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The Danish part of the Central Graben (DCG) is one of the petroliferous basins in the offshore region of north-western Europe. The source rock quality and maturity is here reviewed, based on 5556 Rock-Eval analyses and total organic carbon (TOC) measurements from 78 wells and 1175 vitrinite reflectance (VR) measurement from 55 wells, which makes this study the most comprehensive to date. The thermal maturity is evaluated through 1-D basin modelling of 46 wells. Statistical parameters describ-ing the distribution of TOC, hydrocarbon index (HI) and Tmax are presented for the Lower Jurassic marine Fjerritslev Formation, the Middle Jurassic terrestrial-paralic Bryne, Lulu, and Middle Graben Formations and the Upper Jurassic to lowermost Cretaceous marine Lola and Farsund Formations in six areas in the DCG. For the Farsund Formation the source-rock richness is presented for selected stratigraphic sequences. The upper part of the Farsund Formation is immature in the southern part of the Salt Dome Province, and late oil mature in and near the Tail End Graben and in the Søgne Basin. The lower part of the Farsund Formation is immature in local areas, yet post-mature in the Tail End Graben and in the Salt Dome Province. The Lower and Middle Jurassic shales are gas-prone in most of the DCG. The depth of the oil window, as defined by a VR of 0.6% Ro, ranges between 2200 and 4500 m. The variations are ascribed to heat flow differences in the DCG and can be modelled by a simple depth model, which includes the thickness of the Cretaceous to Palaeo-gene Chalk and Cromer Knoll Groups. According to the model, a thick Chalk Group offsets the oil window to deeper levels, which likely can be attributed to the thermal properties of the highly thermally conductive chalk compared to the underlying less thermally conductive clays. The DCG is an overpressured basin, and high-pressure, high-temperature conditions are expected to occur deeper than 3.8 km except for the Feda and Gertrud Grabens where such conditions, due to generally lower tem-peratures, are expected to occur deeper than around 4.7 km.

Oil and gas production from siliciclastic reservoirs has hitherto been in the Danish Central Graben mostly from Palaeogene and Middle Jurassic sandstone. The Ravn field was the first Upper Jurassic field to start operation. The reservoir is composed of sandstone of the Heno Formation. Production takes place at a depth of 4000 m, which makes Ravn the deepest producing field in the Danish North Sea. The Heno Formation mainly consists of marine shoreface deposits, where foreshore, middle and lower shoreface sandstones constitute the primary reservoir. The results of this study of the diagenetic impact on the mineralogical composition, porosity and permeability are presented here. Microcrystalline quartz has preserved porosity in the sandstone, whereas illite, quartz overgrowth and carbonate cement have reduced both porosity and permeability.

Barrier-island system evolution is controlled by internal and external forcing mechanisms and temporal changes in these mechanisms may be recorded in the sedimentary architecture. However, the precise role of individual forcing mechanisms is rarely well-understood due to limited chronological control. This study investigates the relative role of forcing conditions, such as antecedent topography, sea-level rise, sediment supply, storms and climate changes, on the evolution of a Holocene wave-dominated barrier-island system. This article presents temporal reconstruction of the depositional history of the barrier-island system of Romo in the Wadden Sea in unprecedented detail, based on ground-penetration radar profiles, sediment cores, high-resolution dating and palynological investigations, and shows that ca 8000 years ago the barrier island formed on a Pleistocene topographic high. During the initial phase of barrier evolution the long-term sea-level rise was relatively rapid (ca 9 mm/yr) and the barrier was narrow and frequently overwashed. Sediment supply kept pace with sea-level rise and the barrier-island system mainly aggraded through the deposition of a ca 7 m thick stack of overwash fans. Aggradation continued for ca 1700 years until sea-level rise had decreased to less than 2 mm/yr. In the last ca 6000 years the barrier prograded 4 to 5 km through deposition of a 10 to 15 m thick beach and shoreface unit, despite a long-term sea-level rise of 1 to 2 mm/yr. The long-term progradation was, however, interrupted by a transgression between 4000 years and 1700 years ago. These results demonstrate that the large-scale morphology of the Danish Wadden Sea shoreline influence the longshore sediment transport flux and the millennial-scale dispersal of sediment along the shoreline. On decadal to centennial timescales major storms induced intense beach and shoreface erosion followed by rapid recovery and progradation which resulted in a highly punctuated beach and shoreface record. Major storms contributed toward a positive sediment budget and the sustained surplus of sediment was, and still is, instrumental in maintaining the aggradational–progradational state of the barrier island. This article is protected by copyright. All rights reserved.

Coastal lagoons and beach ridges are genetically independent, though non-continuous, sedimentary archives. We here combine the results from two recently published studies in order to produce an 8000-year-long record of Holocene relative sea-level changes on the island of Samso, southern Kattegat, Denmark. The reconstruction of the initial mid-Holocene sea-level rise is based on the sedimentary infill from topography-confined coastal lagoons (Sander et al., Boreas, 2015b). Sea-level index points over the mid- to late Holocene period of sea-level stability and fall are retrieved from the internal structures of a wide beach-ridge system (Hede et al., The Holocene, 2015). Data from sediment coring, georadar and absolute dating are thus combined in an inter-disciplinary approach that is highly reproducible in micro-tidal environments characterised by high sediment supply. We show here that the commonly proximate occurrence of coastal lagoons and beach ridges allows us to produce seamless time series of relative sea-level changes from field sites in SW Scandinavia and in similar coastal environments.

