eustatic sea level record for the cenomanian late cretaceous extension to the western interior basin usa a combination of biostratigraphic markers ammonites inoceramid bivalves and carbon isotope excursions is employed to establish a high resolution correlation between the middle to late cenomanian successions of the western interior basin usa and the anglo paris basin southern uk sequences identified from sedimentologic criteria in the pueblo succession and elsewhere in the western interior basin are shown to coincide precisely with globally recognized sea level events and were therefore under eustatic control this evidence refutes arguments that cenomanian sequences in the western interior basin were formed by local tectonic events the interaction of longer term tectonic movements and more rapid eustatic change may have simply enhanced the amount of erosion associated with sequence boundaries a crossplot of radiometric ages derived from north american bentonites against an orbitally tuned time scale developed in the anglo paris basin provides support for the argument that the sequences were controlled by the 405 k y long eccentricity cycle

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

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

discontinuity surfaces clinoforms and facies architecture in a wave dominated shoreface shelf parasequence abstract detailed outcrop analysis of a wave dominated shoreface shelf parasequence exposed in the book cliffs utah reveals minor stratigraphic discontinuities which define clinoforms two types of discontinuity are recognized each with a distinctive lithologic character and geometry nondepositional discontinuities are marked by an abrupt decrease in the thickness and amalgamation of storm generated event beds and are interpreted to record hiatuses in sedimentation these discontinuities define clinoforms with a concave upward geometry that dip gently 0 02 0 58 over distances of 800 6000 m down depositional dip erosional discontinuities are marked by an abrupt increase in event bed amalgamation grain size and sand content and are interpreted as enhanced storm wave scours these discontinuities define more steeply dipping 0 22 0 95 concave upward clinoforms that extend over 100 1600 m down depositional dip and 500 1500 m along depositional strike the distribution and amalgamation of minor stratigraphic discontinuities defines linear zones of distinctive facies architecture that are oriented parallel to the paleoshoreline trend using the simple assumption that the shoreface shelf equilibrium profile remained approximately constant for each type of discontinuity throughout shoreface migration the bruun rule intra parasequence facies architecture can be speculatively interpreted in terms of shoreline trajectory which reflects the balance between sediment supply and accommodation the resulting interpretations support the notion that shoreline trajectory exerts a strong control on intra parasequence facies architecture and preservation of the shoreface shelf profile

an example of alternative correlation techniques in a low accommodation setting nonmarine hydrocarbon system the lower cretaceous mannville basal quartz succession of southern alberta chemostratigraphy and heavy mineral techniques have been applied to the lower cretaceous basal quartz in the western canada sedimentary basin the aim of the study is to demonstrate that these two techniques can be used to help understand the complex stratigraphy of reservoirs deposited in low accommodation fluvial settings the basal quartz is an ideal unit to demonstrate their applicability in stratigraphic studies of hydrocarbon reservoirs because extensive mapping and petrographic studies have enabled the establishment of a rigorous stratigraphic framework despite its complexity resulting from deposition in a low accommodation fluvial setting the three component units analyzed in the basal quartz horsefly unit bantry alderson taber bat unit and ellerslie unit each have unique geochemical and heavy mineral characteristics chemostratigraphic analysis shows that silty claystones from the horsefly bat and ellerslie units have distinctly different geochemistry from one another with the variations being caused by changes in clay mineralogy and other components such as feldspar apatite and zircon the geochemistry also suggests periodic volcanogenic input influenced the silty claystones of the basal quartz heavy mineral analysis shows that sandstones from the three units can be distinguished on the basis of ratio parameters such as apatite tourmaline rutile zircon and zircon tourmaline which are controlled by differences in provenance and intensity of weathering during transport

discriminating stacked distributary channel from palaeovalley fill sand bodies in foreland basin settings abstract stacked fluvial distributary channel deposits and palaeovalley fills can form major multi storey sand bodies with similar thicknesses and with lateral extents often greater than a single exposure consequently they can be difficult to tell apart from one another using outcrop data this study addresses this problem by quantitatively analysing the architecture of five stacked fluvial distributary channel deposits and two palaeovalley fills from the pennsylvanian pikeville and hyden formations of the central appalachian basin usa the a priori interpretation of the sand bodies as stacked distributary channels and palaeovalley fills is possible because a robust in place coal seam correlation framework allows for the recognition of different basin scale architectures for each type aspect ratios 1000 and a regional basinward facies shift at the bases of palaeovalley fills sand body thickness storey thickness position and length of storey contacts within the sand body are similar in both types however they can be distinguished by different up system to down system changes in their respective architectures stacked distributary channel sand bodies thin down system display a decrease in storey thickness an increase in the mean position of storey heights in the sand body and a decrease in the length of storey contacts these trends are the result of down system decrease in channel size and confinement associated with radially distributive fluvial systems palaeovalley fill sand bodies thicken down system display an increase in storey thickness a decrease in the mean position of storey heights and a decrease in the length of storey contacts the increase in sand body and storey thickness are the result of down system increases in original channel size consistent with trunk axial fluvial systems fed by tributaries that predominate during valley formation the down system increase in amalgamation reflects a down system decrease in accommodation from the higher subsidence rate active margin of the basin and is therefore not necessarily characteristic of palaeovalley fill architectures in all basin settings this study emphasises the requirement for detailed correlation work and quantitative analysis of external and internal architectures before the interpretation of sand bodies as stacked distributary channels or palaeovalley fills

intra shoreface erosion in response to rapid sea level fall depositional record of a tectonically uplifted strand plain pacific coast of japan this study documents lowering of the surf zone i e the upper shoreface leading to intra shoreface erosion following two rapid relative sea level falls along a tectonically uplifted coast during the holocene and the characteristics of the resultant prograding shoreface deposits these findings are based on high resolution analysis and radiocarbon dating of three new drill cores obtained from the kujukuri strand plain pacific coast of eastern japan combined with previously published borehole data and information on modern shoreline profile adjustments a shallowing upward sandy succession composed of lower and upper shoreface facies foreshore and backshore facies was recognized in the drill cores two rapid falls in relative sea level at 2ae 3t o 2ae6 and 1ae 8t o 2ae0 ka are recorded by downstepping of the base of the foreshore facies and farther seawards by the lowering of an erosional boundary between the upper and lower shoreface facies superimposed bed profiles of an adjacent modern beach define an envelope the base of which reflects shore normal migration of longshore bars and troughs the base of the envelope represents an erosional surface that divides the surface mobile layer above from preserved deposits beneath the surface is concave upwards and steeper than the mean beach profile and exhibits a flat platform approximately at the lower limit of the upper shoreface equating to the storm surf zone the seaward transition of this surface rather than the mean equilibrium profile controls the metre scale to decimetre scale internal structure of the kujukuri shoreface deposits depositional models for sea level fall based on an exponential equilibrium profile do not adequately account for the presence and migration of longshore bars and troughs

signatures of climate vs sea level change within incised valley fill successions quaternary examples from the texas gulf coast abstract the passive margin texas gulf of mexico coastal plain consists of coalescing late pleistocene to holocene alluvial deltaic plains constructed by a series of medium to large fluvial systems alluvial deltaic plains consist of the pleistocene beaumont formation and post beaumont coastal plain incised valleys a variety of mapping outcrop core and geochronological data from the extrabasinal colorado river and the basin fringe trinity river show that beaumont and post beaumont strata consist of a series of coastal plain incised valley fills that represent 100 kyr climatic and glacio eustatic cycles valley fills contain a complex alluvial architecture falling stage to lowstand systems tracts consist of multiple laterally amalgamated sandy channelbelts that reflect deposition within a valley that was incised below highstand alluvial plains and extended across a subaerially exposed shelf the lower boundary to falling stage and lowstand units comprises a composite valley fill unconformity that is time transgressive in both cross and down valley directions coastal plain incised valleys began to fill with transgression and highstand and landward translation of the shoreline paleosols that define the top of falling stage and lowstand channelbelts were progressively onlapped and buried by heterolithic sandy channelbelt sandy and silty crevasse channel and splay and muddy floodbasin strata transgressive to highstand facies scale architecture reflects changes through time in dominant styles of avulsion and follows a predictable succession through different stages of valley filling complete valley filling promoted avulsion and the large scale relocation of valley axes before the next sea level fall such that successive 100 kyr valley fills show a distributary pattern basic elements within coastal plain valleys can be correlated with the record offshore where cross shelf valleys have been described from seismic data falling stage to lowstand channelbelts within coastal plain valleys were feeder systems for shelf phase and shelf margin deltas respectively and demonstrate that falling stage fluvial deposits are important valley fill components signatures of both upstream climate change vs downstream sea level controls are therefore interpreted to be present within incised valley fills signatures of climate change consist of the downstream continuity of major stratigraphic units and component facies which extends from the mixed bedrock alluvial valley of the eroding continental interior to the distal reaches wherever that may be at the time this continuity suggests the development of stratigraphic units and facies is strongly coupled to upstream controls on sediment supply and climate conditions within hinterland source regions signatures of sea level change are critical as well sea level fall below the elevation of highstand depositional shoreline breaks results in channel incision and extension across the newly emergent shelf which in turn results in partitioning of the 100 kyr coastal plain valleys moreover deposits and key surfaces can be traced from continental interiors to the coastal plain but there are downstream changes in geometric relations that correspond to the transition between the mixed bedrock alluvial valley and the coastal plain incised valley channel incision and extension during sea level fall and lowstand with channel shortening and delta backstepping during transgression controls the architecture of coastal plain and cross shelf incised valley fills

