GEUS Bulletin https://geusbulletin.org/index.php/geusb <p>GEUS Bulletin (eISSN: 2597-2154) is the current flagship journal published by the <a href="https://eng.geus.dk/" target="_blank" rel="noopener">Geological Survey of Denmark and Greenland (GEUS)</a>. Previously, the Geological Survey of Denmark and Greenland Bulletin (eISSN: 1904-4666). We are peer-reviewed and diamond open access. GEUS Bulletin publishes geoscience research papers, monographs and map descriptions for Denmark, Greenland and the Arctic region. We believe that open science benefits scientists, industry and society, so we do not charge publication fees and all our articles can be freely downloaded online. IF 2019: 0.680 5-year IF: 0.656</p> <p><strong>GEUS Bulletin is open for submissions to geoscientists whose research is focussed on Denmark, Greenland and the Arctic region. Read more in our <a href="https://geusbulletin.org/index.php/geusb/about">journal scope</a>.</strong></p> Geological Survey of Denmark and Greenland (GEUS) en-US GEUS Bulletin 1604-8156 <p><span data-contrast="auto">GEUS Bulletin is an open-access, peer-reviewed journal published by the Geological Survey of Denmark and Greenland (GEUS). This article is distributed under a&nbsp;</span><a href="https://creativecommons.org/licenses/by/4.0/"><span data-contrast="none">CC-BY 4.0 licence</span></a><span data-contrast="auto">, permitting free redistribution and reproduction for any purpose, even commercial, provided proper citation of the original work. Author(s) retain copyright over the article contents. Read the </span><a href="https://geusbulletin.org/index.php/geusb/oapolicy">full open access policy</a>.</p> New insights from field observations of the Younger giant dyke complex and mafic lamprophyres of the Gardar Province on Tuttutooq island, South Greenland https://geusbulletin.org/index.php/geusb/article/view/6526 <p><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">The Gardar Province of south Greenland is defined by the products of alkaline igneous magmatism during the Mesoproterozoic. The most laterally extensive Gardar intrusions are a series of giant dyke complexes best exposed on the Tuttutooq archipelago. We present new field observations and a geological map of north-east Tuttutooq island that provide fresh insights into the temporal evolution of the Younger giant dyke complex and two associated ultramafic lamprophyres. Our data demonstrate that distinctive crystallisation regimes occurred in different sectors of the dyke complex, leading to the formation of marginal gabbros and ovoid pod-like domains displaying lamination, modal layering and/or more evolved differentiates. We infer that at least two pulses of magma contributed to the formation of the Younger giant dyke complex. In addition, the relative ages of two ultramafic lamprophyre diatremes are constrained and attributed to two distinct phases of rifting in the Gardar Province.</span></p> Lot Koopmans Robert A. Webster Rory Changleng Lucy Mathieson Alasdair J. Murphy Adrian A. Finch William McCarthy Copyright (c) 2021 Lot Koopmans, Robert A. Webster, Rory Changleng, Lucy Mathieson, Alasdair J. Murphy, Adrian A. Finch, William McCarthy https://creativecommons.org/licenses/by/4.0 2021-06-16 2021-06-16 47 10.34194/geusb.v47.6526 The Permian to Cretaceous succession at Permpasset, Wollaston Forland: the northernmost Permian and Triassic in North–East Greenland https://geusbulletin.org/index.php/geusb/article/view/6523 <p><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">Permian to Triassic outcrops in East Greenland diminish significantly northwards. Understanding the northward extent, and nature, of the Permian and Triassic successions has implications for regional palaeogeographic reconstructions and exploration in adjacent offshore basins. Examining the structural relationships between the basement, Permian, Triassic, Jurassic and Cretaceous successions can further our understanding of the tectonic evolution of the region. Here, we describe a hitherto overlooked section through the Permian to Cretaceous from central Wollaston Forland and consider its structural context. The western side of Permpasset forms the upthrown eroded crest of a horst block, which provides exposure of the earliest stratigraphic intervals in the region. The fractured Caledonian basement is overlain by evaporitic marine limestone facies of the Karstryggen Formation, which are succeeded by shallow marine sandstones assigned to the Schuchert Dal Formation, both Upper Permian. The overlying unit records