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

the north american late wisconsin ice sheet and mantle viscosity from glacial rebound analyses abstract observations of sea level and crustal response to glacial loading cycles provide constraints on the mantle rheology function e and as well as on the ice load i with the latter being largely free from a priori glaciological or climate assumptions and appropriate therefore for testing any such hypotheses this paper presents new results for both continental mantle e and i for the late wisconsin ice sheet using geological evidence for relative sea level change rsl and tilting of palaeo lake shorelines complemented with loose constraints from observations of present day radial crustal displacement across north america the focus is on evidence from near or within the former maximum ice margins and the resulting earth response is representative of sub continental mantle conditions the inversion of the sea level information has limited resolution for earth rheology and simple three layer models characterized by depth averaged effective lithospheric thickness h and upper and lower mantle viscosities um and um respectively adequately describe the response function yielding parameters earth model e 6 of h 102 85 120 km um 5 1 1020 3 5 7 5 x1020 lm 1 3 1022 0 8 2 8 x1022 where the numbers in parenthesis are 95 confidence limits the details of the ice sheet with one exception are not strongly dependent on the rheological assumptions within this range the exception is the lower mantle viscosity that remains correlated with the magnitude scaling of the ice sheet a link that is largely broken by introducing constraints from glacial loading effects on the earth s rotation and dynamic flattening the difference between the continental um and the comparable estimate of 1 2 5 x1020 for ocean mantle is statistically significant shoreline gradient information from glacial lakes mcconnell agassiz algonquin and ojibway provide strong constraints on the response within the interior of the ice sheet and the resulting ice sheet model lw 6 is characterized by multiple ice domes from at least 17 18 ka onwards the resolution for earlier periods is largely constrained by global ice volume considerations the two principal domes are over southern nunavut the keewatin dome and over quebec labrador both of 3500 m thickness separated by an ice ridge some 1500 m lower than the domes the latter a requirement imposed by the gradient information over western canada ice thickness gradients east of the cordilleras are partly constrained by the shoreline data for former lake mcconnell as is the lateglacial ice thickness of the keewatin dome and indicate that any ice free corridor between the laurentian and cordilleran components is unlikely to have existed before 13ka reconstructions of the glacial lakes are consistent with the locations and timing of the observational evidence for the four major lake systems with the likely drainage routes identified the evolution of the lw 6 ice volume function expressed as equivalent sea level is characterized by a rapid decrease in ice volume from 15 to 14 5 ka corresponding to the bolling allerod period in the main from rapid ice retreat along the southern margin with further contributions from drainage through the st lawrence river valley and from ice retreat from the major northern straits and gulfs but not hudson strait where the rsl data point to late removal of ice after 10 ka the contribution of the drainage of the lakes to global sea level rise is small

searching for eustasy in deglacial sea level histories abstract perturbations to the earth s gravity field and solid surface associated with glacial isostatic adjustment gia cause the total observable sea level change to depart from the eustatic curve which is defined as a spatially uniform height shift of the ocean surface to accommodate any mass gained lost from grounded ice in this study we apply a state of the art model of gia induced sea level change to quantify the magnitude and spatial form of this departure at the global scale for a range of model parameters with an aim to identify regions that are well suited to obtain accurate and precise estimates of eustatic sea level and therefore past grounded ice volume in general our results indicate that eustatic sea level is not a directly measurable quantity and so must be estimated by subtracting a model derived estimate of non eustatic contributions from observations in this regard we use our results to isolate regions where this procedure can be applied with optimal accuracy and precision that is where 1 the gia predictions are relatively insensitive to plausible ranges in input parameters and 2 where the non eustatic contribution is small i e the predicted sea level closely approximates the eustatic value we present maps that can be employed by the field community to identify areas where sea level reconstructions would be well suited to arrive at robust estimates of eustatic sea level note that sea level changes associated with tectonic motion and changes in ocean water temperature salinity which also lead to departures from eustasy are not considered in this analysis

numerical simulations of tidal and wind driven circulation in the cretaceous interior seaway of north america twenty two numerical experiments using a multi layer numerical model of turbulent flow in shallow seas better define fluid circulation and sediment transport paths in the cretaceous interior seaway of north america each experiment consists of a different combination of paleogeography paleobathymetry coriolis acceleration boundary tidal amplitudes wind stresses and bed friction the paleogeographies and paleobathymetries represent three seaway configurations a seaway of intermediate size and depth 200 m during a transgressive peak t5 in late albian time a seaway of maximum size and depth 400 m during peak transgression t6 in early turonian time and a seaway of minimum size and depth 100 m during a peak regression r8 in the campanian values for the other key model parameters are m 2 co oscillating boundary tides of 0 1 to 0 2 m range at the arctic ocean boundary and 0 5 to 1 m range at the proto gulf of mexico boundary coriolis accelerations corresponding to 30 n 45 n and 60 n latitude chezy friction factors ranging from 31 to 70 m s 1 and average winter winds and two winter storms computed by the community climate model at the national center for atmospheric research for paleogeographic conditions during the late albian results of the numerical experiments and comparison of these results with geologic observations allow the following conclusions 1 circulation in the seaway was generally storm dominated 2 typical winter storms crossing the seaway from west to east generated 0 3 m s 1 shore parallel geostrophic currents on the shelves north of arizona at first flowing weakly to the north but later during the storm flowing strongly to the south 3 extreme storms could have produced 0 8 m s 1 currents over the shelves and 0 3 m s 1 currents in 200 m of water 4 co oscillating tides propagated into the seaway as progressive kelvin waves and therefore tidal ranges in the seaway were mesotidal to macrofdal along the southeastern margin but microtidal everywhere else 5 significant deep water wave heights and periods of the fully developed wave field are predicted to have been 5 to 6 m high and 10 s respectively the northwestern shore of the seaway would have experienced these storm waves approaching from the north and thus net sediment drift should have been to the south limited available field data support these conclusions

