Ostracod palaeoecology and environmental change in the Laptev and Kara seas (Siberian Arctic) during the last 18 000 years

Fossil ostracod assemblages were investigated in five AMS ¹⁴ C‐dated cores from various water depths of the Laptev and Kara seas ranging from the upper continental slope (270 m) to the present‐day shelf depth (40 m). Six fossil assemblages were distinguished. These represent the varying environmental conditions at the North Siberian continental margin since about 18 ka. In the cores from the shelf the ostracod assemblages reflect the gradual transition from an estuarine brackish‐water environment to modern marine conditions since 12.3 ka, as induced by the regional early Holocene transgression. The core from the upper continental slope dates back to c. 17.6 ka and contains assemblages that are absent in the shelf cores. The assemblage older than 10 ka stands out as a specific community dominated by relatively deep‐water Arctic and North Atlantic species that also contains euryhaline species. Such an assemblage provides evidence for past inflows of Atlantic‐derived waters from as early as c. 17.2 ka, probably facilitated by upwelling in coastal polynyas, and a considerable riverine freshwater influence with enhanced surface water stratification owing to the proximity of the palaeocoastline until early Holocene times. In all studied cores, relative increases in euryhaline species dominant in the inner‐shelf regions are recorded in the mid–late Holocene sediments (<7 ka), which otherwise already contain modern‐like ostracod assemblages with relatively deep‐water species. This observation suggests euryhaline species to be largely sea‐ice‐ and/or iceberg‐rafted and therefore may provide evidence for a climate cooling trend.     

Experiments on the photophoretic motion of chondrules and dust aggregates—Indications for the transport of matter in protoplanetary disks

In a set of 16 drop tower experiments the motion of sub-millimeter to millimeter-sized particles under microgravity was observed. Illumination by a halogen lamp induced acceleration of the particles due to photophoresis. Photophoresis on dust-free chondrules, on chondrules, glass spheres and metal spheres covered with SiC dust and on pure SiC dust aggregates was studied. This is the first time that photophoretic motion of millimeter-sized particles has been studied experimentally. The absolute values for the photophoretic force are consistent with theoretical expectations for spherical particles. The strength of the photophoretic force varies for chondrules, dust covered particles and pure dust from low to strong, respectively. The measurements support the idea that photophoresis in the early Solar System can be efficient to transport solid particles outward.     

Übersicht der Veröffentlichungen der U.S. Geological Survey

International Journal of Earth Sciences -     

Impact structures and events - a Nordic perspective

Impact cratering is one of the fundamental processes in the formation of the Earth and our planetary system, as reflected, for example in the surfaces of Mars and the Moon. The Earth has been covered by a comparable number of impact scars, but due to active geological processes, weathering, sea floor spreading etc, the number of preserved and recognized impact craters on the Earth are limited. The study of impact structures is consequently of great importance in our understanding of the formation of the Earth and the planets, and one way we directly, on the Earth, can study planetary geology.
The Nordic-Baltic area have about thirty confirmed impact structures which makes it one of the most densely crater-populated terrains on Earth. The high density of identified craters is due to the level of research activity, coupled with a deterministic view of what we look for. In spite of these results, many Nordic structures are poorly understood due to the lack of 3D-geophysical interpretations, isotopeor other dating efforts and better knowledge of the amount of erosion and subsequent tectonic modifications.
The Nordic and Baltic impact community is closely collaborating in several impact-related projects and the many researchers （about forty） and PhD students （some seventeen） promise that this level will continue for many more years. The main topics of research include geological, geophysical and geochemical studies in combination with modeling and impact experiments. Moreover, the Nordic and Baltic crust contains some hundred suspect structures which call for detailed analysis to define their origin.
New advanced methods of analyzing geophysical information in combination with detailed geochemical analyses and numerical modeling will be the future basic occupation of the impact scientists of the region. The unique Cretaceous/Tertiary boundary （K-T） occurrences in Denmark form an important source of information in explaining one of the major mass extinctions on Earth.     