ancient shelf ridges a potentially significant component of the transgressive systems tract case study from offshore northwest java detailed stratigraphic evaluation of three dimensional 3 d seis mic volumes calibrated with well log and core data from the mio cene section of the offshore northwest java shelf reveals the exten sive presence of preserved shelf ridge deposits these features are long linear bodies ranging from 0 3 to 2 0 km wide more than 20 km long and up to 17 m high on close inspection these features appear to be asymmetric characteristically sharp edged and thicker on one side and gradually thinning with an irregular edge on the other side possible sand waves smaller in scale are observed super imposed on these ridges and oriented oblique to the long axes of the ridges the observed shelf ridge deposits tend to be sand prone and overlie ravinement surfaces the ridges appear to be oriented parallel with the axes of broad paleoembayments associated with the structural fabric of the basin in addition to shelf ridges shelf ribbons possibly less than 5 m thick and less than 100 m wide are also imaged sand ridges are common on modern shelves but significantly less commonly recognized in the subsurface or in outcrop the features observed here represent examples of preserved ancient shelf ridges these ridges are thought to have formed as a result of erosion and subsequent reworking of sand prone deltaic and or coastal plain deposits by shelf tidal currents which became active immediately after shoreline transgression these deposits appear to have migrated across the ancient sea floor and represent an important component of the transgressive systems tract these transgressive systems tract deposits have significant exploration potential because they are commonly sand prone and tend to be encased in shelf mudstone seal facies depending on the degree to which sand is present in interridge locations these linear sand bodies can comprise potential stratigraphic traps begin page 76

palaeoenvironments palaeogeography and physiography of a large shallow muddy ramp late cenomanian turonian kaskapau formation western canada foreland basin the kaskapau formation spans late cenomanian to middle turonian time and was deposited on a low gradient shallow storm dominated muddy ramp dense well log control coupled with exposure on both proximal and distal margins of the basin allows mapping of sedimentary facies over about 35 000 km2 the studied portion of the kaskapau formation is a mudstone dominated wedge that thins from 700 m in the proximal foredeep to 50 m near the forebulge about 300 km distant regional flooding surfaces permit mapping of 28 allomembers each of which represent an average of ca 125 kyr more than 200 km from shore calcareous silty claystone predominates whereas 100 to 200 km offshore mudstone and siltstone predominate from about 30 to 100 km offshore centimetre bedded very fine sandstone and mudstone record along shelf sse directed storm generated geostrophic flows five to thirty kilometres from shore decimetre bedded hummocky cross stratified fine sandstone and mudstone record strongly oscillatory wave dominated flows whereas some gutter casts indicate shore oblique apparently mostly unidirectional geostrophic flows nearshore facies are dominated by swaley cross stratified or intensely bioturbated clean fine sandstone interpreted as recording respectively areas strongly and weakly affected by discharge from distributary mouths shoreface sandstones grade locally into river mouth conglomerates and sandstones including conglomerate channel fills up to 15 m thick locally brackish lagoonal shelly mudstones are present on the extreme western margin of the basin there is no evidence for clinoform stratification which indicates that the kaskapau sea floor had extremely low relief lacked a shelf slope break and was probably nowhere more than a few tens of metres deep the absence of clinoforms probably indicates a long term balance between rates of accommodation and sediment supply mud is interpreted to have been transported 250 km offshore in a sea bed nepheloid layer repeatedly re suspended by storms fine grained sediment accumulated up to a mud accommodation envelope perhaps only 20 to 40 m deep continuous re working of the sea floor by storms ensured that excess sediment was redistributed away from areas that had filled to the accommodation envelope being deposited in areas of higher accommodation further down the transport path the facies distributions and stratal geometry of the kaskapau shelf strongly suggest that sedimentary facies especially grain size were related to distance from shore not to water depth as a result the 100 to 300 m depth interpreted from calcareous claystone facies for the more central parts of the interior seaway might be a significant overestimate

impact of deltaic clinothems on reservoir performance dynamic studies of reservoir analogs from the ferron sandstone member and panther tongue utah subsurface reservoir models are typically limited by a lack of spatially accurate geometric data on bedform architecture and geometry these factors are key controls on fluid flow outcrop analogs have long been used as a source of such data but the capture of sufficiently precise outcrop data is a challenge the study presented in this article used highly accurate geometrical digital geological outcrop data collected using ground based laser scanning light detection and ranging lidar to build and test three dimensional geocellular models of deltaic reservoir analogs two well exposed ancient river dominated delta systems the panther tongue and the ferron sandstone member which both crop out in central utah were digitally mapped to precisely recreate their clinothem and clinoform geometries in geocellular reservoir modeling software such clinoforms are commonly draped with low permeability mudstones that produce reservoir heterogeneity by subdividing the deltaic sand body into a series of dipping sandstone beds clinothems a key aspect of the modeling was to accurately capture these geometries and their effect on simulated fluid flow portions of the two deltaic systems were dynamically analyzed in a reservoir modeling software by simulating production in 41 models these models tested a range of mudstone barrier continuities and permeabilities results quantify how the continuation of the heterogeneities governed the production rate and recovery factor in the panther tongue models mudstone permeability values were more important in the ferron sandstone models with steeper dipping and closer spaced clinothems although production was still influenced by the continuation of the heterogeneities

integrating sandstone petrology and nonmarine sequence stratigraphy application to the late cretaceous fluvial systems of southwestern utah u s a abstract petrographic and dispersal data are essential to correct interpretation of mechanisms that create continental sequence stratigraphic architecture a case study from southern utah demonstrates that upper cretaceous upper santonian campanian alluvial successions in the southernmost part of the cordilleran foreland basin were deposited by fluvial systems of contrasting drainage directions and provenance and suggests that different mechanisms governed their sequence architecture most of the rivers flowed northeast subparallel to the basin foredeep less common fluvial systems flowed to the east southeast the fluvial sandstones fall naturally into four petrofacies 1 quartzofeldspatholithic mean qt61f19l20 2 feldspatholithic qt29f19l52 3 quartzolithic qt75f6l20 and 4 quartzose qt99f1l1 petrofacies 1 and 2 were derived from mixed supracrustal and basement sources to the southwest and south respectively whereas petrofacies 3 and 4 were derived from uplifted thrust sheets of the sevier orogenic belt to the southwest and west respectively only the east southeast flowing rivers transported the quartzose petrofacies the fluvial strata which include the uppermost straight cliffs wahweap and kaiparowits formations form two large scale stratigraphic successions typically interpreted as continental stratigraphic sequences hundreds of meters thick each succession begins with an amalgamated braided fluvial deposit grades to mudstone rich strata with low sandstone body connectivity and culminates in highly connected sandstone bodies with multistory stacking the basal amalgamated deposits of each succession are architecturally similar but their compositional and dispersal characteristics are different quartzofeldspatholithic quartzolithic and quartzose sandstones above the lower base level shift are variable but generally similar in compositional and dispersal characteristics to both underlying and overlying strata a phenomenon termed here congruence in contrast quartzose amalgamated fluvial sandstone above the upper base level shift differs sharply in composition and dispersal direction from underlying and overlying lithic rich strata the foredeep axis controlled the progradation direction of the congruent shift which was likely driven by climatically induced sediment influx a eustatic fall or both in the case of the incongruent shift increased sediment supply permitted the rivers to cross the foredeep temporal association of the upper amalgamated deposit with active structures in the thrust belt and foreland basin indicates that syntectonic thrust uplift not isostatic uplift or climate caused the influx of quartz

