A remarkable discovery of electrum on the island of Sylt, northern Germany, and its Scandinavian origin

An electrum–quartz pebble with a weight of 10.4 g was discovered in a cliff of Saalian glaciogenic sediments on the west coast of the German North Sea island of Sylt in 2012. It has a roundish water-worn appearance and consists of intergrown electrum and milky quartz. It is the largest known electrum find in Germany, and regarding its weight it also ranks amongst the largest gold finds discovered in Germany. We document and characterize this unusual discovery. Furthermore, an attempt is made to investigate its provenance. Therefore, reference samples of southern Scandinavian gold and electrum deposits and occurrences have been studied and compared to the Sylt find. The Au–Ag content determined by electron microprobe (EMP), trace element signature measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and Pb isotope compositions by multi-collector ICP MS (MC-ICP-MS) suggest a southern Norwegian origin. The most probable source might be the Kongsberg ore district or an adjacent, yet undiscovered, mineralization in the Oslo region. In general, Saalian glaciogenic sediments in Schleswig-Holstein (northern Germany) are dominated by rocks of Swedish provenance. Due to the intake of older Elsterian sediments by younger Saalian glaciers, southern Norwegian rocks are also not uncommon in Saalian sediments. A Saalian ice advance or a combination of Elsterian and Saalian ice advances might have provided a transport mechanism for an electrum sample from a south Norwegian mineralization to the island of Sylt.

Sedimentary architecture and landforms of the Late Saalian (MIS 6) ice sheet margin, offshore the Netherlands

Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding the relationships between global climate and sea-level change, and to testing numerical ice sheet models. In this study, we integrate recently acquired high-resolution 2D-seismic reflection and borehole datasets from two windfarm sites offshore the Netherlands to investigate the sedimentary, geomorphological and glaciotectonic records left by the Saalian Drenthe substage glaciation, when Scandinavian land ice reached its southernmost extent in the southern North Sea (ca. 160 ka, Marine Isotope Stage 6). A complex assemblage of glaciogenic sediments and glaciotectonic structures are buried in the shallow subsurface. The northern windfarm site revealed a set of NE-SW oriented subglacial meltwater channels filled with till and glaciofluvial sediments and an E-W trending composite ridge with local evidence of intense glaciotectonic deformation that denotes the maximum limit reached by the ice. Based on the identified glacial geomorphology, we refine the mapping of the maximum ice-sheet extent offshore the Netherlands, revealing that the ice margin morphology is more complex than previously envisaged, displaying a lobate shape. Ice retreat left an unusual paraglacial landscape characterised by the progressive infilling of topographic depressions carved during the ice advance and a diffuse drainage network of outwash channels. The net direction of outwash was to the west and southwest into a nearby glacial basin. Antecedent topography influenced subglacial bed conditions, and their impact on ice dynamics during the glaciation and deglaciation stages. We demonstrate the utility of offshore windfarm data in refining palaeo ice margin limits, and the record of processes interactions preserved in buried landscapes to help inform longer-term drivers of change at low relief ice margins.

Seismic stratigraphy of the Klints Bank east of Gotland (Baltic Sea): a giant drumlin sealing thermogenic hydrocarbons

This work analyses six high-resolution multi-channel seismic profiles across the Klints Bank east of Gotland. The Klints Bank consists of a drop-shaped increase of the Quaternary thickness and is oriented in an approximately north-southern direction with a length of over 50 km, a width of about 15 km and a maximum thickness of 150 m. The glacial origin of the Klints Bank can be verified with the dataset presented in this study. We classify the feature as a (giant) drumlin due to its steep up-ice and tapered down-ice face in combination with an orientation parallel to the ice-flow direction of the Weichselian glaciation. The seismic image of the internal structure of the Quaternary unit shows no uniform stratification or deformation patterns; instead, local sub-parallel reflection patterns interlayered with transparent units are observed. The averaged seismic velocity of this unit is about 2000 m/s, which is interpreted as an autochthonous deposition of glaciogenic sediments. Signs of overprinting are interpreted based on the geometry of the flanks of the structure, which appear mostly in the form of collapse structures and lifted blocks due to compressional thrust faulting. Phase-reversed events within and beneath the Quaternary are perceived as strong evidence of fluid (hydrocarbon) presence within the Klints Bank. Organically enriched Palaeozoic shales in south-easterly direction of the Klints Bank presumably give the origin of these thermogenic hydrocarbons.

