Summary Assessing a hydrocarbon reservoir for development involves using various types of data including seismic acquisitions, analogue production data, and exploration/offset well data. In contrast, assessing saline aquifers for CO2 injection is typically constrained by limited project finances and lack of previous exploration and production experience. As a result, there is a high level of uncertainty regarding depositional environment and the resulting effect of this on CO2 injectivity. The lack of knowledge about a saline aquifer's depositional environment and architecture poses risks when estimating its storage efficiency. These risks may include injecting into isolated compartments or low-quality areas, which can lead to low storage efficiency and faster pressure development. For instance, the stratigraphically-compartmentalized fluvial Tubåen Formation in Snøhvit field of Barents Sea restricted CO2 plume and pressure development. This study employs a stochastic approach to examine how depositional environment impacts storage capacity, injectivity, and pressure development in CO2 sequestration through reservoir simulations. Additionally, this research analyses how depositional environment drives CO2 and pressure plume migration during injection and soaking in periods. The study contributes important insights into assessing geological formations for CO2 storage and optimising deposition-specific limitations and effects.

Submarine lobes form at the distal end of sediment gravity flow systems and are globally important sinks for sediment, anthropogenic pollutants and organic carbon, as well as forming hydrocarbon and CO2 reservoirs. Deep-marine, near bed or bottom currents can modify gravity flow pathways and sediment distribution by directly interacting with the flow or by modifying seafloor morphology. Deciphering the nature of gravity- and bottom currents interaction, particularly in ancient systems, remains a challenge due to the lack of integrated datasets and the necessary oceanographic framework. Here we analyse high-resolution 3D seismic reflection and core data from the Upper Cretaceous interval offshore Tanzania to reveal the interaction of turbidite lobes with fine-grained sediment waves and contourite drift deposits. Contourite drift morphology governs the large-scale confinement style and shape of lobes that range from frontally confined and crescent shaped, to laterally confined and elongated, to semi-confined lobes. Core data reveals massive to cross-laminated high density turbidites in the lobe axis position that show no direct interaction between gravity flows and contour currents. Lobe off-axis and fringe deposits consist of parallel- and ripple-laminated, low density turbidites, which are inter-bedded with bioturbated, muddy siltstones that represent the toes of contourite drifts. Starved ripples, and streaks of up to fine-grained sandstone above individual turbidite beds indicate reworking by bottom currents. This facies distribution reflects the temporal interaction of quasi-steady bottom currents and turbidity currents that interact with the topography and build lobes over short periods of time. Frontally confined turbidity currents form lobes in a fill-and-spill fashion, in which the confinement of turbidity currents causes rapid deposition and obscures any bottom current signal. Lateral confinement causes increased turbidity current runout length, and promotes the development of lobe fringes with a high proportion of bottom current reworked sands. During times when sediment gravity flows are subordinate, contourites accumulate on top of the lobe, confining the next flow and thus modifying the overall stacking pattern of the lobe complex. Although sediment volumes of these bottom current modified lobe complexes are comparable to other deep-marine systems, bottom currents considerably influence facies distribution and deposit architecture.

Dissolution of CO2 is a critical chemical trapping mechanism for the secure storage of CO2 in the subsurface. However, there is considerable uncertainty over the rate and cumulative mass of trapping via CO2 dissolution, particularly over longer timescales. Naturally occurring CO2 reservoirs are valuable analogues that can help to predict the long-term performance of anthropogenic CO2 storage. The 3He and δ13C content within the CO2 in natural analogues can be used to quantify the fraction of gaseous CO2 removed by dissolution. Previous studies show that dissolution is the dominant form of chemical trapping. In the Bravo Dome natural CO2 reservoir, dissolution has likely removed between 20-30% of all gaseous CO2. Here, we present a meta-analysis of dissolution rates constrained from a natural analogue of long-term storage (Bravo Dome), an operating CO2 reservoir (Sleipner) and a sample of published modelling studies. Our analysis tests end-member models for the change in CO2 dissolution rate over time, in order to better constrain the wide range of outcomes that current modelling studies indicate. Results from Bravo Dome are on the low end of the range from modelling studies. Analogue evidence supports a model of the majority of CO2 dissolution occurring during or shortly after CO2 injection into the reservoir, followed by a rapid decline in dissolution rate over time. As natural analogues are the only means to directly assess dissolution rates through geologic time, the analogue database needs to be expanded and here we identify sites that will be prioritized.

