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

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

vertical sequence and lateral transitions in the facies of a barred nearshore environment abstract nine tube cores 7 cm in diameter and up to 150 cm long from a nearshore crescentic bar in kouchibouguac bay new brunswick canada reveal the vertical sequence and lateral transitions of facies previously identified only in shallow box cores the facies are a inner shelf shoreface transition bioturbated fine sands and silts with remnant primary structures b seaward slope planar lamination in medium to fine sands dipping gently seaward and composite bed sets of planar to ripple cross lamination in fine sand chevron lamination is rare c bar crest low angle planar lamination dipping both landward and seaward and medium scale trough cross lamination in medium to coarse sands d landward slope planar lamination dipping landward with small scale la dward dipping trough cross lamination occasionally small to medium scale trough cross lamination is found with seaward dips e trough massively bedded lags of coarse gravelly sands with abundant shell fragments contrast with isolated very thin units of massive silt and units of well sorted sands the latter display subhorizontal planar lamination and small to medium scale trough cross lamination polymodal dips indicate bed form migration landward alongshore and offshore vertical sequences and lateral transitions seaward of the bar crest suggest that three wedge shaped units inner shelf shoreface transition seaward slope bar crest interdigitate in an offlap onlap sequence to landward the trough and landward slope facies interfinger complexly while the crest facies forms a simple onlap over landward slope facies total reworking of sediments within the bar trough system is expected every 5 to 6 years and long term preservation is limited to the inner shelf shoreface transition seaward slope and trough facies

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

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

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

basin scale diagenetic alteration of shoreface sandstones in the upper cretaceous spring canyon and aberdeen members blackhawk formation book cliffs utah abstract leached zones whitecaps and dolomite cement bodies are volumetrically and areally significant features in shoreface sandstones of the upper cretaceous spring canyon and aberdeen members blackhawk formation book cliffs utah quantitative spatial and stratigraphic data of their distribution together with petrography and geochemistry allow development of a model for their formation within a sequence stratigraphic framework leached zones up to 5 m thick and 15 km in lateral extent are present beneath coals capping parasequences concretionary dolomite cement is present in shoreface sandstones downdip of parasequence capping coals and associated whitecaps these concretions are up to 2 m thick and 6 m in length and are present for up to 7 km downdip of these coals petrographic and field data indicate an early diagenetic timing for whitecap and dolomite cement formation 13c data suggest carbonate derivation from detrital dolomite whereas 18o data suggest that cement precipitated from porewater with a significant meteoric component although later diagenetic re equilibration and recyrstallization cannot be rejected we propose that organic acid generation during early diagenesis of coals led to the leaching of detrital dolomite from underlying sandstones and the formation of whitecaps meteoric water flowed basinward in response to base level lowering and sequence boundary development in the upper part of the aberdeen member remobilizing dolomite into shoreface sandstones dolomite precipitation resulted from the mixing of these meteoric fluids with downdip marine pore fluids and the presence of detrital dolomite in the shoreface sandstones that acted as nucleation sites for dolomite precipitation the geometry and extent of dolomite cement in the spring canyon and aberdeen members is in marked contrast to the much greater spatial extent of such cement in low accommodation space settings such as the stratigraphically younger desert member blackhawk formation the relatively simple aggradational to progradational evolution of the spring canyon and aberdeen member parasequences with only minor sequence boundary development in its upper part resulted in spatially limited meteoric fluid input into shoreface sandstones this resulted in dolomite cementation of shoreface sandstones up to a maximum of 7 km downdip of leached zones in the desert member extensive meteoric fluid migration as a result of major sequence boundary development resulted in dolomite cementation of shoreface sandstones for over 25 km downdip of leached zones this highlights that the degree and extent of early fluid diagenesis can be significantly controlled by the nature of sequence development having clear implications for developing predictive models for porosity permeability evolution in sandstone reservoirs

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

shoreline autoretreat substantiated in flume experiments abstract under conditions of constant sediment supply s to the basin and a steady rate of rise a in relative sea level the autoretreat theory predicts that shorelines can retreat landwards at a relatively early stage of delta growth and attain an autobreak state after which the existing subaqueous slope begins to be starved of sediment and thereby lose its clear delta front configuration a numerical model based on this theory further suggests that shoreline migration depends on the inclination of basin s basement slope and subaqueous depositional slope and to a lesser degree on the inclination of subaerial depositional slope two dimensional flume experiments in which a miniature delta is subject to steady forcing a const 0 s const 0 were conducted to test the expectations of the autoretreat theory the experiments consisted of two different series of runs one was of modulation associated with a narrow range of the ratio of water discharge to sediment discharge q s the other was of q s modulation with kept nearly constant the q s ratio was mostly responsible for changes in but also affected to some extent all experimental runs substantiated the landward turnaround feature of shoreline accretion i e autoretreat and the geometrical break of the delta front shape during its retreat phase i e autobreak the obtained shoreline trajectories hold their geometrical patterns even after they were nondimensionalized in terms of the s a ratio a key hypothesis confirmed in the experiments is that a and s can never balance each other both of the experimental series brought some systematic change of shoreline trajectories but the variations of shoreline trajectory due to modulation were much more striking than those related to q s even these contrasting results are consistent with the numerical predictions the present experimental results support the applicability of the autoretreat concept to natural environments and help clarify the processes governing the regression and transgression of a shoreline on a constructional margin

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

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

late cretaceous chronology of large rapid sea level changes glacioeustasy during the greenhouse world we provide a record of global sea level eustatic variations of the late cretaceous 99 65 ma greenhouse world ocean drilling program leg 174ax provided a record of 11 14 upper cretaceous sequences in the new jersey coastal plain that were dated by in tegrating sr isotopic stratigraphy and biostratigraphy backstripping yielded a late cre taceous eustatic estimate for these sequences taking into account sediment loading com paction paleowater depth and basin subsidence we show that late cretaceous sea level changes were large 25 m and rapid k1 m y suggesting a glacioeustatic control three large d 18 o increases are linked to sequence boundaries others lack sufficient d 18 o data consistent with a glacioeustatic cause and with the development of small 10 6 km 3 ephemeral ice sheets in antarctica our sequence boundaries correlate with sea level falls recorded by exxon production research and sections from northwest europe and russia indicating a global cause although the exxon record differs from backstripped estimates in amplitude and shape

