Freshwater Molasse Research Articles

Middle Miocene (Late Badenian) microvertebrates from Hidas, SW Hungary

Up to the present, no terrestrial vertebrate fauna has been published from the pre-Pannonian Miocene of SW Hungary. In 2022 a microvertebrate assemblage was unearthed from a lime mud bed of the Middle Miocene Hidas Formation, in an abandoned coal mining field close to Hidas in the Mecsek Mts. The herpetofauna and the rodent material are described here. Fossil findings point to the Late Badenian MN 7+8 Zone, which, together with the earlier results based on the marine mollusc fauna, narrows the age of the unit to ~13.5–13.3 Ma. The amphibians and reptiles are aquatic, semiaquatic or periaquatic forms. Sedimentary features and the accompanying freshwater gastropod fauna are indicative of a shallow pond or a paludal depositional environment. Crocodylian finds reported earlier from the Hidas Formation indicate a subtropical climate, just before the end of the Miocene warm period in Central Europe. Among the rodents, glirids and flying squirrels as well as Democricetodon and Megacricetodon indicate the presence of humid arboreal vegetation around the site. The rodent taxa are well known from the Middle Miocene faunas of northern Hungary, western Romania and from the Upper Freshwater Molasse of southern Germany and Switzerland. The rodent material does not show characteristics of an insular fauna, e.g. gigantism or endemism. Consequently, although the coeval palaeogeography of the region has been described as an archipelago in the Central Paratethys, with the Mecsek Mts. being one of the islands, the area must have had ecological connections towards the northern and eastern parts of the Pannonian Basin, and the marine areas within the archipelago did not form a barrier against the distribution of microvertebrates. The corridor could have been located towards the NE from the Mecsek Mts., across the elevated basement blocks of central Hungary.

Interprétation de l’hydrogéochimie de la Molasse d’Eau Douce Supérieure (Obere Süßwassermolasse) dans la région de Munich (Bavière, Allemagne) à l’aide d’une analyse multivariée et d’une modélisation géologique en 3D

AbstractIntense use of groundwater in urban areas requires appropriate monitoring, which in turn necessitates proper data management with employment of increasingly sophisticated statistical methods and mapping tools. An example of such an urban area with intensive use of groundwater is the study area of GeoPot Project, namely Munich (Germany) and its surroundings. The aim of the presented study was to provide a description of the hydrogeochemical characteristics of the aquifers occurring in the Quaternary and Upper Freshwater Molasse (German: Obere Süßwassermolasse – OSM) sediments and to further improve the understanding of interactions between the aquifers. The focus was put on the identification of hydrochemical facies, the chemical signatures of different water types, an understanding of occurring processes, and spatial relationships between the aquifers. In order to deal with hydrogeochemical data generated for this study, as well as with data coming from existing external databanks (e.g. BIS-BY), a methodology of quality assurance was developed. The analytical methods focused on multivariate statistics. To enhance the interpretation of the obtained clusters, a recently developed three-dimensional geological model was used for better understanding and presentation. It was found that in the study area, deeper aquifer systems represent the most distinct hydrogeochemical signature of the Na–HCO3 water type. In the remaining clusters, a transition from deeper (alkaline) to shallow (alkaline-earth) groundwater can be observed. The results of the study can be utilized for improved, sustainable groundwater management.

Sedimentology of the Jura Molasse: Miocene tidal clastics and freshwater carbonates from the Tramelan-2 Borehole, NW Switzerland

