Search

The Portfjeld Formation, as originally defined, is the lowermost lithostratigraphic unit of the mainly Lower Palaeozoic Franklinian Basin in southern Peary Land, central North Greenland. The unit crops out semi-continuously from Valdemar Glückstadt Land to Nordenskiöld Fjord but is also recognised locally in northern parts of Peary Land and Wulff Land (western North Greenland). Regionally, it provides a key record of the early, pre-break-up history of the basin. The type succession in southern Peary Land has thus been the focus of recent biostratigraphical, sedimentological and geochemical study. This has demonstrated the composite nature of the unit, a lower interval (c. 190 m thick) of carbonate ramp deposits of Neoproterozoic (late Ediacaran) age being overlain at a karstic unconformity by a shallow marine, mixed carbonate–siliciclastic interval (c. 100 m thick) of probable earliest Cambrian age. Lithostratigraphic revision of this succession is presented here. The Portfjeld Formation throughout North Greenland is elevated to the rank of group, and two new formations are defined in this group in southern Peary Land and immediately adjacent areas: the Ediacaran carbonate-dominated unit is referred to the Slusen Formation, the upper mixed siliciclastic–carbonate unit to the Glaciologelv Formation.

Lower Paleocene marine siliciclastics of the Sobral Formation (Seymour Island, Antarctica) form an important component of a key southern high latitude reference section for the Maastrichtian–Eocene. The formation comprises a coarsening-upward, regressive succession (270 m thick), shallowing from prodeltaic, mud-rich to sandy nearshore sediments. Sedimentary facies analysis, integrated with macrofaunal and microfloral palaeoecological studies, indicate a wave-dominated, tidally influenced deltaic environment. Four depositional sequences (1–4) record the role of relative sea-level changes in controlling the stepwise progradation of the system. Prodeltaic and distal delta-front deposits (Sequences 1, 2), comprise coarsening-upward parasequences of mud-rich heteroliths and bioturbated fine-grained muddy sands displaying draped slump scars. The overlying erosional sequence boundary is marked by incised valleys filled with fluvio-estuarine sediments; succeeding sand-rich facies (Sequences 3, 4) represent the proximal delta front and delta platform. The macro-invertebrate and palynological datasets display contrasting responses to the regressive history of the formation. The macrofaunal record in the distal deltaic sediments reflects the marine influence, though a stratigraphic increase in diversity was controlled both by ecological factors and biotic recovery following the K–Pg event. The associated palynological assemblage also displays a strong marine signal and includes typical outer neritic – oceanic dinoflagellate cyst taxa. A sharp decline in macrofossil diversity and abundance in Sequences 3, 4 is compatible with ecological stress in shallow-water, restricted inshore settings. Though the palynological record at this level is terrestrially dominated, the marine component reflects the cosmopolitan nature of dinoflagellates, displaying the highest diversities in the formation. The regressive Sobral Formation ended a protracted c. 60 Myr history of regional subsidence

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 Germa

Two fully cored boreholes, the Rødryggen-1 and the Brorson Halvø-1, were drilled in Wollaston Forland, North-East Greenland, in 2009 and 2010, respectively. The objective was to test the stratigraphic development of the Upper Jurassic – Lower Cretaceous mud-dominated succession in two different settings within the same fault block of a developing half-graben: centrally (Rødryggen-1 borehole) and near the uplifted crest of the rotating fault block (Brorson Halvø-1 borehole). The drilled deposits are equivalent to the principal petroleum source-rock sequence of the petrolifer-ous basins of North-West Europe, Siberia, and basins off eastern Canada and provide a new record of an important phase of marine deoxygenation in the proto-North Atlantic region.