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

flexural subsidence and basement tectonics of the cretaceous western interior basin united states the flexural subsidence history recorded in cenomanian to early campanian 97 to 80 ma strata in the cretaceous u s western interior basin was studied with two dimensional flexural backstripping techniques results indicate that the flexural subsidence resulting from thrust loading was superimposed on epeirogenic subsidence in the foreland basin the flexural component exhibits significant spatial and temporal variations along both the strike and dip relative to the sevier thrust belt the greatest cumulative subsidence occurred in southwestern wyoming and northern utah concurrent subsidence in northwestern montana and southern utah was insignificant temporal trends in subsidence also show a distinct regional pattern from the cenomanian to late turonian 97 to 90 ma subsidence rates were high in utah and much lower in wyoming and montana in contrast during the coniacian and santonian 90 to 85 ma subsidence accelerated rapidly in wyoming increased slightly in montana and decreased in utah we suggest that these spatially and temporally varying subsidence patterns reflect the interplay of several geodynamic factors including 1 temporal and spatial variation in emplacement of the thrust loads 2 segmentation of the basement into adjacent blocks with different rheological properties 3 reactivation of basement fault trends and 4 regional dynamic topographic effects

effects of ambient currents and waves on gravity driven sediment transport on continental shelves abstract observations from several shelf environments show that down slope gravity driven transport may constitute an important mode of suspended sediment dispersal across shelves and highlight the influence of ambient waves and currents on gravity induced sediment flux the phenomena discussed here involve high concentrations of suspended sediment mixed with seawater and thus differ in genesis from hyperpycnal plumes released directly from sediment laden rivers the field sites examined are the gulf of bohai off the mouth of the yellow river huanghe the northern california shelf off the mouth of the eel river and the louisiana shelf west of the mouths of the mississippi river off the yellow river rapid down slope transport over distances of a few km occurred when frictional resistance induced by strong along shelf currents was temporarily relaxed more prolonged down slope motion over longer distances occurred following floods of the eel river when wave and current agitation provided turbulence to sustain gravity driven transport of fluid mud on the louisiana inner shelf the down slope gravity force was much weaker but observations suggest that thin gravity flows may still have occurred in the presence of waves a simple analytical theory is developed that incorporates the influence of ambient shelf currents on gravity driven transport of suspended sediment this theory is quantitatively consistent with the observations from the three sites if the supply of easily suspended sediment is less than the capacity of ambient currents including waves to carry sediment then intense turbulence limits gravity induced sediment transport by increasing the drag at the base of the flow when ambient currents abruptly cease rapid down slope transport can then occur over short distances until the sediment settles such flows do not remain intensely turbulent because the slope of the continental shelf is too gentle to induce shear instability within the gravity flow the maximum sustained rate of gravity induced sediment transport occurs when ambient currents are strong but the supply of easily suspended sediment exceeds the resuspension capacity of the ambient currents feedback then leads to values of the gradient richardson number ri within the flow that are near the critical value of 1 4 this partially damps bottom drag but still allows the generation of sufficient turbulence to maintain sediment in suspension observations also indicate systematic relationships among ri the supply of easily suspended sediment and the bottom drag coefficient acting on the gravity flow

transport of mud on continental shelves evidence from the texas shelf abstract transmissivity and suspended sediment data from three cruises on the east texas continental shelf confirm that a bottom nepheloid layer bnl exists across the shelf this layer is most turbid in the nearshore and outer shelf regions in addition surface nepheloid layers exist close to shore due to river and bay outflows and on the outer shelf intermediate nepheloid layers are present as a result of quasi horizontal advection from the bnl the character of the bnl is not directly linked to local hydrography or substrate being instead a function of the shelf dynamics in the nearshore regime high energy coastal processes and high sediment input from bays and rivers maintain the bnl at the shelf edge the bnl is formed by near inertial internal waves and shelf waves which resuspend and transport fine sediment present day sediment deposition on the east texas shelf can be directly related to the above processes mud is accumulating in the nearshore environment due to river input and on the inner and midshelf regions as a result of deposition from bnls and snls on the outer shelf bnls and inls transport fine sediment further offshore so that in effect suspended sediment bypasses the outer shelf

experiments on bed configurations in fine sands under bidirectional purely oscillatory flow and the origin of hummocky cross stratification abstract we made experiments on bed configurations in bidirectional purely oscillatory flows at a wide range of oscillation periods t and maximum orbital velocities um in two closed flow ducts 0 1 m and 0 4 m wide the motivation was that understanding of bed configurations in oscillatory flows with long periods and high velocities during storm induced deposition in the shallow ocean is needed for interpreting the stratification in such deposits the ripples produced were classified geometrically as two dimensional 2d or three dimensional 3d in plan view geometry and dynamically as oscillatory current ripples dependent upon the patterns of flow and sediment transport specific to the existence of the oscillation itself and reversing current ripples dependent on he existence of the current in one direction or the other during the oscillation runs in the small duct with effectively 0 19 mm and 0 30 mm sand showed the familiar small 2d oscillatory current ripples at short t and low um passing into much larger ripples with spacing up to 2 m at periods of 6 20 s and velocities up to 1 m s with no apparent limit on size with increasing t and um even in such a narrow duct there was some evidence of 3d geometry of the large ripples runs in the large duct with effectively 0 11 mm sand at a single period of about 9 5 s showed a progression from small 2d oscillatory current ripples through small 3d reversing current ripples to large round crested 3d oscillatory current ripples with prominent superimposed 3d to 2d reversing current ripples the large 3d ripples which increased in spacing to 1 3 m at the h ghest attainable um of 1 m s shifted in position and changed in size with time seemingly at random causing substantial local and temporary erosion and deposition at a given point on the bed there was no net aggradation during the runs but a deposit was synthesized by taking a time series of sidewall bed profiles during a run in which large 3d ripples developed from an initially plane bed and changed irregularly in size and position as they grew toward equilibrium and then plotting the profiles one above the previous with a constant upward increment the resulting stratification is strikingly similar to much hummocky cross stratification in ancient sandstones this suggests that some hummocky cross stratification is generated during sediment fallout from strong purely oscillatory flows at moderate to long oscillation periods as large 3d oscillatory current bed forms develop from a planar bed during strong but waning flow

