Deep-water Clastic Systems Research Articles

Deep-water clastic systems in the Upper Carboniferous (Upper Mississippian–Lower Pennsylvanian) Shannon Basin, western Ireland

The Upper Carboniferous Shannon Basin of western Ireland contains a more-than-2300-m-thick (7540 ft) basin-fill succession, shallowing upward from deep-water to deltaic and incised fluvial deposits. The deep-water basin floor and slope succession is world renowned as an analog for hydrocarbon-bearing deep-water sandstones on several continental margins such as the basins in East and West Africa, South America, the Gulf of Mexico, and not least offshore northwest Europe. The Shannon Basin is frequently visited by both academia and industry for research and training purposes. A series of behind-outcrop research boreholes reveals the subsurface expression of the deep-water rocks and is complemented by seismic-scale cliff exposures. The succession is interpreted as a first-order basin-scale linked sedimentary system. This system can be analyzed using the principles of source-to-sink analysis and leaves the visitor with a complete picture of the basin fill, enhanced by spectacular sedimentological and stratigraphic detail.

Depositional architecture of sand-attached and sand-detached channel-lobe transition zones on an exhumed stepped slope mapped over a 2500 km2 area

The geomorphology and seismic stratigraphy of deep-water clastic systems from slope valleys through channel-levee systems to basin-floor fans have been observed and described in modern and ancient subsurface examples around the world. However, the distribution of sedimentary facies, grain size, and small-scale architectural elements remains poorly constrained. Extensive exposures (>2500 km 2 ) of four stacked deep-water composite sequences have been mapped from heterolithic channel-levee systems on the slope to sand-rich basin-floor deposits. The data set from Units C–F of the Fort Brown Formation in the Permian Laingsburg depocenter of South Africa permits a unique opportunity to document and compare their depositional architecture at a high resolution for tens of kilometers downdip. Isopach thickness maps indicate that compensational stacking across multiple stratigraphic scales occurs on the basin floor, whereas preferred axial pathways were present on the slope, leading to subvertical stacking patterns. Units C and D are sand-attached systems; slope valley systems are mapped to pass transitionally downslope through levee-confined channels to lobe complexes over distances of >30 km. The slope valley fills of Units E and F, however, are separated from their downdip sand-rich lobe complexes by a thin, sand-poor tract several kilometers in length and are termed sand detached. Locally, this sand-poor tract is characterized by a distinctive facies association of thin-bedded turbidites with numerous scours mantled with rip-up clasts, and a top surface that includes megaflutes and remobilized sediments. This assemblage is interpreted to indicate a widespread area of sand bypass. This unique data set provides an exploration-scale insight and understanding of how different segments of a prograding slope evolved over time in terms of gradient, physiography, and hence the degree to which sand was stored or bypassed to the basin floor, and the evolution from sand-attached to sand-detached systems. The development of sand-detached systems suggests that a steeper gradient formed, possibly related to developing underlying structure, that led to the development of a stepped slope profile. The study highlights that updip stratigraphic trapping at reservoir scale can occur with minor bathymetric changes.

Large-volume gravity flow deposits in the Central Carpathian Paleogene Basin (Orava region, Slovakia): evidence for hyperpycnal river discharge in deep-sea fans

Abstract The deep-water clastic systems of the Central Carpathian Paleogene Basin contain megabeds, which are developed in distinctive stratigraphic horizons and can be traced over long distances. These beds are characterized by great individual thickness (4-13 m), uniform lithology and internal structures. On the basis of their lithology, sedimentary structures and sequence development, the megabeds are characterized by 15 individual facies and interpreted from the viewpoint of flow hydrodynamics. The grain-size distribution and internal structures of the megabeds point to their deposition from uniform turbulent flows. The main controlling factor for generation of such large voluminous flows is inferred in the sea-level changes, when a relative rising of sea level during the Eocene/Oligocene boundary was responsible for long-lasting accumulation of the clastic supply at the basin margins. The large volume of detritus from river discharge and ravinement surfaces of flooded land was accumulated on the shore and in the conduit heads where the sediment was remobilized by other triggers. The flows generated by catastrophic floods during the early Rupelian sea-level lowstand are thought to be the most probably triggering mechanism. The large highly erosive hyperpycnal flows from flooding rivers could erode accumulated deposits in the conduit or on steeper basin-margin slopes and could cause progressive increase of the sand volume in the flow. Conduit flushing appears to be the most probable source of sediment for the very large voluminous flows that were responsible for deposition of the Orava megabeds

