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

Localities (Facies and Sponge Analyses) 39
At the “red wall” of this site a big massflow of Adnet limestones crops out comprising slump
folds and megabreccias that slided down onto grey limestones of the Scheibelberg Formation
(Garrison and Fischer 1969; Wächter 1987). At the south-eastern margin of this outcrop the
Adnet limestone pinches out along Triassic coral “reef” limestone. The onset of Liassic
sedimentation is preserved in small crevices or interstices of the rough Triassic relief.
Samples of the spiculite facies were taken at the northeastern slope of the Plattenkogel hill
(locality S1), where a spiculite covers a small clastic sequence that was also sampled to evaluate
the emergence of the sponge fauna. The sequence most likely provides the oldest Jurassic
limestones at Steinplatte buildup slope, thus giving a small insight into the sedimentary
conditions closely after the Triassic-Jurassic boundary event. In the Alpine region, the T-J
boundary interval is often characterized by sedimentary breaks and ferromanganese crusts. Since
a small Fe/Mn crust was also found in association to the Liassic sequence at
Steinplatte/Plattenkogel hill, it was of interest to compare its geochemistry with those of other
Fe/Mn-crusts (see chapter 8.2.) from famous localities of the Northern Calcareous Alps
(localities S3 a,b,c, see supplement 1.2).
Another site at Steinplatte, showing the contact between Triassic and Jurassic sedimentation is
located at the Steinplatte summit, called “Fischer’s Coral Garden” (locality S2). It displays
limestone of the capping facies in which gaps and interstices of the Triassic coral framework are
partly filled with Liassic red sediments.
4.10.1. Plattenkogel hill (ST)
Geological Setting:
� The Plattenkogel hill (TK25 / Blatt 8341 Seegatterl, R 45 4385, H 52 7455) provides a small
sequence of Lower Liassic sediments that is preserved in a shallow depression of the Upper
Rhaetian coral limestone (locality S1, Fig. 18, 20, Pl. 17A). The section starts with a lumachelle
layer and clastic sediments that fill up a small sink hole abutting a little fault. The lumachelle
displays dissolved valves of transported, but often articulated Cardinia shells (3-4 cm in size,
Pl. 17B). Sporadically manganese “Frutexites” structures grew into the mould cavities, before
remaining space was closed by fine detrital sediments and blocky sparite (Pl. 17D, E).
Accessorial fauna comprises ostreoid, pterioid, and pectinoid bivalves and crinoidal fragments.
Intercalated and more matrix-dominated layers show fine-grained biopelsparites/micrites and
intrasparites. The upper part of the sink hole is filled by a small succession of different clastic
sediments, partly fractured, reworked or brecciated, and showing several discontinuities
(Fig. 20).