Freshwater Molasse Research Articles

Distal alluvial deposits in a foreland basin setting‐the Lower Freshwater Molasse (Lower Miocene), Switzerland: sedimentology, architecture and palaeosols

Distal alluvial deposits in a foreland basin setting‐the Lower Freshwater Molasse (Lower Miocene), Switzerland: sedimentology, architecture and palaeosols

Distal alluvial deposits in a foreland basin setting—the Lower Freshwater Miocene), Switzerland: sedimentology, architecture and palaeosols

ABSTRACTThe Lower Freshwater Molasse (Untere Susswasser Molasse) crops out over a wide area of the Swiss Molasse Basin. Coarse grained alluvial fan conglomerates dominate in proximal basin areas along the Alpine front. These conglomerates pass northwards into sandstones and mudstones of an extensive northeastward draining meandering river system which ran parallel to the basin axis. Sedimentological study of outcrops, quarry exposures and boreholes in the basal Miocene (‘Aquitanian‘) has permitted detailed facies analysis of this distal alluvial sequence. The distal Aquitanian is made up of distinct ‘architectural elements’characterized by their geometries and sedimentary structures. Each may be assigned to a particular depositional setting: meander belt, levees, crevasse channels and splays, overbank fines and palaeosols, and lacustrine.Meander belt sandstones were deposited in mixed load channels with a dominant bedload component. Sandstones commonly comprise amalgamated and locally stacked ribbon bodies 2–15 m thick and 150–1500 m wide. Interbedded rippled, laminated and mottled fine grained levee sandstones and siltstones form lenticular packages up to 3 m thick and 30–100 m across. Small scale crevasse channel sandstones 2–4 m thick and 5–10 m across pass laterally into metre scale, medium to fine grained crevasse sandstone sheets. Rare laminated lacustrine siltstones occur only in the north‐east part of the basin. Floodplain mudstones and marls make up the remainder of the succession. These display a variety of pedogenic features recording cyclical palaeosol development. Palaeosols show strong variations in morphology and maturity both laterally across the floodplain and downstream along the basin axis, reflecting local variation in aggradation rate associated with proximity to alluvial channel courses as well as regional variation in subsidence and floodplain drainage.Analysis of the organization and distribution of the various sediment bodies permits reconstruction of the fluvial system and allows development of a model for the sedimentary architecture of the Lower Freshwater Molasse in the study area. Integration of palaeosol studies into a well defined architectural framework assists recognition of areal facies belts and may aid location of sand‐prone sequences in the subsurface.

Fresh-water carbonates from the Lower Freshwater Molasse (Oligocene, western Switzerland): sedimentology and stable isotopes

The Lower Freshwater Molasse of western Switzerland comprises a thick series of continental deposits of Late Oligocene-Early Miocene age. Fresh-water carbonates occur at two main horizons within this succession. Lower Chattian “palustrine” carbonates (Calcaires Inférieurs) show a shallow fresh-water fauna/flora of ostracods and charophytes, but display clear evidence of subaerial exposure in the form of glaebule/pisoid formation, circumgranular cracking, rhizoliths and microkarstic cavities. Repeated desiccation led to locally intense modification by pedogenesis. These horizons record the development of shallow, ephemeral lakes at the northern margin of the Swiss Molasse Basin. Stable isotope analyses were carried out on 46 calcite samples. Data from matrix and intraclasts reveal typical fresh-water compositions ( δ 13C = −5 to −7.5‰; δ 18O = −5.5 to −9‰). A weak co-variant trend suggests deposition in hydrologically closed lakes, although the range of δ 13C values recorded is also consistent with pedogenetic overprinting associated with subaerial exposure. Spar cements and vadose crystal silts display δ 13C compositions from −6 to −7‰, but show light δ 18O values (from −10 to −11‰), recording formation from meteoric waters. Upper Chattian carbonates (Calcaires d'eau douce et dolomie) include algal-ostracodal laminites, interpreted as profundal lake deposits, as well as bioturbated shallow lake charophyte-ostracod mudstones and wackestones, sandy wackestones and white dolomite. Stable isotope analyses (20 calcites, 2 dolomites) show δ 13C values from −2 to −6‰, and δ 18O from −6 to -11‰. Data for laminites and biomicrites plot in different fields; variations in carbon isotopic composition may be attributable to higher organic productivity during high lake stands (the laminites show heavier δ 13C values) or to areal differences in the proportions of biogenic, authigenic and detrital carbonate ( δ 13C values are generally higher in areas of greater detrital carbonate supply). The heavier δ 18O values shown by the dolomites ( δ 13 C = −3‰ = δ 18 O = 0 to −1‰) suggest formation from evolved, evaporitic lake waters. These carbonates record deposition in an extensive, possibly deeper lake complex subject to clastic input from the Alps in the south.

