Sedimentological response to late Mesozoic subduction in the Penninic windows of the Eastern Alps |
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| Authors: | Prof Dr W Frisch |
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| Institution: | (1) Present address: Institut für Geologie und Paläontologie, Sigwartstr. 10, D-7400 Tübingen |
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| Abstract: | Late Mesozoic subduction of Penninic oceanic lithosphere finds its response in the sedimentary record. The corresponding sediments are deposited in a deep-sea trench environment and are developed as distal, partly proximal flysches, containing breccias and olistolites, which are up to kilometer-sized (wildflysch). In the Tauern window this facies is represented by the Nordrahmen zone, which is the equivalent to the Matrei zone. It is proposed to apply the term “Matrei zone” to the entire zone. It forms the high parts of the Bündner Schiefer and Tauernflysch formation. The olistolites derive from the unstable Austroalpine continental margin (Lower Austroalpine). In the Unterengadin window the wildflysch faciès is found in North, Middle and South Penninic position. In that there are kilometer-sized blocks of clearly Lower Austroalpine provenance in a North Penninic position, the Middle Penninic Tasna zone must already have been subducted at the time of emplacement of these olistolites. The Tasna zone itself contains a number of olistolites and disintegrates towards the northeast into a wildflysch zone. Its nappe character is discussed. After earlier fossil findings it is likely that the lower flysch zones of the Unterengadin window contain younger members than the higher ones. Thus, a mechanism of offscraping of the trench sediments and piling up in an accreting wedge above a subduction zone is proposed. |
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