The Tramelan-2 borehole (Canton Bern, Switzerland) continuously cored a 275.60 m sequence of Palaeogene to Neogene sediments, providing a rare opportunity for sedimentological analysis of the Jura Molasse. Lithostratigraphy, sedimentary facies and heavy minerals allow correlation with the classical Swiss Molasse. Evidence for clastic input from Alpine and non-Alpine sources is consistent with deposition at the northern feather edge of the Molasse Basin. Grey sandstones at the base of the succession are tentatively interpreted as fluvial facies of the Lower Freshwater Molasse (USM). These are overlain by erosively-based conglomerates, interpreted as winnowed storm lags of locally-derived clasts and distantly-sourced Alpine material at the transgressive base of the Upper Marine Molasse (OMM). Above this, a range of plane-laminated and cross-bedded bioclastic sandstones are interpreted as the deposits of a meso- or macrotidal flat or estuarine complex. Facies evolution in the upper OMM records a series of stacked regressive cycles within an overall upward trend of reducing current energy, reflecting a transition from offshore to nearshore shallow marine environments. The unconformably overlying Upper Freshwater Molasse (OSM) passes upwards from micaceous siltstones and marls into a series of freshwater carbonates, dominated by lacustrine limestones which are arranged in repeated regressive cycles, each capped by organic-rich horizons. The middle part of the carbonate interval comprises palustrine limestones with pedogenetic fabrics recording periodic subaerial exposure. Stable isotope signatures from the palustrine facies reflect subaerial pedogenetic overprint, while the lacustrine carbonates record cyclical variations in δ13C which may reflect increases in organic material during progressive lake fill and/or an increased influence of aquifer waters during flooding events. The Jura Molasse onlapped a Mesozoic carbonate pediment hosting a regional karst system which remained active at least until the Burdigalian transgression on footwall highs bounding the Delémont Basin, and locally into the Langhian near Tramelan. This configuration controlled subsequent deposition of OSM carbonates which onlapped erosional and potentially early tectonic relief, and were deposited in groundwater-fed seasonal lacustrine/palustrine environments, where the karstic aquifer controls on seasonal hydrology appear to have been comparable to Caribbean freshwater carbonate wetland systems today.

First record of an autochthonous community of fluviatile freshwater molluscs from the Middle/Late Miocene Upper Freshwater Molasse (southern Germany)

First record of an autochthonous community of fluviatile freshwater molluscs from the Middle/Late Miocene Upper Freshwater Molasse (southern Germany)

Event- and biostratigraphic evidence for two independent Ries and Steinheim asteroid impacts in the Middle Miocene

For decades, the Nördlinger Ries and Steinheim Basin in southern Germany have been regarded as a textbook example of a terrestrial impact crater doublet, although the oldest crater lake deposits in both craters suggest a biostratigraphic age difference of ~ 0.5 to 1 Myr. We previously presented stratigraphic arguments that challenged the double impact scenario and favoured a model of two temporally independent impact events in the Mid-Miocene. We here present, for the first time, four localities within a distance of ~ 50–100 km from the Ries and ~ 50–70 km from the Steinheim crater that expose two independent seismite horizons, together unique within the Upper Freshwater Molasse of the North Alpine Foreland Basin, each one featuring impressive water escape structures. The seismite horizons are separated by ~ 10 to 15 m of undisturbed Molasse deposits and, biostratigraphically, by an entire European Land Mammal Zone, thus providing evidence for two independent major seismic events within a time span of ~ 0.5–1 Myr. Both the lower and the upper seismite horizons can be correlated litho- and biostratigraphically with the basal crater lake sediments at the Ries and Steinheim craters, respectively, deposited immediately after the impacts. From a biostratigraphic point of view, the impact event that formed the Steinheim Basin probably occured around 14 Ma, some 0.8 Myr after the ~ 14.81 Ma Ries impact event.

