Pliensbachian, Early Jurassic radiolarians from Mount Rettenstein in the Northern Calcareous Alps, Austria TIM CIFER, ŠPELA GORIČAN, HANS-JÜRGEN GAWLICK, and MATTHIAS AUER Cifer, T., Goričan, Š., Gawlick, H.-J., and Auer, M. 2020. Pliensbachian, Early Jurassic radiolarians from Mount Retten- stein in the Northern Calcareous Alps, Austria. Acta Palaeontologica Polonica 65 (1): 167–207. One of the best preserved Early Pliensbachian radiolarian assemblages from the Western Tethys is described from the grey marly limestone exposed at Mount Rettenstein in the Northern Calcareous Alps, south of the Dachstein Massif. Fourty-five genera and 71 species are documented and illustrated here. Four species are newly described: Tozerium filzmoosense Cifer sp. nov., Loupanus pliensbachicus Cifer sp. nov., Thurstonia? robusta Cifer sp. nov., and Ares rettensteinensis Cifer sp. nov. Radiolarian age is in accordance with ammonoid data from the overlying red marly lime- stone, which was assigned to the upper part of the Lower Pliensbachian. The best equivalent for the radiolarian-bearing lithology is the Dürrnberg Formation, characteristic of the open-marine Hallstatt facies zone. Previously published radiolarian data from the Dürrnberg Formation were re-evaluated and the originally proposed age assignments revised. At two localities, the published Hettangian–Sinemurian age was emended to the early Early Pliensbachian that is in ac- cordance with the age of radiolarians from Mount Rettenstein. We compared the studied fauna from Mount Rettenstein also with two other rich radiolarian assemblages, one from another locality in the Dürrnberg Formation and one from the Gümüslü Allochthon in Turkey, which were assigned to the late Early Pliensbachian and are somewhat younger than the assemblages studied herein. Key words: Radiolaria, Polycystina, systematics, stratigraphy, Jurassic, Western Tethys, Eastern Alps, Austria. Tim Cifer [[email protected]] and Špela Goričan [[email protected]], Ivan Rakovec Institute of Palaeontology, Research Centre of the Slovenian Academy of Sciences and Arts, Novi trg 2, 1000 Ljubljana, Slovenia. Hans-Jürgen Gawlick [[email protected]] and Matthias Auer [[email protected]], Monta- nuniversität Leoben, Chair of Petroleum Geology, Peter-Tunner-Straße 5, 8700 Leoben, Austria. Received 19 March 2019, accepted 9 July 2019, available online 15 January 2020. Copyright © 2020 T. Cifer et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. as blocks in Middle to lower Upper Jurassic mélanges along Introduction the Neotethyan Belt (Missoni and Gawlick 2011 for details). Well-preserved Early Jurassic radiolarian assemblages Radiolarian dating is important for reconstruction and under- standing of the tectono-stratigraphic evolution of the Western are also rare on a global scale (e.g., Yeh 1987; Yao 1997; Tethys and the Northern Calcareous Alps as part of that paleo- Carter et al. 1988, 1998; Matsuoka 1991, 2004; Yeh and geographic realm (Fig. 1). In the Jurassic siliceous deep-wa- Cheng 1998; Whalen and Carter 2002; Goričan et al. 2003; ter sediments (Fig. 2), other index fossils like ammonoids Yeh and Yang 2006; Bertinelli and Marcucci 2011) and are very rare, therefore, Jurassic radiolarians were the focus in the Western Tethyan realm only two lithostratigraphic of many studies in the Northern Calcareous Alps (Kozur units with diverse and well-preserved Pliensbachian assem- and Mostler 1990; Gawlick and Suzuki 1999; Gawlick et al. blages have been described so far: the Dürrnberg Formation 1999, 2001, 2003, 2004; Wegerer et al. 1999, 2001; Missoni in Austria (O’Dogherty and Gawlick 2008) and the grey et al. 2001a, b, 2005; Suzuki et al. 2001; Suzuki and Gawlick bedded limestone of the Gümüşlü Allochthon in Turkey 2003a, b; O’Dogherty and Gawlick 2008; O’Dogherty et al. (De Wever 1981a, b, 1982a, b; Pessagno and Poisson 1981). 2017), but only a few of these studies were concentrated on Pliensbachian and Toarcian radiolarians were revised in a the Early Jurassic taxa (Kozur and Mostler 1990; Gawlick catalogue (Goričan et al. 2006) that served as a taxonomic et al. 2001; O’Dogherty and Gawlick 2008). A precise radi- basis to construct a global radiolarian zonation for this time olarian stratigraphy is needed for the facies reconstruction period (Carter et al. 2010). Radiolarian-bearing successions of the outer passive margin of the Neo-Tethys Ocean in the with ammonite calibration are very rare on a global scale; of Jurassic; the relics of the outer margin are mainly preserved all Pliensbachian successions studied by Carter et al. (2010) Acta Palaeontol. Pol. 65 (1): 167–207, 2020 https://doi.org/10.4202/app.00618.2019 