Growth of fibrous illite may destroy an otherwise promising sandstone reservoir, even sandstones characterized by microquartz coatings. Therefore detailed petrographical and diagenetic investigations were performed in order to understand the factors that control illite precipitation and other factors affecting the reservoir properties in the Upper Jurassic Heno Formation. The Heno Formation is encountered in large parts of the Danish Central Graben, where its lower part – the Gert Member – was mainly deposited in back-barrier environments and its upper part – the Ravn Member – was deposited in a shoreface environment. In total, 215 core samples from 15 wells were investigated petrographically by optical and scanning electron microscopy. This was supplemented by plug porosity and permeability measurements and X-ray diffraction of bulk and clay fraction. The investigations show, among other things, that microquartz coatings may help to preserve porosity and permeability, whereas the permeability is reduced when microquartz occurs combined with fibrous illite. Illite precipitation is largely governed by the amounts of K-feldspar present during burial. Consequently, the initial abundance of K-feldspar (in the sediment source area) and its alteration during and immediately after deposition, in particular during subaerial exposure (at sequence boundaries), has a major influence on the final reservoir properties of the sandstones. The risk of illite precipitation can largely be predicted from the available sediment source material, depositional environment and burial depth.

This study provides a detailed reconstruction of the formation of a wave-dominated barrier island and assesses the sedimentological and morphological effects of sea-level changes on barrier evolution. Sedimentological and stratigraphic characteristics of the Holocene deposits are resolved by percussion cores and an extensive ground-penetrating-radar survey. A high-resolution chronology of the cored barrier island deposits is constructed by optically stimulated luminescence dating. This approach facilitates a high spatio-temporal resolution of the island’s morphological and depositional evolution. The results show that the barrier island experienced multiple phases of transgressions and regressions during the mid- and late Holocene and that these changes were driven primarily by changes in rates of sea-level rise, sediment supply and the impact of storms. Due to the postglacial sea-level rise, the seaward part of the study area was transgressed by the retreating mainland shoreline, forming a back-barrier basin. At the time of the initial transgression, sea level was rising by more than 4.0 mm yr−1. As sea-level rise decreased to less than 2 mm yr−1 the back-barrier basin rapidly started to fill with sediments before being transgressed by the still retreating open-ocean shoreline. These events were associated with periods of very rapid landward displacement of up to 10 m yr−1 of the mainland shoreline. After stabilization of the barrier island in its most eastward (i.e., landward) location, the open-ocean shoreline prograded about 3 km seaward at a rate of > 3 m yr−1 through the deposition of a 7-m-thick sandy beach and shoreface succession. The progradation occurred despite a sea-level rise of about 1.8 mm yr−1. After the regressive period the barrier island once again became transgressive before shifting back to its current regressive stage. The study shows how comparable rates of sea-level rise can result in very different morphological responses for a single barrier island since sediment supply apparently has varied significantly through time. It also appears that a transgressive situation is reached for this particular barrier island for a sea-level rise higher than about 2 mm yr−1. This gives reason for concern since a number of sea-level change scenarios indicate that such a rate will be reached within a few decades.

Coastal lagoons are a typical feature of the landscape in central Denmark. The lagoons formed when basins within the inherited glacial topography were flooded by the mid-Holocene sea-level rise. The transgression initiated coastal geomorphological processes and prompted marine sedimentation in the inundated areas. Despite their common occurrence and wide distribution in the area, coastal lagoons and their deposits have rarely been studied as sedimentary archives. The absolute chronology established for the basal marine deposits in sediment cores retrieved from coastal lagoons on the island of Samso, southern Kattegat Sea, central Denmark, is evidence of a nearly synchronous onset of marine sedimentation at different elevations. This is interpreted as a new indication of a period of very rapid relative sea-level (RSL) rise between 7.6 and 7.2 ka BP. Following a period of RSL highstand, a marked facies change in the deposits from an inactive lagoon yields consistent ages of around 4.1 ka BP and may be an indication of a marked RSL fall. This study illustrates the potential of coastal lagoons as sedimentary archives for the reconstruction of RSL in SW Scandinavia and in similar coastal environments elsewhere.

This study presents a detailed reconstruction of the sedimentary effects of Holocene sea-level rise on a modern coastal barrier system. Increasing concern over the evolution of coastal barrier systems due to future accelerated rates of sea-level rise calls for a better understanding of coastal barrier response to sea-level changes. The complex evolution and sequence stratigraphic framework of the investigated coastal barrier system is reconstructed using facies analysis, high-resolution optically stimulated luminescence and radiocarbon dating. During the formation of the coastal barrier system starting 8 to 7 ka rapid relative sea-level rise outpaced sediment accumulation. Not before rates of relative sea-level rise had decreased to ca 2 mm yr−1 did sediment accumulation outpace sea-level rise. From ca 5·5 ka, rates of regionally averaged sediment accumulation increased to 4·3 mm yr−1 and the back-barrier basin was filled in. This increase in sediment accumulation resulted from retreat of the barrier island and probably also due to formation of a tidal inlet close to the study area. Continued transgression and shoreface retreat created a distinct hiatus and wave ravinement surface in the seaward part of the coastal barrier system before the barrier shoreline stabilized between 5·0 ka and 4·5 ka. Back-barrier shoreline erosion due to sediment starvation in the back-barrier basin was pronounced from 4·5 to 2·5 ka but, in the last 2·5 kyr, barrier sedimentation has kept up with and outpaced sea-level. In the last 0·4 kyr the coastal barrier system has been prograding episodically. Sediment accumulation shows considerable variation, with periods of rapid sediment deposition and periods of non-deposition or erosion resulting in a highly punctuated sediment record. The study demonstrates how core-based facies interpretations supported by a high-resolution chronology and a well-documented sea-level history allow identification of depositional environments, erosion surfaces and hiatuses within a very homogeneous stratigraphy, and allow a detailed temporal reconstruction of a coastal barrier system in relation to sea-level rise and sediment supply.