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

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

modeling of cretaceous foreland basin parasequences utah with implications for timing of sevier thrusting computer modeling suggests that thrusting order can be discriminated on the basis of foreland basin geometry and parasequence stacking patterns the position of sequential thrust sheets relative to the basin affects the amount and distribution of subsidence source terrain elevation and distance from the shoreline and sediment transport into the basin for this study a forward numerical model was constructed to quantitatively simulate the interaction of geologic processes active in the foreland basin setting including thrusting and orogenic development lithospheric flexure orogenic denudation sediment transport across the coastal plain and nearshore deposition in order to isolate the effects of tectonics and sediment supply on nearshore deposition eustatic sea level is held constant model runs simulate two different thrusting sequences foreland stepping in sequence and hinterland stepping out of sequence when in sequence thrusting is modeled sediment is trapped in intra orogen basins because sediment is prevented from reaching the shoreline the basin is underfilled when out of sequence thrusting is modeled sediment is transported from the orogen to the shoreline episodes of thrusting result in subsidence and marine flooding surfaces and resulting accommodation space allows for parasequence development comparing model output to stratigraphy observed in eastern utah suggests that late cretaceous out of sequence uplift and thrust loading resulted in aggradational and progradational parasequence stacking in the campanian blackhawk formation this result supports the theory that the pavant thrust system was active prior to deposition of the blackhawk formation and that the location of thrust shortening shifted toward the hinterland prior to or during blackhawk formation deposition

correlating palynofacies assemblages with sequence stratigraphy in upper cretaceous campanian sedimentary rocks of the book cliffs east central utah some of the most important factors that govern the preservation of depositional sequences in passive margins are the rate of sediment supply the type of sediment subsidence history sea level changes and climate these factors also control the nature of components such as organic matter palynomorphs and other fossils incorporated within the sediments because detrital organic matter palynodebris behave like sedimentary particles their distribution in sediments can be used to infer palynofacies and consequently depositional conditions this study correlates palynofacies assemblages with sequence stratigraphic interpretations of upper cretaceous campanian sedimentary rocks in the book cliffs east central utah namely the kenilworth grassy and desert members of the blackhawk formation mancos shale castlegate sandstone and buck tongue of the mancos shale sedimentological criteria have been used to identify the depositional framework at 8 localities and 12 palynodebris types have been identified in the sediments sporomorphs marine palynomorphs fresh water algae fungal remains amorphous organic matter resins cuticles parenchyma degraded bundles wood black debris and degraded debris the samples and palynodebris were analyzed statistically using average linkage cluster analysis principal components analysis and detrended correspondence analysis cluster analysis yielded seven palynofacies assemblages which have been integrated with sedimentological criteria and correlated with sequence stratigraphic interpretations although all the samples are dominated by woody debris the palynofacies assemblages are defined primarily by marine palynomorphs degraded bundles black debris and sporomorphs and to a lesser extent by cuticles and resins highstand systems tracts and lowstand systems tracts are each represented by major palynofacies assemblages indicating that there is some correlation with sequence stratigraphy two other minor assemblages are indicative of the highstand systems tract in addition three assemblages which are dominated by siltstone and shale samples interbedded with sandstones are richer in black debris this is probably due to the effect of oxidation in the depositional environment and possibly microbial respiration in the interbedded sandstones marine environments are usually characterized by an abundance of marine palynomorphs and palynodebris over sporomorphs and other nonmarine palynodebris and this characteristic has been used to recognize initial marine flooding events and maximum flooding intervals condensed sections in several palynological studies in this study however one possible initial marine flooding event was not easily detected palynologically in situations such as this there is a need to integrate palynology with sedimentological and other criteria in order to establish valid regional sequence stratigraphic interpretations

late cretaceous subsidence in wyoming quantifying the dynamic component the late cretaceous western interior basin of north america is generally considered to have been a retroarc foreland basin flexural backstripping of the stratigraphic record from 97 2 ma to 73 4 ma along a section perpendicular to the wyoming idaho salient of the sevier belt clearly demonstrates that there were components of subsidence in addition to those driven by the thrust and associated sediment loads the simulation demonstrates that the flexural foredeep is only 180 120 km wide and shows a forebulge located near the subsequent laramide rock springs uplift foredeep strata between the rock springs uplift on the east and the thrust front to the west were mostly involved in the eastward overlapping thrust belt or deeply truncated by inferred rebound after 78 5 ma the difference between the observed decompacted cumulative subsidence and the amount of subsidence that can be explained by simple flexural loading the residual subsidence increases from 800 m in eastern wyoming to 1 8 km near the thrust belt the westward thickening upper cretaceous sediment wedge filled the accommodation space generated by downward tilting to the west of the north american cratonic margin by underplating and mantle flow associated with the shallowly subducted farallon plate

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

sevier age ramp style thrust faults at cedar mountain northwestern san rafael swell colorado plateau emery county utah field evidence combined with published and unpublished seismic data supports a new inferred easternmost limit of sevier thrusting during late cretaceous foreland deformation in east central utah imbricate thrust faults are exposed along the western margin of cedar mountain in the northern part of the san rafael swell within the western bounds of the colorado plateau the faults offset jurassic entrada curtis summerville and morrison formations and the lower cretaceous cedar mountain formation strike separations ranging from a few metres to 564 m and stratigraphic separations of as much as 76 m are accommodated by bedding parallel slippage along less competent shales and siltstones and by oblique ramping across more competent sandstones fault zones exhibit breccias drag folds chatter marks and imbricate splay faulted slivers the kinematic mechanism appears to have been a layer parallel shortening accomplished along nearly horizontal nearly east directed compression