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

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

valleys that never were time surfaces versus stratigraphic surfaces discussion strong and paola 2008 have written a seminal paper rich with insights that contribute to our understanding of the origin and time significance of sequence boundaries these insights derive from the animated proxy for natural depositional systems offered by the experimental flume approach their perspective differs from the finished product vantage provided by the rock and sediment record and the work in progress view granted by the recent stratigraphy of extant depositional systems still these rock and recent perspectives provide critical angles to the full view of sequences and through their differing datal slant have already rendered comparatively supportable versions of the strong and paola 2008 conclusions their paper does not well consider the testimony of these other witnesses this discussion provides a few examples where conclusions of strong and paola have more converged with existing field insights and further comments on areas where the flume has enhanced the recent and rock perspectives a central point of strong and paola s paper is that sequence boundaries form as composite surfaces that are never synchronously exposed but instead are cut and reshaped diachronously by sequential scour and burial beneath locally active topography of a larger and laterally migrating fluvial system this process is observed

a real time tephra fallout rate model by a small compact x band multi parameter radar abstract real time monitoring of volcanic tephra fallout rate is an important factor to predict ash plume dispersion and to mitigate risk to air traffic ground based weather radar has been one of the fundamental instruments to detect the plume and derive eruptive source parameters such as the tephra fallout rate the current work presents the use of two small and compact x band multi parameter x mp radars for a new tephra fallout rate model development and the technical aspects of the system in sinabung and merapi volcanoes the new model estimates the tephra fallout rate using two radar parameters the specific differential phase shift parameter and the reflectivity intensity factor total cumulated mass estimated from the radar based tephra fallout rate model from the radar is compared with the plume height model and an empirical radar based model a volcanic eruptive index vei 2 of sinabung generated a plume exceeding 15 km resulting in a maximum tephra fallout rate of 0 58 kg m 2 h 1 and a total tephra mass of 51 106 kg the vei 1 of sinabung caused a plume height of 2 5 km resulting in a maximum tephra fallout rate of 0 3 kg m 2 h 1 and a total cumulated tephra of 9 106 kg in the last case a vei 1 eruption of mt merapi produces a 6 km plume resulting in a maximum tephra fallout rate of 0 28 kg m 2 h 1 and a total cumulated tephra of 35 106 kg the sector range height indicator scan mode strategy in the vei 2 eruption of mt sinabung ran at six degrees azimuth angles capturing only a partial volume of the plume thus the total mass was only 22 of the result from the empirical plume height model even though the plume height was assumed to be equally the same with the maximum height scanned of radar at 7 km in contrast the volumetric scan by a plan position indicator strategy gave a total cumulated tephra mass that matches better to the result of the empirical plume height model at 65 92 based on these results and the ability of the x mp radar to capture the volcanic plume at the same reported onset time we can confirm the importance of an x mp radar for real time tephra fallout monitoring during an eruption

sedimentary response to late quaternary sea level changes in the romagna coastal plain northern italy data from 17 continuously cored boreholes 40 170 m deep reveal the subsurface stratigraphy of the romagna coastal plain sedimentological and microfaunal data allow the distinction of eight facies associations of late pleistocene holocene age including 18 lithofacies and 16 faunal associations ten 14c dates provide the basis to establish a sequence stratigraphic framework for the succession corresponding to the upper part 35 ky bp of the last glacio eustatic cycle the eight facies associations can be grouped into lowstand transgressive and highstand systems tracts the upper part of the lowstand systems tract consists of alluvial plain deposits these accumulated during the late pleistocene when the shoreline was 250 km south of its present day position a pronounced stratigraphic hiatus between 25 and 8 8 ky bp is invariably recorded at the upper boundary transgressive surface of these pleistocene indurated and locally pedogenized alluvial deposits the succeeding postglacial history is represented by a well developed transgressive regressive cycle transgressive deposits interpreted to reflect the rapid landward migration of a barrier lagoon system include two wedge shaped paralic and marine units these thicken in opposite directions and are separated by a ravinement surface above the transgressive deposits the maximum flooding surface mfs marks the change from a transgressive barrier lagoon complex to a prograding wave dominated delta system early po delta the mfs can be traced landwards where it constitutes the base of lagoonal deposits an aggradational to progradational stacking pattern of upper delta plain marsh lower delta plain lagoon bay and delta front beach ridge deposits reflects the progressive increase in the sediment supply accommodation ratio during the following highstand the alluvial deposits capping the sequence accumulated by the 13th century ad in response to an avulsion event that caused abandonment of the former po delta lobe and the northward migration of the po river towards its present position

sequence stratigraphic significance of sharp based lowstand shoreface deposits kenilworth member book cliffs utah the kenilworth member of the blackhawk formation upper cretaceous campanian is nearly continuously exposed from price to hatch mesa in the book cliffs utah five main depositional environments are recognized coastal plain foreshore and upper shoreface lower shoreface inner shelf and incised valley fill deposits the shelf to shoreface deposits combine to form nine coarsening upward wave to storm dominated parasequences that are 7 32 m thick and that split basinward into smaller coarsening upward successions or bedsets that are 2 18 m thick a maximum of four bedsets occurs within an individual parasequence bedset bounding surfaces are occasionally marked by thoroughly bioturbated iron rich carbonate cemented sandstones within the parasequences in the subsu face similar bedset bounding surfaces may act as permeability barriers or baffles leading to reservoir compartmentalization parasequences 1 6 form an aggradational to progradational parasequence set of the highstand systems tract parasequences 7 and 8 occur as sharp based lowstand shoreface deposits at price river and battleship butte forming the attached lowstand systems tract and parasequence 9 forms the transgressive systems tract the base of each lowstand shoreface is marked by an organic rich lag deposit that consists of granules coarse grained sandstone wood fragments coal intraclasts and shell debris the sharp base basal lag deposit and basinward shift in facies delineate a sequence boundary at the base of each lowstand shoreface deposit the presence of two sharp based lowstand shorefaces suggests that the kenilworth lowstand was punctuated by a stillstand the sharp based lowstand shoref ce sandstones form the bulk of the attached lowstand systems tract and represent one end member in a continuum of lowstand deposits the other end member is the detached lowstand systems tract revising existing sequence stratigraphic models to include both types of lowstand systems tracts is a first step toward improving the accuracy of these models which are often used as prospecting tools in lowstand deltaic environments

use of alloformations for definition of holocene meander belts in the middle amite river southeastern louisiana geomorphological studies in drainage basins of the northern gulf of mexico coastal plain have indicated similarities in flood plain character and comparable influences on basin evolution alluvial morphology and stratigraphy can be linked to flood plain evolution through the use of alloformations unconformity bounded stratigraphic units this procedure extends classical terrace mapping concepts to conform with formally defined stratigraphic procedures a meander belt segment of the middle amite river valley in southeastern louisiana was selected to test the applicability of alloformation mapping in part of a regional scale 5 000 km 2 drainage basin three alloformations identified as magnolia bridge mag denham springs ds and watson wat can be differentiated by unconformable boundaries landscape morphology and relative pedogenic development the valley fill consists of a lower sandy and upper silty facies preserved deposits consist of channel lag point bar and scroll bar channel fill and overbank sequences lithofacies and sedimentary environments are dependent on fluvial process and a suite of meander belt environments can be identified within each alloformation surface horizons of alluvial soils are all similar ochric epipedons but subsoil horizons are chiefly stratified parent material on the mag entisols cambic horizons on the ds inceptisols and minimally developed argillic horizons on the wat alfisols allostratigraphy provides an objective method for definition of geologic units that contain genetically related but heterogeneous sedimentary deposits alluvial sediments are differentiated in a manner that successfully integrates geomorphic sedimentologic and pedologic data into significant stratigraphic models this approach is applicable to a wide variety of quaternary settings where prior stratigraphic techniques have resulted in ambiguity

estimation of fe3 from electron microprobe analyses observations on calcic amphibole and chlorite metabasites and metagreywackes from the pelona and rand schists of southern california were analysed using three different electron microprobes for all three instruments the estimated fe3 contents of calcic amphibole chlorite and epidote are positively correlated for some samples there is an additional correlation between high estimated fe3 and the presence of magnetite these results imply that microprobe analyses can be used to discern relative differences in fe3 however microprobe data and calculations on the sensitivity of the correction procedures to systematic analytical errors indicate that estimated values of fe3 are not significant in an absolute sense thus estimates of fe3 are meaningful when comparing samples analysed with a single microprobe but must be used with caution when comparing analyses obtained on more than one probe

practical problems in the application of the sequence stratigraphic method and key surfaces integrating observations from ancient fluvial deltaic wedges with quaternary and modelling studies sequence stratigraphy solved the basic problem that genetically related but different lithofacies were routinely assigned to different lithostratigraphic units defined by arbitrary vertical and horizontal cutoffs stratigraphically important stratal relationships and especially stratal terminations for example lapout can be observed in seismic data and can be documented in continuous outcrops such as in the deserts of the western interior of north america and in closely spaced well log data sets in sparse data sets interpolation of lapout patterns introduces uncertainty in correlation and designation of sequences and systems tracts and their associated surfaces diachroneity of fluvial terrace deposits is documented using detailed facies architectural studies and calls into question the assumed chronostratigraphic significance of many so called sequence boundaries identified in the rocks of the cretaceous interior seaway of north america sequence boundaries formed during prolonged sea level falls may be less chronostratigraphically significant than transgressive surfaces formed during rapid rises as a consequence flooding surfaces are theoretically more significant and also have greater utility as allostratigraphic boundaries although they may also exhibit diachroneity tectonic unconformities produce differential lithospheric deformation which results in angular unconformities although the angle of discordance may be very small in the cretaceous interior seaway of north america such unconformities may be expressed by marine erosion in distal basin settings regional isochronous bentonites provide useful marker beds that clearly illustrate angular discordance in the fluvial realm such tectonic discontinuities may be indicated by changes in palaeocurrent orientations as well as by provenance changes although sequence stratigraphy provides a powerful methodology and theoretical framework for correlating and understanding the evolution of stratigraphic successions in the context of changing accommodation allostratigraphy remains the only accepted scheme for the formal naming of stratigraphic units based on bounding discontinuities whatever type of sequence stratigraphy or allostratigraphy is preferred in all cases it is key to recognize that sequence stratigraphy at its heart is the re ordering correlation and sometimes renaming of stratigraphic units on the basis of bounding discontinuities and their correlative surfaces as opposed to the arbitrary lithofacies oriented approach using broad facies zones for example shazam lines or arbitrary cutoffs such as is used in traditional lithostratigraphy