Facies analysis of five sediment cores and a detailed absolute chronology, consisting of 35 optically stimulated luminescence (OSL) ages, form the basis for reconstruction of the paleoenvironmental evolution of the coastal lagoon behind the barrier island of Fano, in the Northern Wadden Sea, SW Denmark. The lagoonal sedimentary succession was deposited within the last 5500 yr, and 5 principal depositional environments are identified in the lagoonal fill. These are: 1) tidal channel, 2) sand flat, 3) mouth bar, 4) reed swamp, and 5) mudflat/salt marsh. Sand flats are the dominant present day depositional environment, but tidal channel sediments dominate in the five sediment cores, making up 56% of the 15 m of sediment core. Sedimentation in the lagoon alternated between slow vertical aggradation of sand flats (1.5–2 mm yr − 1 ) and very fast lateral progradation of point bars in tidal channels, which caused the formation of a punctuated lagoonal fill. Frequent and comprehensive reworking of the sand flat sediments by tidal channel migration entails loss of sedimentary structures and bioturbation related to sand flat deposits, and old sand flat sediments are only very sparsely preserved. We further conclude that long-term (millennial timescale) sediment accumulation in the lagoon was controlled by rising sea-level, whereas short-term (centurial timescale) sediment accumulation was controlled by local erosion and depositional events caused by lateral migration of channels. Records of short-term sea-level fluctuations are not preserved, due to continuous reworking of the lagoonal sediment within the study area. The paper provides significant inputs to a conceptual model describing the Holocene sedimentation in the sand-dominated tidal lagoon. Furthermore, the study successfully demonstrates the role of OSL dating in deciphering complicated sedimentology and stratigraphy of tidal lagoonal environments.

A chemostratigraphic study of Upper Jurassic sandstones in the northern Danish Central Graben has been undertaken within the framework of a well-defined stratigraphic/sedimentological model based particularly on cored well sections. Two reservoir sandstone units are recognised, the transgressive marginal marine to shoreface sandstone of the Gert Member and the regressive to transgressive shoreface sandstone of the Ravn Member. Both members belong to the Heno Formation, which is equivalent to the Fulmar Formation (UK) and the Ula Formation (Norway). Multivariate analysis of geochemical data from 264 core samples from 8 wells reveals the distinction between the two reservoir sandstones (Gert and Ravn members) and the two offshore claystones (Farsund and Lola formations). Specific elements have proven to be important for this separation and these elements demonstrate differences even in 2-dimensional cross plots. The Farsund Formation is characterised by higher V, U and P 2 O 5 , and lower MgO and K 2 O when compared with the Lola Formation. The Gert Member typically has higher maximum amounts of Cr and TiO 2 than the Ravn Member. The high Cr and TiO 2 content (probably from chrome spinel and Ti-minerals) might be related to a source of exposed Carboniferous sediments in the Gert Ridge area. The Ravn Member is characterised by higher Na 2 O, P 2 O 5 and Th contents than the Gert Member, which may reflect a higher content of plagioclase (Na 2 O) and a changed heavy mineral assemblage. The Mid North Sea High is a likely source for the heavy mineral suite that characterises the Ravn Member. The Rita-1 well, situated closest to the Mid North Sea High, seems to have been more influenced by this source than the other wells. In the Hejre area, a volcanic source supplying K-feldspar may be responsible for the relatively high K 2 O/Al 2 O 3 observed in both the Gert and Ravn members. Hence in addition to differentiation between the two reservoir sands and between the two offshore claystones, this study also illustrates the use of geochemical data for evaluation of source characteristics and dominance of different sediment source areas.

An unusually thick ( c . 88 m), transgressive barrier island and shoreface sandstone succession characterizes the Upper Jurassic Heno Formation reservoir of the Freja oil field situated on the boundary of Denmark and Norway. The development and preservation of such thick transgressive barrier island sands is puzzling since a barrier island typically migrates landwards during transgression and only a thin succession of back-barrier and shoreface sands is preserved. Investigation of the development and geometry of the Freja reservoir sandstones is problematic since the reservoir is buried c. 5 km and seismic resolution is inadequate for architectural analysis. Description of the reservoir sandstone bodies is thus based on sedimentological interpretation and correlation of seven wells, of which five were cored. Palaeotopography played a major role in the position and preservation of the thick reservoir sandstones. Using the nearest maximum flooding surface above the reservoir as a datum for well-log correlations, the base of the barrier island succession in the wells is reconstructed as a surface with steep, seaward-dipping palaeotopography. The relief is c . 270 m over a distance of c . 8 km and dips WNW. As a complementary approach to investigation of the reservoir architecture, a Holocene–Recent barrier island system in the Danish part of the NW European Wadden Sea has been studied and used as an analogue. The barrier island of Romo developed during a relative sea-level rise of c. 15 m during the last c. 8000 years and is up to 20 m thick. To unravel the internal 3D facies architecture of the island, an extensive ground penetrating radar (GPR) survey of 35 km line length and seven cores, c. 25 m long, was obtained. Although the barrier island experienced a rapid relative sea-level rise, sedimentation kept pace such that the island aggraded and even prograded seawards and became wider and longer due to the large surplus of sand.

