A new multidisciplinary biostratigraphic framework, combining dinoflagellate cysts, microfossils, calcareous nannofossils, diatoms and silicoflagellates, is established for the Early to Middle Miocene deep marine clay and siliceous ooze in the southern Norwegian sector of the North Sea, based on core samples from the Valhall and Hod hydrocarbon fields. The framework was successfully tested on the equivalent chronostratigraphic level of several wells based on ditch cutting samples. New biostratigraphic events for the Danish and Norwegian North Sea resulting from this study are successfully used to correlate between the Valhall and Hod areas and supplement published zonation schemes. To our knowledge, this is the first time that diatoms and silicoflagellates from the fine fraction of microfossil samples have been used as correlation tools in the North Sea Basin. Dating of the siliceous/diatomite-rich interval results in a high-resolution (5–15 m intervals) biostratigraphic subdivision. The successful application of the new framework across the Valhall and Hod areas implies that it could also be useful in a more regional context. The new biostratigraphy enables the correlation of the lithostratigraphic units recently defined for the Danish offshore Neogene succession to the study area and the correlation of the sequence stratigraphic surfaces defined for the Danish sector to the southern Norwegian sector.

Mesozoic Oceanic Anoxic Events (OAEs) were linked to the accumulation of organic-rich sediments in response to global climatic and environmental changes, resulting in transient episodes of oceanic deoxygenation. To better understand the evolution of seawater oxygenation in the Boreal Realm during the Early Cretaceous (late Hauterivian – early Aptian), this study presents high-resolution datasets of Rare Earth Element plus Yttrium (REE + Y; REY) patterns and redox-sensitive trace elemental (RSTE) concentrations in the Danish Central Graben (DCG). Oxygenation in the seawater column can be derived from the Cerium (Ce) anomaly (Ce/Ce*), which is based on the premise that Ce acts differently in well-oxygenated environments compared to the other REYs. At the seafloor, anoxia is indicated by the enrichment of RSTEs Vanadium (V) and Uranium (U). A decline in Ce anomaly values and low RSTE concentrations from the late Hauterivian to late Barremian indicates a shift from an oxygen-depleted to a more oxygenated seawater column and seafloor conditions in the Boreal Realm. A similar trend is observed in the Tethyan Realm, suggesting the existence of a global long-term driver of seawater oxygenation level. In the DCG, this long-term trend is interrupted by a brief drop in relative sea level, leading to partial isolation of the basin, reduced ventilation, stratification of the water column and consequently short-term anoxic conditions at the sediment–water interface. This resulted in the deposition and preservation of an organic-rich layer (Munk Marl Bed) during the early Barremian. During the early Aptian, an organic-rich layer (Fischschiefer Member) of regional extent, linked to the global OAE-1a, was deposited. Significantly elevated Ce anomaly values along with increased concentrations of U and V signify anoxic conditions within this Boreal basin, whereas the seawater column in the Tethyan Realm exhibited dysoxic conditions. Variations in anoxia and the fact that some OAEs are only observed locally, leads to the conclusion that short-term regional or local factors can overprint global changes.