a period of fluvial deposition and is not possible to date. However, an Early to Middle Triassic age (Pingo Dal Group) seems most likely, given regional eustatic considerations. This is, therefore, the most northerly record of Triassic strata in North–East Greenland. West of the horst structure, fine-grained sandstones and bioturbated siltstones of the Jurassic (Oxfordian) Jakobsstigen Formation are recorded. These were downfaulted prior to a prolonged hiatus after which both the Triassic and Jurassic strata were draped by Cretaceous shales of the Fosdalen Formation. The Cretaceous succession is overlain by a thick basalt pile of Eocene age, heralding the opening of the North-East Atlantic. Glendonites overlie Oxfordian siltstones at the base of the middle Albian Fosdalen Formation. These were likely winnowed from slightly older Cretaceous strata and overlie the hiatus surface between the Jurassic and Cretaceous. This is the first record of glendonites from the Cretaceous of East Greenland and they are interpreted to record the Circum–Arctic late Aptian – early Albian cooling event.</span></p> Steven D. Andrews Henrik Nøhr-Hansen Pierpaolo Guarnieri Karen Dybkjær Sofie Lindström Peter Alsen Copyright (c) 2021 Steven D. Andrews, Henrik Nøhr-Hansen, Pierpaolo Guarnieri, Karen Dybkjær, Sofie Lindström, Peter Alsen https://creativecommons.org/licenses/by/4.0 2021-07-23 2021-07-23 47 10.34194/geusb.v47.6523 Jurassic stratigraphy of East Greenland https://geusbulletin.org/index.php/geusb/article/view/6521 <p style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">The East Greenland Rift Basin comprises a series of Jurassic subbasins with different crustal configurations, and somewhat different tectonic histories and styles. The roughly N–S elongated basin is exposed in central and northern East Greenland over a length of more than 600 km and a width of up to 250 km. The southernmost exposures are found in the largest subbasin in Jameson Land, while the northernmost exposures are on Store Koldewey and in Germania Land. The focus of the present revision is on the Jurassic, but the uppermost Triassic and lowermost Cretaceous successions are included as they are genetically related to the Jurassic succession. The whole succession forms an overall transgressive–regressive megacycle with the highest sea level and maximum transgression in the Kimmeridgian.</p> <p style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">The latest Triassic – Early Jurassic was a time of tectonic quiescence in East Greenland. Lower Jurassic deposits are up to about 950 m thick and are restricted to Jameson Land and a small down-faulted outlier in southernmost Liverpool Land. The Lower Jurassic succession forms an overall stratigraphic layer-cake package that records a shift from Rhaetian–Sinemurian fluvio-lacustrine to Pliensbachian – early Bajocian mainly shallow marine sedimentation.</p> <p style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Onset of rifting in the late Bajocian resulted in complete reorganisation of basin configuration and drainage patterns, and the depositional basin expanded far towards the north. Post-lower Bajocian early-rift deposits are up to about 500–600 m thick and are exposed in Jameson Land, Liverpool Land, Milne Land, Traill Ø, Geographical Society Ø, Hold with Hope, Clavering Ø, Wollaston Forland, Kuhn Ø, Th. Thomsen Land, Hochstetter Forland, Store Koldewey and Germania Land. Upper Jurassic rift-climax strata reach thicknesses of several kilometres and are exposed in the same areas with the exception of Liverpool Land and Germania Land.</p> <p style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">In the southern part of the basin, the upper Bajocian – Kimmeridgian succession consists of stepwise backstepping units starting with shallow marine sandstones and ending with relatively deep marine mudstones in some places with sandy gravity-flow deposits and injectites. In the Jameson Land and Milne Land Subbasins, the uppermost Jurassic – lowermost Cretaceous (Volgian–Ryazanian) succession consists of forestepping stacked shelf-margin sandstone bodies with associated slope and basinal mudstones and mass-flow sandstones. North of Jameson Land, block-faulting and tilting began in the late Bajocian and culminated in the middle Volgian with formation of strongly tilted fault blocks, and the succession records continued stepwise deepening. In the Wollaston Forland – Kuhn Ø area, the Volgian is represented by a thick wedge of deep-water conglomerates and pebbly sandstones passing basinwards into mudstones deposited in fault-attached slope aprons and coalescent submarine fans.