carbonate cementation in a sequence stratigraphic framework upper cretaceous sandstones book cliffs utah colorado abstract three macroscopic diagenetic features can be recognized in the sandstones of the upper cretaceous desert member of the blackhawk formation and castlegate sandstone of the mesaverde group exposed in the book cliffs utah each of which have distinctive form geometry and stratigraphic distribution diagenetic alterations are 1 leached zones whitecaps up to 10 m thick beneath coal beds 2 large up to 8 m concretionary carbonate cemented bodies in amalgamated shoreface and thin fluvial sandstones and 3 thin up to 2 m laterally extensive carbonate cemented horizons beneath major marine flooding surfaces each feature has distinct petrographic and geochemical signatures and formed through discrete diagenetic processes large isolated carbonate cemented bodies are composed of ferroan dolomite most of which precipitated during early diagenesis field and petrographic data coupled with stable isotope data early cements 13c 2 5 to 3 4o oo vpdb 18o 7 8 to 12 0o oo vpdb 87sr 86sr 0 7078 later cements 13c 3 1 to 5 7o oo vpdb 18o 12 0 to 15 1o oo vpdb 87sr 86sr 0 7093 suggest precipitation from meteoric fluids input into sediments during times of relative sea level fall the source of carbonate for the dolomite cement was dissolution of detrital dolomite from beneath coals by organic acids and subsequent mobilization by meteoric fluids carbonate precipitation in laterally extensive cement horizons appears to have started as a result of hiatus in sediment accumulation during marine flooding events relative sea level rise cement precipitation in these horizons continued through sediment burial as a result of organic matter oxidation reactions in overlying organic rich mudstones the results of this study show a link between sedimentation related to changes in relative sea level and diagenesis leading to the potential for the development of process based predictive models of early diagenesis in depositional successions

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

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

geomorphological and sequence stratigraphic variability in wave dominated shoreface shelf parasequences physical stratigraphy within shoreface shelf parasequences contains a detailed but virtually unstudied record of shallow marine processes over a range of historical and geological timescales using high quality outcrop data sets it is possible to reconstruct ancient shoreface shelf morphology from clinoform surfaces and to track the evolving morphology of the ancient shoreface shelf our results suggest that shoreface shelf morphology varied considerably in response to processes that operate over a range of timescales 1 individual clinoform surfaces form as a result of enhanced wave scour and or sediment starvation which may be driven by minor fluctuations in relative sea level sediment supply and or wave climate over short timescales 10 1 10 3 years these external controls cannot be distinguished in vertical facies successions but may potentially be differentiated by the resulting clinoform geometries 2 clinoform geometry and distribution changes systematically within a single parasequence reflecting the cycle in sea level and or sediment supply that produced the parasequence 10 2 10 5 years these changes record steepening of the shoreface shelf profile during early progradation and maintenance of a relatively uniform profile during late progradation modern shorefaces are not representative of this stratigraphic variability 3 clinoform geometries vary greatly between different parasequences as a result of variations in parasequence stacking pattern and relict shelf morphology during shore face progradation 10 5 10 8 years these controls determine the external dimensions of the parasequence

fluvial and marine controls on combined subaerial and subaqueous delta progradation morphodynamic modeling of compound clinoform development 1 fluviodeltaic systems commonly display a compound clinoform geometry that consists of a subaerial subaqueous delta couplet the extent of subaqueous delta development varies significantly and in modern systems is a function of fluvial input and basin hydrodynamics we present a model of fluviodeltaic progradation in which the repeated occurrence of characteristic terrestrial floods and large coastal storms drives fluvial and shallow marine morphodynamics respectively we couple fluvial and shallow marine sediment dynamics via the surf zone which we collapse to a shock condition and treat as a moving boundary with steady sediment supply and sea level and simple basin geometry our model naturally develops prograding deltas with compound clinoform geometries the subaerial delta grows via fluvial aggradation and shoreface progradation whereas the subaqueous delta expands through foreset progradation with only minor topset aggradation the interplay of fluvial input with the wave current field controls the basic partitioning of sediment between subaerial and subaqueous deltas and by extension the compound clinoform geometry increasing the frequency or magnitude of coastal storms decreasing flood frequency or discharge and reducing grain size all increase the fraction of sediment delivered to the shallow marine environment and the extent of subaqueous delta progradation relative to subaerial delta development our model which emphasizes the intrinsic coupling of fluvial and shallow marine sediment dynamics and downplays the importance of allogenic fluctuations can explain many of the first order morphologic features of natural delta systems including significant lateral separation of the shoreline and clinoform rollover and differing rates of subaerial and subaqueous delta progradation

experiments on oscillatory flow and combined flow bed forms implications for interpreting parts of the shallow marine sedimentary record abstract analog laboratory experiments were conducted to investigate subaqueous bed forms generated under storm like oscillatory and combined flow experiments were carried out in a large wave tunnel and used a range of sand sizes fine and very fine wave periods 10 5 and 8 s oscillatory velocities 0 to 125 cm s and unidirectional velocities 0 to 25 cm s at low unidirectional velocities 10 cm s addition of an increasing collinear oscillatory flow caused the bed to evolve from small scale wavelength 100 cm symmetric orbital ripples to plane bed at higher unidirectional velocities 10 cm s a similar trend was noted but ripples were more asymmetric three phase diagrams are presented to summarize the observed relationships of bed configurations to flow conditions these diagrams are intended to assist in the interpretation of shallow marine sedimentary environments where oscillatory and combined flow are thought to be omnipresent distinctive features of small scale asymmetric combined flow ripples generated are a 3d planform round crest and convex up sigmoidal profile with local pronounced scour at the toe of the stoss side giving the ripple profile a boxy appearance similarly large scale asymmetric combined flow ripples had broad and round crests convex up stoss sides and compressed profiles due to scouring at the toe of the stoss side hummocky bed forms were generated under moderate to high oscillatory velocities and low unidirectional velocities hummocks were not observed as a distinct bed state but rather appeared to mark transitions in bed form scale and symmetry hummocks were more prevalent at longer oscillatory periods and in finer grained sediment stratification produced by synthetically aggrading hummocky bed profiles closely resembles hummocky cross stratification with the introduction of only a small unidirectional flow component hummocks evolve into downstream migrating large scale asymmetric ripples and the resultant cross stratification becomes similar to that produced by unidirectional flow dunes accordingly these experiments suggest that much of the hummocky cross stratification observed in the stratigraphic record is produced by storm generated long period oscillatory dominant combined flows inasmuch as long period high energy waves require deep wide basins to form hummocky cross stratification may therefore serve as a useful indicator of deposition in unrestricted open water conditions