Channel-like features created by erosive submarine debris flows: Field evidence from the Middle Eocene Ainsa Basin, Spanish Pyrenees

We present field evidence from the Middle Eocene deep-marine Ainsa Basin, Spanish Pyrenees, to show channel-like features likely created by erosive subaqueous debris flows. Evidence from this basin suggests that the most erosive subaqueous debris-flows may create megascours removing up to ∼35 m thickness of sandy submarine-fan deposits from base-of-slope and lower-slope settings. This study suggests that individual debris flows may have been more erosive than turbidity currents, an observation that is opposed to many previous studies from the Ainsa Basin and other ancient deep-water clastic systems. In the Ainsa Basin, many of the debris flows deposited pebbly mudstones immediately above the basal erosion surfaces into which gouging flow-parallel grooves and pebble scours left isolated pebbles embedded in the immediately underlying sandstones. In one particularly well-exposed case, the sandstones immediately below the eroding debris flow were incorporated into it and preserved as sheared, disaggregated, brecciated, and partially liquefied sandstone beds within the pebbly mudstone. Our study suggests that erosion by large-volume debris flows in base-of-slope settings can be at least as important, if not more so, than turbidity currents in producing submarine megascours (probably chutes that, in cross section, superficially resemble submarine channels). This has important implications for understanding the erosivity of debris flows versus turbidity currents in modern and ancient environments, and it has significant implications for hydrocarbon reservoir continuity and heterogeneity, including the origin and recognition of mudstone-filled chutes or channels.

Heavy mineral sorting in downwards injected Palaeocene sandstone, Siri Canyon, Danish North Sea

Post-depositional remobilization and injection of sand are often seen in deep-water clastic systems and have been recently recognised as a significant modifier of deep-water sandstone geometry. Large scale injectite complexes have been interpreted from borehole data in the Palaeocene Siri Canyon near the Danish Central Graben of the North Sea hydrocarbon province. The emplacement of large scale injectite complexes has been commonly attributed to seismic activity and consequent sand liquefaction. However, due to very small differences in textural and compositional properties, and the lack of depositional structures in deep-water sandstones, the distinction between “in situ” and injected or remobilized sandstones is often ambiguous. Large scale heavy mineral sorting (in 10 m thick units) is observed in several reservoir units in the Siri Canyon and has been interpreted to represent the depositional sorting. In this study we describe an example of effective shear-zone sorting of heavy minerals in a thin downwards injected sandstone dyke which was encountered in one of the cores in the Cecilie Field, Siri Canyon. Differences in sorting pattern of heavy minerals are suggested as a tool for petrographic/geochemical distinction between “in situ” sandstones and their related injectites, especially where primary sedimentary structures are removed by fluidization or minor remobilization.

Provenance of the northern part of the Kahramanmaraş Peripheral Foreland Basin (Miocene, S Turkey)

The Miocene Kahramanmaraş Peripheral Foreland Basin (KPFB) resemble to classic foreland basin model, with small differences. In the classic model, both the accretionary wedge and foredeep extend lengthways parallel to the plate margin. In addition, accretionary wedge includes wedge top basin or piggy back basin that extends parallel to foredeep. However, the accretionary wedge of the KPFB contains small half-graben type basins that obliquely intersect the plate margin between the Arabian Plate and the Anatolide–Taurides Platform (due to the irregular shape of the plate boundary). Tectonic lineaments controlled the shape and orientation of these basins and larger main depocentre of the KFPB, which were predominantly filled with deep-sea sediments. This paper focuses on the provenance of features of the KFPB, predominantly was fed from the northern basin margin, while also aiming to resolve the complex basin evolution that occurred during the Miocene. Clasts of Palaeozoic and Mesozoic limestone and ophiolites are common components of the confined deep-water clastic systems, which evolved as elongated trenches in the north-western sector of the KPFB during the Early-Middle Miocene. During the Middle Miocene, continuous thrusting of the northern basin margin to south caused depocentre migration to south-east, through the basin interior. At that time, the north-east and central depocentres of the KPFB were filled primarily by clasts of ophiolite and metamorphic units. The tectonic control on basin fill architecture can be observed anywhere in the KFPB. The principal tectonic features controlled the geometry and orientation of the canyon, the channel geometry of the deep-water slope on the northern basin margin, the frequency and distribution of slump-slide-debris flows and the overall pattern of sedimentation cycles in the stratigraphy of the slope and the central basin floor. Some basin sectors have continuously reactivated and as a result, different sediment entry points with substantial local accumulation of sediment and deformation have evolved on the slope and basin floor. Three scales of provenance were used to investigate the source rock: (a) field-based observation and analysis of conglomerate clasts, (b) modal analysis of sandstone facies and (c) geochemical analysis, all of which were in agreement.

