GEUS Bulletin (Geological Survey of Denmark and Greenland)
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Lithostratigraphy of the Portfjeld Group (Ediacaran – lowermost Cambrian) of North Greenland
No full textThe 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
A new digital database of Ellen Louise Mertz’s 1924 ‘Overview of late- and postglacial elevation changes in Denmark’
No full textData from an important historic article on late- and postglacial land-level changes in Denmark and the accompanying map are presented here in a new digital format. The original data were compiled in 1924 by Ellen Louise Mertz and comprise field observations of the marine limit in Denmark made over the late 19th and early 20th centuries. The original tables have been transcribed and expanded into a digital database consisting of 658 entries. The original map sheet has been georeferenced and 392 mapped points have been assigned coordinates. The points are linked to their attributes in the digital data table, making them newly amenable to geospatial analysis in a Geographic Information System. To demonstrate, we briefly present one such application, namely a reproduction and verification of the isolines of raised beach elevation from the original 1924 map
The Kangâmiut dykes in West Greenland: markers of the tectono-metamorphic evolution of the southern Nagssugtoqidian orogen and its foreland
No full textThe general extent and structural evolution of the southern Nagssugtoqidian orogen of West Greenland were first described by Hans Ramberg who based much of his paper on the deformation of the regional Kangâmiut dyke swarm. The southern boundary is marked by a transition from undeformed, discordant dykes in the south to highly deformed dykes and host rocks to the north. Our analysis of the southern Nagssugtoqidian orogen and its southern foreland uses a comprehensive compilation of available data and covers the area from Sisimiut in the north to Alanngua, south of Maniitsoq. This represents almost the entire c. 200 km latitudinal extent of the Kangâmiut dyke swarm and encompasses the complete range of Nagssugtoqidian overprint on these dykes and their country rocks. South of Itillip Ilua (Itilleq), the structural and metamorphic overprints on the dykes exhibit a considerable range in both intensity and P–T conditions between and even within outcrops. In contrast, north of Itillip Ilua, the rocks show more systematic gradual increases in the degree of structural overprints and metamorphic grade, culminating in the Ikertooq thrust zone where granulite facies rocks are brought southwards over amphibolite facies rocks. Currently, available age data from the Nagssugtoqidian orogen permits the identification of two metamorphic episodes at c. 1850–1800 Ma and c. 1780–1720 Ma. These groups of metamorphic ages are supported by recent 40Ar–39Ar ages from dykes in the same area, which cluster at c. 1860 Ma and c. 1740 Ma, respectively. Albeit geographically sporadic, both age intervals support a subdivision of the Nagssugtoqidian structural and metamorphic overprints across the southern Nagssugtoqidian orogen and its foreland into two distinguishable temporal phases. Further geochronological investigations may well, however, find these two phases to be part of a tectonic continuum. For now, it is thought that the older event records south-directed thrusting over the foreland and concomitant loading of this crust, at least as far south as Maniitsoq. This c. 1860–1800 Ma crustal shortening and thrusting likely also closed a depositional basin located at the current latitude of Ikertooq, which could have formed during an early-orogenic extensional event that enabled and accompanied the c. 2035 Ma emplacement of Kangâmiut dykes. Up to 50–100 Ma later, a younger (c. 1780–1720 Ma) phase of shearing and thrusting mainly affected the Itillip Ilua – Ikertooq area and likely overprinted elements of the former event. This local younger overprint generated a separate trend of distinctly northward-increasing deformation and metamorphism
Quantifying seabed geodiversity of the Archipelago Sea, Baltic Sea, Finland
No full textThis study investigated the geodiversity of the Archipelago Sea in the northern Baltic Sea, focusing on geological features and their spatial distribution. By adapting methods used in previous Baltic Sea studies, we conducted spatial analyses of geological data sets including bedrock type, seabed substrates and seabed structures. Bedrock and substrate data were freely available, while seabed structures were modelled from bathymetry data. Geodiversity was quantified using a geodiversity index, which considers the variety of physical elements, roughness and area of the unit. The analyses revealed a diverse seabed environment in the Archipelago Sea with varying geodiversity throughout the study area. Significant features contributing to geodiversity included bedrock fracture and fault zones and large end-moraine formations. Similar patterns have been observed in terrestrial areas of Finland. The analyses also detected relations between archipelago zonation and geodiversity with areas of open sea more homogeneous than the middle and inner archipelago. This study formally recognises the complexity of the seabed in the Archipelago Sea and highlights the importance of understanding the geological processes shaping the region. The results can inform maritime spatial planning and sustainable resource management