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

sequence stacking patterns in the western canada foredeep influence of tectonics sediment loading and eustasy on deposition of the upper cretaceous kaskapau and cardium formations the kaskapau and cardium formations span late cenomanian to early coniacian time and were deposited on a low gradient foredeep ramp the studied portion of the kaskapau formation spans ca 3 5 myr and forms a mudstone dominated wedge thinning from 700 to 50 m from sw to ne over ca 300 km in contrast the cardium formation spans about 2 1 myr is about 100 m thick sandstone rich and broadly tabular the kaskapau and cardium formations are divided respectively into 28 and nine allomembers each bounded by marine flooding surfaces kaskapau allomembers 1 to 7 show about 200 km of offlap from the forebulge accompanied by progradation of thin sandstones from the eroded forebulge crest in contrast kaskapau allomembers 8 to 28 and cardium allomembers c1 to c9 show overall onlap onto the forebulge of about 350 km and contain no forebulge derived sandstones this broad pattern is interpreted as recording a latest cenomanian pulse of tectonic loading which led to shoreline back step in the proximal foredeep and coeval uplift of the forebulge leading to erosion the advance of the sediment wedge after kaskapau allomember 7 is attributed primarily to the isostatic effect of a distributed sediment load the advance of the orogenic wedge had a subordinate effect on subsidence of the forebulge for kaskapau allomembers 1 to 6 isopachs trend north to south suggesting a load directly to the west allomembers 7 to 28 show an abrupt rotation of isopachs to nw se suggesting that the load shifted several hundred kilometres to the south this re orientation might be related to a change from an approximately orthogonal to a dextral transpressive stress regime within the longer term offlap onlap cycle recorded by the kaskapau and cardium formations individual allomembers are grouped into packages reflecting higher frequency onlap offlap cycles each spanning ca 0 5 to 0 7 myr offlap from the forebulge tends to be accompanied by more pronounced transgression in the foredeep whereas onlap onto the forebulge is accompanied by progradation of tongues of shoreface sandstone this relationship suggests that changes in deformation rate in the orogenic wedge modulated proximal subsidence rate enhancing or suppressing shoreline progradation and also causing subtle uplift or subsidence of the forebulge region wedge shaped allomembers in the kaskapau formation contain shoreface sandstone and conglomerate that prograded respectively 40 and 25 km from the preserved basin margin progradation of coarse clastics was limited by rapid flexural subsidence tabular allomembers of the cardium formation imply a low flexural subsidence rate and contain sandy and conglomeratic shoreface deposits that prograded up to ca 180 km from the preserved basin margin this relationship suggests that low rates of flexural subsidence promoted steeper alluvial gradients more vigorous gravel transport and more extensive shoreface progradation overall observed stratal geometry and facies distribution is explained readily in terms of current elastic flexural models most shoreface sandstones in the proximal foredeep show evidence of forced regression eustasy provides the most plausible explanation for relative sea level rise fall cycles on the 125 kyr allomember timescale geometric relationships suggest eustatic oscillations of about 10 m forced regressive shoreface development was suppressed during kaskapau allomembers 1 to 10 when the rate of flexural subsidence was at its highest

isolated highstand shelf sandstone body of turbiditic origin lower kenilworth member cretaceous western interior book cliffs utah usa abstract an isolated highstand shelf sandstone body of turbiditic origin has been identified in the lower kenilworth member hatch mesa area book cliffs utah relative to most other marine mudstone encased isolated sandstone bodies the hatch mesa succession has an abundance of bouma like turbidite beds a greater proportion of mudstone and siltstone is thinner 6 20 m and is weakly coarsening upward these attributes in combination with locally abundant hummocky cross stratified sandstones a paucity of wave ripples in the background fair weather deposits carbonaceous matter in all facies a lack of clinoforms and a low diversity abundance trace fossil suite suggest deposition in a prodelta environment between fair weather and storm wave base a three component shoreface to shelf model consisting of delta front subaqueous channel and prodelta turbidite deposits is proposed to explain the depositional environment and setting of the hatch mesa succession regional correlation has demonstrated that the hatch mesa succession is time equivalent with the second parasequence in the kenilworth kps2 which is characterized by inner shelf turbidite bodies at a number of other localities paleogeographic reconstructions reveal that the hatch mesa succession was deposited at least 16 km basinward of the kps2 lower shoreface in approximately 20 m of water the kps2 hatch mesa sandstone body package is part of the early highstand systems tract indicating that isolated or stray sandstone bodies are not solely restricted to the falling stage or lowstand systems tracts

clinoform development by advection diffusion of suspended sediment modeling and comparison to natural systems clinoforms are the building blocks of prograding stratigraphic sequences these sig moid shaped surfaces can be found forming today on modem deltas sedimentation rate profiles over the clinoform surface of these deltas show low rates of sediment accumulation on both topset and bottomset regions with a maximum accumulation rate on the upper foreset region we pres ent a model for the formation of clinoforms that relies on the interpretation of modem clinoform sedimentation as a result of the distribution of shear stresses at the mouth of a river model clino form surfaces are generated using an equation for the conservation of suspended sediment concentration together with a conservation of fluid equation for simple time averaged flow velocity fields in the model suspended sediment is advected horizontally into a basin and gravitational settling of sediment particles is counteracted by vertical turbulent diffusion in shallow water shear stresses are too large to allow deposition and sediment bypasses the topset region with increasing water depth near bed shear stresses decrease and sediment is allowed to deposit at the foreset region with gradually decreasing rates toward deeper water this sedimentation pattern leads to progradation of the clinoform surfaces through time the clinoform surfaces produced by the model capture the fundamental morphological characteristics of natural clinoforms these include the gradual slope rollover at the topset and bottomset steeper foreset slopes with increased grain size and an increase in foreset slope through time as clinoforms prograde into deeper water because the parameters controlling the model clinoforms have a direct relation to physical quantities that can be measured in natural systems the model is an important step toward unraveling the physical processes associated with these deposits