Two drill cores spanning the Upper Jurassic – Lower Cretaceous succession in Wollaston Forland, North-East Greenland, offer an insight into mud accumulation in an evolving distal fault block. Previous studies have revealed the presence of long-lasting black mudstone accumulation extending through the oxygen-restricted early rift and rift climax phases (Bernbjerg and Lindemans Bugt Formations). Here, we present a detailed description of the sedimentary succession extending into the late syn-rift settings (Palnatokes Bjerg and Stratumbjerg Formations). The results indicate that the Kimmeridgian – lower Volgian early rift-phase was characterised by suspension settling and millimetre-scale event deposition in a tectonically affected, prodeltaic offshore setting. The event-related depositional processes are recorded by starved wave ripples, scour-and-fill structures, putative mud-floccule ripples and mud-dominated gravity-flow deposits. During the middle Volgian – Ryazanian rift climax, the depositional environment evolved into a narrow half-graben that was detached from the proximal depocentre flanking the deltaic coastline, itself dominated by coarse sediment. The correlative sedimentary facies in the detached half-graben are bioclastic and pyrite-rich black mudstones, which document suspension settling and gravity-flow or mass-wasting deposition in sub-storm wave-base slope and basin-floor environments. Black mudstone sedimentation ended abruptly in the late Ryazanian when the accumulation of condensed, bioturbated deep marine marls coincided with broader oceanographic reorganisation concomitant with waning rift activity in the west. Deposition of red bioclastic mudstones with a common gravity-flow component characterised the Hauterivian, potentially representing final draping of the submerged fault block crest. The top of the cored succession is demarcated by dark grey bioturbated mudstones of Barremian age, reflecting the onset of regionally continuous deep marin

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 Lower Cretaceous Tuxen (lower Hauterivian ??? upper Barremian) and Sola (upper Barremian ??? Albian) Formations in the Danish Central Graben (North Sea) constitute one of the oldest chalk successions recorded globally, but have received little attention with regards to sedimentary facies and depositional processes. This study presents the first comprehensive carbonate facies analysis of the succession, retrieved from seven drill cores from the Valdemar and Adda Fields. A total of 50 facies are identi-fied, based on a continuum of six lithologies ranging from chalk to marlstone and tuffaceous siltstone to sandstone that display eight different sedimentary structures or fabrics, and two redox-associated lithological color variations (green and red) in the Adda Field. The eight sedimentary structures record: (i) comprehensive biotur-bation of homogeneous sediment during fully oxygenated benthic conditions and low sedimentation rates; (ii) a similar bioturbation process but in heterogeneous sediment with lithological contrasts permitting visible burrows to form, perhaps due to rhythmic alternation between pelagic (clay-poor) and hemipelagic (clay-rich) sedimentation; (iii) pelagic to hemipelagic suspension settling in dysoxic to anoxic bottom-water conditions; (iv) patchy cementation of the shallow sea bed during incipient hardground formation; (v) reworking of bioclasts and chalk intraclasts by bottom or wave-induced currents and cohesive debris flows; (vi) pressure solution during late burial diagenesis; (vii) shear deformation by intense plastic deformation of unlithified sediment from limited lateral displacement; and (viii) silicification during burial diagenesis. The facies distribution indicates that active tectonism took place prior to the onset of anoxia that resulted in deposition of the Munk Marl Bed, which in the Valdemar Field was followed by tectonic waning and repeated anoxia. The Valdemar Field constituted a basinal depocenter and was flanked to t

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, whil

One active journal. Fourteen legacy titles. More than 3000 articles published since 1893 – some digitised, some not. One full-time member of staff. A small team of dedicated geoscientists. Limited budget. PlanS. Open-source journal software. If these are the ingredients, what is the recipe? Like many surveys, the Geological Survey of Denmark and Greenland (GEUS) has a long history of publishing. Our full catalogue of titles extends back to 1893 and our current title, GEUS Bulletin (www.geusbulletin.org; formerly Geological Survey of Denmark and Greenland Bulletin), has been active since 2003. Our journals have always been grassroots initiatives – run by scientists, for scientists. But two years ago, amid the fast-changing demands of digital publishing, the Survey faced a quandary: should we continue publishing our own journal? At a time of rapid proliferation of journals for any discipline imaginable, what niche did a geographically-focused journal fill? What should we modernise? Could we relaunch as an online, diamond open-access journal on our existing budget? Could we implement more of the services our authors wanted and attract more authors beyond our traditional audience? Two years later, we have successfully re-launched our collection of journals, without increasing our overall budget. Using open-source solutions, we have transformed our print-focused publication workflow to a new online, open-access platform and data repository. We are currently migrating our entire back catalogue of legacy titles to the same platform. Although we only have visitor data for our new platform since November 2020, we can see early signs of increased article views (c. +82% in Nov–Dec 2020, compared with the same months in 2018 and 2019) and a jump in traffic from external websites like Google Scholar (from 5% before re-launch to 35% after re-launch). In this presentation, we present a recipe that we hope other geological surveys, societies and institutions can