regional scale paleobathymetry controlled location but not magnitude of tidal dynamics in the late cretaceous western interior seaway usa despite extensive outcrop and previous sedimentologic study the role of tidal processes along sandy wave and river dominated shorelines of the north american cretaceous western interior seaway remains uncertain particularly for the extensive mid campanian c 75 77 5 ma tidal deposits of utah and colorado usa herein paleotidal modelling paleogeographic reconstructions and interpretation of depositional process regimes are combined to evaluate the regional scale 100 1000km basin physiographic controls on tidal range and currents along these regressive shorelines in the utah bight southwestern western interior seaway paleotidal modelling using a global and astronomically forced tidal model combined with paleobathymetric sensitivity tests indicates the location of stratigraphic units preserving pronounced tidal influence only when the seaway had a deep center 400 m and southern entrance 100 m maximum tidal velocity vectors under these conditions suggest a dominant south easterly ebb tide within the utah bight consistent with the location and orientation of paleocurrent measurements in regressive tide influenced deltaic units the modelled deep paleobathymetry increased tidal inflow into the basin and enhanced local scale 10 100 km resonance effects in the utah bight where an amphidromic cell was located however the preservation of bidirectional mudstone draped cross stratification in fine to medium grained sandstones requires tides in combination with fluvial currents and or local tidal amplification below the maximum resolution of model meshes c 10 km these findings suggest that whilst regional scale controls govern tidal potential within basins localized physiography exerts an important control on the preservation of tidal signatures in the geologic record

control of reservoir geometry and stratigraphic trapping by erosion surface e5 in the pembina carrot creek area upper cretaceous cardium formation alberta canada 1 seven major erosion e surfaces are found within the 100 m thick cardium formation in the subsurface of alberta erosion surface e5 has up to 20 m of erosional relief in the carrot creek area and is cut into originally horizontal open marine sandstones and mudstones the e5 surface has been correlated into the pembina area by construction of a structure map based on 2470 resistivity logs the e5 surface is characterized by a series of sub parallel southeast trending steps with lower areas between the steps this topography is interpreted to have formed during erosional shoreface retreat in a period of alternating transgression and stillstand of relative sea level tectonic tilting of the basin floor is also suggested by the topography of the erosion surface the tilti g is related to the accretion of exotic terranes and loading the continental margin the erosion surface is overlain by a continuous veneer of conglomerate interpreted as a transgressive lag this conglomerate thickens to 20 m in the lower areas at carrot creek where it is interpreted as a shoreface deposit rather than an offshore bar these shoreface conglomerates form important reservoirs the veneer also thickens to about 9 m in parts of pembina but the thick conglomerates occur not in the lows but on top of the steps reconstruction of the geometry of the steps indicates that at times of unusually high sediment supply during transgression conglomerates were deposited as local bars in the lower shoreface the sandstones and mudstones below the erosion surface at pembina shale out northeastward partly forming a stratigraphic trap however these sediments are also truncated by the e5 erosion surface and buried by transgressive mudstones these mudstones contribute significantly to updip stratigraphic trapping the long narrow sand body trends mapped in pembina and adjacent fields are due to the erosive dissection of an originally extensive and continuous sheet of interbedded sandstones and mudstones and not as has been suggested to an offshore bar origin for the fields

depositional remnants part 1 common components of the stratigraphic record with important implications for hydrocarbon exploration and production the preservation of sedimentary strata below erosion surfaces can be highly variable laterally and commonly only small remnants of originally more extensive deposits remain the concept of remnants is not new but their abundance and the fact that they commonly develop below low relief erosion surfaces as well as below those that incise deeply may not be fully appreciated spatial variations in accommodation because of paleotopography synsedimentary and penecontemporaneous tectonics and differential compaction occur on a variety of scales in all depositional settings in low accommodation and shallow shelf settings spatial variations in accommodation commonly result in the formation of remnants ranging in size from small few to tens of square kilometers to basin scale hundreds of square kilometers remnants of porous and permeable facies encased in low permeability facies are an important and relatively common type of stratigraphic trap conceptual models for three scales of depositional remnants are used to illustrate their significance to petroleum exploration and production the recognition of these deposits herein referred to as depositional remnants is commonly critical to depositional systems analysis because stratigraphic terminations caused by erosional truncation must be interpreted differently from those caused by lithofacies change in addition the preserved geometry of remnants can be quite different from the geometry of the original deposit and because geometry is heavily relied upon in interpretations of ancient depositional systems interpreting a preserved geometry as a depositional geometry can result in significant misunderstandings depositional remnants are common in the stratigraphic record and represent an important concept to open up new hydrocarbon plays in mature basins

depositional remnants part 2 examples from the western interior cretaceous basin of north america the western interior cretaceous basin contains numerous examples of depositional remnants partially preserved portions of originally extensive depositional systems emphasis is placed on examples of accommodation remnants i e a type of depositional remnant whose overlying erosion surface displays little relief and is preserved in an area of locally increased accommodation variations in spatial accommodation have been attributed to synsedimentary tectonics erosional topography differential compaction and salt dissolution and are commonly associated with basement faults remnants range in size from small to very large basin scale and larger remnants commonly contain several smaller remnants remnants of shallow marine sandstone encased in shale are an important and common type of stratigraphic trap failure to recognize deposits as only remnants of depositional systems has led to misinterpretations of depositional environment and inaccurate paleogeographic reconstructions

applying uv cameras for so2 detection to distant or optically thick volcanic plumes abstract ultraviolet uv camera systems represent an exciting new technology for measuring two dimensional sulfur dioxide so 2 distributions in volcanic plumes the high frame rate of the cameras allows the retrieval of so 2 emission rates at time scales of 1 hz or higher thus allowing the investigation of high frequency signals and making integrated and comparative studies with other high data rate volcano monitoring techniques possible one drawback of the technique however is the limited spectral information recorded by the imaging systems here a framework for simulating the sensitivity of uv cameras to various so 2 distributions is introduced both the wavelength dependent transmittance of the optical imaging system and the radiative transfer in the atmosphere are modeled the framework is then applied to study the behavior of different optical setups and used to simulate the response of these instruments to volcanic plumes containing varying so 2 and aerosol abundances located at various distances from the sensor results show that uv radiative transfer in and around distant and or optically thick plumes typically leads to a lower sensitivity to so 2 than expected when assuming a standard beer lambert absorption model furthermore camera response is often non linear in so 2 and dependent on distance to the plume and plume aerosol optical thickness and single scatter albedo the model results are compared with camera measurements made at kilauea volcano hawaii and a method for integrating moderate resolution differential optical absorption spectroscopy data with uv imagery to retrieve improved so 2 column densities is discussed

