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  • Author: Felix Schlagintweit x
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Abstract

The benthic foraminifer Rosalina binkhorsti Reuss, 1862, was cosmopolitan in Late Cretaceous to early Paleogene shallow-water seas. It possesses a distinctive composite wall made of a continuous, agglutinated layer discontinuously covered by secondary hyaline outer deposits. Its taxonomic position, phylogeny, morphology, wall structure, and composition have been debated for a long time. Based on abundant, well-preserved material from the Danian of the Kambühel Formation in the Northern Calcareous Alps, Austria, we identify elements in the here emended species Stomatorbina binkhorsti which support a strong affinity to the order Textulariida, within the genus Stomatorbina Dorreen, 1948. Usually regarded as free (non-fixing), S. binkhorsti is here illustrated attached to small bioclasts in high-energy carbonate settings. The attached specimens are juvenile forms with a wall covered by massive hyaline deposits. This observation suggests that secondary lamellar parts added to the wall may have served for stabilisation or fixation to the substrate.

Rosalina binkhorsti Reuss, 1862, war eine in den Flachwassermeeren der Oberkreide und des frühen Paläogens kosmopolitische benthonische Foraminifere. Sie besitzt eine zusammengesetzte Wand, bestehend aus einer kontinuierlichen agglutinierten Lage welche diskontinuierlich von äusseren sekundär-hyalinen Abschnitten bedeckt ist. Ihre taxonomische Position, Phylogenie, Morphologie, Wandstruktur und –zusammensetzung ist seit langem umstritten. Basierend auf gut erhaltenem und reichhaltigem Material aus dem Danium der Kambühel Formation in den Nördlichen Kalkalpen von Österreich, werden Charakteristika identifiziert, welche nachhaltig eine Affinität zur Gattung Stomatorbina Dorreen, 1948 innerhalb der Ordnung Textulariida belegen. Diese Foraminiferenart, gewöhnlich als frei lebend (nicht fixiert) angesehen, wird illustriert fixiert an kleine Bioklasten in einem hochenergetischen karbonatischen Ablagerungsmilieu. Die fixierten Formen sind gewöhnlich juvenile Exemplare deren Wand mehr oder weniger massiv von hyalinen Ablagerungen bedeckt ist. Dies lässt vermuten, dass sekundäre lamellare Ablagerung, die der Wand hinzugefügt werden, eine Rolle in der Stabilisierung oder der Fixierung auf dem Substrat spielten.

Abstract

The causes for the Middle to Late Jurassic tectonic processes in the Northern Calcareous Alps are still controversially discussed. There are several contrasting models for these processes, formerly designated “Jurassic gravitational tectonics”. Whereas in the Dinarides or the Western Carpathians Jurassic ophiolite obduction and a Jurassic mountain building process with nappe thrusting is widely accepted, equivalent processes are still questioned for the Eastern Alps. For the Northern Calcareous Alps, an Early Cretaceous nappe thrusting process is widely favoured instead of a Jurassic one, obviously all other Jurassic features are nearly identical in the Northern Calcareous Alps, the Western Carpathians and the Dinarides. In contrast, the Jurassic basin evolutionary processes, as best documented in the Northern Calcareous Alps, were in recent times adopted to explain the Jurassic tectonic processes in the Carpathians and Dinarides. Whereas in the Western Carpathians Neotethys oceanic material is incorporated in the mélanges and in the Dinarides huge ophiolite nappes are preserved above the Jurassic basin fills and mélanges, Jurassic ophiolites or ophiolitic remains are not clearly documented in the Northern Calcareous Alps. Here we present chrome spinel analyses of ophiolitic detritic material from Kimmeridgian allodapic limestones in the central Northern Calcareous Alps. The Kimmeridgian age is proven by the occurrence of the benthic foraminifera Protopeneroplis striata and Labyrinthina mirabilis, the dasycladalean algae Salpingoporella pygmea, and the alga incertae sedis Pseudolithocodium carpathicum. From the geochemical composition the analysed spinels are pleonastes and show a dominance of Al-chromites (Fe3+–Cr3+–Al3+ diagram). In the Mg/(Mg+ Fe2+) vs. Cr/(Cr+ Al) diagram they can be classified as type II ophiolites and in the TiO2 vs. Al2O3 diagram they plot into the SSZ peridotite field. All together this points to a harzburgite provenance of the analysed spinels as known from the Jurassic suprasubduction ophiolites well preserved in the Dinarides/Albanides. These data clearly indicate Late Jurassic erosion of obducted ophiolites before their final sealing by the Late Jurassic–earliest Cretaceous carbonate platform pattern.