Fossil molluscs from the Middle Miocene of Öhningen, southwestern Germany

Herein, we revise an extensive set of mollusc fossils from the Upper Freshwater Molasse deposits of Öhningen palaeolake (SW Germany; Middle Miocene, MN7). Based on material housed in paleontological collections in Europe and North America, we present the first thorough systematic account of the phylum from this historic locality. A total of ten species were identified from Öhningen: three freshwater gastropods (Lymnaea dilatata Noulet, 1854, Gyraulus cf. applanatus (Thomä), Planorbarius mantelli (Dunker)), two terrestrial gastropods (Granaria cf. schuebleri (Klein), Palaeotachea sylvestrina (Schlotheim)), and five bivalves (Anodonta splendens Goldfuss, A. lavateri (Münster), Pseudunio flabellatus (Goldfuss), “Dreissena” sp., Pisidium escheri (Mayer-Eymar, 1865)). Three freshwater and five terrestrial gastropod genera mentioned in older literature could not be found in the available material. Ours is the first report of a Dreissenidae from Öhningen.

Trace-fossil suites and composite ichnofabrics from meandering fluvial systems: The Oligocene Lower Freshwater Molasse of Switzerland

The Oligocene Lower Freshwater Molasse of Switzerland is host to spectacular outcrops of fluvial deposits. In distal areas of the Swiss Molasse Basin, deposits of a north-eastward draining meandering system are exposed. Combined sedimentologic and ichnologic observations in the Chli Sunnhalde and Roggwil quarries allow an improved understanding of animal-substrate interactions in deposits of meandering fluvial systems. Strata include meander-belt sandstone, levee sandstone and mudstone, crevasse-channel and splay sandstone, floodplain mudstone and sandstone, and paleosols. While the meander belt and the more proximal crevasse-channel deposits are typically unbioturbated, the more distal deposits show a clear biogenic overprint, with distal crevasse-channel, crevasse-splay, and floodplain deposits being intensely bioturbated.Simple grazing and locomotion trails (included in the Cochlichnus anguineus-Helminthoidichnites tenuis suite) were formed subaqueously in ponded areas of the floodplain. Meniscate burrows (Taenidium isp. suite) and root trace fossils occur along the margin of these floodplain water-bodies and at the top of crevasse-splay deposits. Some of the floodplain, crevasse-splay, and crevasse-channel deposits are pervasively bioturbated by crayfish burrows (Camborygma litonomos suite). Crevasse-splay deposits locally host escape trace fossils.Where cross-cutting relationships are apparent, a colonization sequence can be established as follows: the Cochlichnus anguineus-Helminthoidichnites tenuis suite is cross-cut by the Taenidium isp. suite, which in turn is cross-cut by the Camborygma litonomos suite and root trace fossils. Composite ichnofabrics are common in these meandering river deposits, recording progressive lowering of the water table in overbank subenvironments. Frequency of depositional events was a first-order control on degree of bioturbation. Position of the water table and degree of substrate consolidation exerted considerable influence over the types of trace fossils produced. Distinct bioturbation phases may result in the formation of different trace-fossil suites - representative of disparate ichnofacies - preserved on a single bedding plane. This study further supports the notion that meandering fluvial systems are characterized by trace-fossil suites belonging to the Scoyenia, Camborygma and/or Mermia ichnofacies.

Tectonic processes, variations in sediment flux, and eustatic sea level recorded by the 20 Myr old Burdigalian transgression in the Swiss Molasse basin