Scours, and scour fields, are common features on the modern seafloor of deep-marine systems, particularly downstream of submarine channels, and in channel-lobe-transition-zones. High-resolution images of the seafloor have improved the documentation of the large scale, coalescence, and distribution of these scours in deep-marine systems. However, their scale and high aspect ratio mean they can be challenging to identify in outcrop. Here, we document a large-scale, composite erosion surface from the exhumed deep-marine stratigraphy of Unit 5 from the Permian Karoo Basin succession in South Africa, which is interpreted to be present at the end of a submarine channel. This study utilizes 24 sedimentary logs, 2 cored boreholes, and extensive palaeocurrent and thickness data across a 126 km 2 study area. Sedimentary facies analysis, thickness variations and correlation panels allowed identification of a lower heterolithic-dominated part (up to 70 m thick) and an upper sandstone-dominated part (10–40 m thick) separated by an extensive erosion surface. The lower part comprises heterolithics with abundant current and sinusoidal ripples, which due to palaeocurrents, thickness trends and adjacent depositional environments is interpreted as the aggradational lobe complex fringes. The base of the upper part comprises 2-3 medium-bedded sandstone beds interpreted as precursor lobes cut by a 3–4 km wide, 1–2 km long, and up to 28 m deep, high aspect ratio (1:100) composite scour surface. The abrupt change from heterolithics to thick-bedded sandstones marks the establishment of a new sediment delivery system, which may have been triggered by an updip channel avulsion. The composite scour and subsequent sandstone fill support a change from erosion- and bypass-dominated flows to depositional flows, which might reflect increasingly sand-rich flows as a new sediment route matured. This study provides a unique outcrop example with 3D stratigraphic control of the record of a new sediment conduit, and development and fill of a large-scale composite scour surface at a channel mouth transition zone, providing a rare insight into how scours imaged on seafloor data can be filled and preserved in the rock record.

Deep‐water stratigraphic successions from syn‐ to post‐rift stages are an archive of evolving physiographic configurations, and can record axial and transverse sedimentary sources. The healing of topography decreases the influence of syn‐rift structures on sedimentation patterns and transport processes over time, which leads to a long‐term transition from dominantly axial to transverse dispersal patterns. The Halten and Dønna terraces, offshore mid‐Norway, comprise a series of rift‐related sub‐basins established during the Jurassic, which were infilled with sediments during the Cretaceous. The Cretaceous Lysing Formation developed as slope‐ and basin‐floor fans within a series of weakly confined post‐rift sub‐basins with some shallow marine deposits interpreted on the basin margins. A deep‐water setting is supported by seismic interpretation, and bed type and architectural element analysis in all cored and uncored wells in the area. We document that an axial submarine fan system was active throughout the post‐rift stage due to subtle inherited topography from syn‐rift structures, which interacted with locally sourced transverse sediment sources. This led to a complicated stratigraphic architecture, with lobe fringe deposits of the axial fan system juxtaposed with channel‐fills and channel‐lobe transition zone deposits of transverse systems. The refined palaeogeographic reconstruction of the Lysing Formation illustrates how subtle topography can impact sediment routing patterns many millions of years after the end of rifting and can be used for palaeoenvironmental interpretations in other post‐rift settings.