Recently available well data from the northern part of the Danish Central Graben have been analysed to further understand the basin development, biostratigraphy, depositional models and palaeogeography of Upper Jurassic reservoir sandstones, which are the primary exploration targets in this basin. Notably, the discovery of the Hejre accumulation in 2001, where oil has been encountered in Upper Jurassic good reservoir quality sandstones at a depth of more than 5000 m, triggered renewed interest in the Upper Jurassic High Temperature–High Pressure sandstone play in the area. Overall the Danish Central Graben was transgressed from east to west during the Late Jurassic. During the Late Kimmeridgian, marginal and shallow marine sandstones assigned to the Heno Formation were deposited at the margin of the Feda Graben, and on the Gertrud and Heno Plateaus and constitute the reservoirs in the Freja and Hejre discoveries. The sandstones are analogues to the UK Fulmar and Norwegian Ula Formations encountered in several hydrocarbon fields. During the Early Volgian, the transgression continued westwards across the Outer Rough Basin along the margin of the Mid North Sea High, where shoreface sandstones with excellent porosities and permeabilities were deposited close to similar sandstones of the Fulmar Formation in the British Fergus, Fife and Angus fields. During this overall westward transgression, the eastern and central parts of the Danish Central Graben continued to subside and offshore mudstones accumulated, locally intercalated with gravity-flow sandstones. In the easternmost Danish Central Graben, in the Tail End Graben, Upper Kimmeridgian gravity-flow sandstones of the Svane-1 well have proved the presence of gas at c . 6 km depth. Hydrocarbon-bearing Upper Jurassic sandstone reservoirs at significant depths (deeper than 5 km) may form the future exploration targets in the northern part of the Danish Central Graben.

Spit systems are seldom recognized in the pre-Quaternary sedimentary record compared to their common occurrence along present-day coasts and in Quaternary successions. This lack of recognition may partly be due to the lack of widely accepted depositional models describing the facies characteristics of spit systems and their subaqueous platforms in particular. The Skagen spit system is a large active system that began to form 7150 yr bp and from 5500 bp to Recent times it has prograded 4 m year−1 and accumulated 3·5 × 109 m3 of sand. The spit system provides a unique opportunity for establishing a well-constrained depositional model because uplift and erosion have made large windows into the preserved facies, while active spit-forming processes can be examined at the young prograding end of the same system. The depositional model presented here thus builds on excellent outcrops, surface morphology, a well-defined palaeogeography and detailed C14 age control supplemented with observations from continuous well cores and profiles obtained by ground-penetrating radar and transient electromagnetic surveys. The factors that have governed the development of the spit system, such as relative sea-level change, wave and current climate, tidal range, sediment transport and depositional rates are also well-understood. The sedimentary facies of the spit system are grouped into four principal units consisting from below of thick storm sand beds, dune and bar-trough deposits, beach deposits and peat beds. These four units form a coarsening and shallowing upward sand-dominated succession, up to 32 m thick, which overlies offshore silt with a transition zone and is topped by a diastem overlain by young aeolian dune sand. The sedimentary structures and depositional processes are described in detail and integrated into a depositional model, which is compared to other spit systems and linear shoreface models.

Sea level rise may have large implications for low-gradient barrier coastal systems. This problem motivated an integrated ground-penetrating radar (GPR) and sedimentological study of the Romo Wadden Sea barrier island. Crossing W–E and N–S-oriented 100 MHz GPR reflection profiles with a total length of about 30 km were acquired on the island. In this case study, we process and analyze GPR data and investigate the feasibility of using integrated GPR and sedimentological log data to constrain spatial variations in lithology, structures and changing depositional environments of the Romo barrier island. We document different standard processing steps which lead to increased signal-to-noise ratio, improved resolution and trustworthy GPR-to-borehole correlation. The GPR signals image the subsurface layering with a vertical resolution of ~ 0.2–0.3 m. The penetration depth of the GPR reflection signals varies between 7 and 15 m in the interior of the island where the shallow subsurface is not influenced by saltwater intrusion or fine-grained salt marsh sediments. Analysis of common midpoint reflection data constrains the radar wave velocity distribution in the subsurface and facilitates depth conversion of the reflection profiles. The GPR reflections are correlated with sedimentological facies logs, and we test to which extent it is possible to map the architecture of different sedimentary units of the Romo barrier island based on joint interpretation of the GPR and core data. Detailed investigation of signal waveform variations and amplitude decay analysis are used for assessing lateral variation in lithology and composition. The combined GPR and borehole investigations constrain the nature of different marine and aeolian sedimentary sequences that have formed the barrier island system. We observe two prominent reflections which, in general, exhibit good continuity. The upper prominent reflection (0–2 m above present mean sea level (pmsl)) outlines swales and beach ridge flanks. In depressions (swales), this reflection has a complex signature originating from the contrasts in electrical properties caused by the presence of a thin layer of organic mud or gyttja. On the beach ridge flanks, this reflection has a simpler appearance and most likely represents contrasting sandy beds. The lower prominent reflection (0–3 m below pmsl) is relatively strong and represents the top of a clay layer in some areas. In other parts of the data set, this lower reflection is weaker and interpreted to represent the transition between two marine sand deposits of different origin. Mounded structures with internal dipping reflections are interpreted to represent a system of 20–40 m wide and up to ~ 2 m high fossil beach ridges in the shallow subsurface of the Romo barrier island. The base of the beach ridges is found 0–1 m above pmsl. Some beach ridges show signs of erosion, and aeolian dunes have developed above them. The dunes appear with a variety of internal structures, but are often characterised by steeply dipping internal structures.