Sporotrapoidites erdtmanii(Nagy) Nagy, a trapaceous pollen species pertaining to the Oligocene to Pliocene genusHemitrapaMiki

Abstract The dispersed pollen species Sporotrapoidites erdtmanii (Nagy 1979) Nagy 1985 from the Upper Freshwater Molasse (middle Miocene) of the Gallenbach toxic waste dump in southern Germany is correlated with the fossil plant genus Hemitrapa Miki 1952. This pollen species, exhibiting the unique pollen features of the Trapaceae, is described in detail. Morphometric comparison of fossil pollen pertaining to Trapa (Sporotrapoidites illingensis Klaus 1954) with modern pollen of an extant species (Trapa natans L. 1753) clearly differentiates between Hemitrapa and Trapa pollen, Hemitrapa pollen being substantially smaller. Hemitrapa fruits (and pollen) are usually found in combination with other water plants in European localities that reflect a typical Paleo-Potameton/Trapeton in eutrophic lakes in a warm temperate climate.

Measurements of the phase transformation temperature of gypsum-anhydrite, included in quartz, by microthermometry and Raman microprobe techniques

Solid inclusions in quartz samples, collected in Switzerland from the freshwater molasse of Les Éplatures (Vindobonian), from the upper marine molasse of Tavannes (Burdigalian) and from the green marl of Cornaux (Purbeckian), were studied by microthermometry and Raman microprobe techniques. Microthermometry showed that in a temperature range from 130° to 180°C the solid inclusions changed from clear and transparent to dark and opaque. This temperature range corresponds to the gypsum-anhydrite phase transition. Further experiments using a Raman microprobe, showed that the Raman vibrational spectrum at room temperature contains only peaks at the frequency bands of gypsum. Successive heating to 100°, 150° and 200°C indicated partial transformation at ∼150°C, with the intensity of the gypsum bands diminishing as those of anhydrite appeared. The bands of coordinated water shifted towards higher frequency ranges. The transition terminates at 200°C in 24 hr. The Raman spectrum then only contains anhydrite bands, the bands of gypsum having virtually disappeared. These experiments enable, the observation in situ of the transformation of gypsum inclusions to anhydrite, and the determination of the transition temperature.

Rb [sbnd]Sr systematics of rocks related to the Ries Crater, Germany

Rb Sr whole rock/biotite ages of crystalline basement rocks from Ries Crater are 323 ± 8Ma; initial 87Sr/ 86Sr rat are 0.7081 ± 0.0007. These values compare perfectly with those for Moldanubian rocks exposed in the Bayerischer Wald and Schwarzwald. It is demonstrated that impact-related shock pressures up to 15 GPa and temperatures as high as 300°C did not disturb the Rb Sr isotopic systems of the rocks. Comparison of Sr isotopic compositions of Tertiary Upper Freshwater Molasse sediments with those of moldavites suggests that such sediments can be regarded as source material of these tektites. Our data for components of the sediments show that a mixture of clay (weathered crystalline rocks) and secondary carbonates, in addition to detrital quartz, can explain the observed range of 87Sr/ 86Sr ratios in moldavites. A similar comparison of moldavites with bentonites from the Tertiary molasse definitely rules out a genetical relationship between these two materials. We regard liquid/gas-filled bubbles in bentonite glasses as proof of their volcanic nature.

Ground freezing aids Swiss tunnel construction : Aerni, K; Mettier, K Tunn Tunnlg, V13, N3, April 1981, P52–P53

Ground freezing, currently gaining in popularity, was selected as the most suitable method of providing ground stability in the moraine section of an urban motorway tunnel under Zurich where clearance under some of the buildings was as little as 6 M. The ground consists of interbedded marl and sandstone (freshwater molasse), and an area of well compacted moraine with inclusions of non-cohesive silty sand material and the presence of some water under an artesian pressure of up to 3 bar. (Author/TRRL)

Non-marine Rhizocorallium (trace fossil) from the Upper Freshwater Molasse (Upper Miocene) of southern Germany

Non-marine Rhizocorallium (trace fossil) from the Upper Freshwater Molasse (Upper Miocene) of southern Germany

Sedimentpetrographische Beobachtungen aus der Oberen Süßwassermolasse im Bereich von Freising bis Landshut

Sedimentpetrographische Beobachtungen aus der Oberen Süßwassermolasse im Bereich von Freising bis Landshut