Deep-water lobe deposits are arranged hierarchically and can be characterized by high net:gross ratios but poor sand connectivity due to thin, but laterally extensive, shale layers. This heterogeneity makes them difficult to represent in standard full-field object-based models, since the sands in an object-based model are not stacked compensationally and become connected at a low net:gross ratio. The compression algorithm allows the generation of low-connectivity object-based models at high net:gross ratios, by including the net:gross and amalgamation ratios as independent input parameters. Object-based modelling constrained by the compression algorithm has been included in a recursive workflow, permitting the generation of realistic models of hierarchical lobe deposits. Representative dimensional and stacking parameters collected at four different hierarchical levels have been used to constrain a 250 m-thick, 14 km(2)model that includes hierarchical elements ranging from 20 cm-thick sand beds to more than 30 m-thick lobe complexes. Sand beds and the fine-grained units are represented explicitly in the model, and the characteristic facies associations often used to parameterize lobe deposits are emergent from the modelling process. The model is subsequently resampled without loss of accuracy for flow simulation, and results show clearly the influence of the hierarchical heterogeneity on drainage and sweep efficiency during a water-flood simulation.

Submarine slope channel systems have complicated three‐dimensional geometries and facies distributions, which are challenging to resolve using subsurface data. Outcrop analogues can provide sub‐seismic‐scale detail, although most exhumed systems only afford two‐dimensional constraints on the depositional architecture. A rare example of an accessible fine‐grained slope channel complex set situated in a tectonically quiescent basin that offers seismic‐scale, down‐dip and across‐strike exposures is the Klein Hangklip area, Tanqua‐Karoo Basin, South Africa. This study investigates the three‐dimensional architecture of this channel complex set to characterise the stratigraphic evolution of a submarine channel‐fill and the implications this has for both sediment transport to the deep‐oceans and reservoir quality distribution. Correlated sedimentary logs and mapping of key surfaces across a 3 km 2 area reveal that: (i) the oldest channel elements in channel complexes infill relatively deep channel cuts and have low aspect‐ratios. Later channel elements are bound by comparatively flat erosion surfaces and have high aspect‐ratios; (ii) facies changes across depositional strike are consistent and predictable; conversely, facies change in successive down depositional dip positions indicating longitudinal variability in depositional processes; (iii) stratigraphic architecture is consistent and predictable at seismic‐scale both down‐dip and across‐strike in three‐dimensions; (iv) channel‐base‐deposits exhibit spatial heterogeneity on one to hundreds of metres length‐scales, which can inhibit accurate recognition and interpretations drawn from one‐dimensional or limited two‐dimensional datasets; and (v) channel‐base‐deposit character is linked to sediment bypass magnitude and longevity, which suggests that time‐partitioning is biased towards conduit excavation and maintenance rather than the fill‐phase. The data provide insights into the stratigraphic evolution and architecture of slope channel‐fills on fine‐grained continental margins and can be utilised to improve predictions derived from lower resolution and one‐dimensional well data.

Clean basal and capping argillaceous sandstone couplets in deep water settings have been previously interpreted as the result of spatially segregated turbidity currents and debris flows or spatio‐temporal transitioning of a turbulent flow to a transitional/laminar state. However, this paper presents three‐dimensional laboratory experiments demonstrating that a single sediment‐gravity flow can develop sand–mud couplets by autogenic remobilization of sediments that are still in the process of being deposited. This remobilization appears common to flows composed of mixtures of sand and mud with viscosities and strengths measurably greater than water, but not so high as to fully suppress the settling of sand through the depositional current. Dewatering in the early sand deposit acts to lubricate the basal portion of the increasingly muddy upper division of the flow, causing it to accelerate downslope, triggering a secondary flow with a sediment composition distinct from the original mixture. Sediment deposition and remobilization processes in a single sediment‐gravity flow and their resultant deposit were imaged acoustically and cored at representative locations within the deposit. The acoustic data and cores show sand–mud couplets that are qualitatively similar to interpreted turbidite–debrite‐like couplets in natural systems.