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

importance of high frequency tectonic sequences during greenhouse times of earth history the relative importance of tectonism in the stratigraphic record should be more clearly expressed during greenhouse times of earth history due to the lack of overmasking effects of high frequency and high amplitude sea level changes typical for icehouse periods establishment of the importance of tectonism especially at temporal scales comparable to durations of typical transgressive regressive cycles has been plagued by poor temporal resolution our outcrop and subsurface based study of a cenomanian shallow marine siliciclastic interval constrained by bentonite based geochronology and detailed biostratigraphy examines this problem in a 2 2 m y interval we identified four tectonically driven erosional surfaces that dominate preserved stratigraphy biostratigraphic correlation to a sea level curve for the cenomanian where coeval high frequency lowamplitude eustatic cyclicity has been demonstrated allows the first direct comparison of the effects of eustasy and tectonics at temporal scales of hundreds of thousands of years during a global greenhouse time we suggest that minor tectonic pulses locally overshadow the effects of eustasy and exert the dominant control over preserved stratigraphy while subtle tectonic control on sedimentation has been documented throughout the cretaceous western interior the results of this study suggest that much of that deformation occurred at sub million year frequencies and at time scales comparable to eustatic transgressiveregressive cycles

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

anatomy of shelf deltas at the edge of a prograding eocene shelf margin spitsbergen although shelf edge deltas are well imaged seismic features of holocene and pleistocene shelf margins documented outcrop analogues of these important sand prone reservoirs are rare the facies and stratigraphic architecture of an outcropping shelf edge delta system in the eocene battfjellet formation spitsbergen is presented here as well as the implications of this delta system for the generation of sand prone shelf margin clinoforms the shelf edge deltas of the battfjellet formation on litledalsfjellet and hogsnyta produced a 3 5 15 km shelf edge attached slope apron 70 m of sandstones proximally tapering to zero on the lower slope the slope apron consists of distributary channel and mouth bar deposits in its shelf edge reaches passing downslope to slope channels chutes that fed turbiditic lobes and spillover sheets in the transgressive phase of the slope apron estuaries developed at the shelf edge and these also produced minor lobes on the slope the short headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf and the shelf edge position of the discharging deltas made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin the abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane parallel laminae within turbidite beds in the slope channels and thick spillover lobes with repetitive alternations of massive and flatlaminated intervals the examined shelf edge to slope system now preserved mainly below the shelf break and dominated by sediment gravity flow deposits has a threefold stratigraphic architecture a lower progradational part in which the clinoforms have a slight downward directed trajectory a thin aggradational zone and an upper part in which clinoforms backstep up onto the shelf edge a greatly increased density of erosional channels and chutes marks the regressive to transgressive turnaround within the slope apron and this zone becomes an angular unconformity up near the shelf edge this unconformity with both subaerial and subaqueous components is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level the studied shelf margin clinoforms accreted mostly during falling stage sea level below the shelf edge but the outer shelf later became estuarine as sea level became re established above the shelf edge

formation of deep incisions into tide dominated river deltas implications for the stratigraphy of the sego sandstone book cliffs utah u s a abstract the upper cretaceous sego member of the mancos shale in east central utah is composed of tidally deposited sandstones interbedded with intervals containing marine shales and thin wave deposited sandstones the tidal sandstones have been interpreted to comprise multiple amalgamated estuarine valley fills above a major sequence boundary that is incised into distal marine deposits of the underlying buck tongue shale according to this interpretation the deposits constitute the base of a thick transgressive succession within the sevier foreland clastic wedge alternatively lower sego sandstones have recently been interpreted by the authors to be tide dominated river delta deposits in an overall regressive interval of the foreland succession a cross section showing facies variations and stratigraphic surfaces within the lower sego member along 100 kilometers of the eastern book cliffs is used in this paper to refine depositional and sequence stratigraphic interpretations of these tidal deposits particularly the origin of deep incisions within the sego sandstones a strike oriented section of the lower sego member reveals tidal sandstone lenses 40 50 kilometers wide and tens of meters thick separated laterally by areas tens of kilometers wide that have no tidal sandstones facies variations within the tidal sandstones reflect depositional processes on tide dominated deltas that prograded obliquely into the shallow intracratonic western interior seaway of north america two major episodes of delta progradation and subsequent transgressions are interpreted to have formed tidal sandstone layers within the lower sego sandstone thinner tidal sandstone layers of more local extent are interpreted to reflect changes in tidal current strength but not necessarily shifts in shoreline position or major changes in water depth multiple origins are suggested for incised erosion surfaces within the lower sego sandstones firstly the tide dominated deltaic sandstones are floored by laterally discontinuous erosion surfaces these basal surfaces marking abrupt vertical changes in depositional process and coarsening of grain size are interpreted to record tidal scouring of the sea floor during shoreline progradation secondly sharp based upward coarsening deltaic sandstones are cut by numerous deep incisions with tens of meters of relief and locally they are entirely removed by erosion some of this deep erosion within the lower sego sandstone may reflect the upstream avulsion of incised distributaries during forced regression of deltas into the basin whereas others may have formed by tidal erosion of abandoned distributaries during more gradual progradation and subsequent retrogradation of deltas highly variable facies trends within incision fills are related to pronounced changes in sediment supply to different distributaries on the delta to differences between incisions cut during delta regression versus those cut during the start of transgression and to varying distances from delta axes when the entire coast was transgressed the influence of tides waned and wave generated currents ravined delta tops depositional interpretations of the sego member indicate that the buck tongue to neslen interval lies in a broadly regressive part of the foreland basin fill

fluvial response in a sequence stratigraphic framework example from the montserrat fan delta spain abstract exceptional exposure of the montserrat fan delta system eocene in northeastern spain provides an excellent framework to evaluate the alluvial response to sea level changes over two different time scales the alluvial system contains multiple fifth order cycles 104 yr and eight fourth order cycles 105 yr fifth order cycles are characterized by long distance shoreline migrations and occasionally by incised basal scour surfaces but not by changes in fluvial style lithofacies or channel stacking pattern fourth order cycles are composed of stacked fifth order cycles and have non erosional basal boundaries vertical sedimentation rates and channel stacking patterns change significantly within fourth order cycles the lower parts of these cycles referred to as the transgressive facies tract show overall shoreline transgression and associated alluvial deposits contain abundant overbank materials with isolated ribbon channel bodies during this time the supply of terrigenous material to the shoreline was reduced as indicated by sediment starvation offshore the overlying middle part of fourth order cycles the lower regressive facies tract differs only in that shoreline is overall regressive and there is increased clastic supply to the offshore in the upper part of hese cycles the upper regressive facies tract channel stacking geometries become denser and more sheet like shoreline regression is more pronounced and vertical aggradation rates are inferred to be reduced changes in the alluvial system during fourth order cycles are most pronounced adjacent to shoreline and die away upstream over just a few kilometers indicating that the base level signal decays away over the distance of a few backwater lengths channel flow depth slope higher frequency fifth order changes in relative sea level appear to produce the largest shoreline migrations but lower frequency fourth order changes have more impact on the channel stacking architecture of the alluvial systems observed changes in alluvial stacking pattern may be most commonly found in tectonically active rapidly subsiding foreland basins because of their back tilted geometry we propose a model in which sediment is trapped in the proximal basin during times of rapid tectonic subsidence and attendant relative sea level rise progradation occurs as erosion rates in the mountain belt increase and rates of subsidence and relative sea level rise diminish changes in alluvial architecture reflect an increase in sediment flux towards the shoreline as less sediment is trapped upstream hence changes in channel stacking pattern coincident with transgressions and regressions likely reflect the interplay between subsidence and sediment supply in the proximal part of the basin and are not necessari y driven by eustatic sea level changes