high resolution sequence stratigraphic analysis of the shannon sandstone in wyoming using a template for regional correlation abstract recent interpretations of the lower campanian shannon sandstone in the powder river basin wyoming have suggested that it was deposited in falling stage and lowstand incised shorefaces rather than in stacked shelf ridges up to 160 km from shore despite these detailed studies there is no published correlation of the outcrop deposits at salt creek anticline with the subsurface deposits in the hartzog draw heldt draw hd hd area a complete high resolution sequence stratigraphic analysis of the shannon requires that the outcrops at salt creek be correlated with the subsurface fields at hd hd there is little core control in the approximately 30 km between these areas so correlations are based almost entirely on well logs a template has been constructed in the hd hd area where ther is good core and well log control which embodies data from facies facies successions well log signatures and bounding discontinuities the template consists of a regressive surface of erosion rse that forms the base of an incised shoreface sandbody and a transgressive surface of erosion tse that truncates the top of the sandbody and the rse two cross sections have been constructed and the template has been used to guide correlations between salt creek and the hd hd area from the cross sections six progradational events and six transgressions have been defined during shannon time the positions of the rses and tses allow estimates of between a few meters and 60 m for the magnitude of sea level fluctuations that controlled shannon deposition the proposed correlations confirm and reinforce the interpretation of the shannon as a series of incised shoreface sandbodies separated by transgressive systems tract mudstone deposits

paleotectonics and hydrocarbon accumulation powder river basin wyoming the belle fourche arch a subtle northeast trending paleoarch extends across the central part of the powder river basin wyoming to the black hills uplift the arch is the result of differential vertical uplift primarily during cretaceous time on numerous northeast trending structural lineaments lineament trends are identified from structural offsets in the black hills monocline offsets in well defined linear topographic escarpments and by linear drainages which connect trends between the monocline and the escarpments underlying basement zones of weakness are thought to be shear zones of precambrian age analogous to the mullen creek nash fork shear zone of southeast wyoming stratigraphic evidence suggests that the structural lineaments which form the belle fourch arch have rejuvenated periodically throughout the phanerozoic subtle movements along the lineaments have affected depositional environments and hydrocarbon accumulation in virtually all significant reservoirs in the northern two thirds of the basin evidence includes 1 localization of minnelusa formation permian hydrocarbon production along the crest of the arch 2 localization of dakota formation cretaceous alluvial point bar production on the crest of the arch 3 localization of lower muddy formation cretaceous channel deposits parallel with and on the downthrown sides of lineament trends 4 abrupt change in depositional strike of upper muddy formation cretaceous marine bars close to the arch 5 superposition of turner sandstone cretaceous channel deposits alon the trends of muddy channels and 6 localization of virtually all significant upper cretaceous shannon and sussex sandstone offshore marine bar production along the crest of the arch subtle uplift along the arch was persistent during at least lower muddy through sussex deposition a period of about 35 m y

tectonic framework of powder river basin wyoming and montana interpreted from landsat imagery linear features in the powder river basin wyoming and montana were interpreted from landsat images and analyzed to define major lineaments lineaments identified include several that trend northwest and a prominent set that trends northeast these lineaments represent broad 5 10 km or 3 6 mi linear zones where smaller parallel and subparallel linear features are concentrated at the surface the smaller linear features are interpreted as possible expressions of joints fractures folds or lithologic boundaries produced by periodic readjustment along basement block boundaries the lineaments discussed in this report were visually interpreted from maps of linear features and contour maps showing concentrations of linear features lineaments were subsequently compared to mapped structures outcrop patterns geophysical data and isopach maps to assess their geologic significance correlations of these lineaments with mapped structures geophysical gradients or facies changes strongly support the interpretation that they represent the surface expression of boundaries of crustal blocks that have been periodically reactivated through time the northeast and northwest patterns provide evidence that a systematic rectilinear pattern of crustal blocks formed early in the earth s history and has largely controlled subsequent adjustments of the earth s crust these findings suggest the potential for depositional control of sedimentary units by structural adjustments between basement blocks and thus lead to the conclusion that lineaments may be used as guides in petroleum and mineral exploration if favorable source and host rocks are present

variations in shoreface progradation and ravinement along the texas coast gulf of mexico shoreface architecture evolution mid holocene to present and depths of transgressive ravinement were examined from sabine pass at the texas louisiana border to south padre island near the texas mexico border using 30 shoreface transects shoreface transects extend out to 16 m water depth each created from an echo sounding profile and on average seven sediment cores the shoreface is composed of three broad sedimentological facies the upper shoreface composed almost entirely of sand the proximal lower shoreface composed of sand with thickly to medium bedded 50 10 cm mud and the distal lower shoreface composed dominantly of mud with medium to thinly bedded 20 3 cm sand shoreface architecture and evolution is extremely variable along the texas coast shoreface gradients increase from 2 25 m km 1 in east texas to 3 50 m km 1 in south texas shoreface sands coarsen towards south texas east and south texas shoreface deposits are thin and retrograding whereas central texas shoreface deposits are thicker and prograding central texas is characterized by stacked shoreface successions whereas in east texas lower shoreface sands are preserved only in offshore banks preservation of shoreface deposits is low in south texas although eustatic fluctuations and accommodation space have a strong impact on overall mid holocene to present shoreface evolution and preservation potential along strike variations in sediment supply and wave energy are the main factors controlling shoreface architecture the transgressive ravinement surface varies from 6 to 15 m along the texas coast

