Shallow Marine Sandstones Research Articles

A new genus of cassiduloid echinoid from the lower Eocene of the Pacific coast of western North America and a new report ofCassidulus ellipticusKew, 1920, from the lower Eocene of Baja California Sur, Mexico

The cassiduloid echinoidCalilampas californiensisn. gen. and sp. is described from middle lower Eocene (“Capay Stage”) shallow-marine sandstones in both the middle part of the Bateque Formation, Baja California Sur, Mexico, and the lower part of the Llajas Formation, southern California. The new genus is tentatively placed in family Pliolampadidae. The cassiduloidCassidulus ellipticusKew, 1920, previously known only from the “Capay Stage” in California, is also present in “Capay Stage” shallow-marine sandstones of the Bateque Formation.

Stratigraphic control on laterally persistent cementation, Book Cliffs, Utah

Field data from the Upper Cretaceous Blackhawk Formation in the Book Clitfs (Utah–Colorado) demonstrate the presence of laterally extensive carbonate cements beneath major marine flooding surfaces. The occurrence of firmgrounds, compaction around concretions, and high minus-cement porosities indicate that cementation occurred during early diagenesis. It is proposed that the early cementation associated with these marine flooding surfaces occurred as a result of reduced sediment accumulation rates or non-depositional hiatuses linked to abrupt deepening during marine flooding. These reduced sediment accumulation rates extended sediment residence time within early diagenetic zones, leading to enhanced early cementation in shallow marine sandstones and mudstones.

Quantification of Reservoir Geometries and Facies Proportions in Wave-Dominated, Shallow Marine Sandstones: ABSTRACT

To reliably appraise shallow marine hydrocarbon reservoirs, it is important to have a quantitative understanding of the geometries of parasequences, and the spatial distribution of facies within them. This study discusses the quantification of parasequence geometries and intraparasequence facies proportions in wave-dominated, shallow marine strata exposed in large scale outcrops in the Book Cliffs, Utah. The Grassy Member of the Blackhawk Formation consists of two, wave-dominated shallow marine sequences. Sequence 1 of the Grassy Member comprises two parasequences. Analysis of the depositional architecture of Parasequence 1 and Parasequence 2 shows they have very different geometries. Parasequence 1 is an aggradational-progradational parasequence which thickens gradually basinward. In contrast, Parasequence 2 is strongly progradational and shows and abrupt thickening in a basinward direction. Although Parasequence 1 and 2 have different dipsection geometries, analysis of changes in shoreface facies proportions in both, shows they have similar trends in the overall distribution of facies from proximal to distal positions. The Book Cliffs outcrops enable a complimentary analysis of strike geometries and facies proportions to also be undertaken. This study shows that within two progradational parasequences which have different geometries, there is a degree of predictability in the overall distribution of the wave-dominated shallow marinemore » shoreface facies. This suggests that, with an understanding of the large-scale depositional architecture of wave-dominated sandstones in the subsurface, the overall changes in the proportion of shoreface facies within that system can be predicted.« less

Sequence Stratigraphy and Depositional Environments on a Palaeozoic Clastic Ramp Margin, Ahnet-Timimoun Basin, Algeria: ABSTRACT

A wide, ramp margin was developed during the Devonian/Carboniferous in the Ahnet-Timimoun Basin, Algerian Sahara. Variations in relative sea level resulted in rapid, long distance (>500km) lateral translations of the clastic facies belts; this was the main influence on the locations of sand depocentres. The geometry and distribution of both Gedinnian and Emsian shallow marine sandstones is complex. Understanding the influence of relative sea level, shelf processes and local tectonics is essential to predicting the distribution of potential reservoir units. The Silurian to Carboniferous succession preserved in the Ahnet-Timimoun Basin can be divided into two major Transgressive-Regressive cycles, each of approximately 45 million years duration (Ashigill to Siegenian; Siegenian to Tournaisian). The T-R cycles several sequences of approximately 10 million years duration. Major source the basin were deposited in the Early Silurian (Llandovery) and Late Devonian (Frasnian) around the transgressive maximum of the T-R cycles. In the Ahnet-Timimoun Basin, marine sedimentation prevailed across much of the ramp margin. During Gedinnian times (early Devonian), progradational events associated with each sequence deposited a succession of extensive, shallow marine, coarsening-up sandstones. The sequence boundary marking the regressive maximum. Of the first T-R cycle (Siegenian) resulted in a rapid transition from an inner shelfmore » environment to braided rivers which deposited a regional, high N/G sandstone. Sequence boundaries, although marked by rapid basinward shifts in facies belts, are without significant fluvial incision. The transgressive sequence set in the overlying T/R cycle, is marked initially by rapid southwards directed trangression and an extensive ravinement surface of early Emsian age.« less