The topography of the seabed (orientation and gradient) and rheology of the flows greatly influences the character of basin-floor turbidity current deposits. Therefore, submarine fan pinchouts can help to constrain seabed topography and flow behavior at the time of deposition. Although the depositional architecture of submarine lobe pinchouts has been documented in various basin-fills, the quantification of the rates of change at pinchouts in different paleogeographic positions and basin configurations has not been attempted previously. Here, we utilize extensive outcrops and research boreholes from the oblique up-dip pinchout of Fans 3 and 4 and the lateral pinchout of Fan 3 in the Tanqua depocenter, Karoo Basin, South Africa, to compare sedimentary facies and to quantify the rates of change in gross interval thickness. At the oblique up-dip pinchout, Fan 3 thins abruptly at a rate of 12 m/km, while Fan 4 thins at a rate of 4 m/km. Marked differences between Fans 3 and 4 in sedimentary facies and architecture toward the up-dip pinchout, with termination of lobes in Fan 3 and a channel-lobe transition zone and external levee in Fan 4, suggests progradation of the system. The thinning rate of the lateral pinchout of Fan 3 is 2 m/km, with the presence of hybrid beds in the lower part of Fan 3, while the upper part is dominated by structured sandstones and thin-bedded heterolithics. The variations in facies suggest that lobe-scale frontal and lateral pinchouts are stacked at the lobe complex-scale lateral pinchout of Fan 3, highlighting the importance of a hierarchical understanding when studying basin-floor fan pinchouts. The quantified rates of change in fan thickness and sedimentology on the oblique up-dip and lateral fan pinchouts are markedly different. Contrasting pinchout architecture above slopes with subtle differences in gradient and orientation cautions against the simple definition of reservoir input parameters for stratigraphic traps in submarine fan systems.

Initial porosity and permeability in deep-water systems are controlled by primary sedimentary texture and mineralogy. Therefore, understanding the sedimentary processes that control changes in primary texture is critical for improved reservoir quality predictions. A well-constrained, exhumed submarine lobe in the Jaca Basin, and a submarine channel-fill element in the Aínsa Basin, northern Spain, were studied to characterize the depositional reservoir quality in axial to marginal/fringe positions. Construction of architectural panels and strategic sampling enabled analysis of the spatial changes in textural properties, and their relationship to reservoir quality distribution. Samples were analyzed in thin-section to establish how depositional processes inferred from outcrop observations affect textural properties. Results show that high-density turbidites are concentrated in lobe- and channel-axis positions and exhibit good depositional reservoir quality. Lobe off-axis deposits contain high- and low-density turbidites and have moderate depositional reservoir quality. Conversely, low-density turbidites dominate lobe fringe and channel-margin positions and have relatively poor depositional reservoir quality. There is a sharp decrease in depositional reservoir quality between the lobe off-axis and lobe fringe due to: 1) an abrupt increase in matrix content; 2) an abrupt decrease in sandstone amalgamation; and 3) a decrease in grain-size. There is an abrupt increase in depositional reservoir quality from channel margin to channel axis corresponding to: 1) an increase in total sandstone thickness and amalgamation; 2) an increase in grain-size, 3) a decrease in matrix content. Rates of change of key properties are up to two orders of magnitude greater between channel-fill sub-environments compared to lobe sub-environments. Spatial variability in properties of discrete architectural elements, and rates of changes, provides input to reservoir models during exploration, appraisal, and development phases of hydrocarbon fields.

Summary “A 3D geological modelling workflow is presented that tests the impact of fine-scale heterogeneities within a basin-floor lobe complex on reservoir connectivity. Capturing multiscale heterogeneities within deep-water stratigraphy can help to improve reservoir models, and therefore recovery factors. The use of outcrop analogues is a key tool within this process for gaining knowledge on detailed sedimentary architectures and facies relationships. The sand-rich submarine fan systems of the Tanqua depocentre, South Africa, allow a detailed study of individual submarine lobe deposits. Artificial injectors and producers were implemented at various locations in the system after which streamline analysis was performed. The findings show that the lobe architecture model employed has a significant influence on the predictability of the breakthrough time. Differences in facies architecture and lobe-on-lobe amalgamation impact connectivity and macroscopic sweep efficiency, which influence production results. Channelised lobe areas are less predictable reservoir targets owing to uncertainties associated with channel-fill heterogeneities. The implementation of sedimentary detail and the use of realistic sedimentary concepts on the architectural scale are shown to be vital to understand reservoir connectivity and improve predictions of reservoir recovery.”