The Neogene of the Danish North Sea is more than 1200 m thick. Despite being penetrated by numerous wells, formal lithostratigraphic subdivision of this succession has previously been restricted to the lowermost part. This monograph presents a comprehensive lithostratigraphy of the offshore Neogene of Denmark, in part extending recognised onshore units into the offshore realm. The mainly Lower Miocene deltaic deposits are referred to the Ribe Group, which is subdivided into six formations: the Klintinghoved, Bastrup, Arnum, Odderup, Dany (new) and Nora (new) Formations. The lowermost Miocene Vejle Fjord and Billund Formations known from the onshore lithostratigraphy are absent in the offshore wells. The dominantly fully marine Middle and Upper Miocene sediments are referred to the Måde Group, subdivided into the Hodde, Ørnhøj, Gram, Marbæk and Luna (new) Formations; the Luna Formation includes the Lille John Member (new). The Pliocene deltaic deposits are referred to the Eridanos Group (new), which is subdivided into the Vagn (new), Emma (new) and Elin (new) Formations.The depositional history of the Neogene of the Danish North Sea sector is presented based on a detailed reconstruction of subsurface morphology by the mapping of stratigraphical surfaces dated by biostratigraphy. During the Early Miocene, deposition in the Danish North Sea was dominated by progradation from Scandinavia; large deltas built out into the Danish onshore area from the north and north-east. West of the main deltas, muddy contourites periodically accumulated on the slope, accentuating shelf progradation. The Middle and Late Miocene period was mostly characterised by fully marine conditions and deposition of mud. By the end of the Miocene, progradation of delta systems from Scandinavia into the North Sea resumed, and the shoreline reached the westernmost part of the Danish North Sea sector. During the Pliocene, new source areas in central and eastern Europe, such as the Carpathian Mountains, were activated and a huge delta system, the so-called Eridanos Delta, began to fill the North Sea Basin from the east and the south-east. Due to increased subsidence of the basin associated with the loading of sediments of the Eridanos Delta, the northern systems were flooded. Although the Danish North Sea thus mainly received sediments from central Europe during the Pliocene, progradation from Scandinavia resumed at the end of the Pliocene.

Oceanic anoxic events (OAEs) are defined by widespread deposition of organic-rich sediments resulting from transient episodes of oceanic deoxygenation in response to global environmental changes. This study contributes to the understanding of the evolution of seawater oxygenation during the late Hauterivian - early Aptian in the Boreal Realm by introducing a high-resolution dataset of rare-earth element (REE) plus yttrium (Y; REY) patterns and redox-sensitive trace element (RSTE) concentrations from the Danish Central Graben (DCG), North Sea. Changes in oxygenation in the seawater column can be deduced from the Ce anomaly (Ce/Ce*) whereas uranium (U), vanadium (V) and manganese (Mn) concentrations reflect oxygenation conditions at the sediment-water interface. Decreasing Ce/Ce* values and low RSTE concentrations indicate a long-term trend from an oxygendepleted to a more oxygenated water column from the late Hauterivian to earliest Aptian. This long-term trend was interrupted by two shorter-lived deoxygenation events controlled by two contrasting styles of relative sea-level change. First, an early Barremian sea-level fall led to semi-isolated depocentres in the DCG, causing reduced ocean ventilation that triggered stratification of the water column and ultimately anoxic conditions at the sediment-water interface. This resulted in the deposition of the organic-rich, laminated Munk Marl Bed. Second, in the early Aptian, the unfolding of the OAE 1a which was coeval to a global eustatic sea-level highstand resulted in the deposition of the regionally persistent, organic-rich, laminated Fischschiefer Member. Contrary to the oxygen-depleted/ferruginous seawaters in the Tethyan Realm during OAE 1a, the Ce anomaly of the Fischschiefer Member indicates an oxygen-depleted/manganous water column in the Boreal Realm. Regional environmental conditions, such as ocean ventilation, are therefore an important factor with regards to ocean oxygenation, explaining the heterogenous spatial distribution of organic-matter-rich levels associated with OAEs.

In June 2021, a novel Danish national carbon capture and storage strategy was ratified by the Danish Parliament, and this was followed by the initiation of the project ‘CCS2022–2024’, led by the Geological Survey of Denmark and Greenland. In collaboration with other institutions, we acquired and interpreted new 2D seismic data between 2022 to 2024 to investigate and mature eight sites for potential subsurface storage of CO2 in Danish onshore and offshore areas. This Bulletin contains a series of papers that present important results of the work. In this introduction paper, we provide an overview of seismic acquisitions and the interpretation of seismic data together with existing deep wells. The study sites selected are large subsurface structures located in onshore Jylland, Sjælland and Lolland and offshore Denmark in the eastern North Sea. The onshore targets are the Gassum, Havnsø, Rødby, Stenlille and Thorning structures, while the offshore sites comprise the Inez, Jammerbugt and Lisa structures. The project work comprises a series of reports regarding extensive seismic acquisition, processing and interpretation of the new and pre-existing seismic data as well as other publications emanating from the project. This Bulletin and the technical reports present an improved understanding of the formation, composition and geometry of the investigated structures. The studies include the mapping of the reservoir and seal formations, identification of principal faults, interpretation of the stratigraphic and structural development, reservoir and seal characterisation and estimates of the static storage capacity. Hence, this research provides a significant step forward concerning characterisation of the geology and maturation of the potential storage sites. In addition, it has inspired new ideas, including an updated regional stratigraphic interpretation of the Triassic succession of the Danish Basin and correlation with adjacent basins.