A Structurally Complex and Dynamic Reservoir Description for Reservoir Simulation, Kuparuk River Field, Alaska: ABSTRACT

The Kupanuk River Field is a structurally complex giant oil field adjacent to the Prudhoe Bay Field on Alaska`s North Slope. Oil is reservoired within two Early Cretaceous shallow marine sandstone formations, separated stratigraphically by an erosionally truncated marine silt/shale. Subjected to several phases of tectonism, this highly compartmentalized reservoir has been developed on regular 160 acre direct line drive patterns. An integrated team of geoscientists and engineers from BP Exploration (Alaska) Inc. and ARCO Alaska Inc. is presently quantifying the benefits of infill drilling at Kuparuk, and identifying the best locations for well placement. The two primary reservoir characteristics believed to impact the effectiveness of infill drilling are large-scale reservoir heterogeneity, and reservoir comparmentation due to faulting. Multiple thin pay zones within the two reservoir intervals are isolated laterally by faults with magnitudes greater than pay zone thickness. A process and tools designed to construct and maintain a structurally complex reservoir description, shared by the geoscientists and reservoir engineers, are described. Cross-discipline integration is aided by the use of Tech*Logic`s IREX 3-D reservoir modeling and visualization application. The unique architecture of the IREX model allows for representation of very complex structural geometries, and facilitates iteration between reservoir description andmore » simulation, along the seismic to simulation continuum. Modifications to the reservoir description are guided by well-level history matching within the constraints of all available geoscience information. The techniques described will be of particular interest to those working on reservoir description and simulation of structurally complex fields.« less

Architecture of an unconformity-based tidal sandstone unit in the Ametlla Formation, Spanish Pyrenees

This study is concerned with the sedimentary architecture of a shallow-marine sandstone unit in the Lower Eocene Ametlla Formation, Ager Basin, Spanish Pyrenees. The sandstone unit was formed in a tide-dominated setting, and is continuously exposed in a 10.5 km long, mainly strike-parallel, cutcrop. Its base is a prominent unconformity (sequence boundary), and it consists of two sub-units separated by a tidal ravinement surface. Sub-unit 1 (lower sub-unit) formed in an estuarine setting that was created by flooding of an incised valley system. Outside the incised valleys, an oyster bed is present as a lateral equivalent to the estuarine deposits. The sequence bounding unconformity was generated during relative sea-level lowstand, whereas the overlying estuarine and bioclastic deposits of sub-unit 1 formed in the early stages of the transgressive systems tract. In sub-unit 2, above the tidal ravinement surface, estuary mouth-bar and tide-dominated delta deposits are the main facies associations, interfingering with offshore to inner shelf sediments westwards. These deposits formed in later stages of the transgressive systems tract. The large-scale model of the sandstone unit served as a framework within which the internal arrangement of architectural elements (AE) was recorded. Twelve AE were recognized. They mostly have a lensoid geometry, and their lateral transitions are abrupt or occur by interfingering over distances of 50–250 m. The AE distribution shows that the tide-influenced setting was characterized by a high degree of spatial and temporal variability with regard to sedimentary processes. This, together with the prominent thickness variation of the unit studied, makes correlation between vertical profiles difficult, even over distances of only a few hundred metres. Stratal surfaces such as the sequence-bounding unconformity, the tidal ravinement surface, and the flooding surfaces, represent the only reliable correlation markers in this kind of environment.

The use of trend surfaces in palaeoenvironmental reconstructions

Trend surfaces can be produced by a number of mathematical techniques and have been used widely to depict the regional variation of various geological parameters. In this paper, it is demonstrated that trend surfaces can be constructed by a simple graphical method and may be applied successfully to palaeoenvironmental reconstructions using elevation contour of tilted or folded contacts. Two case studies are discussed to illustrate different aspects of the technique. In the first example, the upper contact of a shallow marine sandstone outcropping over an area of roughly 4000 km 2 in the southwestern part of the Sydney Basin (Australia), is restored by means of a first order trend surface. This reveals the palaeotopography as a sinuous shoal trending towards the northnortheast. The second example, from the Beaufort Group of the Karoo Basin (South Africa), restores the basal contact of a fluvial sandstone by means of a second order (quadratic) trend surface. The restored surface portrays the individual thalwegs and islands of a braided stream system over an area of about 4 km 2.