seismogenic sources in the adriatic domain abstract we present an overview of the seismogenic source model of the adriatic domain included in the latest version of the diss database http diss rm ingv it diss and in the european share database http diss rm ingv it share the model consists of composite and individual seismogenic sources located inside and along the margins of the adria plate in order to locate and parameterize the sources we integrated a wide set of geological geophysical seismological and geodynamic data either available from published literature or resulting from our own field work seismic profile interpretations and numerical modelling studies we grouped the sources into five regions based on geometrical and kinematic homogeneity criteria seismogenic sources of the central western adriatic north eastern adriatic eastern adriatic and central adriatic regions belong to the northern apennines external dinarides and offshore domains respectively they are characterized by nw se strike reverse to oblique kinematics and shallow crustal seismogenic depth seismogenic sources of the southern western adriatic region instead are e w striking dextral strike slip faults cutting both the upper and lower crust the fastest moving seismogenic sources are the most southern thrusts of the eastern adriatic and the strike slip sources of the southern western adriatic while the seismogenic sources of the central adriatic exhibit the lowest slip rates estimates of maximum magnitude are generally in good agreement with the historical and instrumental earthquake records except for the north eastern adriatic region where seismogenic sources exhibit a potential for large earthquakes even though no strong events have been reported or registered all sources included in the database are fully geometrically and kinematically parameterized and can be incorportaed in seismic hazard calculations and earthquake or tsunami scenario simulations

a sedimentological and sequence stratigraphic reinterpretation of the upper cretaceous prairie canyon member mancos b and associated strata book cliffs area utah usa the mancos shale book cliffs eastern utah usa represents the open marine mudstones of the cretaceous western interior seaway and encloses the prairie canyon member which is located over 50 km seaward of interpreted contemporaneous highstand shoreline deposits in the blackhawk formation examination of the member reveals that it does not wholly represent offshore deposition as previously interpreted but instead contains three nearshore facies associations 1 tidally influenced fluvial channel fills 2 fluvial dominated delta fronts and 3 weakly storm influenced shorefaces tidally influenced fluvial channel fills are commonly stacked into multistory bodies that can be traced for tens of kilometers at discrete stratigraphic levels defining incised valley fill networks four such incised valley networks are identified at outcrop fluvial dominated deltas and weakly storm influenced shorefaces are eroded into by and lie at the down dip terminations of incised valley fills and are interpreted as forced regressive and lowstand shoreface deposits one incised valley fill appears to be onlapped by additional fluvial dominated deltas which represent pulses of shoreface progradation during an overall transgression forced regressive lowstand and transgressive shorefaces in the prairie canyon member differ significantly from highstand shorefaces in the blackhawk formation the former are sand poor and weakly wave storm influenced whereas the latter are sand rich and wave dominated this change in shoreface style reflects increased mud supply and an enhanced embayment paleogeography during periods of relative lowering of sea level

use of spectral gamma ray data to refine subsurface fluvial stratigraphy late cretaceous strata in the book cliffs utah usa high resolution sub seismic stratigraphic correlation in fluvial strata is extremely difficult using conventional subsurface core and wireline log data e g gamma ray neutron density sonic logs spectral gamma ray logs provide additional data on lithological composition that can aid identification of chronostratigraphic surfaces in a high resolution sequence stratigraphic correlation framework the application of spectral gamma ray data in constructing such a framework is demonstrated using data from exposures and the subsurface from the cretaceous non marine blackhawk formation and castlegate sandstone of the book cliffs area utah usa these strata provide an ideal test case for the use of spectral gamma ray data in fluvial stratigraphy because interpretations can be compared directly with a high resolution sequence stratigraphic framework from coeval shallow marine strata exposed nearby the stratigraphic abundance of coals and relatively uniform th k ratio which indicates uniform clay mineralogy in mudstone sections of the non marine blackhawk formation implies a humid subtropical climate throughout its deposition variations in facies architecture and stratigraphy are therefore interpreted to have been driven principally by fluctuations in relative sea level and hinterland tectonics fluvial and fluvio tidal sandstones within incised valleys which lie above erosional sequence boundaries have a highly variable spectral gamma ray character but locally are marked by distinctive heavy mineral lags and concentrations th consistently 3 ppm on the interfluves of incised valleys sequence boundaries are marked by palaeosols that locally have a distinctive leached potassium depleted character th k ratio 17 lateral variability in spectral gamma ray character of sequence boundaries is consistent with facies and sequence stratigraphic models of the non marine blackhawk formation and castlegate sandstone but sequence boundaries do not exhibit a clear diagnostic character in every location in addition high th k ratios of the type noted at interfluve palaeosols may be produced by potassium depletion beneath coal seams as a result of acid groundwater percolation during early diagenesis and by thorium enrichment in heavy mineral lags within foreshore sandstones these alternative interpretations can be eliminated if high th k ratios occur in intervals lacking coal seams and shallow marine sandstones respectively thus within the context of a sound understanding of detrital mineralogy diagenetic history facies and appropriate sequence stratigraphic models spectral gamma ray data allow sequence boundaries to be identified and correlated in non marine fluvial strata at least 80 km from the interpreted coeval shoreline

shaking intensity thresholds for rock falls and slides evidence from 1987 whittier narrows and superstition hills earthquake strong motion records due to inconsistencies in using descriptive intensity scales to describe earthquake shaking necessary to trigger landslides arias intensity a quantity calculated from seismic strong motion records has been employed as a measure of the seismic energy required to initiate landslides because arias intensity is defined as the sum of all the squared acceleration values from a strong motion record it is a measure of the energy dissipated at a site by shaking it incorporates both amplitude and duration information making it more useful to compare with the failure of slopes than parameters such as peak acceleration arias intensities calculated from the 24 october 1987 superstition hills and the 1 october 1987 whittier narrows earthquakes in southern california allow comparisons with the limits of landslides specifically falls and slides from rock and soil in these two earthquakes these comparisons establish two shaking thresholds for the limits of falls and slides a range of 0 08 to 0 6 m sec is observed for tertiary and younger deposits while the range of 0 01 to 0 07 m sec is observed for mesozoic and older rocks these two ranges of shaking levels are controlled by the relative degree of fracturing and aperture of fracture systems within the two general age groups of rocks and soils in the los angeles area and the imperial valley