Abstract. The stratigraphic architecture of the Swiss Molasse basin, situated on the northern side of the evolving Alps, reveals crucial information about the basin's geometry, its evolution, and the processes leading to the deposition of the siliciclastic sediments. Nevertheless, the formation of the Upper Marine Molasse (OMM) and the controls on the related Burdigalian transgression have still been a matter of scientific debate. During the time period from ca. 20 to 17 Ma, the Swiss Molasse basin was partly flooded by a shallow marine sea striking SW–NE. Previous studies have proposed that the transgression occurred in response to a rise in global sea level, a reduction of sediment flux, or an increase in tectonically controlled accommodation space. Here, we readdress this problem and extract stratigraphic signals from the Burdigalian molasse deposits that can be related to changes in sediment supply rate, variations in the eustatic sea level, and subduction tectonics. To achieve this goal, we conducted sedimentological and stratigraphic analyses of several sites across the entire Swiss Molasse basin. Field investigations show that the transgression and the subsequent evolution of the Burdigalian seaway was characterized by (i) a deepening and widening of the basin, (ii) phases of erosion and non-deposition during Lower Freshwater Molasse (USM), OMM, and Upper Freshwater Molasse (OSM) times, and (iii) changes in along-strike drainage reversals. We use these changes in the stratigraphic record to disentangle tectonic and surface controls on the facies evolution at various scales. As the most important mechanism, rollback subduction of the European mantle lithosphere most likely caused a further downwarping of the foreland plate, which we use to explain the deepening and widening of the Molasse basin, particularly at distal sites. In addition, subduction tectonics also caused the uplift of the Aar massif. This process was likely to have shifted the patterns of surface loads, thereby resulting in a buckling of the foreland plate and influencing the water depths in the basin. We use this mechanism to explain the establishment of distinct depositional settings, particularly the formation of subtidal shoals wherein a bulge in relation to this buckling is expected. The rise of the Aar massif also resulted in a reorganization of the drainage network in the Alpine hinterland, with the consequence that the sediment flux to the basin decreased. We consider this reduction in sediment supply to have amplified the tectonically controlled deepening of the Molasse basin. Because the marine conditions were generally very shallow, subtle changes in eustatic sea level contributed to the formation of several hiatuses that chronicle periods of erosion and non-sedimentation. These processes also amplified the tectonically induced increase in accommodation space during times of global sea level highstands. Whereas these mechanisms are capable of explaining the establishment of the Burdigalian seaway and the formation of distinct sedimentological niches in the Swiss Molasse basin, the drainage reversal during OMM times possibly requires a change in tectonic processes at the slab scale, most likely including the entire Alpine range between the Eastern and Central Alps. In conclusion, we consider rollback tectonics to be the main driving force controlling the transgression of the OMM in Switzerland, with contributions by the uplift of individual crustal blocks (here the Aar massif) and by a reduction of sediment supply. This reduction of sediment flux was likely to have been controlled by tectonic processes as well when basement blocks became uplifted, thereby modifying the catchment geometries. Eustatic changes in sea level explain the various hiatuses and amplified the deepening of the basin during eustatic highstand conditions.

Three-dimensional geological modeling supports a revised Burdigalian chronostratigraphy in the North Alpine Foreland Basin

Precise age data are a basic prerequisite for the correlation of a sedimentary succession with the Global Time Scale, which in turn allows one to place its biotic and other data in a global context. In the North Alpine Foreland Basin (NAFB), a patchy distribution of outcrops and uncertainties in the correlation of strata have led to conflicting age models, in particular for deposits of lower Miocene (Burdigalian) age. Here, we present a new three-dimensional geological model of the SE German sector of the NAFB, covering an area of 13,200 km2, which helps to resolve the discrepancies. The dataset comprises lithostratigraphic information from 150 boreholes, supplemented by magnetostratigraphic data from six outcrops. Computer-based 3D modeling was conducted with the open source software QGIS for a 500-m-thick succession comprising units of the Upper Marine Molasse, the brackish Oncophora Fm and the Upper Freshwater Molasse. The results provide new insights pertaining to (1) the isochrony of strata, (2) subsidence, and (3) synsedimentary tectonics. The new data permit us to reliably place the outcrops within the regional lithostratigraphic scheme, thus enabling a new correlation of their magnetic polarities with the Global Time Scale. On this basis, we propose a revised age model for the middle and upper Burdigalian strata in the eastern part of the NAFB, which is supported by previously reported 87Sr/86Sr age data. The model indicates that the succession is substantially—up to 0.8 Ma—younger than earlier publications have suggested. Furthermore, it implies that the two synsedimentary tectonic events discerned may both be related to the large-scale tectonic movements that affected the NAFB during the late Burdigalian.