Palaeogeography and geodynamic evolution of the Gosau Group of the Northern Calcareous Alps (Late Cretaceous, Eastern Alps, Austria)

The sedimentation of the Late Cretaceous Gosau Group of the Northern Calcareous Alps records the complex geodynamic evolution of the northern part of the Austroalpine microplate. The tectonically controlled sedimentation and facies distribution were mainly governed by the oblique subduction of the Pennic-Ligurian ocean below the Austroalpine margin. Most of the Gosau successions comprise two distinct sedimentary complexes. The Lower Gosau Subgroup (upper Turonian-Campanian) is characterized by terrestrial to shallow-marine facies associations: alluvial fan and fan delta deposits, shallow-marine sandstones and sandy limestones, and storm-influenced nearshore and shelf deposits. During the early Santonian sea-level highstand, a great part of the Northern Calcareous Alps was covered by a shallow shelf sea. Palaeotransport directions point to source areas situated both to the north and to the south of the Northern Calcareous Alps. The Upper Gosau Subgroup (upper Santonian-Eocene) comprises deep-water hemipelagic and turbiditic deposits. Rapid subsidence into bathyal to abyssal depths started diachronously from the northwest (Santonian) to the southeast (Maastrichtian) after a short phase of deformation and erosion. Abyssal deposits in the northern parts of the Northern Calcareus Alps and north-directed palaeotransport indicate a tilting of the slope towards the north. This subsidence pulse is attributed to an event of subcrustal tectonic erosion, probably triggered by the subduction of a topographic high of the South Penninic ocean. The relationships of the Gosau Group of the Austroalpine unit to Late Cretaceous deposits of the Carpathians and Southern Alps are discussed in the framework of a plate tectonic model.

A new species of the oligopygoid echinoidHaimeafrom the lower Eocene of Baja California Sur, Mexico

The oligopygoid echinoidHaimea bajasurensisn. sp. is described from middle lower Eocene (”Capay Stage”) shallow-marine sandstones in the middle part of the Bateque Formation and shallow-marine limestones in the upper part of the Tepetate Formation, Baja California Sur, Mexico. The new species is both the earliest and the westernmost oligopygoid, and the first occurrence ofHaimeain North America.

Origin of quartz cements in some sandstones from the Jurassic of the Inner Moray Firth (UK)

ABSTRACTThe extent of quartz cementation in shallow marine sandstones of the Brora Arenaceous Formation (Oxfordian) is closely related to the occurrence and abundance of Rhaxella perforata sponge spicules. Three cement morphologies are identified, chalcedonic quartz, microquartz and mesoquartz. Chalcedonic quartz forms matrix‐supported cements which preserve moulds of Rhaxella spicules. Chalcedonic quartz crystals have inequant development of crystal faces, on average 0·1 μm in diameter, and are the first formed cement and reveal homogeneous dark grey tones on the SEM‐CL/BEI. Microquartz forms 5–10 μm diameter crystals, which commonly grow on chalcedonic quartz substrates and show various grey tones under SEM‐CL/BEI. Mesoquartz crystals grow in optical continuity with their host grains, have >20 μm a‐axial diameter crystals, and exhibit distinctly zoned luminescence. Although no opaline silica is preserved, the quartz cement is interpreted to have formed from an opaline precursor. Detrital quartz has an average δ18O composition of + 12·2‰ and mesoquartz (syntaxial overgrowth) has an average δ18O composition of +20·0‰. Estimates of the δ18O compositions of microquartz and chalcedonic quartz are complicated by the problem of isolating the two textural types; mixtures of the two give consistently higher δ18O compositions than mesoquartz, the higher estimate being +39·2‰. From oxygen isotope data the formation of quartz, microquartz and chalcedonic quartz is interpreted to have taken place between 35 and 71°C in marine derived pore waters. Organic and inorganic maturation data constrain the upper temperature limit to less than 60°C.