The sandy quartzose parts of the Utsira Formation, the Middle Miocene to mid Pliocene Utsira Sand, extends north–south along the Viking Graben near the UK/Norwegian median line for more than 450 km and 75–130 km east–west. The Utsira Sand is located in basin-restricted seismic depocentres, east of and below prograding sandy units from the Shetland Platform area with Hutton Sands. The Utsira Sand reaches thicknesses up to ca. 300 m in the southern depocentre and 200 m in the two northern depocentres with sedimentation rates up to 2–4 cm/ka. Succeeding Plio–Pleistocene is divided into seismic units, including Base Upper Pliocene, Shale Drape, Prograding Complex and Pleistocene. The units mainly consist of clay, but locally minor sands occur, especially at toes of prograding clinoforms (bottom-set sands) and in the Pleistocene parts, and the total thickness covering the Utsira Sand is in most places more than 800 m, but thins towards the margins.

Well-constrained depositional models are essential for successful exploration and field development. The Skagen spitsystem offers a unique possibility for the establishment of a depositional model constrained by excellent outcrops, well-defined palaeogeography, good age control and detailed observations on hydrodynamics and morphology of the prograding part of the spit-system. The model offers a supplementary interpretation of shallow marine sandstones to the existing delta and linear shoreface models. The sand-dominated Skagen spit-system is c. 22 km long, 4 km wide and up to 35 m thick, with a sand volume of c. 2.2 km3. If filled with oil, this system would contain 0.6 km3 corresponding to 3.8 x 109 barrels assuming a porosity of 30% and an oil saturation of 90%. This is comparable in size with the largest Danish oil field (the Dan field), in the North Sea. Reservoir models for isolated linear ‘offshore’ sandstone bodies have been controversial for many years. Their size and internal indications of palaeocurrent directions are similar to those of the spit-system model, and this model may therefore be applicable for some of these bodies.

Paralic and shallow marine sandstones were deposited in the Danish Central Graben during Late Jurassic rifting when half-grabens were developed and the overall eustatic sea level rose. During the Kimmeridgian, an extensive plateau area consisting of the Heno Plateau and the Gertrud Plateau was situated between two highs, the Mandal High to the north, and the combined Inge and Mads Highs to the west. These highs were land areas situated on either side of the plateaus and supplied sand to the Gertrud and Heno Plateaus. Two graben areas, the Feda and Tail End Grabens, flanked the plateau area to the west and east, respectively. The regressive–transgressive succession consists of intensely bioturbated shoreface sandstones, 25–75 m thick. Two widespread unconformities (SB1, SB2) are recognised on the plateaus, forming the base of sequence 1 and sequence 2, respectively. These unconformities were created by a fall in relative sea level during which rivers may have eroded older shoreface sands and transported sediment across the Heno and Gertrud Plateaus, resulting in the accumulation of shoreface sandstones farther out in the Feda and Tail End Grabens, on the south-east Heno Plateau and in the Salt Dome Province. During subsequent transgression, fluvial sediments were reworked by high-energy shoreface processes on the Heno and Gertrud Plateaus, leaving only a lag of granules and pebbles on the marine transgressive surfaces of erosion (MTSE1, MTSE2). The sequence boundary SB1 can be traced to the south-east Heno Plateau and the Salt Dome Province, where it is marked by sharp-based shoreface sandstones. During low sea level, erosion occurred in the southern part of the Feda Graben, which formed part of the Gertrud and Heno Plateaus, and sedimentation occurred in the Norwegian part of the Feda Graben farther to the north. During subsequent transgression, the southern part of the Feda Graben began to subside, and a succession of backstepping back-barrier and shoreface sediments, 90 m thick, was deposited. In the deep Tail End and Feda Grabens and the Salt Dome Province, sequence boundary SB2 is developed as a conformity, indicating that there was not a significant fall in relative sea level in these grabens, probably as a result of high subsidence rates. Backstepping lower shoreface sandstones overlie SB2 and show a gradual fining-upwards to offshore claystones that are referred to the Farsund Formation. On the plateaus, backstepping shoreface sandstones of sequence 2 are abruptly overlain by offshore claystones, indicating a sudden deepening and associated cessation of sand supply, probably caused by drowning of the sediment source areas on the Mandal, Inge and Mads Highs. During the Volgian, the Gertrud Plateau began to subside and became a graben. During the Late Kimmeridgian – Ryazanian, a long-term relative sea-level rise resulted in deposition of a thick succession of offshore claystones forming highstand and transgressive systems tracts on the Heno Plateau, and in the Gertrud, Feda and Tail End Grabens.