U-Pb isotopic ages and provenance of some far travelled exotic pebbles from glaciogenic sediments of the Polonez Cove Formation (Oligocene, King George Island)

Zircon grains from nine erratic pebbles of granite, granodiorite/tonalite and quartzite from the Polonez Cove Formation (southern King George Island) were studied for their U-Pb isotope ages and provenance. The calculated concordia ages of the studied pebbles are 108.79 ± 0.89 Ma, 119.7 ± 2.2 Ma, 178.6 ± 2.8 Ma, 180.7 ± 1.9 Ma, 207.4 ± 3.1 Ma, 231.1 ± 1.9 Ma, 1087.5 ± 4 Ma and 1833 ± 4 Ma. The source area of individual pebbles was analyzed and defined. Pebbles of crystalline rocks were derived from the Antarctic Peninsula, as well as from the Antarctic mainland. The erratic made of quartzite was eroded from the southernmost part of the Ellsworth Mountains (Linder Pak Member of Howard Nunatak Formation). Our isotope data analytically supports the earlier thesis that the Oligocene ice-sheet covered a substantial part of Antarctica and its nucleus was located in its central part.Supplementary material: The U-Pb isotope data (Table S1) are available at https://doi.org/10.6084/m9.figshare.c.5233335

Exhumed fjords of Namibia: A glimpse of the Late Paleozoic Ice Age in the Karoo Supergroup of the Kaokoland basin

<p>The Late Paleozoic Ice Age (LPIA) is the longest-lived and most extreme glacial period (from ca 360 to 260 Ma) of the Phanerozoic. Over this time span, ice masses are thought to have covered most of Gondwana, from South America to Australia. In southern Africa, the sedimentary, stratigraphic and geomorphic evidence of this glaciation is recorded in the Karoo Supergroup. The Kaokoland region of northern Namibia is characterized by a dense network of deep (200-700 m), large (5-15 km) and U-shaped incised valleys formed during the LPIA (Martin, 1981). A recent reappraisal of the morphology and sedimentary infill of these outstanding geomorphic features attests of their glacial origin. Valley flanks are spectacularly striated and scratched while valley floors are characterized by extensive whalebacks and roches moutonnées. Moreover, the sedimentary infill at the base of these valleys is mainly composed of coarse deposits (conglomerates, diamictites, erratics, striated clasts) interpreted as glaciogenic in origin. Of particular interest, however, is the presence of coarse (ranging from sand to boulders) glaciogenic sediments plastered on the sub-vertical and striated valley sides. Vitally, the elevation of these deposits in the valleys appears to correspond to a linear bench-like level, which may reflect a marginal moraine allowing for the maximum thickness of the LPIA glaciers to be derived, an unprecedented advance. For the first time in the characterization of a pre-Pleistocene glacial epoch, an ice thickness has been inferred. Collectively, these features prove that the valleys were carved and occupied by ice masses during the LPIA from which ice volume, and in turn their contribution to global eustasy, can directly be inferred. In addition, postglacial sedimentary succession abutting on valley flanks and showcasing marine, deltaic and estuarine affinities clearly indicate that these glacial valleys formed fjords in the immediate aftermath of the LPIA, after the retreat of the ice margins. Sealed by the Karoo Supergroup sediments through Carboniferous to early Cretaceous times, these major glaciogenic morphologic features have subsequently been exhumed during the Cenozoic. Thus, some desertic landscapes of northern Namibia correspond to a glacial relief inherited from the LPIA at ca ~ 300 Myr ago.</p><p> </p><p>Martin, H., 1981, The Late Paleozoic Dwyka Group of the South Kalahari Basin in Namibia and Botswana and the subglacial valleys of the Kaokoveld in Namibia, in Hambrey, M.J., and Harland, W.B. (eds.) Earth’s Pre-Pleistocene Glacial Record: New York, Cambridge University Press, 61–66</p>

