Late Palaeogene syn-tectonic volcanic products have been found in the Northern Alpine foreland basin and in the South Alpine hemipelagic basin. The source of abundant volcanic fragments is still in debate. We analyzed the geochronology and geochemistry of detrital zircons, and evaluated their temporal and genetic relationships with potential volcanic sources. The study shows that the detrital zircon U–Pb age patterns have two major age groups: a dominance (ca. 90%) of pre-Alpine zircons was found, as commonly observed in other Alpine flysch formations. These zircons apparently derived from erosion of the early Alpine nappe stack in South Alpine and Austroalpine units. Furthermore, a few Neo-Alpine zircons (ca. 10%) have ages ranging from Late Eocene to Early Oligocene (~ 41–29 Ma). Both source materials were mixed during long riverine transport to the basin margins before being re-deposited by gravity flows. These Palaeogene ages match with the activity of Peri-Adriatic magmatism, including the Biella volcanic suite as well as the Northern Adamello and Bergell intrusions. The values of REE and ¹⁷⁶Hf/¹⁷⁷Hf_(t) ratios of the Alpine detrital zircons are in line with the magmatic signatures. We observe an in time and space variable supply of syn-sedimentary zircons. From late Middle Eocene to Late Eocene, basin influx into the South Alpine and Glarus (A) basins from the Northern Adamello source is documented. At about 34 Ma, a complete reorganisation is recorded by (1) input of Bergell sources into the later Glarus (B) basin, and (2) the coeval volcaniclastic supply of the Haute-Savoie basin from the Biella magmatic system. The Adamello source vanished in the foreland basin. The marked modification of the basin sources at ~ 34 Ma is interpreted to be initiated by a northwestern shift of the early Alpine drainage divide into the position of the modern Insubric Line.

Re-evaluation of the river history, palaeosurface levels and exhumation history in northern Switzerland for the last 10 million years reveals that distinct morphotectonic events about 4.2 and 2.8 million years ago (Ma) caused major reorganisation of river networks and morphosculpture. As a result of the earlier formation of the Swiss Jura, potential relief energy in the piggy-back North Alpine Foreland Basin (NAFB) of northern central Switzerland south of the Jura fold belt was built up after 11–10 Ma. It was suddenly released by river capture at about 4.2 Ma when the Aare-Danube was captured by a tributary of the Rhône-Doubs river system which rooted southeast of the Black forest. This event triggered rapid denudation of weakly consolidated Molasse sediments, in the order of about 1 km, as constrained by apatite fission track data from drillholes in the NAFB. Likely mechanisms of river capture are (a) headward erosion of Rhône-Doubs tributaries, (b) uplift and rapidly increasing erosion of the Swiss Alps after about 5.3 Ma, and (c) gravel aggradation at the eastern termination of the Jura fold belt in the course of eastward and northward tilt of the piggy-back NAFB. A morphotectonic event between 4.2 and 2.5 Ma, probably at about 2.8 Ma, caused a phase of planation, accompanied by local gravel aggradation and temporary storage of Alpine debris. Between 2.8 and 2.5 Ma, the Aare-Rhône river system is cannibalised by the modern Rhine River, the latter later connecting with the Alpine Rhine River.