Taxonomic and ecological recovery from the Cretaceous–Palaeogene (K–Pg) mass extinction 66 million years ago shaped the composition and structure of modern ecosystems. The timing and nature of recovery has been linked to many factors including palaeolatitude, geographical range, the ecology of survivors, incumbency and palaeoenvironmental setting. Using a temporally constrained fossil dataset from one of the most expanded K–Pg successions in the world, integrated with palaeoenvironmental information, we provide the most detailed examination of the patterns and timing of recovery from the K–Pg mass extinction event in the high southern latitudes of Antarctica. The timing of biotic recovery was influenced by global stabilization of the wider Earth system following severe environmental perturbations, apparently regardless of latitude or local environment. Extinction intensity and ecological change were decoupled, with community scale ecological change less distinct compared to other locations, even if the taxonomic severity of the extinction was the same as at lower latitudes. This is consistent with a degree of geographical heterogeneity in the recovery from the K–Pg mass extinction. Recovery in Antarctica was influenced by local factors (such as water depth changes, local volcanism, and possibly incumbency and pre‐adaptation to seasonality of the local benthic molluscan population), and also showed global signals, for example the radiation of the Neogastropoda within the first million years of the Danian, and a shift in dominance between bivalves and gastropods.

The marine, mudstone-dominated Hareelv Formation (Upper Jurassic) of Jameson Land, East Greenland is a representative of the widespread Kimmeridge Clay Formation equivalents, sensu lato, known from the greater North Atlantic region, western Siberia and basins off eastern Canada. These deposits constitute the most important petroleum source-rock succession of the region. The present study reports petroleum geochemical data from the 233.8 m thick succession penetrated by the fully cored Blokelv-1 borehole, and includes supplementary data from outcrop samples and other boreholes in Jameson Land. The succession consists of basinal mudstone intercalated with a significant proportion of gravity-flow sandstones, both in situ and remobilised as injectites. The mudstones are generally rich in organic carbon with values of TOC reaching nearly 19 wt% and high pyrolysis yields reaching values of S2 up to nearly 43 kg HC/ton. Hydrogen Indices are up to 363. The data presented herein demonstrate that weathering of abundant pyritic sulfur adversely affects the petroleum potential of the kerogen in outcrop samples. The succession is thermally immature to early mature, except where intrusions have locally heated adjacent mudstones. The documentation of rich gas/oil-prone Upper Jurassic successions in Jameson Land is important for the assessment of the regional petroleum potential, including the North-East Greenland continental shelf.

Constraining past fluctuations in global temperatures is central to our understanding of the Earth's climatic evolution. Marine proxies dominate records of past temperature reconstructions, whereas our understanding of continental climate is relatively poor, particularly in high-latitude areas such as Antarctica. The recently developed MBT/CBT (methylation index of branched tetraethers/cyclization ratio of branched tetraethers) paleothermometer offers an opportunity to quantify ancient continental climates at temporal resolutions typically not afforded by terrestrial macrofloral proxies. Here, we have extended the application of the MBT/CBT proxy into the Cretaceous by presenting paleotemperatures through an expanded sedimentary succession from Seymour Island, Antarctica, spanning the latest Maastrichtian and Paleocene. Our data indicate the existence of a relatively stable, persistently cool temperate climate on the Antarctic Peninsula across the Cretaceous-Paleogene boundary. These new data help elucidate the climatic evolution of Antarctica across one of the Earth's most pronounced biotic reorganizations at the Cretaceous-Paleogene boundary, prior to major ice-sheet development in the late Paleogene. Our work emphasizes the likely existence of temporal and/or spatial heterogeneities in climate of the southern high latitudes during the early Paleogene.