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

stratigraphical architecture at the muddy margin of the cretaceous western interior seaway southern utah the tropic shale and correlative tununk shale member of the mancos shale accumulated during cenomanian turonian time within prodeltaic environments near the western margin of the western interior seaway of north america stratigraphical and sedimentological analysis has revealed a detailed history of relative sea level change in the thick fine grained succession the tropic and tununk shales were deposited during the greenhorn second order sea level cycle over a time span of about 2 5 million years in southern utah six depositional sequences are superposed upon the record of this long term sea level change the sequences developed during third order relative sea level cycles of hundreds of thousands of years duration and are composed of at least 37 parasequences arranged in retrogradational aggradational and progradational parasequence sets the tropic shale and tununk shale member accumulated just basinward of the axis of maximum subsidence of a foreland basin stratal geometries and facies distribution patterns in the succession indicate that in southern utah the greenhorn cycle was tectonically controlled during the greenhorn transgression and highstand rapid rates of tectonic subsidence trapped terrigenous sediment to the west of the study area in the more proximal foreland at this time hemipelagic facies accumulated at relatively slow rates in southern utah and type 2 sequences developed during third order sea level cycles in contrast during the greenhorn regression rates of thrust induced subsidence in the proximal foreland basin evidently slowed and deltaic clinoforms prograded across the study area at least one forced regression occurred in southern utah at this time and type 1 sequences developed the formation of type 1 sequence boundaries in the upper part of the tropic shale and tununk shale member points to episodes of base level fall and indicates that the six third order sea level cycles recorded in the succession were not the result of changes in sediment supply alone the third order cycles may have been a consequence of episodic tectonism the timing of these cycles however suggests that development of sequences and parasequences in the tropic shale and tununk shale member may have been related to orbital forcing in the milankovitch band glacioeustasy or climatically related fluctuations in the amount of groundwater stored on continents may explain these high frequency sea level changes

gravity driven sediment transport on the continental shelf implications for equilibrium profiles near river mouths an analytical model is developed for equilibrium bathymetric profiles off river mouths associated with the shoreward convex upward portion of subaqueous deltas and clinoforms the model builds on recent field results demonstrating that gravity driven flux of suspended mud is important on shelves provided that wave induced suspension of sediment supports the requisite turbid hyperpycnal layer because the maximum sediment load is determined by the critical richardson number the results are independent of the properties of the suspended mud or the bed the model assumes the equilibrium state to represent a balance between the supply of sediment by a river at the coast and the downslope bypassing of sediment to deep water within wave supported turbid near bed layers progressive seaward increases in bed slope across the convex shelf profile allow the attenuation of wave agitation with depth to be compensated for by a downslope increase in the contribution of gravity the model is consistent with shelf profiles off the mouths of the eel california ganges brahmaputra bangladesh waiapu new zealand po italy and rhone france rivers the equilibrium profile is predicted to be a function of wave climate and riverine sediment supply only with deeper and broader profiles associated with decreasing sediment supply increasing wave height and or increasing wave period

shoreface tongue geometry constrains history of relative sea level fall examples from late cretaceous strata in the book cliffs area utah progradational shoreface tongues preserve a near complete depositional record of relative sea level highstands falls and lowstands two distinct styles of progradational shoreface tongue are examined in an extensive outcrop and subsurface dataset from late cretaceous strata of the book cliffs area utah representing i highstand through attached lowstand progradation and ii highstand through detached lowstand progradation using this dataset key geometrical attributes of the shoreface tongues and their internal facies architecture are identified and quantified that enable the reconstruction of relative sea level fall history for example attached wave dominated lowstand shoreface deposits record a slow 0 2 0 3 mm yr 1 low magnitude 14 m relative sea level fall punctuated by minor rises detached weakly wave influenced lowstand shoreface deposits record a more rapid 0 4 0 5 mm yr 1 high magnitude 45 m relative sea level fall synchronous with a marked change in sediment delivery and depositional process regime at the shoreline

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

characteristic trace fossils in nearshore to offshore sequences upper cretaceous of east central utah more than 20 trace fossil species occur in marine facies of the cretaceous star point and blackhawk formations in the book cliffs and wasatch plateau provinces of utah major genera include ancorichnus arenicolites aulichnites chondrites conichnus cylindrichnus medousichnus ophiomorpha palaeophycus planolites rosselia schaubcylindrichnus scolicia skolithos teichichnus teredolites and thalassinoides newly named taxa include ancorichnus capronus medousichnus loculatus and rosselia chonoides most trace fossils occur in characteristic albeit intergradational ichnofacies correlative with major lithofacies of regressive nearshore to offshore sequences the latter include foreshore foreshore shoreface transition shoreface and offshore facies landward facies are typified by clean well sorted well stratified sparsely burrowed sandstones seaward facies except where interrupted by hummocky bedded sandstones exhibit successively less pure less well sorted and stratified more intensely

evidence of across shelf transport of fine grained sediments turbidite filled shelf channels in the campanian aberdeen member book cliffs utah usa the shore normal transport of fine grained sediments by shelf turbidity currents has been the focus of intense debate over the last 20 years many have argued that turbidity currents are unlikely to be a major depositional agent on the shelf however sedimentological architectural stratigraphic and palaeogeographic data from the campanian aberdeen member book cliffs eastern utah suggests otherwise and clearly demonstrates that storm generated and river flood generated underflows can transport a significant volume of fine grained sediments across the shelf these across shelf flowing turbidity currents cut large subaqueous channel complexes up to 7 m deep tens of kilometres basinward of their time equivalent shoreface the shelf channels were filled with organic rich siltstones mudstones and very fine to fine grained bouma like sandstone beds including wave modified turbidites hyperpycnites and classical turbidites deposition was above storm wave base palaeocurrent data reveal an overwhelmingly dominant across shelf east south east offshore directed transport trend tectonic activity and or concomitant palaeogeographic reorganization of the basin may favour the generation of these turbidite rich shelf deposits by altering the relative balance of wave versus fluvial energy increased erosion and sediment supply rates because of tectonic uplift of the hinterland may have increased the probability of fluvial dominance along the coastline and hence the possibility of submarine channelization in front of the river mouths additionally the coastline may have become more sheltered from direct wave energy thus allowing the fluvial processes to dominate seasonal increases in rainfall and storm activity may also favour the generation of across shelf underflows on wave dominated shorelines isolated shelf channels and lobes are most likely to be found down dip of fluvial feeder systems in relatively high sediment supply settings these features are also most likely to occur in systems tracts that straddle a sequence boundary especially those which are tectonically generated as these would enhance the potential for altering basin morphology and hence the balance of fluvial and wave energy isolated shelf channels are recognized in older and younger strata in the book cliffs region implying that wave supported gravity flows were a recurrent phenomena in the campanian of utah it is probable that isolated shelf bodies are preserved in other stratigraphic intervals in the cretaceous western interior of north america and other basins worldwide and are currently being overlooked or misidentified shoreface to shelf facies models should be revised to incorporate turbidite rich shelf deposits in some shelf settings

