Lithostratigraphy and Biostratigraphic Markers
of the Reuchenette Formation (Late Jurassic; Kimmeridgian)
in Northwestern Switzerland
*Geologisch-Paläontologisches
Institut, Bernoullistrasse 32, CH-4056 Basel;
**Naturhistorisches Museum, Augustinergasse 2, CH-4001
Basel;
*** Office du Patrimoine historique, Section de
Paléontologie, Hôtel des Halles, CH-2900
Porrentruy;
****Staatliches Museum für Naturkunde, Rosenstein 1,
D-70191 Stuttgart
The facies of the deposited calcareous shallow water platform sediments of the Reuchenette Formation (Kimmeridgian sensu gallico) in Northwestern Switzerland is mainly controlled by relative sea level fluctuations. Sedimentological investigations and analysis of lithology of several sections from the northern (Ajoie) and the southern Jura mountains (region of Biel) reveal, that the Kimmeridgian deposits can be subdivided into sedimentary cycles of different scales.
Deposits of the Lower Kimmeridgian indicate depositional environments shifting from subtidal conditions in semi-restricted lagoons to low energy conditions in tidal flats. The sediments are mainly composed of marly and bioturbated wackestones (subtidal) with brackish and freshwater excursions and signs of emersion (mudcracks, dinosaur tracks, birds eyes, plant remains).
Deposits of the Upper Kimmeridgian indicate more open marine sub- to intertidal depositional environments (coral hedges, bio-laminites, cross bedding). The sediments mainly consist of mud- and grainstones.
Marl excursions in the Lower and Upper Kimmeridgian (Banné Member and virgula-Unit) hypothetically deposited during phases of flooding of the platform, show amongst others faunal elements the presence of ammonites. These ammonites indicate that both units are older than previously assumed. The Banné Member can be assigned to the divisum-Zone the virgula-Unit to the Upper acanthicum-Zone.
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