Abstract New carbon isotope results obtained from cores from the Fehmarn Belt (German Basin), along with hitherto unpublished detailed results obtained from brachiopods collected in the 1970s from the Hemmoor section, NW Germany, present the opportunity to revise the holostratigraphy of the Danish Basin and erect a complete chronostratigraphical scheme for the upper Campanian–Maastrichtian of the Boreal Realm based on records from the Danish and North German basins. The correlation of all studied sections is ensured by previously erected high-resolution bulk carbonate carbon isotope records. A number of issues arising from the standard Upper Cretaceous (UC) calcareous nannofossil biozonation scheme for the Boreal Realm are discussed and lead us to propose a new subzonation for the Danish Basin. Carbon isotope records allow correlation to Gubbio, Italy, the Tethyan bio-magnetostratigraphic reference, and to the astronomically calibrated ODP site 762C, Indian Ocean. Revised correlations ensure the application of magnetostratigraphy, a numeric timescale and stacking of 405 kyr cycles to the new scheme, thus erecting a detailed chronostratigraphy for the upper Campanian–Maaatrichtian of the Boreal Realm.

Abstract The Lower Cretaceous (upper Hauterivian–Albian) pelagic and hemipelagic carbonates of the Tuxen and Sola Formations in the Danish Central Graben, North Sea, constitute one of the oldest chalk successions recorded globally, but have received less attention than the Upper Cretaceous–Danian Chalk Group. This paper presents an updated depositional model for the succession drawn from synthesis of the latest published sedimentological and stratigraphic results, and correlation of 11 wells in the Valdemar, Boje, Adda and Tyra Fields. Four depositional sequences, deposited on a relatively deep subphotic shelf, record c. 20 Myr of transgressive–regressive cycles, including: (1) late Hauterivian–earliest Barremian highstand and differential subsidence, resulting in aggradation across a westward-dipping ramp; (2) early Barremian eastern (Adda Field) inversion causing plateau condensation, sediment bypass and sourcing of gravity flows, followed by lowstand-controlled basin isolation and associated anoxia (Munk Marl Bed), and finally late Barremian tectonic quiescence and highstand with deposition of clean reservoir chalk; (3) latest Barremian lowstand causing filling of local depocentres, interrupted by early Aptian transgression-controlled anoxia during the global Oceanic Anoxic Event 1a (Fischschiefer Member), and finally late Aptian highstand; and (4) latest Aptian–earliest Albian lowstand causing local erosion and heightened influx of clay.

Since 1976 more than 25,000 Arctic sediment samples have been processed for their palynological, nannofossil, or microfossil content at the Geological Survey of Greenland (GGU) and the Geological Survey of Denmark (DGU); both institutes are now merged into the Geological Survey of Denmark and Greenland (GEUS). The samples represent nearly all ages from the Neoproterozoic to the Neogene, though dominated by the Mesozoic. A large proportion of the samples were processed for palynomorphs. Up to ten slides have been produced for each palynological sample and usually one slide is produced for each nannofossil and microfossil sample, making the GEUS collection one of the largest Arctic slide collections with more than 200,000 slides. All type specimens and some specimens illustrated in publications listed here have been assigned MGUH numbers ( Museum Geologica Universitas Hafniensis) and are housed in the type collection of the Geological Museum of the University of Copenhagen, now part of the Natural History Museum of Denmark.