Randpazifische Tektonik und Vulkanismus im südlichen Chile

Zusammenfassung Die Struktur des südlichen Chile zwischen 37° und 42° S wird beschrieben. Die Anden gingen teils aus einer jurassisch-unterkretazischen Eugeosynklinale, teils aus magmatischer Regeneration gondwanischer Relikte hervor. Es überwiegt E-vergenter Falten- und Schuppenbau. In den Längstalbecken begann die Senkung im Eozän auf vorwiegend präkambrischem Sockel. Die Küstenkordillere besteht großenteils aus präkambrischen Para-Serien, welche seit der Oberkreide in die randpazifische Tektonik einbezogen wurden. Im Schelfgürtel herrscht seit der Oberkreide Sedimentation auf instabilem, antithetisch brechendem Sockel. Die Andesit-Förderung erfolgte längs geradliniger Fronten, welche sich mehrfach verlagerten. Beim Erdbeben von 1960 wurde der Krustenblock zwischen Kontinentalrand und Anden als Ganzes westwärts bewegt und gekippt. Ein Krustenmodell wird entworfen und dessen Entwicklung unter dem Aspekt der Kontinentaldrift Südamerikas diskutiert.

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The structure of Southern Chile between 37° and 42° S is described. The Andean cordillera is the result partly of a Jurassic-lower cretaceous eugeosyncline and partly of magmatic regeneration of gondwanian residues. Eastoverturned fold and imbricate structure predominates. In the basins within the longitudinal valley subsidence started in the Eocene mainly on a precambrian basement. The coast range consists mostly of precambrian para-series, which were included in the marginal pacific tectonics since the Upper Cretaceous. In the shelf region sedimentation takes place since the Upper Cretaceous on an unstable, antithetic breaking basement. Andesites erupted along straight fronts, which changed position several times. During the earthquake in 1960 the crustblock between the continental margin and the main cordillera moved westwards and tilted as a whole. A crust-model is traced out; its development is discussed under the aspect of the continental drift of South America.

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Résumé Ce traité comprend la structure du Chili méridional entre 37° et 42° S. La cordillère des Andes résulte d'une part d'un eugéosynclinal jurassique-crétassique inférieur, d'autre part d'une régénération magmatique des restes gondwaniens. Dans cette cordillère une structure plissée et écailleuse prédomine qui est déversée vers l'Est. Dans les bassins de la vallée longitudinale le sous-sol dont le socle était surtout précambrien, avait commencé à se tasser pendant l'époque de l'Eocène. La cordillère côtière se compose en grande partie de para-séries précambriennes, qui furent comprises dans la tectonique pacifique marginale depuis le Crétacé supérieur. Dans la région de la plate-forme continentale il y a une sédimentation depuis le Crétacé supérieur; le socle y était instable et se cassait antithétiquement. Les points d'éruptions des andésites s'alignaient; ces fronts tout droits changeaient de places plusieurs fois. Pendant le tremblement de terre en 1960 tout le bloc crustal qui se trouvait entre le talus continental et la cordillère des Andes fut mis en mouvement vers l'Ouest et basculé entièrement. Un modèle de l'écorce est tracé dont le développement est discuté sous l'aspect de la translation continentale de l'Amérique du Sud.

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Composition and Flux of Holocene Sediments on the Eastern Laptev Sea Shelf, Arctic Siberia

A 467-cm-long core from the inner shelf of the eastern Laptev Sea provides a depositional history since 9400 cal yr. B.P. The history involves temporal changes in the fluvial runoff as well as postglacial sea-level rise and southward retreat of the coastline. Although the core contains marine fossils back to 8900 cal yr B.P., abundant plant debris in a sandy facies low in the core shows that a river influenced the study site until 8100 cal yr B.P. As sea level rose and the distance to the coast increased, this riverine influence diminished gradually and the sediment type changed, by 7400 cal yr B.P., from sandy silt to clayey silt. Although total sediment input decreased in a step-like fashion from 7600 to 4000 cal yr B.P., this interval had the highest average sedimentation rates and the greatest fluxes in most sedimentary components. While this maximum probably resulted from middle Holocene climate warming, the low input of sand to the site after 7400 cal yr B.P. probably resulted from further southward retreat of the coastline and river mouth. Since about 4000 cal yr B.P., total sediment flux has remained rather constant in this part of the Laptev Sea shelf due to a gradual stabilization of the depositional regime after completion of the Holocene sea-level rise.