water load definition in the glacio hydro isostatic sea level equation abstract models of glacio hydro isostatic rebound and the concomitant sea level change have been progressively improved over the past three decades recently the procedures used by the group at the australian national university anu for the hydro isostatic component of the theory have been questioned quat sci rev 21 2002 409 although the details of the anu group s procedures have not been published because they are mainly computational in nature rather than representing significant conceptual advances because of this criticism we set out here in detail the procedures that have been used for the treatment of the migration of shorelines as sea levels rise and fall the effect of retreat and advancing grounded ice on shelves and shallow seas and the transitions from grounded to floating ice and vice versa we conclude that there is no basis for the criticism that these formulations and their implementation provide a high resolution and complete description of both sea level change and of the estimates of volumes of ice exchanged with the oceans the results from this formulation are confirmed by the entirely independent analyses of milne et al quat sci rev 21 2002 361 and mitrovica and milne geophys j int 2002 submitted for publication who conclude that our formulation is significantly more accurate than the procedure advocated by peltier science 265 1994 195 rev geophys 36 1998a 603 geophys res lett 25 1998b 3955

the toarcian bajocian deltaic system in the north german basin subsurface mapping of ancient deltas morphology evolution and controls research focussing on the morphology and morphodynamics of modern river deltas has contributed much to the understanding of reservoir geometry and prediction of hydrocarbon splays and deep geothermal aquifers the interplay of allogenic and autogenic controls results in complex histories of modern river deltas comprising subsequent regressive and transgressive stages of delta formation the application to ancient examples is still ambiguous and in particular the detailed morphological description of ancient deltas is often hampered by limited subsurface data this basin scale study employs a data set of 15 cored wells and more than 450 logged wells in combination with lithofacies biofacies and architectural analysis to reconstruct high resolution subsurface facies and sand thickness maps of the toarcian bajocian deltaic system in the north german basin the results of this study show the evolution from smaller elongate river dominated delta types in the lower and upper toarcian 15 000 to 20 000 km and a larger lobate river dominated delta in the upper aalenian 40 000 km to a cuspate mixed river dominated and wave modified delta in the upper bajocian 25 000 km the river dominated parts are composed of subsequently formed of distributary deltaic channel belts and associated sheetsands of the delta plain and distributary mouth bar complexes with bar finger sand architectures of the delta front increasing marine processes in the bajocian resulted in modification of delta complexes forming a shoreface setting with foreshoals arc like chains of ooid bearing barrier shoals and back barrier lagoons the complex history of the toarcian bajocian deltaic system was mainly controlled by allogenic sea level fluctuations that triggered the delta progradation and subordinately by allogenic basin reorganisation autogenic process change of channel avulsion led to locally reduced sediment flux and culminated in lobe abandonment and transgressive shorelines differential compaction of underlying deltaic deposits result in strong differences in accommodation space and contributed to much to large scale delta shifts 300 km this article is protected by copyright all rights reserved

stratigraphic architecture of a net transgressive marginal to shallow marine succession upper almond formation rock springs uplift wyoming u s a abstract the upper part of the almond formation records the overall retreat of a wave dominated shoreline and associated lagoons or bays exposures of these strata on the eastern flank of the rock springs uplift wyoming u s a enable analysis of their stratigraphic architectures along sections oriented oblique to depositional strike the upper almond formation comprises at least nine vertically stacked regressive transgressive cycles the regressive component of each cycle consists of thick up to 22 m laterally continuous wave dominated shoreface and overlying coastal plain deposits that occur in paleoseaward locations and have abrupt 400 m paleolandward pinchouts the transgressive component of each cycle consists of one or more bay fill successions that occur in paleolandward locations and gradually thin in a paleoseaward direction transgressive bay fill deposits in each cycle are thick up to 18 m and associated with preservation of surfaces that record in progressively paleoseaward locations initiation of a lagoon or bay transgressive surface erosional retreat of tidal inlet channels tidal ravinement surface and the shoreface wave ravinement surface and marine flooding marine flooding surface this architecture records regression of a strandplain or wave dominated delta and subsequent transgression of a barrier island and spit with associated lagoon or bay the occurrence of such thick and fully preserved bay fill successions indicates that accretionary transgressive shoreline trajectories were developed strongly aggradational to weakly retrogradational stacking of successive regressive transgressive cycles results in a layered stratigraphic architecture with laterally continuous shoreface sandstone layers interbedded with bay fill shale layers shoreface sandstones layers pinch out up dip abruptly 400 m into bay fill shales and have limited vertical connectivity sandstones within bay fill and coastal plain deposits occur as small laterally discontinuous bodies of variable geometry and connectivity however these sandstones may provide additional connectivity where they erode through bay fill shales between two shoreface sandstone layers

shannon sandstone in wyoming a shelf ridge complex reinterpreted as lowstand shoreface deposits abstract the shannon sandstone campanian of wyoming was formerly interpreted as two stacked shelf ridge complexes sand was believed to have been transported from a time equivalent shoreline 110 150 km to the west and reworked or molded into ridges at the depositional site we show that this time equivalent shoreline section at lucerne wyoming consists of not one shoreface sandbody but two superimposed they are both storm dominated and the lower one terminates in beach facies capped by root traces there must have been a rise in relative sea level of at least 14 m to make accommodation space for the second shoreface sandbody in the salt creek area and the adjacent subsurface teapot dome there are two sandier upward facies successions in the lower succession there are abrupt vertical acies contacts between offshore bioturbated sandstones thicker hummocky cross stratified sandstones and coarser cross bedded sandstones there is also evidence that the cross bedded sandstones rest erosively on underlying facies the trace fauna in the sandstones includes macaronichnus segregatis rosselia socialis and ophiomorpha the m segregatis suggests a foreshore or upper shoreface depositional environment and r socialis indicates a lower to middle shoreface neither are characteristic of a shelf ridge complex the abrupt and probably erosive facies contacts along with the trace fauna suggest that the cross bedded sandstones in this succession represent a shoreface deposit that formed during a stage of actively falling relative sea level overlyi g muddy bioturbated sandstones indicate that shoreface deposition was terminated by a transgression the upper sandier upward succession contains facies and trace fauna similar to those of the lower succession and is also interpreted as a prograding shoreface rather than the sand moving 110 150 km from the shoreline and then being molded into shelf ridge complexes at salt creek we suggest that the shoreline moved into the salt creek area as the result of a fall in relative sea level it was transgressed and moved back westward a second fall of relative sea level moved the shoreline back to salt creek and a final transgression terminated shannon deposition