Large-scale conical sandstone intrusions and polygonal fault systems in Tranche 6, Faroe-Shetland Basin

Kilometre-scale sandstone intrusions are important components of many deep-water clastic systems. They result from the remobilisation and injection of sand during early stages of burial, and are commonly found in fine-grained mudrocks containing a pervasive polygonal fault network. This paper uses three-dimensional seismic data, from the Faroe-Shetland Basin, on the UK Atlantic margin, calibrated to nearby wells, to examine the relationship between an extensive system of large downward-tapering conical sandstone intrusions to the pervasive polygonal fault network present within the surrounding encasing host mudstones. The intrusions were injected upwards during the Late Miocene through Eocene/Oligocene claystones with a pre-existing polygonal fault network to form conical bodies up to 300 m high within the ∼700-m-thick claystone sequence. This study shows that polygonal faults and the discordant limbs of conical sandstone intrusions form two distinct dip populations with little overlap that have average dips of 58° and 26°, respectively. Polygonal faults display decreasing dip with increasing depth. However, conical sandstone intrusion dip is uniform throughout the Eocene–Oligocene succession. These observations lead us to conclude that the geometry of conical sandstone intrusions is not greatly affected by the presence of a pre-existing polygonal fault network, nor is it affected by increased overburden pressure with depth. Therefore, the 10–50° dip range displayed by the limbs of conical sandstone intrusions observed within the study area is a fundamental property of conical sandstone intrusions. The presence of a widespread region of conical sandstone intrusions in the Faroe-Shetland Basin has important implications for vertical fluid migration in the region. The Eocene–Oligocene claystones in the region have very low permeability, but the presence of large-scale conical sandstone intrusions and any possible feeder systems is likely to provide high-permeability fluid conduits through this sequence. In effect, the otherwise good regional caprock provided by the Eocene–Oligocene claystone sequence is breached by a network of sandstone intrusions possibly resulting in reduced hydrocarbon-trapping potential beneath the seal.

Submarine fan morphology and lithology distribution: a predictable function of sediment delivery, gross shelf-to-basin relief, slope gradient and basin topography

Over the last decade comprehensive exploration for turbidite plays has been rewarded by a significant number of hydrocarbon discoveries. However, the industry is still critically challenged with respect to appropriate and refined prediction of sand/shale distributions within these depositional systems. Along with a strong and sustained commercial interest in these plays, extensive subsurface datasets, including a new generation of core- and well/log-calibrated seismic facies suites, have become available. Based on this valuable information, systematic 2D and 3D seismic sequence stratigraphical analysis with particular focus on seismic facies and seismic geomorphology was performed in five different basins along North and South Atlantic margins. Each subsurface example was characterized with reference to its relative sequence stratigraphic order within a hierarchy. Evolving geological parameters like shelf accommodation, shelf-break position, slope gradient, slope and basin bathymetry/topography and third-, fourth- and occasionally fifth-order stacking patterns were assessed within second-order cycles in each case. Based on these observations, recognition criteria for subsurface lithology prediction were derived. Conceptual knowledge from outcrop analysis was an essential and integral part of the interpretation process throughout the study. The subsurface recognition criteria, highlighted in this study, emphasize similarity and variability between two end-member basin styles: high shelf-to-basin relief/sediment under-filled basins where sand-prone nearshore systems do not prograde over deep-water fan systems in a second-order cycle context; low shelf-to-basin relief/sediment over-filled basins where sand-prone nearshore systems do prograde over deep-water fan systems in a second-order cycle context. The most striking contrast with respect to deep-water reservoir sandstone distribution in the two basin categories relates to the fourth- and fifth-order stacking patterns of fan building-block cycles within second- and third-order cycles, which tend to show low progradation/aggradation ratio in the high relief basins and high progradation/aggradation ratio in the low relief basins. Given an understanding of geological context, these seismically identifiable patterns provide more accurate prediction of sand and shale distribution within deepwater clastic systems.