Diagenetic destruction of reservoir potential in shallow marine sandstones of the Broadford Beds (Lower Jurassic), north-west Scotland: depositional versus burial and thermal history controls on porosity destruction

The Broadford Beds are a shallow marine mixed siliciclastic-carbonate unit up to 140 m thick that crops out in the northern Inner Hebrides adjacent to a major Tertiary igneous centre. The formation can be divided into three lithological units: a lower limestone-dominated unit, a middle unit of muddy, calcareous sandstones and an upper unit of cleaner sandstones. The limestones underwent early meteoric diagenesis and early diagenetic processes in the overlying sandstones included the precipitation of berthierine, corrensite, phosphate and a small amount of Mg calcite. The most abundant burial cement is ferroan calcite, most of which precipitated during Mesozoic burial at depths of about 1 km. These cements were sourced through the chemical compaction of depositional carbonate within interbedded muddier horizons. Later calcite cements were precipitated in fractures from meteoric fluids during Late Jurassic — Early Cretaceous inversion and Early Tertiary uplift and a final stage of calcite cementation was associated with Tertiary hydrothermal activity. Other burial diagenetic phases include quartz overgrowths and chlorite. Quartz cementation was initiated before the main phase of calcite cementation, but the most significant quartz cementation accompanied the formation of chlorite during Tertiary hydrothermal activity. Overall the most significant factor leading to porosity loss in the Broadford Beds was the abundance of detrital clays and depositional carbonate in the original sediment. This led to extensive calcite cementation that both occuluded primary pores and inhibited the formation of secondary porosity.

High-resolution sequence stratigraphy of Cretaceous shallow marine sandstones, Book Cliffs outcrop, Utah, USA - application to reservoir modelling

In recent years the financial cost of offshore oil and gas field development has promoted intense interest in the quantitative 3D description of hydrocarbon reservoirs, utilizing workstation technology. The main aims of this procedure are to produce volumetric models for the spatial distribution of reservoir/non-reservoir elements, using both deterministic and probabilistic geostatistical techniques to interpolate weIl data into the inter-weIl volume.

Conglomerate Fabric and Paleocurrent Measurement in the Braided Fluvial System of the Promina Beds in Northern Dalmatia (Croatia)

In the alluvial part of the Promina beds of northern Dalmatia (Late Eocene to possible Early Oligocene age) the main, SW-ward paleocurrent pattern was determined from clast orientation measurements within massive and flat-bedded conglomerates. Preferred clast fabric, facies characteristics, and downward transition into shoreline and shallow-marine sandstone and conglomerate suggest a prograding, braid delta system.

Evidence for meteoric recharge in the San Joaquin basin, California provided by isotope and trace element chemistry of calcite

Calcite cements were analysed petrographically and geochemically to document patterns of meteoric recharge into marine sandstones in the San Joaquin basin, California. Calcite cements in shallow marine sandstones in the eastern basin are pure (>96 mol.% Ca, <2 mol.% Mg, <1 mol.%Fe) relative to low temperature marine calcites (91–94 mol.% Ca) in central basin turbidite sandstones. Calcite cements with volumes >32% and δ 18O PDB<−10‰ record early meteoric flushing of marine sandstones. Timing of meteoric infiltration varied on a bed scale; calcite cements with meteoric and marine δ 18O and point-counted volumes of 26–27% appear 5 m apart. The purity of low temperature calcite (<70°C crystallization) may be the most effective regional indicator of meteoric exposure. The magnesium, iron and manganese content of calcite is distinct from reservoir to reservoir. Pore fluids were apparently compartmentalized on reservoir scales (10 8–10 9 m 3) and rates of locally variable dissolution reactions and calcite crystallization exceeded the flushing rates of reservoirs. If meteoric recharge began shortly after the deposition of marine shelf sandstones (approximately 23 Ma), then calcite cements record downdip infiltration at an average rate of 1 mm/year, less than some recorded rates of gravity-driven flow.

Geometrical arrangement of calcite cementation within shallow marine sandstones-Reply

Abstract Calcite cementation within shallow marine sandstones typically occurs as (1) continuously cemented layers, (2) layers of concretions, and (3) concretions scattered throughout the sandstone. This paper presents a model for the nucleation and diffusion-controlled growth of calcite cement which explains how these three types of calcite cementation arise by diagenetic redistribution of carbonate fossils originally contained within the sandstones. The model predicts that nucleation points in a system where clastic carbonate is concentrated in layers, will be confined to these layers, and a continuously cemented layer or a layer of stratabound concretions will form from the carbonate fossil-rich layer depending upon the original amount of clastic carbonate present within the layer. The semi-regular distance observed between stratabound concretions is a result of each nucleation point lowering the concentration of dissolved calcite in the surrounding sandstone and thereby inhibiting nucleation in close proximity to earlier formed nuclei. In a system with a homogeneous distribution of clastic carbonate, no preferred levels of nucleation are present, and this explains how a uniform three-dimensional distribution of concretions may arise. Flattening of concretions parallel to bedding is a natural consequence of diffusion-controlled growth in a system where the clastic carbonate is concentrated in layers, and need not have anything to do with permeability anisotropy. Formation of continuous calcite cemented layers by merging of concretions explains why closely spaced vertical geochemical profiles through a calcite cemented layer often are widely different.