Increased uranium concentrations in ground and surface waters of the Swiss Plateau: A result of uranium accumulation and leaching in the Molasse basin and (ancient) wetlands?

Increased uranium (U) concentrations are found in certain ground and surface waters of the Swiss Plateau. Analysis of more than 100 public fountains revealed that increased 238U concentrations frequently occur close to the interface between the Lower Freshwater Molasse and the Upper Marine Molasse, cropping out in the western part of the Swiss Molasse Basin. Out of these locations, Mont Vully, situated ca. 20 km west of Berne, was studied in detail. As this hill consists of the two aforementioned stratigraphic Molasse units, it represents an ideal case study. Two springs at the northern slopes of Mont Vully exhibit the highest 238U concentrations with more than 300 mBq/L and were thus monitored for almost two years in order to screen possible seasonal variations. Further water samples were collected from spring captures, creeks and drainage pipes. The pipes drain the farmland north of Mont Vully showing 238U concentrations with more than 600 mBq/L. In order to discover the reason for the duplication in concentration, gamma dose rate measurements were accomplished on the farmland, revealing elevated dose rates of up to 160 nSv/h. These are located above ancient pathways of creeks that originated from Mont Vully. At these locations with elevated dose rates, three shallow sediment drill cores were taken and analyzed for their U content. The sediment cores can essentially be divided into three parts: (i) an upper soil with common U concentrations of about 30 Bq/kg 238U, (ii) an U-rich peat horizon with concentrations of up to 500 Bq/kg 238U, and (iii) an impermeable clay unit that acts as an aquitard with again minor 238U concentrations. Radiocarbon dating of the U-rich peat horizon reveals ages younger than 8.1 kyrs. This study suggests that a wetland was formed on top of the impermeable clay layer after the last glaciation during the Holocene. The stream waters with 238U concentrations of more than 300 mBq/L originating from Mont Vully contributed significantly to the water supply for the development of the wetland. Due to the reducing conditions that are present in wetlands, the dissolved U in the incoming streams was reduced and adsorbed onto organic matter. Accordingly, an entrapment for U was generated, persisting for at least 6 kyrs – a sufficient time to accumulate up to 500 Bq/kg. In the course of the last century, numerous wetlands in Switzerland were drained by capturing streams and installing drainage pipes to make the land suitable for agriculture. This kind of melioration was also done at the wetlands north of Mont Vully resulting in a subsequent change in redox conditions within the soil. The solubility of U depends on its oxidation state and U can be oxidized by oxygen-rich rainwater. The rainwater leached the U adsorbed on the peat yielding 238U concentrations of more than 600 mBq/L. Consequently, the duplication of 238U concentrations in the drainage water as compared to the original concentration that creeks brought into the ancient wetlands has been clarified during this study. Twenty of the analyzed public fountains in the Swiss Plateau exhibited a 238U concentration of more than 50 mBq/L. All of them could have contributed to the formation of a wetland after the last glaciation, which leads to the assumption that the situation at Mont Vully is not a singularity in the Swiss Plateau.

In situ testing of barrette foundations for a high retaining wall in molasse rock

Barrettes are common foundations for high-rise buildings, especially because of their high bearing capacity, for vertical as well as for lateral loads. In this paper, it is shown how these were adopted and tested for anchoring a 27 m high retaining wall in rock on a slope located in the centre of Zurich. The monolithic 10 × 1 × 25 m deep barrettes, excavated and built in layered rock (Upper Freshwater Molasse), are also intended to stabilise the slope. The main contribution to their bearing capacity is given by the contact strength between the reinforced concrete and the rock. Two full-scale pull-out tests, instrumented by distributed fibre-optical measurements, are carried out to investigate the contact strength between rock and reinforced concrete. The results show that dilatancy at the contact caused by the irregular excavated surface has a strong influence on the bearing capacity. Additionally, the distributed fibre-optic instrumentation allowed progressive crack propagation of the reinforced concrete in the barrettes to be detected during the test. Inverse analysis of the rock and concrete tensile properties are obtained within a finite-element calculation, which takes into account the non-linear properties of the reinforced concrete and the rock.