A complete updated and revised lithostratigraphic scheme for the Jurassic succession of the onshore and offshore Danish areas is presented together with an overview of the geological evolution. The lithostratigraphies of Bornholm, the Danish Basin and the Danish Central Graben are described in ascending order, and a number of new units are defined. On Bornholm, the Lower–Middle Jurassic coal-bearing clays and sands that overlie the Lower Pliensbachian Hasle Formation are referred to the new Sorthat Formation (Lower Jurassic) and the revised Bagå Formation (Middle Jurassic). In the southern Danish Central Graben, the Middle Jurassic succession formerly referred to the Lower Graben Sand Formation is now included in the revised Bryne Formation. The Lulu Formation is erected to include the uppermost part of the Middle Jurassic succession, previously referred to the Bryne Formation in the northern Danish Central Graben. The Upper Jurassic Heno Formation is subdivided into two new members, the Gert Member (lower) and the Ravn Member (upper). The organic-rich part of the upper Farsund Formation, the former informal ‘hot unit’, is established formally as the Bo Member. Dominantly shallow marine and paralic deposition in the Late Triassic was succeeded by widespread deposition of offshore marine clays in the Early Jurassic. On Bornholm, coastal and paralic sedimentation prevailed. During maximum transgression in the Early Toarcian, sedimentation of organic-rich offshore clays took place in the Danish area. This depositional phase was terminated by a regional erosional event in early Middle Jurassic time, caused by uplift of the central North Sea area, including the Ringkøbing–Fyn High. In the Sorgenfrei–Tornquist Zone to the east, where slow subsidence continued, marine sandy sediments were deposited in response to the uplift. Uplift of the central North Sea area was followed by fault-controlled subsidence accompanied by fluvial and floodplain deposition during Middle Jurassic time. On Bornholm, deposition of lacustrine muds, fluvial sands and peats dominated. The late Middle Jurassic saw a gradual shift to shallow marine deposition in the Danish Central Graben, the Danish Basin and Skåne, southern Sweden. During the Late Jurassic, open marine shelf conditions prevailed with deposition of clay-dominated sediments while shallow marine sands were deposited on platform areas. The Central Graben received sand by means of sediment gravity flows. The clay sediments in the Central Graben became increasingly rich in organic matter at the Jurassic–Cretaceous transition, whilst shallow marine coarse-grained deposits prograded basinwards in the Sorgenfrei– Tornquist Zone.

Extreme storms and storm surges may induce major changes along sandy barrier coastlines, potentially causing substantial environmental and economic damage. We show that the most destructive storm (the 1634 AD storm) documented for the northern Wadden Sea within the last thousand years both caused permanent barrier breaching and initiated accumulation of up to several metres of marine sand. An aggradational storm shoal and a prograding shoreface sand unit having thicknesses of up to 8 m and 5 m respectively were deposited as a result of the storm and during the subsequent 30 to 40 years long healing phase, on the eroded shoreface. Our results demonstrate that millennial-scale storms can induce large-scale and long-term changes on barrier coastlines and shorefaces, and that coastal changes assumed to take place over centuries or even millennia may occur in association with and be triggered by a single extreme storm event.

The Jurassic succession of the northern part of the Danish Central Trough is subdivided into six depositional sequences based on a multi-disciplinary study, including sedimentology, biostratigraphy, seismic interpretation, structural interpretation, log correlation, geochemistry and palynofacies analysis. Three of these sequences include significant sandstone deposits that represent potential reservoirs. The lowermost sequence 1 contains Upper Kimmeridgian backbarrier and shoreface sandstones of the'basal sandstone unit' and the Heno Formation deposited within a transgressive and a highstand systems tract, respectively. Sequence 2 includes Upper Kimmeridgian middle shoreface sandstones of the Heno Formation deposited within a transgressive systems tract. Within sequence 6, Middle-Upper Volgian distal turbidite sandstones have been recognized. These are interpreted as having been deposited within a lowstand and transgressive systems tract and may constitute a reservoir elsewhere in the basin. The sequence stratigraphic boundaries of this study do not match those proposed by the Exxon group. In this rift setting, sequence development was probably controlled predominately by tectonism; eustasy was of subordinate importance.