geometry and facies of stacked shallow marine sandier upward sequences dissected by erosion surface cardium formation willesden green alberta willesden green field is a long narrow sandstone body completely encased in marine mudstones the field is late cretaceous turonian in age and contains as many as seven stacked sandier upward sequences the sequences are as much as 12 m 39 3 ft thick are stratigraphically distinct and do not offlap systematically each sequence begins with marine bioturbated mudstones and passes upward into storm dominated shallow marine sandstones each sequence shows a lateral shaling out from hummocky cross stratified sandstone into bioturbated mudstone isopach maps show that the sequences thin basinward at a rate of 15 67 cm km 9 45 42 21 in mi and suggest dispersal directions ranging from north northeast to southeast the stack of marine sequences is dissected by a basin wide erosion surface that initially formed subaerially following a major relative lowering of sea level during ensuing transgression a series of stepped shorefaces was cut into the stack of sequences removing all evidence of subaerial exposure the shorefaces in most places are overlain by a thin pebble veneer which in turn is buried by thick transgressive marine mudstones in places the pebble veneer thickens into conglomerates as much as 20 m 65 6 ft thick that form reservoirs at carrot creek pembina and ferrier as well as willesden green these conglomerates are interpreted to have been deposited at river mouths and locally reworked along the shoreface by waves during continued transgression the stacked sequences a d shoreface conglomerates were buried by marine mudstones overall reservoir characteristics are determined by the geometry and stacking of the sequences stratigraphic traps have been formed partly by lateral shaling out and partly by mud draped incised shorefaces locally shoreface gravels are good reservoirs and the overlying transgressive mudstones form the traps we believe that the long narrow geometry of the field represents an erosional remnant of a formerly continuous sand sheet the field is not an offshore bar

the so2 camera a simple fast and cheap method for ground based imaging of so2 in volcanic plumes 1 so2 flux is widely monitored on active volcanoes as it gives a window into the hidden subsurface magma dynamics we present here a new approach to so2 flux monitoring using ultraviolet imaging of the volcanic plume through carefully chosen filters to produce images of so2 column amount the so2 camera heralds a breakthrough in both our ability to measure so2 flux at unprecedented frequencies 2 hz and at unprecedented accuracy thanks to the application of correlation techniques to determine wind speed directly from the images and the ability to measure the whole profile simultaneously in this paper we detail the commercially available pieces required to construct the so2 camera introduce a retrieval scheme to determine so2 amounts from the images and present results from a field campaign in november 2005 on sakurajima volcano japan

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

shannon sandstone depositional model sand ridge dynamics on the campanian western interior shelf the campanian shannon sandstone member of the cody shale forms the reservoir for several significant oil fields in the western powder river basin of wyoming the extensive data set available for this economically important unit makes it one of the best known ancient analogs to the sand ridges of modern shelf seas the shannon sandstone was deposited as linear ridges by intermittent along shelf southerly storm flows in a transgressive middle to outer shelf environment of the cretaceous interior seaway comparison of shannon sandstone bodies with modern sand ridges shows that they were formed in response to the kind of flow field observed over the modern systems the long axes of these bodies are aligned northwest southeast to north northwest south southeast the sandstone bodies are asymmetric in transverse section northeastern flanks are shorter and steeper than the gentle accretion surfaces on the southwestern flanks paleocurrent direction is southerly hence the sandstone bodies are aligned obliquely with respect to the prevailing transport direction as required by hydrodynamic theory the four basic lithofacies types recognized in these sand ridge deposits are cross bedded sandstone thin bedded sandstone bioturbated silty sandstone and lenticular bedded to bioturbated siltstone the cross bedded lithofacies has tabular trough glauconitic trough cross bedded and bioturbated variants this lithofacies grades down section and down current into a thin bedded lithofacies comprising flaser to wavy bedded sandstone and low angle laminated sandstone this thin bedded lithofacies overlies a widespread massively bioturbated sandstone lithofacies which in turn rests disconformably on a siltstone lithofacies the distribution of lithofacies within a shannon sandstone body is most readily explained in terms of the velocity distribution over a sand ridge and textural modification by the distortion of the regional flow field over the growing sand ridge the up current flank underwent erosion and deposition occurred on the crest and down current side so that the sand ridge grew and migrated in a southwestward direction each sand ridge served as a fractionation mill in which successive environments on the transport pathway across the ridge extracted successively finer grades of sand from the transported load

sun photometer and lidar measurements of the plume from the hawaii kilauea volcano pu u o o vent aerosol flux and so2 lifetime 1 aerosol optical depths and lidar measurements were obtained under the plume of hawaii kilauea volcano on august 17 2001 9 km downwind from the erupting pu u o o vent measured aerosol optical depths at 500 nm were between 0 2 0 4 aerosol size distributions inverted from the spectral sun photometer measurements suggest the volcanic aerosol is present in the accumulation mode 0 1 0 5 micron diameter which is consistent with past in situ optical counter measurements the aerosol dry mass flux rate was calculated to be 53 mg d 1 the estimated so2 emission rate during the aerosol measurements was 1450 mg d 1 assuming the sulfur emissions at pu u o o vent are mainly so2 not aerosol this corresponds to a so2 half life of 6 0 hours in the atmosphere