</p> <p style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">The lithostratigraphic scheme established mainly in the 1970s and early 1980s is here revised on the basis of work undertaken over subsequent years. The entire Jurassic succession, including the uppermost Triassic (Rhaetian) and lowermost Cretaceous (Ryazanian–Hauterivian), forms the Jameson Land Supergroup. The supergroup is subdivided into the Kap Stewart, Neill Klinter, Vardekløft, Hall Bredning, and Wollaston Forland Groups, which are subdivided into 25 formations and 48 members. Many of these are revised, and 3 new formations and 14 new members are introduced.</p> Finn Surlyk Peter Alsen Morten Bjerager Gregers Dam Michael Engkilde Carina Fabricius Hansen Michael Larsen Nanna Noe-Nygaard Stefan Piasecki Jens Therkelsen Henrik Vosgerau Copyright (c) 2021 Finn Surlyk, Peter Alsen, Morten Bjerager, Gregers Dam, Michael Engkilde, Carina Fabricius Hansen, Michael Larsen, Nanna Noe-Nygaard, Stefan Piasecki, Jens Therkelsen, Henrik Vosgerau https://creativecommons.org/licenses/by/4.0 2021-07-09 2021-07-09 47 10.34194/geusb.v46.6521 Estimating pesticides in public drinking water at the household level in Denmark https://geusbulletin.org/index.php/geusb/article/view/6090 <p><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">Pesticide pollution has raised public concern in Denmark due to potential negative health impacts and frequent findings of new substances after a recent expansion of the groundwater monitoring programme. Danish drinking water comes entirely from groundwater. Both the raw groundwater and the treated drinking water are regularly monitored, and the chemical analyses are reported to a publicly available national database (Jupiter). Based on these data, in this study we (1) provide a status of pesticide content in drinking water supplied by public waterworks in Denmark and (2) assess the proportion of Danish households exposed to pesticides from drinking water. ‘Pesticides’ here refers also to their metabolites, degradation and reaction products. The cleaned dataset represents 3004 public waterworks distributed throughout the country and includes 39 798 samples of treated drinking water analysed for 449 pesticides (971 723 analyses total) for the period 2002–2019. Of all these chemical analyses, 0.5% (</span><em style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">n</em><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;"> = 4925) contained a quantified pesticide (&gt;0.03 μg/l). Pesticides were found at least once in the treated drinking water at 29% of all sampled public waterworks for the period 2002–2019 and at 21% of the waterworks for the recent period 2015–2019. We estimate that 56% of all Danish households were potentially exposed at least once to pesticides in drinking water at concentrations of 0.03–4.00 μg/l between 2002 and 2019. However, in 2015–2019, the proportion of the Danish households exposed to pesticides (0.03–4.00 μg/l) was 41%. The proportion of Danish households potentially exposed at least once to pesticides above the maximum allowed concentration (0.1 μg/l) according to the EU Drinking Water Directive (and the Danish drinking water standard) was 19% for 2002–2019 and 11% for 2015–2019. However, the maximum concentrations were lower than the World Health Organization’s compound-specific guidelines. Lastly, we explore data complexity and discuss the limitations imposed by data heterogeneity to facilitate future epidemiological studies.</span></p> Denitza D. Voutchkova Jörg Schullehner Carina Skaarup Kirstine Wodschow Annette Kjær Ersbøll Birgitte Hansen Copyright (c) 2021 Denitza D. Voutchkova, Jörg Schullehner, Carina Skaarup, Kirstine Wodschow, Annette Kjær Ersbøll, Birgitte Hansen https://creativecommons.org/licenses/by/4.0 2021-04-12 2021-04-12 47 10.34194/geusb.v47.6090 Monitoring for seismological and geochemical groundwater effects of high-volume pumping of natural gas at the Stenlille underground gas storage facility, Denmark https://geusbulletin.org/index.php/geusb/article/view/5552 <p><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">The large natural gas storage facility at Stenlille, Denmark, has been monitored to investigate the effect of pumping large amounts of gas into the subsurface. Here, we present a new dataset of microseismicity at Stenlille since 2018. We compare these data with methane in groundwater, which has been monitored since gas storage