Sequence stratigraphic interpretation of paralic successions is complicated by the complex interfingering of marine and continental strata. The successions may also include terrestrial extensions of marine parasequences and completely independent lacustrine parasequence analogues. Failure in recognizing the possible interbeddding of these two independent parasequence types may lead to construction of sequence stratigraphic schemes based on incompatible data sets. We have studied a Lower Jurassic paralic section from the Baltic island of Bornholm, situated in the Tornquist Zone, which demarcates the transition from the stable Precambrian Baltic Shield to the subsiding Danish Basin and Danish-Polish Trough. The Hettangian-Sinemurian Sose Bugt Member (Ronne Formation) of Bornholm includes lacustrine, fluvial and restricted marine, estuarine deposits reflecting the basin-margin position. Biostatigraphic resolution is poor and a sequence stratigraphic interpretation of the paralic succession is far from straightforward. A multidisciplinary approach including facies analysis, recognition and lateral trading of key surfaces, palynostratigraphy, palynofacies, coal petrography, palaeopedology, clay mineralogy and source rock geochemistry is applied in order to obtain a high degree of precision in the interpretation of the paralic facies. In this way four sequences are recognized in the overall backstepping lacustrine to estuarine succession. Marine and marginal marine parasequences are distinguished from their purely lacustrine analogues, and an internally consistent sequence stratigraphic scheme is proposed. This is compared and tentatively correlated with fossiliferous marine sediments in the Danish Basin and with published eustatic cycle charts.

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 Sogne 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 Ringkobing 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 large Storegga slide, which occurred on the Norwegian Atlantic shelf ∼8150 yr ago, triggered a tsunami that has been identified in sediment deposits along the coasts of Greenland, Norway, the Faroe Islands, the Shetland Islands, Scotland, and the northernmost coasts of England, but hitherto not along the southeastern shores of the North Sea. It has generally been assumed that the shallow continental shelf of the North Sea attenuated and dissipated the energy of the tsunami before it reached those coastlines. We used radiocarbon and optically stimulated luminescence dating as well as stratigraphic, lithologic, chemical, and palynological analyses of sediment cores to identify tsunami deposits on the barrier island of Romo located on the southwestern North Sea coast of Denmark. We show that tsunami sediments were deposited in a freshwater paleolake that is located ∼16 m below present-day mean sea level. The tsunami sediment run-up was between 1.5 m and 5.5 m above the contemporaneous sea level. Our results demonstrate that the Storegga slide tsunami propagated across the wide (>500 km) and relatively shallow (depth

The Utsira Formation covers an area of at least 75×450 km 2 with its main, sandy depocentre in the southern Norwegian Viking Graben. Here in the Sleipner area, the formation is c. 300 m thick and pinches out to the west, south and east. It consists of unconsolidated, very fine- to medium-grained sand mainly composed of quartz with small amounts of glaucony, shell fragments and lignite, probably deposited by turbidite flows. Earlier biostratigraphical studies of the Utsira Formation have been based on cuttings and the age has been considered to be mainly Late Miocene potentially including latest Middle Miocene and earliest Pliocene. In the present study, core samples from the well 15/9-A23 situated in the Sleipner area have been studied. Dinoflagellate cysts were prepared from seven samples of very fine- to fine-grained sand taken from a core in the interval of 1080.0–1084.99 m. A mixture of Middle and Upper Miocene stratigraphic marker-species indicate significant reworking of older species into younger strata. The main stratigraphical problem is therefore to distinguish reworked species from the in situ flora. The presumed in situ dinoflagellate flora comprises overall Upper Miocene to Pliocene species with relatively few species of precise and clear stratigraphical significance. A single record of Selenopemphix armageddonensis in the lowest sample suggests top Miocene or younger strata. Several dinoflagellate cysts in the assemblage are well known from the Pliocene or even the Pleistocene of the North Atlantic region. Some acritarchs are particularly characteristic of the Pliocene of the northern North Atlantic region. This age is supported by the presence of species such as Hystrichokolpoma rigaudiae and Reticulatosphaera actinocoronata which are reported to range into the Lower Pliocene in the northern North Atlantic region. But the youngest possible age of these samples based on the content of dinoflagellate cysts is strongly dependent on the interpretation of which species that are considered reworked. However Amiculosphaera umbracula , Invertocysta lacrymosa and Ataxiodinium zevenboomii are generally reported to reach stratigraphically not much higher than mid-Pliocene. The age of the cored interval of the Utsira Formation is therefore considered to be Early Pliocene, and this makes a significant part of the formation younger than indicated by previously published biostratigraphic data.

The two neighbouring basins, the Danish Central Graben and the Norwegian-Danish Basin were both affected by the regional uplift of the North Sea and adjacent areas in the early Middle Jurassic that caused the formation of a regionally extensive unconformity. The uplifted area was not a simple dome structure but of a more irregular shape with an east-west oriented branch that included the Ringkobing-Fyn High and much of the Norwegian-Danish Basin and the Fennoscandian Border Zone. Late Aalenian-Bajocian deposition was confined to fault-controlled depocentres in both the Danish Central Graben and the Norwegian-Danish Basin. An initial southward slope in the Danish Central Graben changed to a north- to eastward slope before the end of the Middle Jurassic, and the change possibly coincides with the formation of a conspicuous sequence boundary in the Bathonian. The depositional area began to expand in the late Middle Jurassic as a result of a regional sea-level rise. In the Danish Central Graben, accelerating half-graben subsidence during the Callovian-Early Kimmeridgian enhanced the sea-level rise. Several periods of rapid subsidence during the Callovian-Volgian (mainly in the Oxfordian-Early Kimmeridgian and latest Kimmeridgian-Middle Volgian) gave accommodation space to more than four kilometres of marine mud. A break in subsidence in the late Kimmeridgian, probably related to a change of fault directions, resulted in deposition of shallow marine sandstones on platforms and hanging-wall slopes. The Norwegian-Danish Basin was characterised by a small rate of subsidence and continuous expansion of the depositional area throughout the Late Jurassic. The slow subsidence and a large supply of sediment from the Fennoscandian Border Zone caused repeated progradational events from the northeast. Hydrocarbon discoveries are known only from the Danish Central Graben where Middle Jurassic and Upper Jurassic reservoirs have been charged from Upper and to a smaller degree Middle Jurassic source rocks. Within the Norwegian-Danish Basin, reservoir rocks are abundant in the Upper Triassic-lowermost Jurassic, the Middle Jurassic and Upper Jurassic successions. The presence of mature source rocks, however, is the main risk factor as they most likely only occur within Lower Jurassic mudstones deeply buried in rim-synclines and in local grabens.