controls on the deposition and preservation of the cretaceous mowry shale and frontier formation and equivalents rocky mountain region colorado utah and wyoming regional variations in thickness and facies of clastic sediments are controlled by geographic location within a foreland basin preservation of facies is dependent on the original accommodation space available during deposition and ultimately by tectonic modification of the foreland in its postthrusting stages the preservation of facies within the foreland basin and during the modification stage affects the kinds of hydrocarbon reservoirs that are present this is the case for the cretaceous mowry shale and frontier formation and equivalent strata in the rocky mountain region of colorado utah and wyoming biostratigraphically constrained isopach maps of three intervals within these formations provide a control on eustatic variations in sea level which allow depositional patterns across dip and along strike to be interpreted in terms of relationship to thrust progression and depositional topography the most highly subsiding parts of the rocky mountain foreland basin near the fold and thrust belt to the west typically contain a low number of coarse grained sandstone channels but limited sandstone reservoirs however where subsidence is greater than sediment supply the foredeep contains stacked deltaic sandstones coal and preserved transgressive marine shales in mainly conformable successions the main exploration play in this area is currently coalbed gas but the enhanced coal thickness combined with a mowry marine shale source rock indicates that a low permeability basin centered play may exist somewhere along strike in a deep part of the basin in the slower subsiding parts of the foreland basin marginal marine and fluvial sandstones are amalgamated and compartmentalized by unconformities providing conditions for the development of stratigraphic and combination traps especially in areas of repeated reactivation areas of medium accommodation in the most distal parts of the foreland contain isolated marginal marine shoreface and deltaic sandstones that were deposited at or near sea level lowstand and were reworked landward by ravinement and longshore currents by storms creating stratigraphic or combination traps enclosed with marine shale seals paleogeographic reconstructions are used to show exploration fairways of the different play types present in the laramide modified cretaceous foreland basin existing oil and gas fields from these plays show a relatively consistent volume of hydrocarbons which results from the partitioning of facies within the different parts of the foreland basin

storm deposition in marine sand sheets wall creek member frontier formation powder river basin wyoming abstract the turonian cretaceous wall creek member frontier formation and equivalent turner sandy member carlile shale powder river basin wyoming were deposited on the western margin of the north american seaway the seaway occupied the foreland of the sevier orogenic belt the wall creek turner interval is up to 67 m thick and consists of shale sandstone and minor conglomerate and bentonite deposition occurred during rising sea level following an approximately 90 ma lowstand sandstone and mudstone of the wall creek were deposited in thin shelf sand sheets 6 15 m thick up to approximately 120 km from equivalent shorelines shelf sand sheets dip gently seaward core and outcrop show shelf sandstone of the wall creek in the powder river basin to consist of burrowed to bioturbated medium scale cross beds near horizontal laminated beds and ripple laminated beds reactivation surfaces and mud drapes are common the lack of consistent periodicity across cross sets in foreset angle and thickness and unperiodic spacing of reactivation surfaces mud drapes and burrowed intervals suggest that tides were not an important transport process over most of the depositional area the dominance of storm currents over tides is also indicated by variable bed thickness structure type grain size and degree of burrowing vertically much of the mud separating beds and draping foresets likely represents sedimentation from river floods following storm events p

shannon sandstone in hartzog draw heldt draw fields cretaceous wyoming usa reinterpreted as lowstand shoreface deposits abstract the lower campanian shannon sandstone at hartzog draw heldt draw powder river basin wyoming is interpreted in the literature as a shelf ridge complex deposited 160 km from the contemporaneous shoreline this interpretation poses difficult problems and does not discuss the significance of bounding discontinuities preserved in the sandbodies cross sections show that the shannon sandstone is present at several stratigraphic horizons and is bounded by regionally extensive discontinuities the presence of these bounding discontinuities suggests that fluctuations in relative sea level were important in controlling geometry of sandbodies on the shannon shelf in the hartzog draw heldt draw area of wyoming the base of the shannon is a planar surface with respect to a lower bentonite marker and is characterized by the abrupt appearance of bioturbated sandstone on top of black basinal mudstone siderite pebbles 1 cm in diameter are common at this contact in hartzog draw the bioturbated sandstone interval has an average thickness of 10 m and is separated from an overlying unit of cross bedded fine to medium sandstone up to 20 m thick by a ubiquitous 50 cm thick horizon of mud clasts in a cross bedded highly glauconitic medium sandstone these three units are laterally continuous in hartzog draw except where removed by erosion the top of the shannon is marked by an abrupt change from the cross bedded sandstone or bioturbated medium sandstone to laminated black mudstone mud clasts siderite pebbles chert grains and glauconite mark this abrupt contact suggesting erosional transgression this surface can be traced westward where in many areas it is a mud on mud contact marked by a lag of shell debris this transgressive surface which terminates shannon deposition is characterized by at least one regionally extensive onlapping marker in the hartzog draw heldt draw area the presence of depositional discontinuities in the shannon sandstone is suggested by 1 the sharp basal contact 2 the lateral continuity of individual facies 3 the abrupt vertical facies changes and the association of mud clasts siderite pebbles and glauconite accompanying these abrupt juxtapositions of facies 4 the stratigraphic variability and 5 the termination of shannon deposition by erosive transgression marked by onlapping markers these depositional discontinuities are the bounding discontinuities these bounding discontinuities have asymmetrical one sided scour morphologies with steeper landward margins that flatten basinward these geometries and the linearity of the overlying sandstone and the troughs defined by these scoured surfaces suggest incised shoref ce profiles truncated by erosive transgression thus the shannon sandstone in hartzog draw heldt draw is reinterpreted as a lowstand shoreface deposit

deltaic deposits formed under spatially and temporally variable accommodation regimes a plausible alternative explanation for isolated shallow marine sandstone bodies sequence stratigraphic concepts and nomenclature are predicated on the assumption that at any time accommodation conditions are in phase across a depositional basin in certain situations however such as in evolving retroarc foreland basins the sense of accommodation may be spatially variable because of the growth of intrabasinal structures herein we present evidence for the accumulation of a fluvially dominated deltaic sandstone under strong forcing from spatially and temporally variable low accommodation within the cretaceous western cordilleran foreland basin of north america the peay sandstone member is a coarsening upward sandstone body thick that is extensive across much of the eastern half of the present day bighorn basin of wyoming it is remarkable for its elongate planform geometry extending many tens of kilometers across the basin and for distal thickening patterns that are at face value difficult to reconcile with conventional facies models for deltaic systems the sandstone shows some of the characteristics of falling stage and lowstand deltas extending far into the basin from the contemporary shoreline to the west lack of a preserved delta plain topset but is not incised into its substrate and does not show a descending regressive trajectory with respect to underlying strata we submit that the peay sandstone member was formed under a regime of both temporally and spatially variable accommodation forced by the heterogeneous growth of the forebulge within the western cordilleran foreland basin and suggest that the origin of some other apparently isolated sandstone bodies in this and other basins might also be explained in a similar manner

