GEUS Bulletin (Geological Survey of Denmark and Greenland)
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The Kangâmiut dyke swarm in West Greenland: a new map and insights into their tectonic evolution
No full textThis contribution presents a new map of the Palaeoproterozoic Kangâmiut dyke swarm in Central West Greenland. The map is based on publicly available aerial imagery, the scale and quality of which allowed for quick and efficient interpretation across a large area. The Kangâmiut dyke swarm has played a pivotal role in the identification and characterisation of the southern margin of the Nagssugtoqidian orogen. Change in dyke orientation from NNE-trending in the south to ENE-trending farther north is accompanied by increasing deformation in both dykes and host rocks. The zone where dykes and host rocks are totally parallelised defines the southern structural and metamorphic front of the Nagssugtoqidian orogen. We document variable changes in orientation of the dykes and their density to estimate the crustal extension accompanying dyke emplacement. The average width of the 123 dykes is 25 m (80% are <50 m). These dykes occur with an average frequency of 3.4 dykes per km and make up 6–11% of the outcrops. These data reveal subordinate groups of dykes with ESE and NE orientations and track regional changes. At present, their ages relative to the dominant NNE-trending swarm are not known. The swarm generally extends from south of Maniitsoq northwards to the Ikertooq shear zone; however, we identified features north of the Ikertooq shear zone, which we speculatively interpret to represent the northernmost occurrence of the Kangâmiut dyke swarm. The tectonic consequences of this interpretation – if correct – allow us to estimate the amount of shortening across the Ikertooq shear zone during the Nagssugtoqidian orogeny to be more than 150 km. If the other major tectonic boundaries in the orogen, including the Nordre Strømfjord shear zone, were the loci of similar shortening, the current extent of the orogen may represent only a fraction of pre-Nagssugtoqidian crust in Central West Greenland
Assessment of formation brine salinity, pressure and temperature in selected structures in eastern Denmark and implications for CO2 storage
No full textCO2 storage presents new risks and challenges, where the properties of formation water play an important role. These challenges include reduced injectivity and storage capacity due to salt precipitation, viscous fingering caused by viscosity contrasts between CO2 and brine and diminished CO2 solubility in formation waters. Understanding these factors and developing predictive models for pressure distribution are essential for successful CO2 storage projects. This study presents salinity (Cl and total dissolved solids), density, temperature, pressure, halite (NaCl) saturation, CO2 solubility and viscosity of formation waters across five CO2 storage sites in Denmark (Stenlille, Gassum, Rødby, Lisa and Inez), covering eight reservoirs (one in the Frederikshavn Formation, four in the Gassum Formation and three in the Bunter Sandstone and Skagerrak Formations). Salinity assessments are based on existing brine data or, where unavailable, a reference salinity model developed from a water chemistry database with 77 analyses from 28 wells in the Danish Basin and adjacent regions. The model was created using Partial Least Squares regression, accounting for local geological developments and subsurface salts. We report high chloride levels (182 000–202 000 mg/L) and densities (1.21–1.23 kg/L) in the Bunter Sandstone and Skagerrak Formations, while the Gassum and Frederikshavn Formations are undersaturated with halite, exhibiting lower chloride levels (99 000–148 000 mg/L) and densities (1.11–1.17 kg/L). These differences suggest a higher risk of mineral precipitation due to brine evaporation in dry CO2, and a higher risk of density override due to significant density contrast, which will hamper filling efficiency in older reservoirs. Modelling shows that CO2 solubility reaches 33.9 g CO2/L, with a 37% reduction due to chemical and pressure–temperature variations. Conceptual fluid flow modelling is recommended to further assess brine–rock–CO2 interactions. The salinity model has implications for geothermal reservoir assessment and can be applied regionally
A chemistry and microbiology data set for meltwater rivers in south-western Greenland (2017–2021)
No full textMeltwater rivers in Greenland transport large quantities of freshwater from the Greenland ice sheet and local glaciers to the ocean, significantly influencing marine ecosystems and global biogeochemical cycles. With accelerating ice melt due to climate change, understanding the biogeochemistry of these rivers is critical. Here, we present a data set providing comprehensive biogeochemistry data from 28 meltwater rivers in south-western Greenland. Spanning a period from 2017 to 2021, it includes data on nutrients and other ions, trace metals, sediment, radio and water isotopes, microbiology and cyanotoxins, sampled during field campaigns in June and August–September. This data set offers valuable insights for research on glacial meltwater, biogeochemistry and microbiology, addressing key knowledge gaps in these fields
