The sedimentary succession of the Col de la Plaine Morte area (Helvetic Alps, central Switzerland) documents the disappearance of the northern Tethyan Urgonian platform in unprecedented detail and suggests stepwise platform demise, with each drowning phase documented by erosion and phosphogenesis. The first identified drowning phase terminated Urgonian carbonate production in a predominantly photozoan mode. Using a correlation of the whole-rock δ 13 C record with the well-dated record from SE France, its age is inferred to as Middle Early Aptian (near the boundary between the weissi and deshayesi zones). A subsequent drowning phase is dated by ammonites and by a correlation of the whole-rock δ 13 C record as Late Early Aptian (late deshayesi to early furcata zone). A third drowning phase provides an ammonite-based age of Early Late Aptian (subnodosocostatum and melchioris zones) and is part of a widely recognized phase of sediment condensation and phosphogenesis, which is dated as latest Early to Middle Late Aptian (late furcata zone to near the boundary of the melchioris and nolani zones). The fourth and final drowning phase started in the latest Aptian (jacobi zone) as is also indicated by ammonite findings at the Col de la Plaine Morte. The phases of renewed platform-carbonate production intervening between the drowning phases were all in a heterozoan mode. During the ultimate drowning phase, phosphogenesis continued until the Early Middle Albian, whereas condensation processes lasted until the Middle Turonian. Coverage of the external margin of the drowned Urgonian platform by a drape of pelagic carbonates started only in the Late Turonian. During the Santonian, the external part of the drowned platform underwent normal faulting and saw the re-exposure of already lithified Urgonian carbonates at the seafloor. Based on the here-inferred ages, the first drowning phase just precedes oceanic anoxic episode 1a (OAE 1a or "selli event") in time, and the second drowning phase partly overlaps with OAE 1a. The onset of the third drowning event slightly predates two further periods of increased organic-matter accumulation in the Vocontian Basin (Noir and Fallot levels), and the onset of the fourth and final drowning phase may coincide with two further periods of increased organic-matter accumulation in the Vocontian Basin (Jacob and Kilian levels, part of OAE 1b). These correlations indicate a relationship between the so-called anoxic episodes and the stepwise demise of the Urgonian platform, even if the onset of environmental change is registered earlier on the platform than in basinal sediments.
Early Aptian sediments mostly referred to as "upper Orbitolina beds" are known from a relatively small number of outcrop areas throughout the distal part of the Helvetic Zone of Switzerland, Austria and Germany. These sediments are here formally defined as a new, basal member of the Garschella Formation; the Grünten Member. Equivalent and correlatable sediments also exist in the Vercors region of the French Dauphinée Zone. The historical type section (holostratotype) of the Grünten Member is situated on the Grünten Mountain in southern Germany. A new type section (lectostratotype) for the Grünten Member is chosen in the better suited Bauen-Brisen area of Central Switzerland and an additional reference section (hypostratotype) is defined near the Rawil Pass in the Bernese Oberland of Switzerland. In relatively proximal settings, the Grünten Member overlies Early Aptian limestones of the Urgonian Carbonate Platform (Schrattenkalk Formation), documenting its demise and early "drowning". In relatively distal settings, it overlies the contemporary hemipelagic sediments of the Drusberg and Mittagspitz Formations. In complete successions, the Grünten Member is in turn overlain by the basal, phosphoritic Luitere Bed of the Brisi Member (Garschella Formation) documenting the continuing "drowning" of the Urgonian Carbonate Platform in the Late Aptian. The Grünten Member essentially consists of a single stratigraphic sequence, beginning with a marly base and gradually passing to crinoidal limestones at its top. Rare ammonite finds as well as sequence stratigraphic correlations suggest a late Early Aptian age (parts of the Deshayesi and Furcata Ammonite Zones). In the relatively proximal reference section of Rawil, the Grünten Member contains two phosphoritic horizons. Phosphateenriched horizons are also known from other proximal sections of the Grünten Member. ZUSAMMENFASSUNGAus einer relativ kleinen Anzahl von Aufschlussgebieten quer durch den distalen Teil der Helvetischen Zone der Schweiz, Österreichs und Deutschlands sind frühaptische Sedimente, zumeist unter dem Namen "obere Orbitolinenschichten" bekannt. Diese Sedimente werden hier, unter dem Namen Grün-ten-Member, formell als neues basales Member der Garschella-Formation definiert. Äquivalente und korrelierbare Sedimente existieren auch in der Vercors-Region der französischen Zone Dauphinoise. Das historische Typusprofil (Holostratotyp) des Grünten-Members liegt auf dem Grünten-Gipfel in Süd-deutschland. Ein neues Typusprofil (Lectostratotyp) für das Grünten-Member wird in der besser geeigneten Bauen-Brisen Region der Zentralschweiz gewählt und ein zusätzliches Referenzprofil (Hypostratotyp) wird nahe des Rawilpasses im Berner Oberland der Schweiz definiert. In relativ proximalen Situationen überlagert das Grünten-Member frühaptische Kalke der Schrattenkalk-Plattform (Schrattenkalk-Formation), ihren Niedergang und ihr frühes "Ertrinken" dokumentierend. In relativ distalen Positionen überlagert es die gleichaltrigen hemipelagischen Sedimente der Drusberg-und ...
A variety of geological, hydrochemical and isotopic techniques were applied to explain the origin of exceptionally high radon levels in the St.Placidus spring near the city of Disentis in the Swiss Alps, where an average of 650 Bq/L 222 Rn was measured. 222 Rn is a radioactive noble gas with a half-life of 4 days, which results from the disintegration of radium ( 226 Ra). The high radon levels can neither be explained by generally increased radium content in the fractured aquifer rock (orthogneiss), nor by the radium concentration in the spring water. It was possible to show that there must be a productive radium reservoir inside the aquifer but very near to the spring. This reservoir mainly consists of iron and manganese oxides and hydroxides, which precipitate in a zone where reduced, iron-rich groundwaters mix occasionally with oxygen-rich, freshly infiltrated rainwater or meltwater. The iron, as well as the reduced and slightly acid conditions, can be attributed to pyrite oxidation in the recharge area of the spring. Radium cations strongly adsorb and accumulate on such deposits, and generate radon, which is then quickly transported to the spring with the flowing groundwater.
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