Spit systems are often important components of Recent deltas and coastal plains, where waves redistribute fluvial-derived sediments and they show large variations in terms of size, volume and grain size. However, spit systems are likely to form along any wave-influenced coastline and may form where faulted terrains of poorly to moderately lithified rocks are exposed to wave erosion. In such areas large spit systems are likely to be formed down-current from fault escarpments, along fault crests and on fault ramps, but appear to have been overlooked in the geological record. The Holocene-Recent Skagen Odde spit complex has developed within the last 8000 years and is still growing. The most important factors that have governed its growth are well-known, including climate, sea-level changes, palaeo-relief, free fetch, tidal range, progradation and sediment transport rates. The spit system has developed down-current from a steep slope comparable to a fault escarpment. It shows a triangular form with sides of 30-40 km and it contains 5-10 km 3 of sand. The main part of the spit system consists of five sedimentary units that constitute a shallowing-upward shoreface succession: (lower) storm sand; bar-trough sand; beach sand; peat and (upper) modern aeolian sand. The succession was formed during a forced regression as uplift outpaced eustatic rise. As the average basin-floor gradient has been steeper than the shoreline trajectory, the accommodation increased during basinward progradation of the spit system, and the resulting succession represents an accretionary, forced regression. The spit-system model may serve as an analogue to ancient fault-related shoreface sandstones without associated fluvial or deltaic deposits.

Several well-preserved Late Pleistocene spit systems occur uplifted in northern Jylland, Denmark. Their present-day morphological expression allows detailed study of spit growth patterns while the internal sedimentological organisation can be examined in a series of pits distributed along the length of the spits. Two characteristic vertical sequences are recognized in the systems. The first (Sequence I) consists of a giant-scale cross-bedded foreset unit, overlain by topset and beach units, while the second (Sequence II) consists of the foreset unit overlain by bar-trough and beach units. The two sequence types pass laterally into each other with a short overlap zone. They can be interpreted in terms of Meistrell's (1966, 1972) model for spit-platform growth based on scaled wave tank experiments. The giant-scale cross-bedded unit corresponds to prograding of a coarse-grained subaqueous spit-platform while the topset, bar-trough and beach units reflect the growth of the subaerial spit. The alternation between sequence I and II reflects the inversely related growth of the spit and platform structures: when the rate of subaqueous platform progradation declines, the subaerial spit grows uniformly, and when the platform progrades uniformly spit growth declines. The model is probably only valid for relatively coarse-grained systems because only these deposits would have a relatively steep front. The water depth in which the spit system progrades and thus bottom topography, determines the thickness of the giant-scale cross-bedded foreset unit because the water depth over the top of the platform is relatively constant. If the water is less than a few metres deep the spit-platform is not developed as seen where the Late Pleistocene spit systems prograded over elevations of the sea bottom. Conversely, the correct recognition of spit-platform sequences allows precise determination of sea-level and water depth at the time of formation. Finally, the model adds one further mode of formation of giant-scale cross-bedding to those already known from fluvial transverse, lateral and point bars, subtidal sand waves and Gilbert deltas.

CO2GeoNet is a Network of Excellence on the geological storage of CO2, initiated by the EC's 6th research framework programme in 2004 and integrating Europe's key research institutes to create a scientific reference body dedicated to the development of CO2 geological storage as a viable option for mitigating climate change. It has gained international recognition through bodies such as CSLF and IEA-GHG. It emerges as the world's largest integrated scientific community on this theme. In 2008, the network has been transformed into a legally registered Association, thus reinforcing its identity as a durable entity engaged for the safe and reliable deployment of CO2 geological storage. CO2GeoNet's activities encompass joint research, training, scientific advice, and information and communication on CO2 geological storage. © 2009 Elsevier Ltd. All rights reserved.

This paper describes an ongoing multidisciplinary study on the development of the barrier islands in the Danish Wadden Sea (Vadehavet), carried out by the Department of Geography and Geology at the University of Copenhagen and the Geolo gical Survey of Denmark and Greenland (GEUS). Nine sediment cores each c. 25 m long and a total of c. 45 km ground penetrating radar (GPR) profiles have been acquired on the islands of Rømø and Fanø. Geochemical and palaeontological analyses and dating of 150 core samples using optically stimulated luminescence (OSL) are in progress. This multidisciplinary approach has given new insights into the sedimentary architecture and development of the island, and the study is expected to result in a new detailed facies model. Such models are essential for an assessment of the effects of rising sea level associated with global warming. The new facies model can also be used as an analogue for subsurface oil or water reservoirs in similar sedimentary settings. This article presents selected core and GPR data from the Rømø barrier island.