New data on the Miocene dormouse Simplomys García-Paredes, 2009 from the peri-alpin basins of Switzerland and Germany: palaeodiversity of a rare genus in Central Europe

Simplomys, a dormouse with a simple dental morphology compared to other glirids, shows a continuous evolution in Spain during the end of the Ramblian and up to the middle Aragonian, the stratigraphic frame considered in this work. In contrast, the record of the genus in Central Europe is reduced to a few localities spanning from the early to the middle Miocene. We review the record from the Burdigalian to Langhian equivalent to the deposition of the uppermost Upper Marine Molasse (OMM) to the lower part of the Upper Freshwater Molasse (OSM) and conclude the occurrence of three distinct species. The youngest species, Simplomys simplicidens, is recognised in Schonenberg (Germany, MN5) and Courrendlin-Sole (Switzerland; MN4). Material from a fissure filling near Glovelier (Switzerland, MN4) supplied the new species, Simplomys hugi, whereas the localities Petersbuch 2 and Erkersthofen 2 (both fissure fillings from Germany, MN4) contain species closely related to it. Finally, and pending further advances in the taxonomy of the Iberian Simplomys, the oldest population from the fissure filling of Schnaitheim (Germany; MN3) remains in open nomenclature (Simplomys sp.). The genus Simplomys has not been recorded eastwards from the Swabian and Franconian Jura Plateaus from Germany and its youngest occurrence in Schonenberg is correlated to the South German local scale OSM C+D, at around 15.5 Ma.

Miocene continental gastropods from Dischingen, Germany

Here is given an account, based on museum collections, of the fossil land and freshwater gastropods from Dischingen (Baden-Württemberg state, SW Germany). The fossiliferous outcrops belong to the Silvana Beds unit of the Upper Freshwater Molasse group, of late Early to early Middle Miocene age (Neogene European Land Mammal Zone MN 5). In total, 35 gastropod species were found (seven freshwater and 28 terrestrial), mainly belonging to Pulmonata, but also with representatives of Neritimorpha and Caenogastropoda. Seven species are reported here for the first time from Dischingen: Palaina diezi, Radix socialis, Granaria sp., Serrulina? sp., Discus pleuradrus, Punctum pumilio, and Oxyloma minima.

A New Tribe of the Subfamily Cyladinae (Coleoptera, Brentidae) in the Miocene of Germany

A new tribe, new genus, and new species, Miocenocylas heeri gen. et sp. nov. from the Middle Miocene of Oeningen, Germany (Baden-Wurttemberg; Sarmatian, Upper Freshwater–Molasse Formation) are described. They differ from the tribe Cyladini in the free club articles, antennae inserted near the apex of the rostrum, procoxae located in the middle of the prosternum, the longer pronotum, and in the indistinct elytral striae.

Fossil Land and Freshwater Gastropods from the Miocene of Hohenmemmingen, Germany

Abstract Herein we present an account of the fossil terrestrial and freshwater gastropods from the locality of Hohenmemmingen (Baden-Wurttemberg state, SW Germany) based on museum collections. The fossil outcrops belong to the Silvana Beds of the Upper Freshwater Molasse, being of Early/Middle Miocene age. In total, 23 gastropod species, all pulmonates, are documented in the material (whereas 33 species had been previously reported in the literature): five freshwater species and 18 terrestrial. From an actualistic palaeoecological approach, this palaeoevironment featured a humid and warm forest cover, with a well-vegetated and likely shallow water body.