quantitative evaluation of the transporting capacity of unconformities a case study from the zhongguai area junggar basin nw china abstract unconformities are special geologic bodies with a three layer structure including the rock above the unconformity a weathered clay layer and a leached rock the upper wuerhe upper permian bottom unconformity in northwest junggar basin is the main pathway system linking the zhongguai zg lift with hydrocarbon source kitchens based on the log response characteristics of the unconformity s vertical structure and core calibration a principal component analysis pca was applied to extract and identify the evaluation parameters of the unconformity s vertical structure on the basis of darcy s law the quantitative characterization formula of the unconformity s transport capacity with an actual geological significance was established after taking several factors into consideration the migration probability of the unconformity was used to evaluate the possibility that the unconformity acted as a migration pathway consequently a relationship between the migration probability and the evaluation parameters was developed to analyze the effectiveness of these parameters in characterizing the transporting capacity of the unconformity this study shows that the quotient of the two principal components extracted from the conventional logging curves pc1 pc2 have different reference values in the leached and parent rocks the distribution of thicknesses of the weathered clay layer and the leached rock is well matched with the distribution of paleogeomorphology the parameters representing only a single geological factor are not enough to determine whether the unconformity acted as a migration pathway the flow coefficient cf containing multiple factors can effectively and clearly identify the transporting capacity of the unconformity considering the positive correlation between the parameter cf and the migration probability of the unconformity the oil and gas shows of the area with a parameter cf greater than 10 10 4 cm2 s are abundant which is the superior transporting area of the unconformity and there is a good matching relationship between the distribution of the superior transporting area of the unconformity and that of the hydrocarbon distribution

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

local tectonic control on parasequence architecture second frontier sandstone powder river basin wyoming the cenomanian second frontier sandstone one of the major producing units of the frontier formation in the powder river basin wyoming is a basin isolated sand body that pinches out to zero thickness in both seaward and basinward direction the second frontier has previously been viewed as a single relatively homogeneous wave dominated sediment succession our high resolution study integrating detailed facies relationships in outcrop core and well logs shows that the second frontier sandstone comprises an offlapping parasequence set formed from seven regionally mappable wave dominated parasequences the parasequences are bounded by minor flooding surfaces that represent previously unrecognized potential flow barriers or baffles parasequence boundaries are oriented obliquely to the well defined regional north northwest south southeast elongated trend of the unit and successive parasequences offlap to the south in an along strike direction the seaward pinch out of the second frontier sandstone is depositional in nature as illustrated by well preserved healing phase deposits whereas the basinward pinch out is caused by marine truncation over a tectonically uplifted area parasequence architecture was strongly affected by syndepositional tectonic movement which determined both 1 the distribution of the entire parasequence set forming a depositional remnant and 2 the position and shape of parasequences internal to the remnant the second frontier is thus interpreted as a depositional remnant of a once more extensive wave dominated deltaic shoreface complex

topography and significance of a basinwide sequence bounding erosion surface in the cretaceous cardium formation alberta canada abstract the cardium formation turonian coniacian upper cretaceous of the western interior seaway alberta contains six marine sandier upward successions bounded by seven basin wide erosion surfaces in the subsurface erosion surface e5 is associated with major oil and gas fields and is penetrated by thousands of wells a topographic map of e5 based on 6126 well logs and over 1100 measured cores shows a series of subparallel elongate highs steps and lows which trend northwest southeast parallel to tectonic trends and to the actively rising cordillera to the southwest the steps are about 10 km apart and the relative relief step to adjacent low is up to 25 m the steps are asymmetrical with a steeper face to the northeast the e5 erosion surface cuts into offshore marine hummock cross stratified sandstones and interbedded mudstones and it records a lowering of relative sea level our interpretation suggests that erosion was in neither a fully subaqueous nor a fully subaerial environment instead it involved relative sea level lowering and subaerial erosion followed by major modification of the landscape during transgressive shoreface erosion at times of relative stillstand during overall transgression gravel was supplied to the shoreface and was reworked a short distance alongshore by waves these conglomerates now form important oil and gas reservoirs the asymmetry of the steps and lows indicates that the originally flat sea floor was tilted northeastward immediately before erosion giving a gradient of about 1 1000 during transgression shorefaces were incised into the tilted surface to form a stepped morphology also during transgression the sea floor was gradually restored to its pre tilting position each of the six marine sandier upward sequences along with the erosion surface at the top occupies an average of 470 000 years and we estimate that transgression took at least 100 000 to 200 000 years

relation between single very long period pulses and volcanic gas emissions at mt asama japan 1 multiple volcanic observations conducted at mt asama japan provide evidence of a link between single very long period vlp seismic pulses and volcanic gas emissions so2 flux measurements were conducted on 2 june 2009 when mt asama was producing ash free eruptions with vlp pulses gas bursts from a vent at the crater bottom following the vlp pulses provided an excellent opportunity to examine the relation directly the so2 emission for each eruption was calculated by integrating high temporal so2 flux data obtained by the so2 imaging system and subtracting the contribution from quiescent degassing from fumaroles around the crater bottom a seismic moment of vlp pulse was estimated by the waveform inversion we observed seven eruptions and obtained the proportional relation between vlp pulse moment and so2 emission the relation determined is consistent with the vlp source model these observational results are the first report of a quantitative comparison between single vlp pulse moment and volcanic gas emission