Sedimentary architecture of a canyon-style fairway feeding a deep-water clastic system, the Miocene Cingöz Formation, southern Turkey: significance for reservoir characterisation and modelling

The sedimentary architecture of a submarine canyon-fill supplying sediment to a deep-water fan system in the Adana Basin, southern Turkey is described and quantified. The canyon is at least 9-km long, 3–4-km wide, asymmetric in cross-section and has an exposed fill, 360-m thick consisting of sands and gravels deposited in sheets across the entire width of the canyon. Normal graded and nongraded pebbly sandstones reflecting deposition from both waning and waxing high-density turbidity currents dominate these deposits. Facies are identified and correlated between closely spaced sedimentary logs. A hierarchy of bedding scales is recognised, ranging from individual beds and their sedimentary structures through 3–21-m-thick packages of beds to 100+m thick major units. This hierarchy provides the framework for computer-generated 3D models where sandstone bodies and facies are stochastically modelled to provide a better understanding of the internal sedimentary architecture within similar types of canyons in subsurface or in areas of poor exposure.

Geostatistical integration of rock physics, seismic amplitudes, and geologic models in North Sea turbidite systems

Turbidite reservoirs, deepwater clastic systems often characterized by complex sand distribution, stretch the limits of conventional seismic and geostatistical modeling and analysis. Nevertheless, such reservoirs must produce at a high rate to cover large drilling and production costs. Hence, reservoir heterogeneity must be accurately quantified and the associated uncertainty measured to determine the investment risk.

Architectural elements in a high-continuity sand-prone turbidite system, late Precambrian Kongsfjord Formation, northern Norway: Application to hydrocarbon reservoir characterization

Quantifying the geometry of high-continuity (relatively unconfined) sand-prone systems in deep-water sedimentary environments is important both for a better understanding of the intrinsic nature of these systems (volumetrics, stacking patterns, etc.) and for the potential application of this data to modeling the depositional characteristics of such systems for basin analysis and reservoir modeling. A quantitative methodology is presented for defining the geometry of architectural elements within sedimentary systems. This methodology is then applied to a detailed analysis of sand-rich, deep-water systems, with examples from the late Precambrian Kongsfjord Formation, Arctic Norway, and other published outcrop and subsurface data. The efficacy of the scheme is demonstrated by its ability to discriminate effectively between reservoir architectural elements of differing scales within environments (e.g., individual beds, packets of beds) and also between environments (e.g., abyssal plain, outer-fan lobe, and submarine channel deposits). This scheme permits a quantitative, more objective, means of comparing modern and ancient, including subsurface, depositional systems. The methodology and analysis presented here provide important geometrical and geological information on architectural elements at the subseismic, typical interwell scale. The data produced by this methodology should prove useful for reservoir production and development techniques. This methodology also should have applicability in exploration, through its application to architectural elements at the fan and basin scale. In exploration and production (Begin page 1732) in deep-water clastic systems, the available data, which are commonly extremely expensive to collect, typically consist of seismic data (with high aerial but relatively poor vertical resolution) and generally few wells (with high vertical resolution but extremely low aerial resolution). Therefore, information derived from suitable outcrop analogs on the geometry of fan elements augments significantly the typically sparse available industry data from exploration and production. In reservoir development and production, standard industry disciplines such as reservoir engineering and reservoir modeling (both deterministic and stochastic) should benefit from the approach taken in this article. This is because this article provides additional information on internal reservoir heterogeneity and architecture that is directly applicable to these disciplines. The application of standard geostatistical techniques to assess the spatial continuity of individual elements (such as variogram analysis) has the potential to further extend the results derived from this methodology and analysis.