Sedimentary facies in the distal parts of deep-marine lobes can diverge significantly from those predicted by classical turbidite models, and sedimentological processes in these environments are poorly understood. This gap may be bridged using outcrop studies and theoretical models. In the Skoorsteenberg Fm., a downstream transition from thickly-bedded turbidite sandstones to argillaceous, internally layered hybrid beds is observed. The hybrid beds have a characteristic stratigraphic and spatial distribution, being associated with bed successions which generally coarsen- and thicken-upwards reflecting deposition on the fringes of lobes in a dominantly progradational system. Using a detailed characterisation of bed types, including grain size, grain fabric and mineralogical analyses, a process-model for flow evolution is developed. This is explored using a numerical suspension capacity model for radially spreading and decelerating turbidity currents. The new model shows how decelerating sediment suspensions can reach a critical suspension capacity threshold beyond which grains are not supported by fluid turbulence. Sand and silt particles, settling together with flocculated clay, may form low yield-strength cohesive flows; development of these higher concentration lower boundary layer flows inhibits transfer of turbulent kinetic energy into the upper parts of the flow ultimately resulting in catastrophic loss of turbulence and collapse of the upper part of the flow. Advection distances of the now transitional to laminar flow are relatively long (several km) suggesting relatively slow dewatering (several hours) of the low yield strength flows. The catastrophic loss of turbulence accounts for the presence of such beds in other fine-grained systems without invoking external controls or large-scale flow partitioning, and also explains the abrupt pinch-out of all divisions of these sandstones. Estimation of the point of flow transformation is a useful tool in the prediction of heterogeneity distribution in subsurface systems.

Improved prediction of the recovery of oil-in-place in basin-floor fan reservoirs requires accurate characterization and modelling of multiscale heterogeneities. The use of outcrop analogues is a key tool to augment this process by documenting and quantifying sedimentary architecture, hierarchy and sedimentary facies relationships. A 3D geological modelling workflow is presented that tests the impact of fine-scale heterogeneities within basin-floor lobe complexes on reservoir connectivity. Construction of geological models of a basin-floor lobe complex allows realistic depositional architecture and facies distributions to be captured. In addition, detailed models are constructed from channelized areas within a basin-floor lobe complex. Petrophysical modelling and streamline analysis are employed to test the impact on reservoir connectivity between lobe models with: (i) vertically stacked facies with coarsening- and thickening-upwards trends in all locations; and (ii) lateral facies changes with dimensions and distributions constrained from outcrop data. The findings show that differences in facies architecture and, in particular, lobe-on-lobe amalgamation have a significant impact on connectivity and macroscopic sweep efficiency, which influence the production results. Channelized lobe areas are less predictable reservoir targets owing to uncertainties associated with channel-fill heterogeneities. The use of deterministic sedimentary architecture concepts and facies relationships have proven vital in the accurate modelling of reservoir heterogeneities.

Recent studies characterizing outcrop analogues of deep-water lobe reservoirs have demonstrated that these deposits are stacked in a hierarchical manner with characteristic element scales that vary between turbidite systems. Static connectivity and dynamic numerical modelling studies of idealized, non-hierarchical lobe systems have identified the presence of discrete net-gross or amalgamation ratio thresholds that control connectivity and flow. The objectives of the current work are to compile a geostatistical description of the hierarchy; to develop a hierarchical modelling scheme able to apply these conceptual and quantitative constraints; and, from these, to assess the importance of honoring the hierarchy in reservoir modelling.

Reservoir modelling and production forecasting are challenging as we are trying to describe the whole reservoir and predict the dynamic behaviour of all the wells based on a limited amount of measurements. Taking advantage of all the data available at various scales, and understanding the uncertainties in the reservoir model and the flow simulations, become then important to allow for robust development and operation for a field. In a dynamic uncertainty analysis, an accurate representation of the uncertainties in the reservoir model is preferred, and several realisations that are all probable within the uncertainty span should be considered. An integrated and automated modelling workflow that contains the whole modelling chain from depth conversion to flow simulation is then very useful. This has been demonstrated on a field development case from deep-water Gulf of Mexico. The uncertainties related to compartmentalisation are believed to be among the most important factors contributing to the total uncertainty in the in-place volumes and the recovery factor for this field. Thus fault uncertainties are incorporated into the reservoir model and their impact on the fluid flow are evaluated. An improved uncertainty estimate for the reserves is then achieved, which contributes to reduce the investment risk.