was established in 1989. Further, we conducted a controlled 172 day microcosm experiment of methane oxidation on an isolated microbial community under both aerobic and anaerobic conditions. For this experiment, water was filtered from a well at Stenlille with elevated levels of thermogenic methane and ethane. No microseismic activity was detected in the gas storage area above an estimated detection level of ML 0.0 for the established network. The long-term monitoring for methane in groundwater has still only detected one leak, in 1995, related to a technical problem during injection. The microcosm experiment revealed that oxidation of methane occurred only under aerobic conditions during the experiment, as compared to anaerobic conditions, even though the filtered water was anoxic</span></p> Trine Dahl-Jensen Rasmus Jakobsen Tina Bundgaard Bech Carsten Møller Nielsen Christian Nyrop Albers Peter H. Voss Tine B. Larsen Copyright (c) 2021 Trine Dahl-Jensen, Rasmus Jakobsen, Tina Bundgaard Bech, Carsten Møller Nielsen, Christian Nyrop Albers, Peter H. Voss, Tine B. Larsen https://creativecommons.org/licenses/by/4.0 2021-03-22 2021-03-22 47 10.34194/geusb.v47.5552 Validation of airborne and satellite altimetry data by Arctic Truck citizen science https://geusbulletin.org/index.php/geusb/article/view/5369 <p><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">The elevation of ice sheets changes due to climate change, and satellite altimetry is the preferred tool for measuring ice sheet-wide height changes. </span><em style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">In situ</em><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;"> validation is needed to ensure the quality of the observed elevation changes, but the cost often limits the amount of </span><em style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">in situ</em><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;"> data which can be collected. As more tourists are accessing the ice sheets, citizen science might provide </span><em style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">in situ</em><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;"> data in an environmentally friendly and cost-efficient way. Here, we investigate the opportunistic kinematic global positioning system (GPS) profiles across the Greenland ice sheet, collected by the </span><em style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">American-Icelandic expedition on the Greenlandic icecap 2018</em><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">. The collected GPS data are in good agreement with the widely used NASA’s Operation IceBridge Airborne LiDAR data measured within ± 10 days, with an average difference of 10.7 cm ± 11.7 cm. The main difference is attributed to changes in the compaction of the snow while driving and changes in the tires’ pressure. The kinematic GPS data are then compared with data from the European Space Agency’s CryoSat-2 mission. Here, an average bias of 92.3 cm ± 65.7 cm in the two records is observed between the spring CryoSat-2 and the truck GPS data obtained largely in the dry-snow zone. This suggests that the surface penetration of Ku-band radar on the Greenland ice sheet and the observed magnitude are consistent with the literature. Finally, we compared the 2018 GPS data to a profile obtained in 2005 near Kangerlussuaq, West Greenland. Here, the records show an average ice-elevation decrease of 9 m, with peaks at 26 m. These results show that the citizen science kinematic GPS data can provide high-resolution data necessary for the validation of satellite altimetry, with the added benefit of potential direct sampling properties of the surface and firn. Linking up with citizen-science expeditions is a beneficial way of providing cost-effective satellite validations and may also have a societal impact by involving more people in the climate monitoring of ice sheets.