The extensive Late Cretaceous – Early Paleogene sedimentary succession of Seymour Island, N.E. Antarctic Peninsula offers an unparalleled opportunity to examine the evolutionary origins of a modern polar marine fauna. Some 38 modern Southern Ocean molluscan genera (26 gastropods and 12 bivalves), representing approximately 18% of the total modern benthic molluscan fauna, can now be traced back through at least part of this sequence. As noted elsewhere in the world, the balance of the molluscan fauna changes sharply across the Cretaceous – Paleogene (K/Pg) boundary, with gastropods subsequently becoming more diverse than bivalves. A major reason for this is a significant radiation of the Neogastropoda, which today forms one of the most diverse clades in the sea. Buccinoidea is the dominant neogastropod superfamily in both the Paleocene Sobral Formation (SF) (56% of neogastropod genera) and Early - Middle Eocene La Meseta Formation (LMF) (47%), with the Conoidea (25%) being prominent for the first time in the latter. This radiation of Neogastropoda is linked to a significant pulse of global warming that reached at least 65°S, and terminates abruptly in the upper LMF in an extinction event that most likely heralds the onset of global cooling. It is also possible that the marked Early Paleogene expansion of neogastropods in Antarctica is in part due to a global increase in rates of origination following the K/Pg mass extinction event. The radiation of this and other clades at ~65°S indicates that Antarctica was not necessarily an evolutionary refugium, or sink, in the Early – Middle Eocene. Evolutionary source – sink dynamics may have been significantly different between the Paleogene greenhouse and Neogene icehouse worlds.

The article focuses on a study undertaken by the Chalk Group on the western onshore region of the Danish Basin in Eastern Denmark related on the seismic stratigraphy and sedimentary architecture of the region. The study is undertaken through subdividing the northern North German Basin and the south-western Danish Basin on digital reflection using 2-dimensional digital and scanned seismic profiling. The results of the study sh regional trends related to the active indicate active inversion.

The lower Cambrian Sirius Passet Lagerstätte (∼518 Ma) consists of mudstones about 8 m thick located in the Franklinian Basin of North Greenland. We analyzed major and trace elements plus the S, C, Cu, Fe, Zn, and Mo isotope compositions. Factor analysis allowed the lithology of the mudstone to be broken down into variable proportions of two inputs, a dry felsic component and a hydrous mafic component (smectite or chlorite). Zircons U-Pb ages indicate multiple sources, the local Proterozoic basement of Northern Greenland (1250–2400 Ma) and Pan-African felsic magmas (620–650 Ma) from across the Iapetus ocean. Diagenesis involved the reduction of Fe, S, and Mo from seawater and pyritization. The Sirius Passet Lagerstätte formed in oxygen-starved muds inhibiting degradation of organic matter underneath a well-ventilated water column. The chemistry of the samples, their very fine grain size, their apparent lack of graded bedding, and the age of zircons suggest that the Lagerstätte may represent wind-blown dust deposited on the continental slope.

Ancillary localities for the Sirius Passet biota (early Cambrian; Cambrian Series 2, Stage 3) are described from the immediate vicinity of the main locality on the southern side of Sirius Passet, north-western Peary Land, central North Greenland, where slope mudstones of the Transitional Buen Formation abut against the margin of the Portfjeld Formation carbonate platform. Whilst this geological relationship may extend over more than 500 km east-west across North Greenland, known exposures of the sediments yielding the lagerst tte are restricted to a 1 km long window at the south-western end of Sirius Passet.

palaeontology, sedimentology