Seismic investigations of eight geological structures for potential storage of CO2 in Denmark: an introduction
No full textIn 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
The limitations of nitrate-sensitive zoning for groundwater protection from pesticides in Denmark
No full textPesticides and degradation products are a major challenge for groundwater management in Europe, and in Denmark where drinking water relies entirely on groundwater. To protect drinking water resources, local Danish authorities must take groundwater-protective measures in areas designated as sensitive to pollution; however, official zonation for pesticides is lacking. Nitrate-sensitive groundwater abstraction areas have been used instead. The goal of our study was to test the appropriateness of this groundwater protection strategy. We used Køge municipality (Denmark) as a focus area and tested how our findings upscale to the national level. The data for Køge municipality included 1070 individual groundwater samples, analysed for at least one of 366 pesticide compounds during the period 2012–2022, which were aggregated at the well-screen level by the median. Four pesticide compounds (2,6-dichlorobenzamide (BAM), desphenylchloridazon (DPC), N,N-dimethylsulphamide (DMS), 1,2,4-triazole) and three pesticide groups (phenoxyalcanoic acids, triazines and dimethachlor and its metabolites) were found with the highest detection frequency in the study area. We found that groundwater pollution with pesticide compounds was not limited to nitrate-sensitive areas in Køge municipality or in Denmark as a whole. Therefore, nitrate-sensitive areas can only be used partially for identifying pesticide-sensitive groundwater abstraction areas. The management implication is that placing protective measures only within nitrate-sensitive areas would be insufficient to fully address the risk of future groundwater pesticide pollution. We identified knowledge gaps and discussed a potential way forward with a more integrated management of groundwater protection in Denmark
Traverse Route from Pituffik to Warming Land, North Greenland
No full textWe examine the feasibility of an overland motorised traverse from Pituffik to Greenland’s oldest ice outcrop in Warming Land, North Greenland. We assess a 778 km overland traverse that departs Pituffik via the Nunatarssuaq Take-Off Ramp, which is an alternative to the more frequently used, but more heavily crevassed, Thule Take-Off Ramp. The traverse route includes brief sea ice and primitive road conditions, each c. 4% of the route length, and a lengthy ice sheet segment (c. 92% of the route length). This study outlines challenges for each of these traverse segments, including primitive road conditions and snow cover, seasonality of extreme cold conditions (air temperatures below –30°C), seasonality of surface melting and softening (air temperatures above 0°C), sea-ice thickness and potential ridging hazards, and ice dynamics and potential crevasse hazards. Ongoing work is required for annual vetting of the traverse route to ensure operational safety. The optimal operational window for such a traverse is departing Pituffik in mid-April and returning in mid-May. In comparison to aircraft-supported ice-sheet fieldwork, scientific traverses offer the opportunity for more intensive ground-based science, while significantly reducing carbon emissions. Based on previously reported traverse fuel consumptions, a ground traverse from Pituffik to Warming Land would use 90% less fuel than aircraft supported fieldwork. This assessment underscores the potential for sustainable ground-based access to Greenland’s oldest ice outcrop and other science sites within the region
A review of subsurface geosystems and de-risking offshore construction in the Danish North Sea
No full textThe renewable energy transition has increased the demand for offshore construction in the Danish North Sea energy sector. This development underpins the need for further investigation of potential geological hazards and associated risks to avoid accidents involving people, the environment or infrastructure. A scientific approach to de-risking requires an understanding of the seabed and the buried geosystems. Understanding geosystems is the first step in the de-risking process of offshore construction. In this study, we review three key geosystem elements in the Danish North Sea, represented by (1) shallow stratigraphy and geomorphology, (2) glacial tectonics and salt movement and (3) subsurface fluid migration. We summarise the current state of knowledge of these geosystem elements and identify multiple risks associated with each geosystem in the region. Such investigations are critical for understanding the geotechnical behaviour of the subsurface and identifying and de-risking of potential geohazards during the construction of future energy developments in the Danish North Sea region
A hidden succession revealed: Cretaceous and Paleocene sediments and a native-iron-bearing lava flow in cores near Qullissat, Disko, West Greenland