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

temporal significance of sequence boundaries abstract this paper analyses the temporal significance of stratigraphic surfaces bounding the marine portions of the depositional sequence genetic stratigraphic sequence and transgressive regressive sequence these bounding surfaces known as the correlative conformity c c maximum flooding surface mfs and conformable transgressive surface cts respectively may either be defined on the basis of stratal stacking patterns which we call type a surfaces or on the basis of water depth changes and relative sea level changes which we call type b surfaces the type a mfs and cts are time lines in a depositional dip section corresponding to the turnaround points from shoreline transgression to regression and vice versa they separate prograding coarsening upward from retrograding fining upward geometries with a timing determined by the interplay between the rates of sedimentation and relative sea level rise in the shoreline area the timing of type a mfs and cts is not affected by the offshore variations in sedimentation and subsidence rates but it is only controlled by the shoreline movements and the associated facies shifts the type a c c separates rapidly prograding and offlapping forced regressive strata from the overlying lower rate prograding and aggrading normal regressive strata this surface is diachronous younger basinward with the rate of offshore sediment transport the timing of the type a c c in the shoreline area corresponds to the end of relative sea level fall but it develops under relative sea level rise conditions offshore the timing of the type b mfs and cts depends on the offshore variations in the sedimentation and subsidence rates these surfaces defined on the basis of bathymetric changes become younger and older seaward respectively tending to merge together offshore the type b c c marks the end of relative sea level fall in any point along a depositional dip section it is diachronous older basinward as its timing depends on the offshore variations in subsidence rates the diachroneity of type b surfaces reaches a quarter of the period of the highest frequency variable whichever that is among the eustasy tectonics or sedimentation controls types a and b surfaces merge together in the shoreline area but they become temporally divergent offshore deepening upward and shallowing upward facies should not be confused with transgressive and regressive systems tracts the latter are strictly controlled by the shoreline movements which determine the direction of facies shifts and the stratal stacking patterns

sharp based flood dominated mouth bar sands from the burdekin river delta of northeastern australia extending the spectrum of mouth bar facies geometry and stacking patterns abstract distinguishing the deposits of mouth bars from delta distributary channels in the rock record may not be as straightforward as often portrayed because mouth bar deposits can be more variable than usually presumed mouth bars with triangular plan view subaerial geometry are well developed at the mouth of the modern burdekin river of northeastern australia this planform is intermediate between the elongate lozenge shaped mouth bars typical of river dominated deltas and the beach ridge geometries characteristic of wave dominated deltas surface and shallow subsurface bar deposits are predominantly moderately sorted coarse grained sand similar to that of adjacent lower delta plain channel floor sedimentary textures are modified at seaward sides of mouth bars by waves into a foreshore of well sorted fine to medium grained sand and mouth bar sands pass distally and laterally into more mud dominated lithologies the holocene section beneath the lower delta plain is dominated by 5 8 m thick sharp based bodies of coarse grained sand texturally indistinguishable from the modern mouth bar with no vertical grain size trend a slight upward fining trend or in a few cases a coarsening upward trend these sand bodies have low angle seaward dipping internal bedding surfaces and are bounded by surfaces of similar attitude the holocene burdekin delta was and is flood dominated rather than strongly wave influenced as proposed previously and prograded by rapid deposition of mouth bars during river floods most of which last for only a few days mouth bar construction takes place over tens of years the variable vertical grain size profiles of mouth bar deposits suggests formation by both aggradation and progradation and this is supported by the cross sectional geometry of mouth bar clinoform sets imaged geophysically once a mouth bar has become emergent and is stabilized by vegetation a new bar is initiated seaward in this way delta lobes are constructed over 100s to 1000s of years before being abandoned following an avulsion of the trunk river channel to another part of the delta caution is needed in the interpretation of ancient shallow water deltaic successions where sharp based fining upward mouth bar deposits may be confused with distributary channel facies

process regime changes across a regressive to transgressive turnaround in a shelf slope basin eocene central basin of spitsbergen abstract the sedimentological architectural and stratigraphic database from one investigated shelf margin clinothem complex in the eocene central basin of spitsbergen suggests that dominating process regimes and facies products may change several times during a sea level cycle even though the basin wide processes are constant continuous mountainside exposures were investigated by a combination of walking out of stratigraphic surfaces and geometrical elements closely spaced detailed vertical sections and tracing on helicopter photo mosaics the clinothem complex represents a regressive to transgressive shoreline complex and consists of five clinothem sets recognized by specific stacking patterns and sedimentary facies the regressive part preserves wave and river dominated deltaic deposits in a progradational to aggradational stacking pattern the delta clinothems consist of tide influenced distributary channels wave and hyperpycnal flow dominated mouth bars that on the shelf sourced turbidite filled slope channels and slope lobes the transgressive part of the clinothem complex preserves strongly tide dominated estuarine deposits underlain by tidal ravinement surfaces that cut down into deposits of wave dominated deltas this change in facies product on the inner shelf from wave to tidal at the regressive to transgressive turnaround was however not a basin wide process change inasmuch as the distributary channels also reflect tidal influence this suggests that tidal currents were present only in areas protected from waves and amplified by the lateral confinement of the estuary there was a process regime change on the middle to outer shelf from wave dominated highstand and falling stage delta complex to river dominated and wave influenced early lowstand delta complex the delta complex prograded across the shelf during highstand and during falling stage the relative sea level fall forced the deltas out to shelf edge the early lowstand delta mouth bars are volumetrically dominated by hyperpycnites indicating dominance of riverine processes the proportion of the hyperpycnal flow deposits decreased during the late lowstand and the delta complex became wave dominated anew the process regime change from wave dominance to fluvial dominance and back to wave dominance is interpreted to have occurred due to the seaward and then landward shift of the feeding river system whereas the tidal effects were dependent on shelter from waves and on the shoreline configuration

evolution of an ancient coastal plain palaeosols interfluves and alluvial architecture in a sequence stratigraphic framework cenomanian dunvegan formation ne british columbia canada to date discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on floodplains has primarily been from a conceptual standpoint few case studies are available against which to test ideas one hundred and thirty metres of non marine strata of the dunvegan formation were examined in 14 closely spaced sections in the canyon of the kiskatinaw river ne british columbia canada this site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments fluvial channels in the kiskatinaw river section are of two types small single storey very fine to fine grained sandstone ribbons with w t ratios 30 are interpreted as the deposits of meandering rivers filling incised valleys interchannel facies include the deposits of crevasse channels and splays lakes floodplains and palaeosols floodplain palaeosols consist of laterally heterogeneous simple palaeosol profiles and pedocomplexes similar to modern entisols inceptisols and hydromorphic soils interfluve sequence bounding palaeosols adjacent to incised valleys are laterally continuous up to 3 m thick and can be reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure colour degree of rooting and 3 micromorphological features such as evidence of bioturbation clay coatings ferruginous features and sphaerosiderite interfluve palaeosols are similar to modern alfisols and ultisols correlation of the local stratigraphic succession with the regional sequence stratigraphic framework based on 2340 well logs and 60 outcrop sections shows that the vertical changes in coastal plain character more coals and lakes vs more pedogenesis can be related to relatively high frequency base level cycles eustatic that are expressed as transgressive regressive marine cycles in downdip areas regional isopach maps show that these cycles were progressively overprinted and modified by an increasing rate of tectonic subsidence in the north and west the character of palaeosols developed on aggrading floodplains primarily reflects local sediment supply and drainage in contrast well developed interfluve palaeosols record pedogenesis during periods of reduced or negative accommodation base level fall vertical changes in floodplain palaeoenvironments and palaeosol types reflect changes in accommodation rate the detailed micromorphological analysis of interfluve palaeosols represents a powerful application of an under used technique for the recognition of key surfaces in the geological record this has broad implications for non marine sequence stratigraphy

sequence stratigraphy of experimental strata under known conditions of differential subsidence and variable base level sequence stratigraphy has been applied from reservoir to continental scales providing a scale independent model for predicting the spatial arrangement of depositional elements we examine experimental strata deposited in the experimental earthscape facility at st anthony falls laboratory focusing on stratigraphic surfaces defined by discordant contact geometries surfaces analogous to those delineated in the original work on seismic sequence stratigraphy in this controlled setting we directly evaluate critical sequence stratigraphic issues such as stratigraphic horizon development and time significance as well as the internal geometry and migration of the bounded strata against the known boundary conditions and depositional history four key stratigraphic disconformities defined by marine downlap marine onlap fluvial erosion and fluvial onlap are mapped and vary greatly in their relative degree of time transgression marine onlap and downlap contacts closely parallel topographic surfaces time surfaces and prior to burial approximate the instantaneous offshore topography these stratal bounding surfaces are also robust stratigraphic signals of relative base level fall and rise respectively marine onlap surfaces are of special interest they tend to be the best preserved discordance where widespread allogenic based onlap surfaces subdivide otherwise amalgamated depositional cycles amidst cryptic stacks of marine foresets however local autogenic based marine onlap discordances are present throughout the fill a critical distinguishing feature of allogenic onlap is the greater lateral persistence of the discordance surfaces defined by subaerial erosional truncation and fluvial onlap do not have geomorphic equivalence because channel processes continually modify the surface as the stratigraphic horizons are forming hence they are strongly time transgressive last the stacking arrangement of the preserved bounded strata is found to be a good time averaged representation of the mass balance history

rates controls and sand body geometries of transgressive regressive cycles cretaceous moosebar and gates formations british columbia the moosebar and gates formations lower cretaceous in northeastern british columbia consist of seven transgressive regressive sequence nonmarine sediments are thickest in the south and pinch out northward the sequences are laterally persistent extending east from the foothills for 240 km 150 mi the orientation of maximum transgressive and regressive limits in five cycles occurs within an east west trending zone 30 40 km 19 25 mi wide a recurring northward bulging sediment depocenter near the alberta british columbia border was fed by a series of stacked northerly flowing rivers the rivers were a major source of sediment for gravel beaches to the north and east isopach maps of marine sandstone and conglomerate show a series of west northwest east southeast o iented sand bodies 60 70 km 37 43 mi wide parallel with the shorelines each coastline prograded northward as a shoreline attached strand plain and a series of arcuate or cuspate deltas gates formation marine nonmarine cyclicity is a series of fourth order cycles superimposed on a major third order cycle the cyclicity and lateral extent of the sequences can be explained as a result of tectonic thrusting and loading superimposed on the trend of the peace river arch the influence of eustatic sea level variations and sedimentologic switching of point sources had minimal effect coastal retreat ranged from 437 to 875 m 1 000 years 1 433 to 2 780 ft 1 000 years coastal progradation ranged from 218 to 437 m 1 000 years 175 to 1 433 ft 1 000 years the duration of several transgressive regressive cycles was 103 000 275 000 years