Introducing INPOX: a method for informed point extraction from geological 2D surfaces exemplified on the Danish national hydrostratigraphic model
No full textThis study presents a probabilistic method for extracting informed points from geological surfaces, named INPOX. The method generates a probability map from the existing surface by calculating the Laplacian at each location and combining it with a user-defined transfer function. A set of points from the surface is then extracted with a density proportional to the probability map. The method allows a de-coupling of the most informative points in the surface from points carrying less or even biased information. INPOX can be applied on any geological surface where the user needs to retrieve the structurally relevant parts and remove the information created by the initial interpolation. Here, we test INPOX on synthetic data, with and without supressing interpolation artifacts. In both cases, the informed points extracted with INPOX outperforms a uniform probability map in recreating the original features. We show that the method requires a minimum of points to be extracted for INPOX to be more informative than a uniform point retrieval. Finally, to showcase the strength of the method in both retrieving the relevant geological features and suppressing the existing interpolation artifacts, we apply INPOX to a real case surface from the Danish national hydrostratigraphic model
The Scriniodinium crystallinum dinoflagellate cyst zone in the Middle–Upper Oxfordian, Upper Jurassic, Ilimananngip Nunaa (Milne Land), East Greenland
No full textThe biostratigraphy of the Jurassic in East Greenland is historically based on macroscopic fossils. Stratigraphy based on palynomorphs (spores, pollen and dinoflagellate cysts) has progressed more slowly and sporadically. The Scriniodinium crystallinum dinoflagellate cyst Zone is identified in middle – upper Oxfordian strata of Ilimananngip Nunaa (Milne Land), central East Greenland. The lower boundary is defined by the last occurrence of Trichodinium scarburghense in the Cardioceras tenuiserratum ammonite Zone. The upper boundary is defined by the last occurrence of S. crystallinum in the uppermost Amoeboceras rosenkrantzi ammonite Zone. However, the subzonal division of the S. crystallinum Zone recorded in North-West Europe is not identified in Greenland. Eighteen characteristic dinoflagellate cyst events are considered stratigraphically significant and useful in East Greenland. Fifteen of these events provide an informal, detailed stratigraphical subdivision of the S. crystallinum Zone into 10 subunits. Identification of the zone is an addition to the previously defined upper Bathonian – middle Oxfordian zonation, where the uppermost palynostratigraphical event was recorded to be the last occurrence of T. scarburghense. With this study, the correlation of dinoflagellate cyst and ammonite stratigraphy in the lower and middle Oxfordian is slightly modified. The S. crystallinum Zone documented here, in combination with the zonation used for the stratigraphy of the Blokelv-1, Rødryggen-1 and Brorson Halvø-1 cores of the Upper Jurassic to Lower Cretaceous, completes the dinoflagellate cyst stratigraphy of the marine Jurassic in East Greenland. Together with previous studies of spores and pollen in less marine units, the first complete palynological Jurassic stratigraphy is thus established for the Jurassic succession in East Greenland
Beach-ridge formation as a possible indicator for an open Limfjord – North Sea connection
No full textRaised beach ridges are prograded sequences of wave-built deposits that may provide valuable information about past relative sea-level changes, climate change and coastal evolution. In the Limfjord in northern Denmark, the Early and Middle Holocene sea-level changes are well-constrained. However, our understanding of Late Holocene sea-level fluctuations is limited, and the exact period when the coastal barrier between the Limfjord and the North Sea formed remains uncertain. In this study, we use optically stimulated luminescence (OSL) dating to determine the age of raised beach ridges at Gjellerodde in the western part of the Limfjord. The OSL ages presented here indicate that the beach ridges formed during three periods at 3.3–2.7, 1.4–1.0, 0.2–0.1 ka. In addition our data suggest a c. 0.2 mm/yr relative sea-level fall during the Late Holocene. The three distinct periods of beach-ridge formation coincide with periods when the Limfjord was open towards the North Sea as documented in historical records and marine records. This suggests that OSL dating of beach ridges can be used as a potential indicator for determining when the connection between the Limfjord and the North Sea was open in the Late Holocene
Open access nationwide data sets for drinking water hardness at public waterworks and their water supply areas in Denmark
