• journal_title：Micropaleontology
• Contributor：Luis O’Dogherty ; Markus Bill ; Špela Gorican ; Paulian Dumitrica ; Henri Masson
• Publisher：Micropaleontology Project
• Date：2005-
• Format：text/html
• Language：en
• Identifier：10.2113/gsmicropal.51.6.425
• journal_abbrev：Micropaleontology
• issn：0026-2803
• volume：51
• issue：6
• firstpage：425
• section：Paleoceanography

The determination of radiolarite ages of supraophiolitic rocks date the expansion age of oceanic crust. Radiolarites from the Gets nappe, a decollement cover nappe, provide the means of dating selected localities of outcropping oceanic crust based on their radiolarian faunas. Some studied samples from the ophiolitic mélange (Perrière series) have a very well preserved and highly diverse radiolarian fauna of biochronological significance. The age of the radiolarites is established by correlation with the biozonation of Baumgartner et al. (1995b), which indicates a Bathonian age for the oldest radiolarian assemblages. Accordingly, these radiolarites represent remains of the oldest sediments recorded after the opening of the Piemont-Ligurian Ocean. This age is in agreement with those recently established by isotopic methods (166 ± 1 Ma U-Pb and 165.9 ± 2.2 Ma ⁴⁰Ar/³⁹Ar) in the associated gabbros from the ophiolitic mélange. The isotopic age and paleontological results are important because they represent the oldest dating of the oceanic crust of the Piemont-Ligurian Ocean, proving a Late Bajocian-Early Bathonian age for the oceanization in the western Tethys.

The systematic part presents a complete Bathonian radiolarian assemblage from two of the best preserved samples; the illustrated assemblage contains 180 species attributed to 66 genera (44 nassellarians, 22 spumellarians and 1 entactinarian). Twenty new species and three new genera (Helvetocapsa, Plicaforacapsa and Theocapsomella) are formally described.