the importance of sea level fluctuations in the formation of linear conglomerate bodies carrot creek member of cardium formation cretaceous western interior seaway alberta canada abstract the raven river member of the cardium formation turonian upper cretaceous in the carrot creek area of alberta contains two coarsening upward sequences of marine mudstones and sandstones the lower sequence coarsens from black mudstones into bioturbated fine grained sandstones and is capped by a gritty siderite horizon which probably indicates a pause in deposition the sandstones of the upper sequence contain hummocky cross stratification suggesting open marine deposition below fairweather wave base the two sequences are scoured to variable depths by a major erosion surface which has a relative relief of up to 20 m a structure map and three dimensional mesh diagrams of this surface suggest four topographic elements a relatively high terrace a bevel at which und rlying beds are truncated and a series of bumps and hollows these are interpreted to represent a remnant erosional topography which gradually fades away into the final topographic element the smooth basin plain the erosion surface is covered with conglomerate assigned to the carrot creek member of the cardium the conglomerate thickness reaches about 20 m against the bevel and in some of the hollows but usually thins to a veneer on the terrace on top of the bumps and on the distal basin floor the conglomerate bodies are relatively long and narrow and trend northwest southeast they are overlain by marine mudstones of the dismal rat member the elongate conglomerate bodies appear at first sight to be another case of western interior seaway offshore bars encased in marine mudstones many tens of kilometers seaward of time equivalent shoreline deposits however the erosion surface indicates that the conglomerates are not genetically part of the underlying coarsening upward sequence we propose a rapid relative lowering of sea level following deposition of the hummocky cross stratified sandstones the shoreline advanced many kilometers northeastward into the basin and during stillstand wave erosion cut a new shoreface profile the bevel during this lowstand incised rivers supplied gravel to the shoreface waves worked the gravel alongshore against the bevel and into the erosional hollows subsequent transgres ion spread some gravel southwestward back across the terrace storms transported gravel stringers into the transgressive muds accumulating in the hollows other erosional surfaces of this type exist in alberta at the cardium viking and bad heart horizons and in new mexico at the gallup tocito horizon suggesting that sea level changes and shoreface incision may be an alternative explanation for other long narrow offshore bars encased in marine shales

tectonic influence on deposition and erosion in a ramp setting upper cretaceous cardium formation alberta foreland basin this paper presents the results of a combined outcrop and subsurface investigation of the upper cretaceous cardium formation in northwestern alberta and adjacent british columbia canada more than 100 measured core and outcrop sections combined with more than 1100 well logs were used to examine stratigraphic relationships in an area of over 45 000 km2 the cardium consists of stacked regressive transgressive cycles deposited during shoreline progradation along the western margin of a foreland basin occupied by the western interior seaway in general these cycles consist of shoaling upward successions highstand systems tracts composed of shoreface sandstones and conglomerates and heterolithic offshore deposits capped by transgressive erosion surfaces linear incised lowstand coarse grained shoreface deposits are present at some stratigraphic levels a single thick locally more than 20 m thick in the study area nonmarine wedge that overlies shoreface sandstones is interpreted to represent deposition during rising sea level rather than accumulation behind a prograding strandline preservation of the incised lowstand shoreface deposits is associated with topographic breaks in places trends of isopachs facies transitions erosional bevels on transgressive erosion surfaces synsedimentary faults and modern production trends can be directly superimposed and closely correspond to basement structural trends this suggests that basement structures were being remobilized during cardium deposition possibly in response to thrusting in the orogen c belt

new age interpretation of bell creek sandstone powder river basin montana and wyoming abstract published data interpret the oil productive sandstone muddy formation at the bell creek and ranch creek fields t8s r54e and t9s r53e as marine deltaic and barrier bar sandstones that are facies equivalent to or younger than freshwater channel deposits on the east and south core and log studies now show the bell creek sandstone an informal member of the muddy formation to be removed by postdepositional erosion of an incised valley between the fields thus impermeable valley fill shale siltstone and sandstone with thin coals are younger than the adjacent bell creek sandstone the stratigraphic relationships are as follows 1 the bell creek sandstone was deposited as a widespread regressive sandstone genetically related to the underlying marine skull creek shale 2 the younger incised valley between the bell creek and ranch creek fields is approximately 1 mi 3 km wide contains up to 30 ft 9 m of impermeable fill trends north south and probably connects with a major southwest trending valley 8 mi 26 km to the south rocky point field area and 3 valley fill forms the seal along the east side of ranch creek and possibly east of bell creek as well isopach thinning of the combined interval of skull creek shale and muddy formation indicates a northeast trending paleostructure that may have controlled facies distribution drainage incisement patterns and fluid migration the new age interpretations can be related to a sea level highstand for deposition of the skull creek and overlying bell creek sandstone erosion of valleys related to a lowstand fill of the valleys during a rising sea level followed by deposition of the marine mowry shale under highstand conditions end of article last page 870

tectono sedimentary control on modern sand deposition on the forebulge of the western taiwan foreland basin abstract whether the formation of the isolated sand body deposition in the forebulge area of a foreland basin system is structure or deposition controlled has puzzled geologists for decades although sand body deposition is generally believed to be indicative of the position of the flexural forebulge in a foreland basin the formation of a modern sand body in the forebulge area is thus examined by multi scale geophysical observations based on combined reflection seismic profiles and compressed high intensity radar pulse chirp profiles across the sand deposition along the forebulge of the western taiwan foreland basin wtfb which is a late miocene present foreland basin in the overfilled stage these profiles suggest that the accumulation of the sand deposits along the forebulge of the wtfb is not directly associated with forebulge faultings the relief map of the forebulge deposit substratum shows a northwestward tilting slope and the isopach of the forebulge sand body indicates that a large part of the sand body accumulated along the axis of the taiwan strait and the subdued forebulge of the wtfb the difference between the prevailing directions of tidal currents between the taiwan strait and the east china sea reflects the probable sedimentary influence of the cratonward migrating fold thrust belt within a foreland shelf we suggest that the formation and distribution of the sand deposits along the forebulge of the wtfb are generally controlled not only by the transverse downslope sedimentation but also longitudinal hydrodynamic processes at distal parts of the foreland basin our explanation provides a plausible tectono sedimentary cause of the sand body deposition in the forebulge area in an overfilled foreland basin the sedimentary dynamics of the sand body in the taiwan strait may be applicable for understanding the formation of isolated sand bodies in the distal part of the cretaceous western interior foreland basin