No full textThree spatiotemporal data sets of drinking water hardness in Denmark (version 1) are presented here: (1) annual drinking water hardness at public waterworks (1905–2023); (2) annual drinking water hardness at their water supply areas (1978–2023) and (3) the latest drinking water hardness at the water supply areas (1980–2023). Raw data were extracted from the Jupiter database for groundwater and drinking water data in Denmark, and were quality-assured. Hardness was calculated after semi-automatic outlier exclusion based on Ca and Mg, or if not available, the reported total hardness. Data were further aggregated at the waterworks level by the annual mean and at the supply area level by the weighted mean (weighted to waterworks annual abstraction volumes). Temporal and spatial gaps were filled prior to these aggregations. Various stakeholders could benefit from these open access data. They provide a societal service in response to increased public interest in drinking water hardness. The research community could use the data in environmental, exposure or epidemiological assessments. Finally, the water supplies and the public sector could benefit from these data as they provide a nationwide overview of current and past drinking water hardness in Denmark and highlight the geographic areas that lack recent data, most probably due to de-regulation
Early Cenomanian ammonites from East and North-East Greenland
No full textEarly Cenomanian (100.5–95.7 Ma) ammonite faunas from East and North-East Greenland collected by the late Simon Kelly and colleagues are described. The assemblages are dominated by typically boreal Schloenbachia varians (J. Sowerby 1817). Also present are Parapuzosia (Austiniceras) austeni (Sharpe 1855) and species of more typically Tethyan genera. These include Phylloceras (Hypophylloceras) lombardense (Joly 2000), Gaudryceras (Gaudryceras) cassisianum (d’Orbigny 1850), Gaudryceras (Mesogaudryceras) leptonema (Sharpe 1855), and the hypermorphic tetragonitine Titanoleioceras boreale gen. et sp. nov. Previously known only from Geographical Society Ø and Traill Ø, the newly described material extends the distribution of these early Cenomanian faunas northwards to Hold with Hope and south to the Kangerlussuaq Basin. The phylloceratids, gaudryceratids, and tetragonitids in these assemblages are probably not preserved in their preferred original habitats, but rather drifted to their respective sites of burial during or after their lifetime
Petrology of the Skaergaard Layered Series
No full textThe Skaergaard intrusion is a layered, ferrobasaltic intrusion emplaced during the Early Eocene into the rifting volcanic margin of East Greenland. The magma chamber crystallised in response to cooling from the roof and margins upwards and inward, forming upper, marginal and bottom series, the latter referred to as the Layered Series. The phase layering in the bottom series suggests an evolved, olivine-normative tholeiitic melt saturated in plagioclase and olivine, followed by augite, and then simultaneously by ilmenite and magnetite forming primocrysts. Pigeonite appears in the lower parts and continues until the centre of the series. Apatite appears in the upper part concurrently with liquid immiscibility. Cryptic variations of the individual primocrysts record a systematic upward increase in iron and decrease in magnesium for the mafic minerals and a systematic increase in sodium and decrease in calcium for plagioclase. The appearance of pigeonite is caused by reactions and crystallisation in the trapped melt and by subsolidus adjustments without this phase reaching liquidus saturation. The high mode of olivine at the base of the upper part with the appearance of apatite is interpreted to mark the onset of liquid immiscibility. This may have led to the separation of conjugate melts with granophyre migrating upward and the basic component largely staying stationary or sinking. Petrologic and geochemical observations indicate differentiation in the lower part of the intrusion, principally controlled by crystal fractionation with the efficiency of fractionation controlled by the evolution and escape of liquid from the solidifying mush. During the final stages of solidification, the onset of liquid immiscibility and termination of melt convection impeded differentiation. Modelling by perfect Rayleigh fractionation shows that major and included trace elements conform reasonably to observations, while excluded elements deviate from model predictions. This decoupling is caused by the mobility of a granophyre component formed in the trapped melt and in the main residual magma chamber. Consequently, the sampled gabbros may not be representative of the final solid-melt mush. By restoring the gabbros to their original mush compositions, it is possible to constrain granophyre migration pathways. We suggest that the granophyre formed in the trapped melt in the lower part of the intrusion mostly migrated laterally through pressure release pathways to form lenses and pockets with only limited upward migration into the main magma reservoir. Near the end stage of differentiation, the residual magma exsolved and formed complex mixtures of ferrobasaltic and granophyric melts. Estimates predict that a substantial amount of the granophyric melt penetrated as sills into the downward crystallising, upper part of the body as well as into the host rocks. The redistribution of granophyric melts within the solidifying crystal mush complicates predictions of trapped-melt content and mass-balance calculations but helps to explain apparent decoupling of included and excluded trace elements, especially towards the end stages of evolution. Final crystallisation was controlled mostly by in situ crystallisation leaving complex mixtures of ferrodiorite and granophyre components.