Porifera-microbialites of the Lower Liassic (Northern Calcareous ...

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As facies analysis by Stanton and Flügel (1989; 1995) have shown, only a minor part of the
Steinplatte buildup is formed by a real reef framework, thus the whole complex is rather
described as an “accretionary distally steepened ramp” the top of which was partly overgrown by
separate bushlike corals (capping facies) in a late Upper Raethian stage. At the end of Triassic,
the coral growth stopped, whereas the paleo-relief of the carbonate platform still existed until
Middle Liassic time. Just on top of the buildup the Triassic-Jurassic interval encompassing the
decease of the coral fauna is concealed by a small sedimentary break. Only some traces of fresh-
water diagenesis in the capping facies might indicate short-termed falls of the sea level at
Steinplatte buildup (Stanton and Flügel 1989). In contrast to the elevated platform position,
sedimentation continuously passed into grey cherty limestones in adjacent basins (Hettangian
Kendlbach Formation and Hettangian-Sinemurian Scheibelberg Formation). Predominantly the
latter are characterized by varying, often high amounts of siliceous sponges and/or siliceous
bulbs (Mostler 1986; Krainer and Mostler 1997). They are frequently exposed at the toe of
Steinplatte buildup slope at Kammerköhr Alpe and also at several outcrops in the Unken
syncline (e.g. at Scheibelberg locality and at Karnergraben) that extends north of the Steinplatte
buildup.
First Hettangian to Sinemurian sedimentation at the northern slope of Steinplatte “reef” shows an
onlap of red condensed limestones indicating a drowning of the platform during Lower Liassic
time. A wedge of these sediments is cut by a trail surrounding the Plattenkogel hill, north of
Steinplatte summit (Fig. 18C, 19).
Fig. 19. Northern slope section of Steinplatte “Reef" (N of Waidring, Austria) and its paleogeographic position.