The alternating marlstone and chalk of the Lower Cretaceous succession in the Danish Central Graben (DCG) are important for the understanding of the evolution of the larger North Sea Basin. This study focusses on the clay mineral assemblages of the upper Hauterivian – lower Aptian in the DCG and Danish Basin (DB) and their implications. Clay mineral assemblages are predominantly used to assess palaeoclimate. In this study, however, they were additionally used in a source-to-sink context. Kaolinite was found to form a dominant component of the clay mineral assemblage in the sampled wells of the DCG and in the DB, suggesting that a feldspar- or kaolinite-rich source was present and actively eroded in the region during the Early Cretaceous. Moreover, a decreasing gradient west to east of average kaolinite content is observed in the three studied wells for the early Hauterivian to late Barremian (BC9-BC17), with the highest content observed in the North Jens-1 well (av. 74%), followed by the Boje-2C well (av. 49%) and lastly in the Vinding-1 well (av. 39%). Due to the relatively rapid settling of kaolinite in marine environments compared to other clay minerals, this gradient suggests that the main clay mineral source was located in the south-western part of the DCG. Isochore maps, a new palaeogeographic map of the DCG and the western part of the German sector of the North Sea illustrates where Lower Cretaceous rocks are absent in this region, due to either erosion or non-deposition. Potential subaerially exposed highs included the distant Baltic Shield to the north, the Ringkøbing–Fyn High to the east and the Heno Plateau within the DCG, with the latter being located closest to the North Jens-1 well and containing feldspar-rich sandstones of the Heno Formation (upper Kimmeridgian – lowermost Volgian/Tithonian). During the Early Cretaceous, part of the Heno Formation was potentially subaerially exposed or subject to wave reworking/erosion in parts of the Danish and German sectors. The sandstones could weather into kaolinite and this structural high is therefore suggested to have been the main source area for this part of the DCG, with minor sediment influxes from the Ringkøbing–Fyn High and Baltic Shield. In addition, the overall decrease in kaolinite in the DCG from the late Hauterivian to the late Barremian indicates a climatic change towards drier conditions, with some minor, slightly more humid periods.

Summary The Greensand project aims to develop Paleogene sands in the Siri Canyon offshore Denmark for safe long-term CO2 storage with the initial focus on the Nini West depleted oil field. The seal consists of a primary caprock succession of marine shales from the Horda to mid Lark formations and a secondary caprock succession from the mid to upper Lark formation, totalling approximately 900 meters in thickness including sandy siltstone beds in the secondary seal. The applied work stream extensively examines the geological seal parameters using a multidisciplinary framework. This includes determining elemental composition, mineralogy, grain size distribution, porosity, permeability, specific surface area, pore throat size distribution, and capillary entry pressure data from core and cuttings samples in the Nini area. Digital rock analysis was conducted on cuttings representing sandy siltstone beds within the secondary seal. A petrophysical workflow is described, incorporating algorithms for calculating grain size fractions, total porosity, grain density, specific surface area, and permeability utilizing wireline logs based on analytical data. Highest seal capacity was found in the smectite rich primary seal compared to the illite-kaolinite dominated secondary seal. The study documents that the seal exhibits a high capacity for withholding CO2 in the subsurface.

The Deep Adda-1 well in the Danish Central Graben, North Sea, provides a record of mid-Cretaceous sedimentation on the eastern flank of the intrabasinal Adda–Tyra inversion high. An upper Hauterivian – lower Barremian core in the Tuxen Formation spans the lower boundary of the laminated organic-rich Munk Marl Bed (MMB), a key marker bed in North Sea Cretaceous stratigraphy. Multidisciplinary sedimentological–biostratigraphic–palaeoecological data document the abrupt environmental shift at this boundary. The upper Hauterivian – lowermost Barremian lower Tuxen Formation (nannozones BC10 – lowermost BC14), beneath the MMB, represents a well-ventilated, current-swept setting supporting a diverse benthic fauna and characterized by a condensed succession with hardgrounds, at one level defining a biostratigraphic hiatus, and stacked, thin shallowing-upward parasequences. The succeeding lower Barremian MMB (nannozone BC14) attests to poorly oxygenated bottom waters and a total lack of epi- and infauna; the calm, inhospitable sea floor was intermittently disturbed by muddy turbidity currents and debris flows. The base-MMB surface is a complex fractured hardground indicative of relative sea-level fall and protracted winnowing of the cemented sea floor. The Deep Adda-1 core thus records a sea-level excursion that accompanied the onset of early Barremian oxygen depletion in concert with additional potential forcing factors such as coeval volcanism and watermass warming.