The new Early Miocene bat records from the Molasse sites of South Germany

Abstract Fossil bats are described from deposits of the Upper Freshwater Molasse of the Forsthart and Rembach sites in East Bavaria of South Germany (MN 4). The material comprises 13 fragments, representing at least six different species, all belonging to Vespertilionidae. A fossil form from Rembach, close to the Oriental clade of Hesperoptenus, represents the first and oldest fossil record of this clade in Europe. The assignment of bat records to extant Oriental clades Hesperoptenus and Submyotodon in Rembach, as well as different forms of Miostrellus in Forsthart indicate considerable diversity in Early Miocene vespertilionid bats, and have exciting palaeobiogeographic implications. Fossils are discussed in regards to taxonomic, stratigraphic and palaeoecological significance.

Sediment routing evolution in the North Alpine Foreland Basin, Austria: interplay of transverse and longitudinal sediment dispersal

AbstractIntegration of detrital zircon geochronology and three‐dimensional (3D) seismic‐reflection data from the Molasse basin of Austria yields new insight into Oligocene‐early Miocene palaeogeography and patterns of sediment routing within the Alpine foreland of central Europe. Three‐dimensional seismic‐reflection data show a network of deep‐water tributaries and a long‐lived (>8 Ma) foredeep‐axial channel belt that transported Alpine detritus greater than 100 km from west to east. We present 793 new detrital zircon ages from 10 sandstone samples collected from subsurface cores located within the seismically mapped network of deep‐water tributaries and the axial channel belt. Grain age populations correspond with major pre‐Alpine orogenic cycles: the Cadomian (750–530 Ma), the Caledonian (490–380 Ma) and the Variscan (350–250 Ma). Additional age populations correspond with Eocene‐Oligocene Periadriatic magmatism (40–30 Ma) and pre‐Alpine, Precambrian sources (>750 Ma). Although many samples share the same age populations, the abundances of these populations vary significantly. Sediment that entered the deep‐water axial channel belt from the west (Freshwater Molasse) and southwest (Inntal fault zone) is characterized by statistically indistinguishable age distributions that include populations of Variscan, Caledonian and Cadomian zircon at modest abundances (15–32% each). Sandstone from a shallow marine unit proximal to the northern basin margin consists of >75% Variscan (350–300 Ma) zircon, which originated from the adjacent Bohemian Massif. Mixing calculations based on the Kolmogorov–Smirnoff statistic suggest that the Alpine fold‐thrust belt south of the foreland was also an important source of detritus to the deep‐water Molasse basin. We interpret evolving detrital zircon age distributions within the axial foredeep to reflect a progressive increase in longitudinal sediment input from the west (Freshwater Molasse) and/or southwest (Inntal fault zone) relative to transverse sediment input from the fold‐thrust belt to the south. We infer that these changes reflect a major reorganization of catchment boundaries and denudation rates in the Alpine Orogen that resulted in the Alpine foreland evolving to dominantly longitudinal sediment dispersal. This change was most notably marked by the development of a submarine canyon during deposition of the Upper Puchkirchen Formation that promoted sediment bypass eastward from Freshwater Molasse depozones to the Molasse basin deep‐water axial channel belt. The integration of 3D seismic‐reflection data with detrital zircon geochronology illustrates sediment dispersal patterns within a continental‐scale orogen, with implications for the relative role of longitudinal vs. transverse sediment delivery in peripheral foreland basins.

Eomys helveticus n. sp. and Eomys schluneggeri n. sp., two new small eomyids of the Chattian (MP 25/MP 26) subalpine Lower Freshwater Molasse of Switzerland

Abstract Two new small Eomys species of the Chattian Lower Freshwater Molasse of Central Switzerland are described. Eomys helveticus n. sp. and Eomys schluneggeri n. sp. from the localities Rigi 1 and Rigi 2 are characterized by their relatively small dimensions and the metalophid of the lower molars not being connected to the anterolophid. In addition, E. schluneggeri n. sp. shows some morphological similarity to the genus Eomyodon Engesser, 1987. The two new Eomys species have so far never been found in any of the numerous MP 25 and MP 26 localities in Central Europe. In both faunas Eomyidae and Gliridae were extremely frequent, whereas the Theridomyidae, usually the most frequent rodent family in the Late Oligocene, were very rare or absent. We interpret these peculiarities as being linked with the special ecological conditions, namely a relatively wet, forested environment.

