Middle and Late Jurassic radiolarians from the Neotethys suture in the Eastern Alps

Abstract. Cherty limestones, marls and radiolarites are widespread in the Hallstatt Melange of the Northern Calcareous Alps. The melange was formed during the Neotethyan orogeny in a series of deep-water basins that progressively developed in front of the advancing nappe front. The low thermal overprint of these rocks favors the good preservation of radiolarians (polycystines) that have been used for dating and reconstructing the Jurassic tectonostratigraphy of the area. This paper describes rich Middle—Late Jurassic radiolarian faunas from four localities in the Hallstatt Melange near Bad Mitterndorf in Austria. Two different successions, both spanning from the Bathonian to the Oxfordian, are dated. In the first succession, the radiolarites are intercalated between or occur as matrix in mass-flow deposits originating from the accretionary wedge. The second succession is nearly 100m thick but is devoid of mass-flow deposits and documents a continuous radiolarite deposition in greater distance from the nap...