Effective stratigraphical subdivision of the Humber Group and the Late Jurassic evolution of the UK Central Graben

New biostratigraphical analysis of the Humber Group sediments from the UK North Sea Central Graben, using integrated palynological and micropalaeontological zonation schemes, allows substage resolution and basin-wide discrimination of subunits of the Heather Formation/Kimmeridge Clay Formation, and associated sandstones. The integrated use of both zonation schemes is particularly important because thermally mature Humber Group sediments buried below 12 000 ft in the Central Graben cannot be dated consistently to substage level using palynology alone. Poor data and the undiagnostic log character of the mudstones and shallow marine sandstones have resulted in a simple lithological scheme being widely applied, with all sandstones assigned to the Fulmar Formation and mudstones to the Heather Formation and the Kimmeridge Clay Formation. Previous generalized usage of the Fulmar Formation for all Upper Jurassic shallow marine sandstones is inappropriate. The Upper Oxfordian Puffin Formation is present in the northern and western Central Graben. The largely Kimmeridgian Fulmar Formation is restricted to the south and east, and the coeval Ula Formation flanks the Jæren High. These three units are all interpreted as syn-rift sandstones, locally sourced from uplifted and eroded fault block crests within and marginal to the Central Graben. Latest Kimmeridgian or younger shallow marine sandstones are largely confined to platform areas outside the graben, and can be related to regressive phases.

Middle to Late Jurassic basin evolution and sandstone reservoir distribution in the Danish Central Trough

During the Mid- to Late Jurassic, long-term eustatic sea-level rise and half-graben subsidence in the Danish Central Trough resulted in a major transgression. Deposition of widespread alluvial plain sediments in the Søgne Basin and Tail End Graben was terminated in the Late Bathonian due to bypass and erosion following a short-term relative sea-level fall. The sea-level fall was followed by a relative sea-level rise during the Callovian which caused the development of a transgressive succession of coastal plain and shallow marine deposits. The transgressive succession consists of several prograding sediment wedges commonly terminated by a coal bed and a flooding surface. As transgression continued during the Late Jurassic, the shoreline shifted westwards. Transgressive Oxfordian shoreface to back-barrier sandstones were deposited. Another short-term relative sea-level fall occurred during the Kimmeridgian during which regressive shoreface to beach sandstones were deposited. During the Late Kimmeridgian and Volgian, the long-term relative sea-level rise resulted in deposition of thick Volgian offshore claystones in the central part of the Central Trough (Heno Plateau, Gertrud Graben and Feda Graben). During the Volgian and Early Cretaceous, the transgression continued towards the west and shallow marine sandstones may have been deposited along the western margin of the Central Trough fringing the Mid North Sea High (Grensen Nose Basin and Outer Rough Basin). Along the Ringkøbing Fyn High in the easternmost part of the Central Trough, Volgian and Early Cretaceous fan-delta sandstones and basin floor turbidite sandstones are interstratified with offshore claystones.

The Lower Kaskapau Formation (Cenomanian): A Multiple-Frequency, Retrogradational Shelf System, Alberta, Canada

The Cenomanian to earliest Turonian (Cretaceous) Kaskapau Formation in northwestern Alberta and adjacent British Columbia contains three shallow-marine shelf sandstone bodies encased in shale: the Doe Creek, Pouce Coupe, and Howard Creek members. These sandstone bodies were deposited in a retrogradational pattern, subparallel to the paleoshoreline of the underlying Dunvegan Formation. They represent distal-deltaic sedimentation during sea level lowstands or stillstands that punctuated the overall transgression represented by the shale of the Kaskapau Formation. A thin, slightly to nonbioturbated finely interbedded sandstone, siltstone, and shale facies containing syneresis cracks and no benthic foraminifera (facies 4) may be important paleoenvironmentally, representing th leading edge of a progradational wedge. The sandstone bodies are bounded by disconformities. The lower disconformity is erosive, perhaps the result of wave scour associated with a minor fall in relative sea level. The upper disconformity is a flooding surface formed as relative sea level subsequently rose. Within the Doe Creek Member, the overlapping I, N, and A reservoir sandstone bodies suggest an oscillatory shoreline caused by high-frequency, relative sea level fluctuations during the overall transgression. As such, the succession represents a transgressive, high-frequency sequence set. The Howard Creek Member is directly overlain by the Second White Speckled Shale (Turonian), which represents a condensed section having good source rock potential. The latter unit was deposited durin the peak of the marine transgression corresponding to an eustatic highstand.

