Departement Geowissenschaften – Universität Freiburg
Foraminifera, Ostracoda and other microfossils of the
Southern Upper Rhine Graben
Claudius Pirkenseer
About 270 samples from two drillcores and several field outcrops covering the entire Paleogene
succession of the southern Upper Rhine Graben were investigated on microfossils. The main focus was
aimed at a complete record of Foraminifera (about 180 taxa) and Ostracoda (50 taxa) and their
palaeoenvironmental, palaeogeographic and biostratigraphic implications. A thorough taxonomic
description of the ostracod assemblages was carried out. Additionally treated fossil groups include
Charophyta, fish otoliths, Bolboforma and calcareous nannoplankton. For the first time bird remains are
documented from the southern Upper Rhine Graben.
While the entire Eocene succession proved to be nearly barren of fossils, the two Rupelian
transgression-regression cycles (Earliest Rupelian “Zone fossilifère”, Late Rupelian “Série grise”) in the
Upper Rhine Graben are well traced by the correlating microfossil assemblages.
Both transgressions start off with fully marine outer shelf to upper bathyal Ostracoda and
Foraminifera assemblages. In both cases the maximum flooding is achieved early in the sequence
cycle. In the second Rupelian transgression the benthic and small sized planktonic Foraminifera
associations indicate cold to temperate water temperature. While generally well-oxygenated bottom
waters and sediments prevailed during the initial phase (“Marnes à foraminifères”), they abruptly
changed to suboxic and anoxic conditions in the subsequent “Schistes à poissons”. Nannofossils
indicate increased freshwater influx or occasional over-stratification in this unit.
The corresponding regressive phases of the “Zone fossilifère” and the “Série grise” are
characterized by mass occurrences of brackish ostracods. The two species Hemicyprideis helvetica and
H. basiliensis were analysed against the palaeoecologic background of the “Marnes à Cyrènes” and are
now interpreted to represent two ecomorphotypes of the species Hemicyprideis helvetica.
Palaeobiogeographic relations confirm a marine incursion of northwest European provenance in
the Early Rupelian “Zone fossilifère”. Similar results apply to the “Série grise” deposits. While the Upper
Rhine Graben was not connected to the Paratethys during the first Rupelian transgression, some
simultaneously occurring ostracod species and the benthic Foraminifera associations of the “Série grise”
suggest at least occasional connections between the two basins in the Late Rupelian. This interpretation
is supported by a higher rate of endemism of the ostracod assemblages in the “Zone fossilifère” than in
the “Série grise”.
The data derived from planktonic Foraminifera assemblage ranges is distorted by the
simultaneous occurrence of facultative reworked Eo-Oligocene species and implies an estimate of a Mid
P20 to P21a age for the “Série grise” deposits. This corresponds to a NP23-24 age indicated by
calcareous nannoplankton in the basal “Série grise”, by Charophyte assemblages from the “Marnes à
Cyrènes” and the lower part of the Niederroedern Formation (possibly Chara microcera – zone) and by
a Bolboforma event in the middle “Marnes à Cyrènes” (Bolboforma latdorfensis zone). The occurrence
of Palaeolebias symmetricus (OT-02 zone) suggests a Late Rupelian to earliest Chattian age for the
Niederroedern Formation in the research area.
Abundant reworked mainly Cretaceous and Lutetian to Priabonian planktonic Foraminifera from
the Late Rupelian “Série grise” are documented, figured and interpreted in relation to similar
occurrences in the northern part of the Upper Rhine Graben and the Mainz Basin as well as possible
source areas. Abundant reworking starts in the Late Rupelian lower “Couches à Mélettes” and reaches
its acme in the “Marnes à Cyrènes”. Only sparse records are documented from the subsequent
Niederroedern Formation.
The Foraminifera are supposed to be reworked from the alpine domain by a northwards trending
drainage system in accordance with a extensive prograding deltaic-system located close to the southern
margin of the research area. Geodynamic implications include already uplifted Eocene sediments within
the central and southwestern Helvetic realm in the Late Rupelian.
Jury:
Prof. Jean-Pierre Berger, Leiter der Dissertation, Universität Freiburg, Schweiz
Prof. Bettina Reichenbacher, Ext. Gutachterin, Universität München, Deutschland
Dr. Peter Schäfer, Ext. Gutachter, Landesamt für Geologie und Bergbau,
Rheinland Pfalz, Deutschland
Dr. Silvia Spezzaferri, Interne Gutachterin, Universität Freiburg, Schweiz
Prof. Andreas Strasser, Jurypräsident, Universität Freiburg, Schweiz