seismic models of a shelf margin depositional sequence upper san andres formation last chance canyon new mexico abstract the seismic resolution of stratal geometries and facies distributions observed in san andres formation permian outcrops in last chance canyon guadalupe mountains new mexico is studied by seismic modeling of a published detailed stratigraphic cross section the outcrops in last chance canyon are composed of two fourth order depositional sequences an aggrading carbonate bank upper san andres 3 usa3 followed by a strongly progradational offlapping mixed carbonate siliciclastic succession upper san andres 4 usa4 each sequence comprises a number of subsidiary high frequency sequences fifth order two alternative impedance models were used model a in which all facies transitions are reflecting boundaries and model b in which only time significant surfaces act as reflectors and lateral facies transitions are represented by horizontal velocity gradients the vertical incidence modeling technique was used to compute perfectly migrated time and depth sections with different frequencies using a low frequency wavelet 25 hz the sequence boundary separating the two fourth order cycles usa3 and usa4 is poorly imaged instead one is tempted to incorrectly interpret an onlap pattern generated by a high frequency cycle within usa4 as this major sequence boundary in addition the 25 hz runs show toplap and downlap lap out patterns in an overly oblique fashion obscuring true asymptotic stratal relationships both at 35 hz and 50 hz profiles based on model b image the genetic structure of both usa3 and usa4 relatively well at 50 hz model a incorrectly shows a transition from a ramp to a rimmed margin within usa4 the 35 hz models are qualitatively compared with a published exxon production research co seismic line located approximately 50 km along depositional str ke to the northeast model a shows an unexpected good match with the exxon seismic line whereas model b comes much closer to the depositional anatomy observed in outcrop our results show that the resolution of stratal geometries and facies distributions in last chance canyon is strongly related to carbonate sandstone alternations and the way impedance contrasts at carbonate sandstone transitions are represented

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

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

high resolution sequence stratigraphic correlation between shallow marine and terrestrial strata examples from the sunnyside member of the cretaceous blackhawk formation book cliffs eastern utah the sunnyside member of the upper cretaceous blackhawk formation in the book cliffs of eastern utah provides an ideal opportunity to investigate high resolution sequence stratigraphic correlation between shallow marine and terrestrial strata in an area of outstanding outcrop exposure the thick laterally extensive coal seam that caps the sunnyside member is critical for correlating between its shallow marine and terrestrial components petrographic analysis of 281 samples obtained from 7 vertical sections spanning more than 30 km 18 mi of depositional dip enabled us to recognize a series of transgressive regressive coal facies trends in the seam on this basis we were able to identify a high resolution record of accommodation change throughout the deposition of the coal as well as a series of key sequence stratigraphic surfaces the stratigraphic relationships between the coal and the siliciclastic components of the sunnyside member enable us to correlate this record with that identified in the time equivalent shallow marine strata and to demonstrate that the coal spans the formation of two marine parasequences and two high frequency fourth order sequence boundaries this study has important implications for improving the understanding of sequence stratigraphic expression in terrestrial strata and for correlating between marine and terrestrial records of base level change it may also have implications for improving the predictability of vertical and lateral variations in coal composition for mining and coalbed methane projects

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

mechanisms for forming discontinuity surfaces within shoreface shelf parasequences sea level sediment supply or wave regime abstract a 2d process response model was used to evaluate potential mechanisms involved in the formation of small scale stratigraphic variability that is observed within progradational wave dominated shoreface shelf parasequences model experiments which are based on scenarios that consist of a 25 ky progradational phase suggest that discontinuity surfaces form when either sediment supply or sea level fall rapidly or when wave height regime increases over relatively short time periods 102 104 y during coastal progradation in these cases mean deposition rate near the lower shoreface drops which combined with coastal progradation results in a discontinuity surface both observed and simulated discontinuity surfaces form predominantly in lower shoreface deposits and bound meter scale stratigraphic cycles simulations show that wave regime variability affects the shoreface shelf to a much greater depth than minor sea level change therefore facies shifts along wave climate induced bounding surfaces occur over wider reaches of the shoreface shelf system than sea level induced facies shifts high frequency variability in sediment supply rate results in the formation of discontinuity surfaces across which there are no distinct facies shifts

onlap offlap and the origin of unconformity bounded depositional sequences christie blick n 1991 onlap ofttap and the origin of unconformity bounded depositional sequences mar geol 97 35 56 unconformity bounded depositional sequences represent the fundamental building blocks of sedimentary successions they are typically characterized by onlap at the base and by offlap at the top and they tend to be markedly asymmetrical with onlap accounting for a larger part of any cycle of sedimentation than offlap offlap cannot be attributed solely to erosional truncation but instead implies that sequence boundaries develop over a finite interval of time depositional sequences are commonly associated with a cyclic arrangement of facies but transgressive regressive cycles are out of phase with respect to sequence boundaries which in down dip locations are both overlain and underlain by progradational deposits and hence form during times of regression of the shoreline these observations are used to develop some ideas about the origin of unconformity bounded sequences with reference to the inter related roles of changes in depositional base level and sediment supply in particular it is shown than onlap and offlap are due to lateral migration of a line of critical bypassing defined so as to incorporate the effects of sediment loading and compaction as well as the rate of change of elevation with respect to sea level downward shifts in onlap may be achieved by either an increase in the rate of eustatic fall or a decrease in the rate of tectonic subsidence and it is premature to assume that eustatic and tectonic controls on sea level may be distinguished solely on the basis of the frequency of depositional cyclicity small shifts in the position of onlap can also be produced by changes in sediment supply and more attention needs to be paid to the influence of sediment supply in the development of minor boundaries unconformities related to eustatic fluctuations are thought to correspond approximately to times of relatively rapid sea level fall inflection points but questions remain about the existence of possible leads and lags of up to cycle and hence about the degree to which sequence boundaries of eustatic origin may vary in age both within a given basin and from one basin to another

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

onshore to offshore anatomy of a late quaternary source to sink system po plain adriatic sea italy abstract in understanding the evolution of siliciclastic systems late quaternary analogs may enable reliable predictive models of facies tract architecture the po plain adriatic sea system where a wealth of research has been conducted during the last 20 years represents one of the most intensively investigated late quaternary successions with the aid of a chronologically well constrained stratigraphy paleoenvironmental evolution is tracked for the first time from fluvial to deep marine realms over 1000 km in length vertical stacking trends onshore and stratal terminations offshore are the key observations that allow identification of surfaces with sequence stratigraphic significance systems tract boundaries in the distinct segments of the system recurring motifs in stratigraphic architecture showing tight coupling of sedimentary responses among source area catchment basin and coastal and marine depocenters reveal a cyclicity driven by glacio eustatic fluctuations in the milankovitch band due to high rates of subsidence middle pleistocene forced regressive systems tracts are exceptionally expanded and the mis5e mis2 interval late pleistocene preserves a nearly continuous record of fourth order 100 kyr stepwise sea level fall the stratigraphic architecture of last glacial maximum deposits highlights the genetic relations between channel belt development pedogenesis and sediment delivery to the lowstand delta through narrow incised valley conduits the late glacial holocene succession records the last episode of sea level rise and stabilization through well developed patterns of shoreline transgression regression tst hst that can be readily traced updip from offshore to onshore locations architectural styles across the whole system reflect a dominance of allogenic forcing in the tst as opposed to a predominantly autogenic control on stratigraphic development in the hst external drivers of facies architecture were also effective on millennial timescales the younger dryas cold reversal which marks the transgressive surface on land records a short lived episode of subaqueous progradation that is correlative onshore with widespread immature paleosol development and small sized channel belt formation quantitative assessment of sediment budgets over different time intervals requires precise positioning of the key bounding surfaces based on this approach we outline for the first time over the entire po adriatic basin an estimate of the sediment volumes stored in each systems tract