The understanding of the climatic evolution during the Early Cretaceous in general, and across Oceanic Anoxic Event 1a (OAE-1a) in particular, has generally been derived from Tethyan localities, implying large uncertainties about their significance at a global scale. In this study, high-resolution clay-mineral assemblage analyses have been performed on the Hauterivian to lower Aptian cored section of the North Jens-1 well, located in the Danish Central Graben, North Sea, in the Boreal Realm. Large amounts of detrital kaolinite are observed throughout the core, indicating the presence of a local, kaolinite-rich source. A long-term decline in kaolinite content is recorded from the upper Hauterivian to the lowermost pre-OAE-1a Aptian, followed by a sharp rise within the OAE-1a interval. This trend is similar to that observed in the Tethyan Realm, where a supra-regional climatic evolution is observed, including: (i) relatively humid conditions in the late Hauterivian; (ii) a shift towards overall drier conditions in the latest Barremian - earliest Aptian; and (iii) renewed humid conditions during the unfolding of OAE-1a. However, the precise timing of climate change across OAE-1a differs between the Tethyan and Boreal Realms. The shift towards humid conditions coincides with the onset of OAE-1a (segment C3) in the Tethyan Realm, followed by a return to drier conditions in the second half of the event. In the Boreal Realm, however, the onset of OAE-1a was characterised by a relatively dry climate, followed by an increase in humidity within its middle part (segments C4-C5) that persisted through the remainder of the early Aptian. Consequently, there was a non-linear change in precipitation patterns across latitudinal belts during the unfolding of OAE-1a. Similar conclusions have been drawn for other OAEs, suggesting a more complex weathering feedback mechanism during hyperthermal events than generally assumed.

Squat lobsters within Galatheoidea are very diverse with over 1,300 extant species that live in all marine ecosystems, but their fossil record, starting in the Middle Jurassic, consists of only similar to 200 species. Consequently, much remains to be learned about their biodiversity, phylogeny, and paleobiogeography. We describe five new species (Galatheites sforum n. sp., Kimmeridgian, Late Jurassic, Germany; Vasconilia zapotitlanensis n. sp., Barremian, Early Cretaceous, Mexico; Eomunidopsis texcalaensis n. sp., Barremian, Early Cretaceous, Mexico; Protomunida bennickei n. sp., Danian, Paleocene, Denmark; and Protomunida eurekantha n. sp., Danian, Paleocene, Denmark) and one new genus (Tethysgalathea n. gen., Ypresian, Eocene, Italy). We further reassign Munida cretacea (Albian, Early Cretaceous, Texas, USA) to Galathea?, return Eomunidopsis? cobbani (Campanian, Late Cretaceous, Colorado, USA) to its original genus, report on the second occurrence of Vetoplautus latimarginus Robins et al., 2013 (Tithonian, Late Jurassic, Czech Republic), and reinstate Palaeomunidopsis moutieri (middle Bathonian, Middle Jurassic, France) as the oldest galatheoid known to date. The five new species, all found in limestones containing corals, increase galatheoid diversity in the fossil record by 2.5%. Finally, the common yet hitherto unrecognized Protomunida eurekantha was discovered by making casts of external molds, revealing distinct spines on the posterior margin that are more difficult to see in internal molds and specimens with cuticle due to breakage. Collecting and studying the external molds for galatheoids and other fossil decapods could yield additional cryptic species.