The late Eocene-to-early Oligocene Taveyannaz Formation is a turbidite series deposited in the Northern Alpine Foreland Basin (close to the Alpine orogenic front). Double dating of zircons with the fission-track and the U–Pb methods is applied on samples from the Taveyannaz Formation to reconstruct the exhumation history of the Central-Western Alps and to understand the syn-collisional magmatism along the Periadriatic lineament. Three samples from this unit show similar detrital zircon fission-track age populations that center at: 33–40 Ma (20%); 69–92 Ma (30–40%); and 138–239 Ma (40–50%). The youngest population contains both syn-volcanic and basement grains. Combined with zircon U–Pb data, it suggests that the basement rocks of Apulian-affinity nappes (Margna Sesia, Austroalpine) were the major sources of detritus, together with the Ivrea Zone and recycled Prealpine flysch, that contributed debris to the Northern Alpine Foreland Basin. Furthermore, the rocks of the Sesia–Lanzo Zone or of equivalent units exposed at that time presumably provided the youngest basement zircon fission-track ages to the basin. The Biella volcanic suite was the source of volcanogenic zircons. Oligocene sediment pathways from source to sink crossed further crystalline basement units and sedimentary covers before entering the basin from the southeast. The lag times of the youngest basement age populations (volcanic zircons excluded) are about 11 Myr. This constrains average moderate-to-high exhumation rate of 0.5–0.6 km/Myr in the pro-side of the orogenic wedge of the Central Alps during the late Eocene to early Oligocene.

Zusammenfassung: Die gesetzlichen Vorgaben und das Regelwerk der Aufsicht in der Schweiz sehen vor, dass ein geologisches Tiefenlager an einem Standort realisiert wird, dessen geologische Eignung durch Daten und Prozessverständnis gezeigt werden kann. Der systematische Umgang mit Ungewissheiten ist ein zentraler Teil des Sicherheitsnachweises. Das Aufzeigen der Robustheit eines Lagersystems und der Unempfindlichkeit gegen eine Vielzahl möglicher zukünftiger Entwicklungsszenarien stellen Schlüsselelemente in der Nachweisführung dar.Für den Umgang mit Ungewissheiten wird in diesem Artikel ein schematisches Vorgehen aufgezeigt. Ein Rückblick über die Geschichte der Entsorgung in der Schweiz und insbesondere über das seit 2008 laufende Standortauswahlverfahren zeigt die Anwendung dieses Vorgehens, in dem Ungewissheiten zunächst auf ihre Sicherheitsrelevanz geprüft werden, anschließend zu klären ist, inwiefern Ungewissheiten durch Anpassungen ausgeschlossen werden können bzw. einzubeziehen sind. Bei einem Einbezug sind schlussendlich die Ungewissheiten genauer zu bestimmen oder in ihrer Wirkung einzugrenzen. An konkreten Beispielen wird das systematische Vorgehen erläutert.

Lake Öhningen (Middle Miocene, Mammal Neogene Zone MN7) on the southern flank of the Schiener Berg (SW Germany) is one of the most iconic European Fossil-Lagerstätten, yet the depositional environment and age of its sediments have remained poorly constrained. In 2021, a new excavation in the historical upper quarry exposed 8 m of lacustrine sediments, representing the upper part of the known deposits. The succession comprises calcareous laminites, unstructured and laminated clays and silts, marls and limestones, a conspicuous interval of micaceous fine sands and calcarenites with well-developed ripple marks, and several tuffite layers. The laminites are largely unfossiliferous and lack petrographically resolvable varve couplets, contrasting sharply with the organic-rich, varved laminites of ‘textbook’ meromictic maar-lake Fossil-Lagerstätten. The rippled sandstones document phases of shallow, higher-energy conditions and significant input of reworked Molasse sand from the catchment, most likely via tributaries and weather-generated inflow. Together with the mixed facies pattern, this challenges the traditional interpretation of Öhningen as a classic maar lake. Two brown tuffites interbedded within the lacustrine succession yield apatite fission-track ages of 13.7 ± 0.5 Ma (lower Serravallian), providing the first robust absolute ages for the Öhningen Beds. These ages are slightly older than the Herrentisch Deckentuff (12.6 ± 0.4 Ma) and overlap with published ages of the Wangen tuff cone, placing Lake Öhningen within an early phase of Hegau volcanic activity and confirming its MN7 assignment from biochronology. We interpret Lake Öhningen as a small, stratified but hydrologically open lake influenced by episodic volcanic, fluvial, and storm events, and recommend the neutral term ‘Lake Öhningen’ rather than ‘Öhningen Maar’ for this depositional system. Graphical abstract