvial channels at the base which represent lowstand to early transgressive deposits and 2 onlapping transgressive bay fill deposits that are locally interbedded at the top with isolated small channels attributed to flood tidal deltas the erosional bases of the fluvial facies correspond to sequence boundaries these are interpreted to result from relative sea level falls successive fluvial and bay fill facies are separated by flat erosional surfaces of high acoustic amplitude which extend laterally across the entire composite valley locally beveling sequence boundaries and creating terraces on the valley walls these flat facies contacts are interpreted as bay ravinement surfaces produced by waves in an estuarine setting the larger scale stacking pattern of the depositional sequences defines a progradational retrogradational trend in which the lowest sequence is mainly constituted by fluvial channel deposits whereas upper sequences display mostly bay fill facies the sequences are related to fifth order glacioeustatic fluctuations whereas their progradational retrogradational trend reflects fourth order eustatic variations and or rapid tectonic tilting of the area as indicated by the presence of two incision orientations the preservation of the system took place during a third order sea level rise and was favored by subsidence of the margin leading to its present occurrence down to 240 m below present sea level

lowstand deltas in the frontier formation powder river basin wyoming implications for sequence stratigraphic models deposits of lowstand deltas formed on the floor of the cretaceous interior seaway of north america are found in the cenomanian lower belle fourche member of the frontier formation central wyoming sandstones located in similar distal basin locations hundreds of kilometers basinward of highstand shoreline deposits form important hydrocarbon reservoirs isolated within marine shales but interpretation of their origin has been highly controversial the distribution geometry and internal facies of these sandstones are documented by an extensive outcrop study and regional subsurface correlations to develop genetic facies models for these deposits this integrated record of lithofacies ichnofacies palynofacies paleocurrent data bedding relationships and isolith maps incorporates observations from nearly 100 measured outcrop sections and about 550 subsurface well logs four episodes of sediment progradation and subsequent transgression each left behind gradually upward coarsening deltaic sandstones that have eroded tops these deltaic sandstones have a lobate to elongate geometry basinward dipping internal clinoform bedding radiating paleocurrents a low to moderate degree of shallow marine burrowing and show variable wave influence and tidal influence on deposition delta plain paralic and nonmarine facies have been eroded from the top of deltaic successions erosion surfaces capping progradational deltaic successions are the only stratal discontinuities that can be mapped regionally and they appear to record transgressive ravinement enhanced over areas of structural uplift compared with lowstand surfaces of erosion which record the bypass of sediments basinward low accommodation during lowstands left little room for sandstones to stack vertically and successive episodes of delta progradation were offset along strike more tide influenced delta deposits formed within shoreline embayments begin page 262 defined by the topography of older wave influenced delta lobes and subtle syndepositional deformation of the basin floor standard sequence stratigraphic terminology is difficult to use in broad lowstand systems like the frontier formation because sandstones do not show simple vertical stacking patterns major stratal discontinuities can form by processes other than lowstand fluvial erosion and minor syndepositional deformation of the basin floor exerts a first order influence on depositional and sediment preservation patterns although many basin distal sandstones have been interpreted to be deposits of offshore bars shelf isolated valley fills and stranded shorelines the frontier formation examples documented here suggest that many of these deposits may be top eroded deltas formed where rivers delivered sediment to lowstand coastlines the external geometry and internal heterogeneities of hydrocarbon reservoirs found in these types of deposits reflect processes active on the low accommodation deltaic shoreline even in cases where subsequent ravinement has significantly truncated the deposits during transgression