Understanding of the shallow shelf system in the Danish Basin during the Early Cretaceous has benefitted significantly from studying the previously overlooked Hauterivian–Aptian section of the Vedsted Formation of the Vinding-1 drill core. The presence of chalks in this section demonstrates that carbonate-rich pelagic sediment accumulated locally in the siliciclastic-dominated Danish Basin and that benthic carbonate production was insignificant. The area was not a carbonate platform in the Early Cretaceous and does not indicate any reworked carbonate supply from platform environments in the vicinity. The scarcity of benthic macrofossils in the cored section is due to the lack of a specialised boreal chalk fauna at that time, and the adjacent nearshore environment apparently did not support any substantial benthic carbonate production. A revised biostratigraphy of the cored section is presented based primarily on calcareous nannofossils, supported by foraminifera, ostracods, and belemnites. Four lithofacies describe the spectrum from marlstone to slightly marly chalk, and the facies succession characterises four depositional units recording two discrete transgressive–regressive cycles. The study provides a depositional record that permits sequence stratigraphic correlation to the Valdemar and Adda Fields in the Central Graben.

Natural fractures and discontinuities have significant impact on subsurface flow conditions and thus production, of carbonate reservoirs, particularly in low-permeability sediments such as chalk-marl successions characterizing the Lower Cretaceous reservoirs in the Danish North Sea. Yet the diversity and distribution of the fractures are often poorly understood and largely underestimated. In heterogeneous, tight carbonate reservoirs, natural fractures can enhance permeability, as well as create secondary porosity and promote connectivity between reservoir compartments. The Valdemar Field, Danish Central Graben, represents the only producing field from the Lower Cretaceous in the Danish sector of the North Sea. The main reservoirs are confined to the Tuxen and Sola Formations. A new reservoir zonation is proposed based on facies characteristics and fracture patterns to consist of the lower Tuxen, middle-upper Tuxen, lower-middle Sola and upper Sola units with the Munk Marl Bed and Fischshiefer Member forming major reservoir barriers between the lower and the middle-upper Tuxen, and the lower-middle and the upper Sola units, respectively. The reservoir intervals are of heterogeneous nature and composed of interbeds of five main facies comprising chalk, slightly marly chalk, marly chalk, chalky marlstone and marlstone. Six types of natural fractures and discontinuities are identified in the Valdemar Field based on core studies: cemented fractures, deformation bands, open fractures with plumose structures and hackle marks, shear fractures, small-offset shear fractures and rubble zones. The most dominant fracture type within all facies is the open fractures with plumose structure and hackle marks followed by small-offset shear fractures, shear fractures and rubble zones. Cemented fractures and deformation bands are less dominant. The small-offset shear fractures, shear fractures and open fractures with plumose structures and hackle marks are flow enhancing, while the cemented fractures and deformation bands are neutral or flow reducing. Rubble zones are also recorded throughout the core material. If these represent naturally fractured zones, present under subsurface conditions, they would be strongly flow enhancing. The flow-enhancing natural fractures (open fractures, shear fractures and small offset shear fractures) have densities of 7.2/m in the chalk, 5.0/m in slightly marly chalk, 3.1/m in marly chalk, 4.8/m in the chalky marlstone while they are absent in the marlstone. The flow-enhancing fractures have densities of 4.6/m in the lower Tuxen reservoir, 4.0/m in the middle-upper Tuxen reservoir, 2.7/m in the lower-middle Sola reservoir, and 7.4/m in the upper Sola reservoir. This study provides a detailed analysis of the natural fractures and discontinuities occurring the Lower Cretaceous succession of the Danish North Sea Basin, and their relation to the sedimentary facies and reservoir units.