The age of volcanic tuffs from the Upper Freshwater Molasse (North Alpine Foreland Basin) and their possible use for tephrostratigraphic correlations across Europe for the Middle Miocene

The Middle Miocene Upper Freshwater Molasse sediments represent the last cycle of clastic sedimentation during the evolution of the North Alpine Foreland Basin. They are characterized by small-scale lateral and temporal facies changes that make intra-basin stratigraphic correlations at regional scale difficult. This study provides new U–Pb zircon ages as well as revised 40Ar/39Ar data of volcanic ash horizons in the Upper Freshwater Molasse sediments from southern Germany and Switzerland. In a first and preliminary attempt, we propose their possible correlation to other European tephra deposits. The U–Pb zircon data of one Swiss (Bischofszell) and seven southern German (Zahling, Hachelstuhl, Laimering, Unterneul, Krumbad, Ponholz) tuff horizons indicate eruption ages between roughly 13.0 and 15.5 Ma. The stratigraphic position of the Unterneul and Laimering tuffs, bracketing the ejecta of the Ries impact (Brockhorizon), suggests that the Ries impact occurred between 14.93 and 15.00 Ma, thus assigning the event to the reversed chron C5Bn1r (15.032–14.870 Ma) which is in accordance with paleomagnetic evidence. We combine our data with published ages of tuff horizons from Italy, Switzerland, Bavaria, Styria, Hungary, and Romania to derive a preliminary tephrochronological scheme for the Middle Miocene in Central Europe in the age window from 13.2 to 15.5 Ma. The scheme is based on the current state of knowledge that the Carpathian–Pannonian volcanic field was the only area in the region producing explosive calc-alkaline felsic volcanism. This preliminary scheme will require verification by more high-quality ages complemented by isotopic, geochemical and paleomagnetic data.

A strontium isotope and trace element geochemical study of dolomite-bearing bentonite deposits in Bavaria (Germany)

AbstractThe Landshut bentonites that formed from Ca- and Mg-poor rhyolitic tuffs in a fluviatile-lacustrine depositional environment of the Miocene Upper Freshwater Molasse, southern Germany, contain abundant palustrine, pedogenic and groundwater carbonates. Geochemical analyses of dolomites, calcites and smectites from bentonites of various environments by X-ray diffraction, thermal ionization mass spectrometry, inductively coupled plasma-mass spectrometry, and handheld X-ray fluorescence yield new insights into the compositions of fluids and sources of imported components involved in carbonate formation and bentonitization, as well as the timing of bentonite formation. Evaporated, Sr-rich brackish surface water with a molar Mg/Ca ratio of 2–5, derived mostly from the weathering of detrital carbonates, was involved in dolomite and bentonite formation in palustrine and some pedogenic environments. However, Sr-poor groundwater with a molar Mg/Ca ratio of ∼ 1 and a stronger silicate weathering component caused bentonite and calcite formation in strictly pedogenic and groundwater settings. The 87Sr/86Sr and molar Mg/Ca in the smectite interlayers indicate later cation exchange with water having more radiogenic Sr sources and smaller molar Mg/Ca ratios. The Rb-Sr data indicate the common presence of detrital illitic phases in the <0.2 μm fractions of the bentonites. Cogenetic palustrine dolomite and a single smectite residue sample which lacks this detrital illitic phase provide an age constraint for bentonitization at 14.7 ± 4.1 Ma identical to primary ash deposition. Thus a rapid onset of bentonitization of accumulated ash and dolomite formation in evaporation-driven wetland environments is indicated for the genesis of the Landshut bentonites.