No full textOver long stretches of the north-east coast of Qeqertarsuaq (Disko), the sediments in the Nuussuaq Basin and their relations to the volcanic rocks are concealed beneath numerous landslides. Two cores south of Qullissat drilled by Falconbridge Ltd in 1994, targeting a native-iron-bearing igneous body assumed to be a sill, present well-preserved sections through the hidden succession. We have dated the sediments in the cores palynologically. The lower part comprises 115 m of deltaic deposits, including coal seams, of the Cretaceous Atane Formation, Qilakitsoq Member (late Turonian to early Coniacian age), which has not been recorded on Disko before. The two cores and five short coastal cliff sections are mutually correlatable and correlate further to the coal seams earlier mined at Qullissat; the coals are hereby dated for the first time. The Cretaceous rocks are overlain by 15 m of marine deposits, mainly mudstones, of the Danian Eqalulik Formation, with a hiatus of c. 24 million years. The igneous body of native-iron-bearing basaltic andesite has a thick, red-oxidised, vesiculated and brecciated top zone and is interpreted as a subaerial lava flow belonging to the Asuk Member of the Vaigat Formation. The flow has run perhaps up to 20 km from the eruption site to the sea, where it ponded and attained a thickness of 138 m, the thickest lava flow in the West Greenland Basalt Group. The flow is overlain by 22 m of non-marine sandstones and mudstones of the Atanikerluk Formation. The core correlation indicates the existence of a fault with c. 90 m vertical displacement between the two drill sites. The structural relations of the various parts of the Atane Formation along the north-east coast of Disko necessitate the assumption of another hidden, prevolcanic fault south of Qullissaaqqat
Miocene vegetation and climate in the eastern North Sea Basin, onshore Denmark, compared to the present
No full textDespite often being referred to as a ‘coolhouse climate’, the climate during the Miocene (23.03–5.33 Ma) was overall humid, warm and temperate. It was paced by orbitally driven cooler periods (the Oligocene–Miocene Transition and Mi-events) overprinted by a climatic optimum. Global cooling during the Late Miocene brought more arid conditions with climate seasonality, which varied across western Eurasia. Sedimentary archives from onshore Denmark comprise shallow marine siliciclastic deposits and discrete brown coal layers. Hence, they allow us to infer past climates and environments using both marine and terrestrial fossils. The backbone for Miocene stratigraphy and palaeoclimate reconstruction in the eastern North Sea Basin (present-day Denmark) is the Sønder (Sdr.) Vium sediment core, which penetrates a shallow marine succession and spans an interval from c. 22 to 8 Ma. Here, we present an improved age model for the core. During the Miocene, forested lowlands predominated in the eastern North Sea Basin. Coastal areas included rich riparian landscapes and delta areas of lignite-forming swamp forest. Compilations of existing proxy records (pollen, spores, leaves, plant fragments and the organic biomarkers alkenones and membrane lipids) collectively show that the climate here was warm and moist during the Early and Middle Miocene, while the Late Miocene was characterised by climate cooling and modernisation of the vegetation. The interval preceding the Miocene Climatic Optimum was already warm and moist, and the onset was not characterised by a significant increase in temperature and precipitation. Instead, the palynoflora indicates homogeneous vegetation and only a weak signal of warming shown by a minor increase of, for example, sabaloid palms and Mastixiaceae
Applying geotechnical borehole databases in the search for interglacial deposits in Denmark
No full textGeotechnical investigations conducted in preparation for infrastructure development provide high-quality borehole data in standardised digital formats. In Denmark, such geotechnical borehole data are not required to be reported to the national well database (Jupiter) and are mainly archived in privately owned databases. Accessible interglacial and interstadial terrestrial deposits are rare in Denmark, and these borehole data have the potential to identify interglacial and interstadial deposits, with significant implications for ongoing palaeoclimate, palaeoenvironmental and archaeological research. In this study, we compiled data from six major geotechnical companies, resulting in a database with over 550 000 boreholes. From this database, we identified 1850 boreholes containing samples associated with interglacial and interstadial ages. Through extensive filtering for well-documented lacustrine or palustrine deposits, we selected 161 boreholes and referenced them to 39 different geographical occurrences. Of these 39 occurrences, 36 were either new terrestrial deposits or provided substantial new records to known interglacial and interstadial sites. Our findings demonstrate that access to these privately owned geotechnical borehole data can be a valuable resource for identifying rare near-surface geological deposits, allowing the discovery of several new Pleistocene sedimentary archives that warrant further investigation