An outgrowth of the 2008 AAPG Hedberg Conference on Sediment Transfer from Shelf to Deep Water, Studies in Geology 61 was designed specifically to explore the growing interest in hyperpycnal and associated flows and hyperpycnites as significant contributors to the deep-water sedimentary record. The topic of hyperpycnal flows and their deposits, hyperpycnites, has recently emerged as the latest in a long list of hotly debated topics on deep-water sedimentary processes, environments, and deposits. This collection of chapters offers important new insights into the sediment delivery system to deep-marine waters.

Gravity-driven flows on the seafloor are the largest, yet least well understood, sediment transport agents on Earth. Recent exploration wells in ultradeep basins have revealed the presence of large sandy submarine fan systems of enigmatic facies types, many hundreds of kilometers from paleocoastlines. These sedimentary deposits often defy conventional turbidite or debrite interpretations, having a character suggestive of deposition from flows with transient turbulent-laminar rheologies. In the Wilcox Formation (Gulf of Mexico), inferred transitional flow deposits have distinctive stratigraphic stacking patterns, from fine-grained debrites to coarser grained turbidites. The vertical sequence of beds is here inferred to reflect the longitudinal bed distribution in response to lobe progradation, and demonstrates a transition from well-mixed turbulent flow, to progressively more rheologically stratified flow, and eventually to fully laminar flow. The progressive development of internal rheological boundaries resulted in a high-concentration but fluidal basal layer, and an upper quasi-laminar layer with an overriding sheared dilute turbidity current. The long runout of the flows is linked to their high silt and clay content; it is most likely flow expansion at the channel-lobe transition that drives flow transformation. This process-based model may be applicable to many deep-water settings and provides a framework within which to interpret the stratigraphic and spatial distribution of these complex deposits.

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

A comparison between tidal bars from a deltaic to estuarine complex in the Middle Devonian Baltic Basin shows contrasts in sedimentary structures and bar preservation, related to changes from a regressive to transgressive setting. Detailed facies analysis of the 20-30 m thick tide-dominated estuarine Amata Formation is combined with previous analysis of the underlying deltaic Gauja Formation in order to develop specific criteria for differentiating between estuarine tidal bars and deltaic tidal bars.The estuarine tidal bars are characterized by: 1) preserved bar topsets; 2) dominantly landward palaeocurrent directions; 3) well to very-well-sorted, very fine- or fine-grained sandstones; and 4) overall retrogressive stacking with overlying marine mudstones. These bars, were deposited in the outer estuary, as elongated sand bodies. Tidal currents dominated the depositional regime, seen from the abundant tidal facies, and high energy is suggested by low abundance of mudstone drapes and mica drapes.The deltaic tidal bars are characterized by: 1) eroded bar topsets; 2) dominantly basinward palaeocurrent directions; 3) poorly sorted sandstone with grain-size ranging from very fine sands to granules; and 4) overall progradational stacking patterns. These tidal bars were situated seaward of the delta plain. Strong fluvial influence is reflected by coarse-grained, poorly sorted sandstone, mudstone and pebble clasts and the predominately basinward palaeocurrent directions.The criteria listed above can all be useful for separating between the two tidal-bar types in basins with similar settings as the Devonian Baltic Basin, however, to be used as a general facies model, the criteria must be filtered for local variations. We suggest that characteristics which occur due to the regressive to transgressive stacking patterns of tidal bars; the different palaeocurrent directions, and the preservation versus truncation of tidal bars, are broad diagnostic criteria that could be applied to other basins. (C) 2009 Elsevier B.V. All rights reserved.