Geological-Engineering Evaluation: Castilla and Chichimene Fields, Cubarral Association Contract, Colombia

A multidisciplinary geological and engineering evaluation project was undertaken for fields within the Chevron Colombia operated Cubarral Association Contract. The goal of the project was to combine geological and engineering evaluations to form a strategy for maximizing the efficiency of ongoing field development, recompletion, and production procedures. The Association Contract is located in the Llanos basin about 100 km southeast of Bogota. The fields: Castilla, Chichimene NE and Chichimene SW contain approximately 2200, 100, and 65 MMBO in place, respectively. The Guadalupe sandstone produces 14-21[degrees] API oil. The geological evaluation consisted of three phases: (1) revision of the structural interpretations, (2) detailed stratigraphic analyses, and (3) delineation of tilted fluid contacts and determination of original-oil-in-place. Structural interpretations show that reservoir properties and continuity are strongly affected by depositional environment which varies between the fields. A major facies change between massive, braided-stream sandstones at Castilla and deltaic to shallow marine sandstones at Chichimene northeast is reflected in production characteristics. The fields show strongly tilted oil-water contacts due to regional hydrodynamic gradients. Geometrical and hydrodynamic calculations were used to delineate the direction and magnitude of the tilts to assess original oil-in-place.

The Middle Jurassic Vardekløft Formation of East Greenland—analogue for reservoir units of the Norwegian shelf and the Northern North Sea

The Mesozoic rift basin of East Greenland was uplifted during the Tertiary, and provides excellent exposures of Mesozoic sediments of the same age and type as those occurring deeply buried in the shelf seas around the northern North Atlantic. This paper outlines the preliminary results of field work on the Middle Jurassic Vardekløft Formation, which is the best exposed analogue to the main reservoir rocks of the Northern North Sea and the Norwegian shelf. The formation is up to 600 m thick and is of Boreal Bajocian–Callovian age. The sediments were deposited during a period of sea-level lowstand followed by an overall rise. The base of the formation is an important sequence boundary and the top is a maximum flooding surface, separating the formation from the overlying downlapping Olympen Formation and its correlatives. The Vardekløft Formation consists of shallow marine sandstones of the Pelion Member, which pass basinward into offshore siltstones of the Fossilbjerget Member. The boundary between the two members is strongly diachronous, younging sourcewards toward the north along the basin axis, with a major northward displacement (&gt; 100 km) in the Pompeckji Zone. Internally, the formation is composed of up to 30 coarsening-upward units. The thickness of the units appears to vary in cyclical fashion upward through the member. The units typically consist of a lower, commonly very thin, fine-grained sandstone or siltstone, a middle fine-grained laminated to rippled sandstone, and an upper medium- to very coarse-grained cross-bedded, multi-storey sandstone, topped by a marine flooding surface. This facies succession reflects deposition during overall decreasing water depth. The widespread lateral continuity of the lower, commonly erosional, boundary of the multi-storey sandstone facies suggests that the top part was deposited during relative sea-level fall. This is supported by the high degree of reworking and abundance of coarse-grained sandstone and pebble conglomerate. Different types of flooding surfaces are recognized, showing distinct proximal–distal change in amount of winnowing and erosion. Three orders of relative sea-level changes which probably had significant influence on sandbody distribution and geometry can be recognized. The longest cycle had a duration of c . 20 Ma. It corresponds to the Vardekløft Formation and Olympen Formation which form a crude transgressive–regressive cycle deposited during initial lowstand and succeeding rise, and during highstand and early lowstand, respectively. An intermediate cyclicity is recognized in the stacking pattern of the coarsening-upward units, suggesting cyclical changes in the rate of long-term sea-level rise. A minimum rate of relative rise characterized the Middle and Upper Boreal Bathonian Ishmae–Variabile Zones. High rates of relative sea-level rise characterized the Boreal Bajocian Borealis–Indistinctus Zones and the Lower Callovian Apertum–Calloviense Zones. Finally, the individual coarsening-upward units represent short-term cycles of relative sea-level changes. Comparison with contemporaneous reservoir units such as the Rannoch, Etive and Tarbert formations of the Brent Group in the Northern North Sea shows many similarities in depositional motifs, including vertical and lateral changes in facies development and stacking patterns.