3 d architecture and sequence stratigraphic evolution of a forced regressive top truncated mixed influenced delta cretaceous wall creek sandstone wyoming u s a abstract ground penetrating radar gpr is used to delineate the 3 d facies architectural elements and examine the evolution of a top truncated forced regressive mixed influenced delta front in the cretaceous wall creek member of the frontier formation wyoming the gpr data provide a bridge between outcrop facies architecture and recently published high resolution 2 d seismic studies of quaternary delta systems the gpr data were integrated with outcrops photomosaics cores and gps data two orthogonal grids of 2 d gpr profiles provide information on the 3 d facies architecture and stratigraphy of the deltaic deposits three main gpr architectural elements are identified within the delta front 1 mouth bars are characterized by seaward dipping reflections foreset beds in dip view and mounded bidirectionally downlapping reflections in strike view 2 shallow delta slope channels show truncation and onlap and also show low angle landward northwest dipping reflections the mouth bars are locally interrupted by 3 sub horizontal radar reflections that are interpreted as tidally modulated bars within the mouth bar radar facies both top preserved proximal and top truncated distal examples are observed top preserved proximal bars show evidence of mounded bar crests and landward accretion as is observed in the upstream end of mouth bars on the modern atchafalaya delta in the gulf of mexico distal bar deposits primarily comprise the top truncated seaward dipping foresets the gpr interpretation shows two laterally overlapping delta lobes interpreted to represent autocyclic delta switching the older lower lobe forms a fan shaped delta lobe composed of top truncated coalesced mouth bars the second phase of bars is largely top preserved building over the older bars the presence of thicker bedsets and upstream accretion suggests that the younger lobe was quickly abandoned as seen in the overlying transgressive ravinement although marine erosion during transgression was less effective on these later stage bar deposits ravinement increased landward a comparison of the architectural elements at a more regional scale in two separate wall creek delta lobes murphy creek and raptor ridge 30 km apart indicates that the bar complexes were deposited on the delta fronts as accretionary forced regressive deposits during a relative sea level fall the older river dominated deltaic deposits at the murphy creek site prograded southeastward 124 whereas the younger and more tidally influenced raptor ridge bar deposits expanded southward 171 before final abandonment and regional transgression the most distal lowstand lobe sediments within the offlapping parasequence at raptor ridge are more completely preserved and also show the greatest tidal influence compared to the more severely top truncated murphy creek which is in an otherwise more landward location this challenges the notion that tidal facies are predominantly associated with transgressive or highstand systems tracts greater preservation of deltaic facies in forced regressive and lowstand deltas as shown here has also been documented in quaternary shelf edge deltas such as the lagniappe in the gulf of mexico and the mahakham in kalimantan

low sea level tidal origin of celtic sea sand banks evidence from numerical modelling of m2 tidal streams abstract numerical modelling of m 2 tidal streams in the celtic sea with a sea level lowered by 100 m indicates tidal currents about twice as strong as those at present such currents would have been sufficient to generate and maintain the linear tidal sand banks now found in that region as moribund bedforms furthermore an indicated clockwise rotation of the major axes of the tidal ellipses at a sea level lowered by 100 m with respect to the present day is in the correct sense to further the comparison with modern examples of actively maintained linear tidal sand banks

living deep sea benthic foraminifera from the warm and oxygen depleted environment of the sulu sea the semi enclosed oligotrophic sulu sea is characterised by warm ca 10 c and oxygen depleted 32 m from 56 samples from surface down to 5 cm the stained foraminiferal assemblages of the sulu sea comprised 285 species including 137 agglutinated and 148 calcareous species standing stock values ranged from 595 individuals 10 cm2 on the continental slope to 100 individuals 10 cm2 in the abyssal zone generally in the low productivity and low oxygen environment of the sulu sea stained assemblages are characterized by low standing stock values moderate dominance and low diversity the combination of poor rates of c org flux and low dissolved oxygen content in bottom waters are the main factors controlling the deep sea benthic fauna in the sulu sea the foraminiferal abundances in the upper bathyal zone respond to both food fluxes and oxygen concentrations most of the epifaunal oxyphilic species have their lower limit of occurrence at a water depth of approximately 2000 m dissolved oxygen 1 25 ml l in the sulu sea at constantly dysoxic 1 ml l o2 sites from the lower bathyal and abyssal zone the assemblages comprised low oxygen tolerant species and are more dependant on c org fluxes the correlations between benthic foraminiferal faunas and c org flux and dissolved oxygen values are very good with correlation coefficients of r2 0 956r2 0 956 and 0 88 respectively the living deep sea foraminiferal assemblages consisted mainly of agglutinated tests with dominant species such as lagenammina difflugiformis ammoscalaria tenuimargo various reophax species and small 70 m trochamminaceans like portatrochammina wiesneri stained individuals of the calcareous parrelloides bradyi type 2 occurred in low numbers at oxygen poor sites down to a depth of 5 cm in the sediment column the only stained calcareous infaunal species found deeper than 4000 m was valvulineria mexicana average living depth of 3 cm the general microhabitat preferences of common species were consistent with those from other studies although due to the unique combination of poor food supply and dysoxic conditions most of the infaunal species had shallower average living depths than those reported from other dysoxic locations

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