late quaternary sedimentation lower colorado river gulf coastal plain of texas investigations in the lower colorado river valley gulf coastal plain of texas have resulted in the development of a spatially and temporally controlled history of changes in channel and flood plain erosional and depositional processes when combined with paleoclimatic and stratigraphic data from the upper colorado river drainage and the record of glacio eustasy in the gulf of mexico this study permits evaluation of the relative influence of different external controls on channel and flood plain behavior the development of alluvial landforms and the development of alluvial stratigraphic sequences late pleistocene and holocene alluvial deposits of the lower colorado river have been subdivided into allostratigraphic units with chronological control afforded by radiocarbon ages in the bedrock confined valley up to 10 m of late pleistocene 20 000 14 000 yr b p sediments referred to as the eagle lake alloformation ela underlie a terrace at 17 20 m above the present day channel deposition of the ela was followed by bedrock valley incision then deposition of a complex holocene valley fill referred to as the columbus bend alloformation cba columbus bend allomembers 1 and 2 cba 1 and cba 2 underlie a terrace at 12 14 m above the present day channel cba 1 was deposited 12 000 5 000 yr b p whereas cba 2 was deposited 5 000 1 000 yr b p columbus bend allomember 3 cba 3 consists of channel and flood plain deposits that represent the past 600 yr of activity allostratigraphic units within the lower colorado valley correlate with allostratigraphic units in major valley axes of the upper colorado drainage and with records of climatic and environmental change suggesting that alluvial deposits record basinwide responses to climatically controlled changes in discharge regimes and sediment supply basal unconformities for holocene valley fills however appear to be 1 000 2 000 yr younger in the upper colorado drainage than they are in the lower colorado valley this time transgressioe episode of bedrock valley cutting was initiated by climatically controlled reductions in sediment supply but conditioned by limits on rates of up stream propagation of incision through a large drainage basin by contrast unconformities within holocene valley fills document time parallel episodes of flood plain abandonment and soil formation but little additional bedrock valley cutting and indicate decreased flood magnitudes following shifts to drier climatic conditions flood plain morphology and sedimentary facies changed through time in response to changes in climate coupled with a protracted degradation of upland soil mantles which altered the rate at which precipitation was transferred to stream channels as runoff during the late pleistocene through middle holocene runoff was filtered through deep upland soils floods were for the most part less flashy and contained within channel perimeters and flood plains were constructed by lateral migration without significant vertical accretion hence the ela and cba 1 contain few vertical accretion facies exposure of bedrock surfaces during the late holocene resulted in increased flood stages deep overbank flooding and construction of flood plains by vertical accretion hence cba 2 and cba 3 contain thick vertical accretion facies allostratigraphic units and bounding unconformities persist through the bedrock confined valley to the quaternary alluvial plain but stratigraphic architecture changes substantially in the downstream direction as a result of the last glacio eustatic cycle on the alluvial plain late holocene cba 2 and modern cba 3 deposited contemporaneously with the present interglacial highstand onlap and bury the ela and cba 1 which were emplaced during the last full glacial lowstand and the transgression that followed

correlation techniques perforation strategies and recovery factors an integrated 3 d reservoir modeling study sirikit field thailand production in the sirikit oil field of the phitsanulok basin thailand commenced in 1982 the field has an stoiip stock tank oil initially in place of approximately 800 mmbbl million barrels to date more than 130 wells have been drilled and over 100 mmbbl produced reservoir management studies into optimizing recovery and identifying unswept oil volumes are ongoing so as to maximize the venture s profitability this work includes 3 d three dimensional static and dynamic modeling this study is one such exercise whereby different geological correlation techniques and perforation strategies were analyzed for their potential impact on recovery factors the sirikit field and adjacent satellite fields are composed of predominantly lacustrine mouth bar and fluvial deposits two correlation techniques lithostratigraphy and chronostratigraphy were employed to generate two 3 d reservoir architectures using the shell proprietary 3 d static reservoir modeling system geocap significantly different recovery factors are derived from 3 d dynamic flow simulation of these architectures no vertical upscaling 2 x 2 areal upscaling within the shell proprietary reservoir simulator mores when good quality sands observed on well logs are perforated in both models the lithostratigraphic correlation model results in an absolute 3 higher recovery factor than that of the chronostratigraphic correlation model in relative terms this represents a 43 higher recovery factor this suggests that if a lithostratigraphic correlation model is assumed then for this perforation strategy the recovery factor would be overestimated by 3 absolute and 43 relative if the chronostratigraphic interpretation represents the actual subsurface architecture in addition the architecture of the chronostratigraphic model results in the lateral correlation of the thicker upper mouth bar sands with good quality thin bedded toeset sands and shales heterolithics these thin bedded sands are only marginally resolvable on wireline logs and have not generally been perforated in the sirikit field when these thin bedded heterolithics are additionally perforated in the 3 d model an absolute increase in recovery factor of 2 is observed over the same model that has only the upper mouth bar sands perforated in relative terms this represents a 28 improvement in the recovery factor this work confirms and partially quantifies the impact that the choice of mouth bar correlation style can have on recovery factors as predicted by 3 d dynamic reservoir models however the chronostratigraphic model described in this paper represents an end member connectivity scenario whereby sand body continuity is relatively low due to continuous dipping shale barriers further work is required to quantify the recovery factors for the whole spectrum of potential chronostratigraphic model connectivity scenarios

siliciclastic sequence stratigraphic patterns in foreland ramp type basins stratal patterns within shelf depositional sequences are dependent on tectonically controlled subsidence rates and their regional patterns in active tectonic basin settings regional subsidence patterns can be very different from passive continental margin settings resulting in substantial modifications of the basic sequence stratigraphic model in ramp type foreland basins on the tectonically active side subsidence rates decrease seaward in contrast with passive continental margins where the opposite subsidence pattern exists analysis of the interplay between eustasy and subsidence suggests the existence of two tectono stratigraphic zones occurring proximally and distally with respect to the basin margin zone a is defined as the region within which the rate of subsidence always exceeds the rate of eustatic fall consequently relative sea level rises continuously during a eustatic cycle albeit at varying rates zone b is defined as the region within which the rate of eustatic fall periodically exceeds the rate of subsidence resulting in an interval of relative sea level fall during a eustatic cycle on the tectonically active sides of foreland basins zone a lies on the landward side of the basin margin proximal to the orogenic belt and zone b lies seaward off zone a away from the orogenic belt where subsidence rates are lower on passive continental margins because of the opposite subsidence patterns zone a lies seaward of zone b where subsidence rates are greater the location of the shoreline relative to these zones determines the stacking patterns and stratal discontinuities within a depositional sequence if the shoreline remains in zone a then only type 2 sequence boundaries will occur if sufficient sediment flux is available allowing the shoreline to prograde into zone b then type 1 sequence boundaries can occur in foreland basins these type 1 sequence boundaries would become type 2 sequence boundaries updip in zone a the pattern of seaward decreasing subsidence on the tectonically active sides of foreland basins results in characteristic longitudinal facies and stratal patterns when the two zones occur the updip region of the basin proximal to the orogenic belt is characterized by nearly continuous nonmarine deposition albeit at varying rates the downdip region is characterized by forced regressions and deposition primarily of lowstand and transgressive systems tracts a transitional region containing deposits of all three systems tracts commonly occurs between the updip and downdip areas

autostratigraphy a framework norm for genetic stratigraphy abstract autostratigraphy is the stratigraphy generated by large scale autogenic processes and needs to be heeded because of a current overreliance on allogenic controls in sequence stratigraphy key principles of autostratigraphy emerging from the theory of autoretreat and a new understanding of alluvial grade derive from the non equilibrium stratigraphic response i e the general lack of equilibrium configuration of depositional systems the non equilibrium behavior of fluvial deltas during times t of steady dynamic forcing leads to variable stratigraphic response that is the inevitable result of length d and time scaling particular to the depositional system rather than necessarily reflecting any sudden or unsteady change in the rate of allogenic forcing some abrupt breaks in the stratigraphic record are not necessarily associated with changes in allogenic conditions but can result from purely autogenic processes of the system when t is comparable to or longer than 1 the depositional system takes the non equilibrium large scale autogenic response 2 the superposition of autogenic and allogenic components of the forcing is prominently nonlinear and thus 3 sequence stratigraphic models that have been built on the assumption of equilibrium response are incorrect autostratigraphic analysis makes it possible to detect and identify complex autogenic responses and unsteady allogenic events in the stratigraphic record by quantifying a temporal change in the magnitude of d autostratigraphy thus functions as a norm for genetic stratigraphy

digital outcrop models applications of terrestrial scanning lidar technology in stratigraphic modeling abstract laser ranging is extremely accurate and efficient terrestrial scanning lidar light detection and ranging applied to outcrop stratigraphic mapping enables researchers to capture laser range data at a rate of thousands of individual x y z and laser intensity points per second these data in conjunction with complementary remotely and directly sampled data are used to conduct high precision facies characterization and to construct 3d geological computer models outcrop data are presented here to explain our workflow and to discuss the construction of rock based 3d digital outcrop models doms reproducibility and quantification are the drivers of this methodology high resolution terrestrial lidar acquisition processing interpretation and visualization are discussed and applied to mapping of geological surfaces in three dimensions laser generated models offer scientists an unprecedented visualization medium in a quantitative 3d arena applications of this technology include constructing and visualizing complex 3d earth models from outcrops for improved reservoir modeling flow simulation in hydrocarbon and aquifer systems and property modeling to constrain forward seismic modeling