ABSTRACT: Criteria for Defining the Base-of-Slope for Deep Water Clastic Systems, Upper Brushy Canyon Formation, West Texas

ABSTRACT: Criteria for Defining the Base-of-Slope for Deep Water Clastic Systems, Upper Brushy Canyon Formation, West Texas

Vertical and lateral organization of a carbonate deep-water slope marginal to a submarine fan system, Miocene, southern Turkey

Organization is recognized in the forereef–deep water slope–submarine fan system of the Burdigalian-Langhian Kaplankaya Formation. A basinwards transition from a prograding shelfal reef complex, through forereef talus, deep-water slope and laterally encroaching bypass deep-water clastic system is described, although the deep-water slope makes up the bulk of the succession. Considerable thickness variations occur between the reef and deep-water clastic complexes; these are controlled by sea-floor topography, carbonate foreslope gradient and degree of mass wasting off the platform and foreslope. The vertical and lateral heterogeneity of the Kaplankaya deep-water slope system is described from a number of localities along a 40-km-long and up to 3-km-wide exposed section of the northern margin of the Miocene Adana Basin, a foreland basin setting resulting from thrust sheet loading from the north during the Tauride Orogeny. Detailed field mapping is supplemented with vertical sedimentary logs, photomosaics, palaeontological and petrological data to investigate stratal variation, diagnostic architectural elements, controls on slope progradation, differential timing of basinward encroachment of the reefal complex and lateral onlap of the deep-water clastic system onto the slope. Three-dimensional models are presented showing the vertical and lateral facies associations in different parts of the deep-water slope system, and provide a basis for architectural prediction of geometry and relative position in such environments.

Sand body geometry in a sand-rich, deep-water clastic system, Miocene Cingöz Formation of southern Turkey

Three types of sandstone bodies, canyon-fill, tongues and lobes are recognized, and their geometry and spatial organization described within an elongate, W–E trending deep-water clastic system. The canyon-fill comprises sheet-like, fining upward packages that pinch-out rapidly (over 20 m laterally) where they onlap against the basin margin slope to the north. To the south, bed packages pinch-out more gradually over 400–500 m where they are confined by basin floor topography that forms one margin to the canyon. Down-system from the canyon, tongues form narrow and elongate (0.5–1 km wide and 25 km long) sandstone bodies. They are non-erosive, and are thus not channels, but sedimentation is focused within palaeotopographic lows formed by basement structure and differential compaction. Lobes occur close to the mouth of the canyon, overlying the tongues. Packages of lobes (net sandstone ∼80%) and interlobe deposits (net sandstone ∼40%) are cut by distributary channels that allow sediment to bypass the lobes. The overall asymmetric geometry and elongate nature of this sand-rich deep-water clastic system, and consequently sandstone distribution and architecture, are controlled by the basin margin slope and basin floor palaeotopography.

Regional implications of structural and eustatic controls in the evolution of submarine fans: an example from the Miocene Adana Basin, southern Turkey

Deep-sea fan development is generally thought to be controlled by a combination of changes in sea level, the shape and size of the basin in which the fans are growing, and the nature of the source area. The Early Miocene evolution of the eastern Mediterranean involved significant accumulation of deep-water clastic sediment in which the importance of each of these controlling factors can be evaluated. The deep-water clastic system located in the Adana Basin has been studied in detail. Two contemporaneous, small, radial, sand-rich submarine fans (one in the west and one in the east) exhibiting different scales, fan types and styles of deposition have been recognized within the Cingöz turbidite sequence of the northern Adana Basin in southern Turkey. Sedimentological studies indicate that the fans were controlled externally by tectonics and relative eustatic sea-level fall during late Serravallian time, in combination with the nature of the source area to the north. The internal architectural stacking patterns and external geometry of the two fan systems were strongly affected by the interaction of local tectonics and turbidity current pathways, including a major topographic confinement to the southeast that forced a vertical aggradation of the eastern fan and an east–west elongation of the western fan. This paper describes a classic example of a well-exposed deep-water clastic system where (1) tectonically driven sea-floor topography, (2) syn-sedimentary tectonism and (3) eustatic rise in sea level, are the primary controls on its development.

Abstract: Seismic Lithofacies in North Sea Deep Water Clastic Systems

Abstract: Seismic Lithofacies in North Sea Deep Water Clastic Systems