Bio- and chronostratigraphy of the Middle Triassic Reifling Formation of the westernmost Northern Calcareous Alps |
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| Authors: | Thomas Brühwiler Peter A Hochuli Roland Mundil Wolfgang Schatz Peter Brack |
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| Institution: | 1.Pal?ontologisches Institut und Museum der Universit?t Zürich,Zürich,Switzerland;2.Berkeley Geochronology Center,Berkeley,USA;3.Didaktikzentrum der ETH Zürich,Zürich,Switzerland;4.Departement Erdwissenschaften,ETH Zürich,Zürich,Switzerland |
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| Abstract: | New finds of fossils including bivalves, ammonoids, brachiopods and palynomorphs from the Middle Triassic Reifling Formation
significantly improve the age assignment for this unit in Liechtenstein and Vorarlberg. The lower part of the Reifling Formation
is tentatively referred to the Late Anisian Paraceratites trinodosus Zone and somewhat older levels, whereas the uppermost part reaches the Ladinian Protrachyceras archelaus Zone (ammonoid zonation). The Middle Triassic successions of the study area are correlated with the coeval South Alpine reference
section at Bagolino (Brescian Prealps), which also bears the Ladinian GSSP. The comparison shows that the Reifling Formation
in the study area is age-equivalent with the South Alpine Prezzo Limestone and the Buchenstein Formation. A volcanoclastic
layer in the upper part of the Reifling Formation at Flexenpass yields a U-Pb zircon age of 239.3 +/- 0.2 Ma. This value is
slightly older than previously published minimum ages from equivalent horizons in the Southern Alps; the difference is thought
to be mainly due to improved pre-treatment of zircons (annealing/chemical abrasion), which significantly reduces the effects
of Pb loss. The new radio-isotope age further constrains the stratigraphical age of the Reifling Formation and supports the
proposed biostratigraphy-based correlation of Middle Triassic successions in the Eastern and Southern Alps.
Editorial handling: E. Erba & J.-P. Billon-Bruyat |
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| Keywords: | Middle Triassic Reifling Formation Buchenstein Formation biostratigraphy U/Pb zircon dating |
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