Vertical distribution of aerosols in dust storms during the Arctic winter

<p>High Latitude Dust (HLD) contributes 5% to the global dust budget, but HLD measurements are sparse. Iceland has the largest area of volcaniclastic sandy desert on Earth where dust is originating from volcanic, but also glaciogenic sediments. Total Icelandic desert areas cover 44,000 km<sup>2</sup> which makes Iceland the largest Arctic as well as European desert. Icelandic volcanic dust can be transported distances > 1700 km towards the Arctic and deposited on snow, ice and sea ice. It is estimated that about 7% of Icelandic dust can reach the high Arctic (N>80°). It is known that about 50% of Icelandic dust storms occurred during winter or subzero temperatures in the southern part of Iceland. The vertical distributions of dust aerosol in high atmospheric profiles during these winter storms and long-range transport of dust during polar vortex condition were unknown.</p><p>Dust observations from Iceland provide dust aerosol distributions during the Arctic winter for the first time, profiling dust storms as well as clean air conditions. Five winter dust storms were captured during harsh conditions.  Mean number concentrations during the non-dust flights were < 5 particles cm<sup>-3 </sup>for the particles 0.2-100 µm in diameter and > 40 particles cm<sup>-3</sup> during dust storms. A moderate dust storm with > 250 particles cm<sup>-3</sup> (2 km altitude) was captured on 10<sup>th</sup> January 2016 as a result of sediments suspended from glacial outburst flood Skaftahlaup in 2015. Similar particle number concentrations were reported previously in the Saharan air layer. Detected particle sizes were up to 20 µm close to the surface, up to 10 µm at 900 m altitude, up to 5 µm at 5 km altitude, and submicron at altitudes > 6 km.</p><p>Dust sources in the Arctic are active during the winter and produce large amounts of particulate matter dispersed over long distances and high altitudes. HLD contributes to Arctic air pollution and has the potential to influence ice nucleation in mixed-phase clouds and Arctic amplification.</p><p> </p><p>Reference:</p><p>Dagsson-Waldhauserova, P., Renard, J.-B., Olafsson, H., Vignelles, D., Berthet, G., Verdier, N., Duverger, V., 2019. Vertical distribution of aerosols in dust storms during the Arctic winter. <strong>Scientific Reports </strong>6, 1-11.</p>

The extent of middle Pleistocene ice cap in the coastal Dinaric Mountains of Croatia

Solitary limestone blocks and groups of blocks occur on Risnjak and Velebit Mountains and on the northern Adriatic islands of Krk and Rab. Previous researchers have interpreted some of these as a) erratic blocks, b) corrosional remnants, or c) rockfalls. We have studied their mode of occurrence and composition, and revised previous interpretations of their origin in the light of transport mechanism and depositional processes. After analyzing the context of the block positions and the physical processes responsible for their emplacement, and taking into account their sedimentological context (their association with glaciogenic sediments), we herein propose a glacial origin for most of these blocks. However, some blocks are indeed shaped by sub-soil corrosion, as evidenced by their structure. The interpreted erratic blocks on the inner northern Adriatic Sea islands document the presence of middle Pleistocene glaciation of Dinaric Mountains though not its maximal extent, which is still unclear as the ice terminus was in the area that is inundated by postglacial rise of Adriatic Sea. The reconstructed ice cap area, which extended along the coastal mountains from Risnjak Mt. to south Velebit Mt. and across the range from Lika Polje to Rab Island, is conservatively estimated to be 5400 km2.