</span></p> Andreas Stokholm Sine M. Hvidegaard Rene Forsberg Sebastian B. Simonsen Copyright (c) 2021 Andreas Stokholm, Sine M. Hvidegaard, Rene Forsberg, Sebastian B. Simonsen https://creativecommons.org/licenses/by/4.0 2021-05-28 2021-05-28 47 10.34194/geusb.v47.5369 Middle Jurassic sandstone deposition in the Wandel Sea Basin: evidence from cardioceratid and kosmoceratid ammonites in the Mågensfjeld Formation in Kilen, North Greenland https://geusbulletin.org/index.php/geusb/article/view/5342 <p>Age assessments from both palynostratigraphy and macrofossil biostratigraphy of the sandstone-dominated Mågensfjeld Formation, Wandel Sea Basin, North Greenland were hitherto hampered by post-burial thermal degradation of dinoflagellate cysts and a lack of well-preserved macrofossils. The formation was previously assigned to the Upper Cretaceous based on erroneous fossil identifications. Finds of cardioceratid and kosmoceratid ammonites during recent field work now provide the first age control of the unit, demonstrating it to be of late Bajocian – late Bathonian and perhaps Callovian (Middle Jurassic) age. This makes it among the oldest Jurassic units, perhaps even Mesozoic units, recorded in Kilen, North Greenland and eastern North Greenland. Previously, the complex structural and tectonic evolution of the area was poorly understood, and the structural relation of the Mågensfjeld Formation to the surrounding Mesozoic units was a puzzle. The new age assessment simplifies the structural situation in the area significantly. Further, the inference of a large reverse fault previously required to explain the proximity of the Mågensfjeld Formation to neighbouring Jurassic units is now unnecessary. The data show that the Wandel Sea Basin was influenced by the Middle Jurassic transgression and had sufficient accommodation space for marine deposition earlier than previously thought. The unit serves as a key datapoint and analogue for possible Middle Jurassic units in adjacent offshore basins.</p> Peter Alsen Jussi Hovikoski Kristian Svennevig Copyright (c) 2020 Peter Alsen, Jussi Hovikoski, Kristian Svennevig https://creativecommons.org/licenses/by/4.0 2020-12-21 2020-12-21 47 10.34194/geusb.v44.5342 Fingerprinting sources of salinity in a coastal chalk aquifer in Denmark using trace elements https://geusbulletin.org/index.php/geusb/article/view/5336 <p><span style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; display: inline !important; float: none;">Salinity levels above the drinking water standard (&gt;250 mg/l Cl<sup style="color: #000000; font-family: 'Times New Roman'; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">–</sup>) are observed at shallow depth in a Maastrichtian chalk aquifer on the island of Falster, south-eastern Denmark. To understand the source of the salt, 63 samples from 12 individual, 1 m, screened intervals between 14 and 26 m b.s. were collected from 1 May to 4 June 2018. The samples were collected during a tracer test to estimate the dual porosity properties of the chalk and were analysed for a wide range of elements. Furthermore, samples from the Baltic Sea and from deeper saline aquifers in the area (40 and 85 m b.s.) were analysed for comparison. The geochemical data were analysed using an unsupervised machine-learning algorithm, self-organising maps, to fingerprint water sources. The water composition in the screened intervals at various stratigraphic levels has specific geochemical fingerprints that are maintained for the first days of pumping and are distinct amongst the different levels. This suggests an evolution in water composition because of reaction with the chalk. Water composition is distinct from both seawater from the nearby Baltic Sea and salty water from deeper levels of the reservoir. Thus, neither up-coning of salty water nor intrusion of seawater caused the elevated salinity levels in the area. The slightly saline composition of groundwater in the shallow aquifer (14–26 m b.s.) is more likely because of incomplete refreshing of the salty connate water in the chalk during the Pleistocene and Holocene. Furthermore, the geochemical fingerprint of salty water from the deeper aquifer at 40 m was similar to water from the Baltic Sea, suggesting a Baltic Sea source for salt in the aquifer at 40 m b.s., <em style="color: #000000; font-family: 'Times New Roman'; font-size: medium; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">c.</em> 100 m from the coast. Statistical analysis based on self-organising maps is an effective tool for interpreting a large number of variables to understand the compositional variation in an aquifer and a useful alternative to linear dimensionality-reduction methods such as principal component analysis. The approach using the multi-element analysis combined with the analysis of self-organising maps may be useful in future studies of groundwater quality.</span></p> Christian Knudsen Klaus Hinsby Rasmus Jakobsen Lars Juul Kjærgård Per Rasmussen Copyright (c) 2021 Christian Knudsen, Klaus Hinsby, Rasmus Jakobsen, Lars Juul Kjærgård, Per Rasmussen https://creativecommons.org/licenses/by/4.0 2021-07-23 2021-07-23 47 10.34194/geusb.v47.5336