168 ACTA PALAEONTOLOGICA POLONICA 65 (1), 2020 A Juvavic units (provenance of the Meliata Vienna and Hallstatt Mélange) Molasse Zone Tirolic units and equivalents with Meliata, Teichl Fault B Salzburg Hallstatt, Tauglboden and Rofan Mélange A l p s Ennstal Fault Bavaric units and equivalents C a l c a r e o u s Lower Austroalpine and Central Alpine N o r t h e r n Rechnitz Mesozoic units and equivalents Niedere window Palaeozoic units, weakly metamorphosed Silvretta Tauern window Tauern Styrian crystalline basement nappes Austroalpine mega-unit Ötztal Lienz Dolomites aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaEngadin Basin Penninic and Helvetic zones window Periadriatic Lineament aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaD r a u - R a n g e 50 km aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaKoschuta and Hahnkogel units major disintegration lines during aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaSouthernAlps Miocene lateral extrusion B Salzburg Ebensee ultra Tirolic unit Salzach valley St. Gilgen upper Tirolic unit Osterhorn SonntagshornBlock Bad Ischl Hallein Block lower Tirolic unit Berchtesgaden BD Block Bad Goisern Lofer Berchtes- Bad Aussee gaden Gosaukamm Abtenau Te Hallstatt Bad Mitterndorf present-day erosional margin of NCA Dachstein Block Werfen Re graben ennengebirge Gröbming Filzmoos strike-slip fault Hochkönig-TBlocks Mandling Blocks pre-Cretaceous nappe borders Schladming 10 km Fig. 1. A. Structural overview maps of the Alpine orogen, showing the situation of the central Northern Calcareous Alps. B. The middle sector of the central Northern Calcareous Alps with locations mentioned in the text indicated (modified from Frisch and Gawlick 2003). Abbreviations: Re, Mount Rettenstein; BD, Bad Dürrnberg; Te, Teltschengraben. only those in western North America were dated with am- Klaus Formation (Auer et al. 2009). The latter is overlain by monites. Therefore, the studied succession in the Northern Oxfordian radiolarites of the Ruhpolding Radiolarite Group Calcareous Alps provides unique opportunity to test the age (Auer et al. 2009) and the Kimmeridgian–Tithonian Plassen ranges of radiolarian species with ammonite dating. Formation (Schlagintweit et al. 2007) that represents the The tectono-stratigraphy of Mount Rettenstein (Fig. 3) youngest part of the succession on Mount Rettenstein (Auer has been intensively studied for nearly 100 years with var- et al. 2006, 2009). Well-preserved Early Jurassic radiolar- ious attempts to explain the stratigraphy and its tectonic ians from the basal grey marly limestone were attributed framework (Trauth 1926, 1928; Spengler 1943; Ganss et to the Early Pliensbachian (Goričan et al. 2009; Cifer et al. al. 1954; Tollmann 1960; Auer et al. 2009). The radiolari- 2017) but not studied in detail. an-bearing limestone form the lower part of the Rettenstein The aim of this study is a precise age assignment and a sys- succession sensu stricto (Auer et al. 2009; Fig. 3C) occur tematic description of radiolarian assemblages from Mount above the Hallstatt Mélange (in the sense of Gawlick and Rettenstein. These rich assemblages may augment signifi- Frisch 2003), which is underlain by rocks of the Werfen cantly the known radiolarian diversity in the Pliensbachian imbricated Zone. The Rettenstein succession sensu stricto of the Western Tethys and improve the published strati- (Fig. 4) consists of Lower Jurassic grey, partly siliceous graphic ranges of taxa. A comparison with previously known marly limestone at the bottom, followed by red limestone Pliensbachian assemblages of this realm is also presented. often attributed to the Adnet Formation (Tollmann 1960; The type material of the new species, described herein, is Hirschberg and Jacobshagen 1965). In contrast, Meister deposited in the palaeontological collection of the Slovenian and Böhm (1993) pointed out that there is no difference Museum of Natural History under numbers PMS 2393– in the microfacies between the grey marly limestone and 2399. These collection numbers refer to SEM stubs with the red marl. The Middle Jurassic Klaus Formation follows several specimens; each specimen/photograph has an addi- above a hiatus. Upsection, the Rettenstein Debris Flow cuts tional number indicated under the heading Type material. erosionally through the higher part of the Middle Jurassic Other illustrated specimens are stored at ZRC SAZU, PIIR. CIFER ET AL.—EARLY JURASSIC RADIOLARIANS FROM THE ALPS 169 Bavaric units Tirolic units Jurassic Hallstatt Mélange = resedimented Juvavic Lower Upper units (eroded nappe stack) Berriasian drowning Cretaceous Aptychus Aptychus Lst. Oberalm Fm.