structural sedimentologic and sea level controls on sand distribution in a steep clinoform asymmetric wave influenced delta miocene billund sand eastern danish north sea and jylland abstract the lower miocene billund sand of jylland denmark provides an excellent opportunity to study the distribution of sands and the types of clinoform generated by a wave dominated delta prograding into a deep shelf environment in particular seismic sections the sand rich parts correlate with parallel clinoformal seismic facies in which the clinoforms dip 7 to 10 the stacking pattern of this seismic facies also indicates whether the progradation occurred during rising or falling sea level by displaying an ascending or descending shoreline trajectory respectively the billund delta was deposited in the eastern north sea basin during the early miocene and is on the available data recognized as a nw to se trending feature it forms a wave dominated delta with thick sand bodies deposited in relatively deep waters 100 m at the river mouth and in the up drift area of newly formed delta lobes sands and muds associated with a spit complex or a lagoonal complex dominated the down drift area in the distal delta front area alternating sands and muds were laid down the sands associated mainly with storm events progradation of the studied part of the delta occurred during high sea level and a subsequent fall in sea level that was caused by a eustatic fall during the mid aquitanian early miocene although sand intervals 10 to 20 m thick are common throughout the delta complex the thickest up to 100 m and cleanest sand is found in units deposited in narrow bands within structural lows and during periods of forced regression the billund delta may be an excellent analogue for hydrocarbon bearing wave dominated deltas and seems to exhibit similarities to jurassic deposits in the north sea area

accommodation succession δa δs sequence stratigraphy observational method utility and insights into sequence boundary formation the future of sequence stratigraphy depends on stratigraphers making observations with a common method so that physical frameworks can be clearly separated from interpretations of driving mechanisms depositional sequence boundary selection is a well known controversy that could be resolved with objective recognition criteria accommodation succession sequence stratigraphy refines traditional methods using sedimentary facies facies associations vertical stacking stratal geometries and stratal terminations as the objective record of competing rates of accommodation change and sediment fill through time observations are placed in context of lateral transgression and regression and vertical aggradation and degradation movement of shoreline through time across multiple timescales in hierarchal stacks the repeating motif consists of a subaerial unconformity and its correlative subaqueous surface overlain in coastal settings by a basinward shift in coastal onlap and strata with progradational to aggradation stacking then retrogradation and aggradation progradation degradation stacking these stacking patterns are bounded by key surfaces recognized by stratal terminations and characteristic vertical successions of facies this pattern is independent of time duration or position on a sea level curve but incorporates data resolution regional extent and hierarchal stacking examples from multiple datasets show the utility and objectivity of the method and provide insights into sequence boundary formation

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

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

extensive thin sequences spanning cretaceous foredeep suggest high frequency eustatic control late cenomanian western canada foreland basin early late cenomanian rocks of the doe creek unit are near the base of the kaskapau formation and were deposited in a broad very shallow embayment that occupied the foredeep of the western canada foreland basin the doe creek unit consists of 13 upward shoaling sequences typically 3 10 m thick subsurface correlation shows that sequences can be traced for 100 350 km from the fore deep toward the forebulge on the proximal and distal margins of the embayment each sequence is capped by a flooding surface commonly underlain by a paleosol developed in marine mudstone in the center of the embayment most sequences are capped by one or more isolated sharp based sandstone bodies interpreted as lowstand delta front deposits flooding surfaces on top of each sequence are continuously traceable in well logs from the foredeep to the vicinity of the forebulge implying simultaneous transgression across the basin every sequence shows an abrupt upward shallowing usually to emergence that was caused by accommodation loss not sediment accumulation a vertical relative sea level excursion of 10 m on a time scale spanning a maximum range of 9 74 k y is estimated for each sequence because transgressions and regressions appear to be in phase across the basin sequences are better explained by eustasy rather than by flexural reciprocal sedimentation a glacioeustatic mechanism provides the most likely explanation

geology and stratigraphy of fluvio deltaic deposits in the ivishak formation applications for development of prudhoe bay field alaska significant remaining reserves in prudhoe bay field are confined within deltaic rocks at the base of the triassic ivishak sandstone the initial stratigraphic characterization of the prudhoe bay reservoir was lithostratigraphically based and it depicted this basal reservoir interval as tabular zones between marine shale and overlying coarse grained fluvial sandstones a reassessment of this interval based on cores and genetic stratigraphic correlations depicts en echelon offlapping fluvially dominated deltaic wedges reservoir quality rocks occur in distributary mouth bar distributary channel and fluvial facies associations a paleogeographic reconstruction of one delta lobe includes an alluvial plain crossed by channels of possibly braided or low sinuosity rivers this alluvial plain graded into a delta plain cut by distributary channels that fed distributary mouth bars on a broad delta front river dominance is inferred from the abundance of unidirectional current structures normally graded beds soft sediment deformation and general absence of wave formed tidal and biogenic structures slumping and growth faulting locally replaced coarsening upward deltaic successions with sharp based overthickened mouth bar and distributary channel deposits mudstones deposited following delta lobe abandonment form laterally extensive flow barriers between lobes compartmentalization is most pronounced distally where deltaic sandstones are overlain by and pass laterally into marine shale proximally fluvial and deltaic sandstones are juxtaposed across erosional contacts improving reservoir continuity this stratigraphic interpretation is corroborated by production and surveillance data plus an interference test locally stratigraphy and poor waterflood performance reflect completions in diachronous sandstones that originated in separate deltaic lobes previously poor well performances were attributed to sandstone pinch outs in some cases production can be enhanced with recompletions rather than infill drilling nonconventional wells planned and completed with the benefit of detailed facies association correlations currently are recovering millions of barrels of previously bypassed oil

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

response of coastal plain rivers to falling relative sea level allogenic controls on the aggradational phase this study combines mathematical modelling and supporting flume experiments to address the problem of how coastal plain rivers respond to a steady fall in relative sea level the theoretical component of the study focuses on the development of a moving boundary model of fluviodeltaic progradation that treats rigorously the dynamics of the shoreline and alluvial basement transition the upstream limit of the alluvial river system dimensional analysis and numerical solutions to the model governing equations together suggest that at first order coastal plain rivers will remain aggradational on a timescale that varies with allogenic sediment and water supply and the fall rate of relative sea level in natural fluviodeltaic systems this intrinsic timescale is likely to vary by several orders of magnitude suggesting that the aggradational phase of river response can be geologically long lived at second order the duration of alluvial aggradation is controlled by two dimensionless numbers that embody system geometry and the kinematics of alluvial sediment transport model predictions were tested in a series of carefully scaled flume experiments the level of agreement between predicted and measured trajectories for the shoreline and alluvial basement transition strongly suggests that the moving boundary theory developed here successfully captures the response of small scale fluviodeltaic systems to falling sea level the results of this study have several sequence stratigraphic implications a fall in relative sea level at the shoreline is not a sufficient condition for river incision the onset of alluvial degradation and sequence boundary formation need not coincide with a maximum in the rate of sea level fall and the onset of sequence boundary formation is sensitive to allogenic sediment supply

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

global correlation of cenomanian upper cretaceous sequences evidence for milankovitch control on sea level we have investigated the sequence stratigraphy of two widely separated marine cenomanian successions in southeast india and northwest europe and used high resolution ammonite biostratigraphy to demonstrate that sea level changes are globally synchronous and therefore must be eustatically controlled sequence scale sea level changes in the cenomanian were driven by the long eccentricity cycle 400 k y in the milankovitch band we hypothesize that during pre quaternary time the third order sequences of vail and haq are essentially a sediment response to sea level changes driven by the 400 k y cycle construction of a relative sea level curve for the marginal marine succession in india demonstrates that the short term sea level changes are rapid 10 100 m m y and have a magnitude of 2 20 m glacioeustasy is a possible but unproven driving mechanism

systems tracts and depositional sequences in a carbonate setting a study of continuous outcrops from platform to basin at the scale of seismic lines abstract the application of sequence stratigraphy concepts to carbonates is feasible and this paper presents an example of its successful application the continuity and lateral extent of outcropping sedimentary sections observed at the scale of a seismic line from platform to basin in the southern vercors plateau western alps france confirm the validity of sequence stratigraphy concepts when applied to carbonate depositional systems from the stratal patterns displayed in outcrop we determined that carbonate lowstand systems tracts are major components in the basin even in the deep pelagic realm transgressive and highstand systems tracts are very thin a response to starvation in contrast on the shelf transgressive and highstand systems tracts are the major components carbonate lowstand and shelf margin systems tracts pinch out in the vicinity of the offlap break it clearly appears that the stratal patterns and stratal termination patterns of carbonate systems tracts especially of carbonate lowstand systems tracts are basically similar to those of siliciclastic systems tracts this study documents that carbonate platforms may provide the basin with carbonate clastics during periods of relative sea level falls and lowstand this is one of the most controversial aspects of the application of sequence stratigraphy concepts in carbonate environments a second controversial aspect of the application of sequence stratigraphy concepts to carbonate rocks is the distinction between transgressive and regressive facies cycles and depositional sequences and systems tracts this paper demonstrates that the shoreline position for carbonates which indicates the facies transgression or regression is independent of prograding or retrograding shelf breaks the stratal pattern and facies within systems tracts vary depending on the overall evolution of the accommodation space i e on their position within the transgressive and regressive cycles

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