An integrated seismic–stratigraphic study of the Lower Cretaceous Cromer Knoll Group was undertaken as part of a recent comprehensive analysis of the Upper Jurassic – lowermost Cretaceous petroleum system in the Danish Central Graben. This study of the basal group of the post-rift package yielded an updated regional assessment of the distribution of the Valhall, Tuxen, Sola and Rødby Formations. This is documented by four high resolution isochore maps (presented here) that record temporal shifts in subsidence patterns from the latest Ryazanian to the earliest Cenomanian. The distribution and thickness variation of the mud-dominated Valhall Formation (latest Ryazanian – early Hauterivian) at the base of the group attests to the progressive fill of inherited syn-rift morphology. The dominant depositional theme is thus ponding in, and onlap from, the main inherited depocentres, although growth faults and incipient inversion locally controlled stratigraphic architecture, and new depocentres were initiated in the east of the graben (Ål and Outer Rough Basins). The isochores for the succeeding, increasingly chalk-rich Tuxen, Sola and Rødby Formations (Hauterivian – earliest Cenomanian) document the regional weakening of syn-rift patterns but emphasize the shift in sedimentation patterns controlled by accelerating inversion activity in the east (Adda–Tyra area, Søgne Basin) and increased local subsidence. The latter sometimes coincided with syn-rift depocentres, such as the Roar Basin and the Arne-Elin Graben, but was also significant in the new Early Cretaceous depocentres in the west of the graben, particularly the Outer Rough Basin. The evolution of the Early Cretaceous basin recorded by this dataset reveals significant shifts in the subsidence pattern in the late Valanginian – early Hauterivian, in large part due to early inversion in the east, and during the late Aptian – early Albian when subsidence was focussed in central and western sub-basins, probably locally due to salt withdrawal. These events, in combination with sea-level change, had implications for the accumulation and preservation of Barremian and early Aptian reservoir chalks.

By stacking recorded wave trains in a graphical strain-time-amplitude domain, we demonstrate that an early shear wave feature marks a converted shear to compressional to shear wave and not the transmitted shear wave. Elastic wave velocities of compressional and shear waves propagating through sedimentary rocks are often coupled with bulk density to derive the rock stiffness. Acquiring the transit time of compressional and shear waves often involves manual picking of wave arrival times from wave trains recorded in the laboratory or by well-logging tools. Picking of the compressional wave arrival time is commonly accepted as straightforward. Oppositely, detecting the shear wave arrival and picking its arrival time is often troublesome because the transmitted shear wave partly converts to compressional waves and back to a secondary shear waves, concealing the transmitted shear wave arrival in the wave train. We illustrate the difficulty of shear wave detection in wave trains recorded on highly porous chalk plug samples from the Danish North Sea Basin in laboratory settings. Wave trains were recorded on plugs dry, Tap-water, or Isopar-L saturated during uniaxial strain compaction. The recorded shear wave trains showed two distinct features, which could be interpreted as the transmitted shear wave first arrival, we denoted them as early and late arrivals. However, as only one feature can mark the arrival of the transmitted shear wave, we propose a disclosure strategy combining a graphical representation of stacked wave trains (Figure 1) with rock physical modelling.

The Faxe limestone quarry in eastern Denmark exposes Danian (Lower Paleocene) cool-water carbonate deposits. They constitute remnants of an apparent build-up that covers about 12 km2 today. The Danian deposits at Faxe are conspicuous due to their pronounced thickness of coral limestone relative to the regional carbonate system. In the Faxe quarry, scleractinian corals are uniquely exposed in up to 30 m high mounds. The rapid accumulation of scleractinians combined with induration of the mounds may locally have protected the limestone from Quaternary glacial erosion and created a Danian thickness anomaly at Faxe. The position of Faxe above a local fault-bounded basement high and the extent of coral limestone has been better defined by new mapping. A mapped lithostratigraphic surface in the quarry reveals the large-scale organisation of nested bryozoan mounds on three elongated ridges striking NW–SE. The main scleractinian coral mounds are located above this horizon. Data for reservoir characterisation, mainly of the bryozoan mounds, were collected as photographs of the outcrop, petrophysical and petrographical data from cored boreholes, and as ground-penetrating radar sections. Old boreholes and measured sections were used to reconstruct the build-up, and new nannofossil data allow a discussion of stratigraphy and accumulation rate. The petrophysical data show that common mound-building bryozoan packstone has higher permeability and lower capillary entry pressure than chalk, whereas less commonly occurring grain-dominated packstone and grainstone deposits from local higher-energy sites of the mound complex were found to have reduced amounts of coccolith mud, significantly higher permeability and a higher degree of lithification. Based on biostratigraphic age constraints, correlation of flint – limestone couplets and recog-nised hierarchical patterns, we develop a cyclostratigraphy for the middle Danian and suggest that cyclicity in lithology and petrophysical characteristics of bryozoan limestone are controlled by precession and eccentricity of the orbit of the Earth.