vertical and lateral variation in the petrography of the upper cretaceous sunnyside coal of eastern utah usa implications for the recognition of high resolution accommodation changes in paralic coal seams the sunnyside member of the upper cretaceous blackhawk formation in the book cliffs of eastern utah is composed of coal bearing coastal plain strata and wave dominated shoreface deposits the member includes a thick up to 6 m laterally extensive coal seam which formed in a large ombrotrophic raised mire parallel to the shoreline of the western interior seaway the petrographic composition of the sunnyside coal was investigated by means of maceral analysis and telovitrinite reflectance determinations of closely spaced samples taken from seven vertical sections through the seam sampling was carried out in a combination of outcrop and underground mine sites using lithotype logging to determine sample spacing the excellent exposure in the study area enables accurate stratigraphic correlation between sampling localities which are spread over more than 30 km of depositional dip and 50 km of depositional strike the correlation of petrographic trends between the seven sampled sections demonstrates the reproducibility of the results and suggests that they represent regional scale accommodation changes as opposed to localised variation in the mire on this basis we are able to identify a high resolution record of accommodation change throughout the deposition of the sunnyside coal spanning two cycles of increasing and decreasing accommodation we are also able to identify a marine flooding surface within the coal which can be traced down depositional dip into the time equivalent shallow marine strata where it represents a parasequence boundary the proportion of detrital minerals is used as the main discriminator of accommodation trends within the coal other useful indicators of conditions in the mire include semifusinite pyrite and isometamorphic variations in telovitrinite reflectance

oolitic ironstone of the cretaceous western interior seaway east central utah abstract a thin but distinctive red weathered oolitic ironstone occurs 7272within the upper cretaceous mancos shale of east central utah it is characterized by a grain supported ooid rich lithology containing iron clay berthierine muscovite hematite goethite and carbonate minerals around clastic nuclei associated grains of phosphatic material bone and fish teeth are common admixed with fossil hash and wood pieces internal structures within the mappable oolitic ironstone bodies include channel scours cross bedding contorted bedding load structures mud rip up clasts and marine trace fossils the oolitic ironstone is encased within the mancos shale and cannot be traced laterally however four additional facies occur in vertical succession with the ironstone inoceramus mounds siltstone shale fine grained channel sandstone and coarse grained lithic sandstone the sedimentologic features of the oolitic ironstone and its associated facies indicate a prodelta environment influenced by river dominated flooding in the delta front environment providing sand fed through small channels and by fluctuating or alternating sea floor bottom conditions due to periodic storm or current action the oolitic ironstone is inferred to have formed as shoals within the inner shelf like setting a key factor in formation of the oolitic ironstones is eustatic control in the western interior seaway the ironstone was deposited during a relative sea level low and then winnowed during a transgressive rise to create a condensed section thus the interval is an important stratigraphic marker in an otherwise monotonous section of shale and it represents a parasequence boundary expression in offshore deposits where eustatic influences are commonly difficult to recognize

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

stratigraphic significance of ooidal ironstones from the cretaceous western interior seaway the peace river formation alberta canada and the castlegate sandstone utah u s a ooidal ironstones form prominent units and an appreciation of their sedimentological and stratigraphic significance is important for the interpretation of sedimentary successions ooidal ironstones from the albian paddy member of the peace river formation alberta canada and the campanian castlegate sandstone of the mesaverde group in colorado have been analyzed the ooidal ironstones are associated with a major sequence boundary and subsequent transgressive surface both are interpreted to have been deposited under conditions of low net sediment accumulation in well oxygenated bottom water conditions with episodic storm events reworking the sediments the paddy member ironstone is interpreted to have been deposited in an estuarine environment and the castlegate ironstone is interpreted to have been deposited in a shallow marine environment both ironstones are dominated by berthierine ooids and grain rimming and pore filling siderite with later ferroan dolomite and calcite in the castlegate ooidal ironstone petrographic geochemical and isotopic evidence coupled with thermodynamic considerations indicates that the ooidal ironstone mineralogy formed during suboxic diagenesis the conditions required for suboxic diagenesis were extensive sediment reworking and slow net sediment accumulation rates we propose that these conditions arose as a result of marine transgression during the initial relative sea level rise following the development of a sequence boundary ooidal ironstone formation ceased once sedimentation rates increased and transgression deepened water depths considerably these results illustrate the association between ooidal ironstones and major stratal surfaces in sedimentary successions and highlights the complexity that early diagenesis at such surfaces can take

a model for migrating shelf bar sandstones in upper mancos shale campanian northwestern colorado the duffy mountain sandstone was deposited by migrating submarine shelf bars that are now completely encased in marine mudstones of the mancos shale upper cretaceous the shelf bars were deposited at least 10 mi 16 km offshore and stood approximately 100 to 150 ft 30 to 46 m above a shallow shelf the bars were never emergent but were shallow enough for fair weather waves to form ripples along their crests these elongate sand bodies trend northeast southwest approximately parallel to the shoreline the sediment was probably derived from reworking of transgressed littoral deposits in southwestern wyoming four subenvironments are recognized 1 landward flank of the shelf bar the back bar 2 the axial crest of central bar 3 a seaward facing ramp subfacies and 4 the shelf upon which the shelf bars migrated two major processes were active during deposition 1 fair weather longshore southwesterly currents and 2 storm erosion and westerly across the shelf bar sediment transport during fair weather sand waves transported sediment along the central bar while the back bar and shelf were being bioturbated storms eroded the seaward face of the bar and portions of the central bar creating hummocky erosion surfaces eroded sediment transported across the bar was deposited in coarsening upward spillover lobes in the back bar after the storm waned sediments deposited in t e back bar were bioturbated and sand waves were deposited on the eroded central bar migration of sand waves onto the eroded face of the bar formed the ramp facies as the shelf bar migrated the central bar facies climbed stratigraphically over the back bar facies the direction of shelf bar migration was probably controlled by the interaction of fair weather and storm sediment transport