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

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demosponges. At the top, the lower slumping mass of Hornsteinknollenkalk passes into red
Adnet limestones. Samples from the transition (samples GK 12 a-d) have shown an increase of
crinoidal debris while sponge spicules seem to be absent in the overlying Adnet facies.
Sponge Analyses:
� Fleckenkalke and Hornsteinknollenkalke show isolated spicules of Lyssacinosida and
fragments of Hexactinosida. Exact classification of the sponges is difficult because spicules are
often dislocated and broken. The preservation of only a few skeletal fragments in between high
amounts of scattered spicules leads to the assumption that sponge remains were subjected to
dislocation, presumably due to sliding events and/or bioturbation. Corroded fragments of skeletal
structures are most likely the result of microbially induced calcification processes that began to
stabilize collapsing sponge remains concurrent or before they were dislocated. Ghost structures
and/or preserved spicules in cherty bulbs alludes at the formation of most of the bulbs by the
silicification of matrix inside spicule clusters or remnants of sponge skeletons.
4.2. Mühlstein-South (MS) + Mörtlbachgraben (G)
Geological Setting:
� At the southern flank of the Mühlstein mountain (ÖK50 / Blatt 94 Hallein, R 07 3458,
H 52 8820), southeast of the Glasenbach gorge, a profile exposes the transition between grey
limestone facies of the deeper Kössen basin and red limestone facies of the drowned Triassic
platform edge (Fig. 5, Pl. 2A). The outcropping sequence is quite similar to the one at the
“Mörtlbachgraben” (ÖK50 / Blatt 94 Hallein, R 07 3903, H 52 8720), at the road between the
Wiestal-Stausee and Gaißau (Fig. 6, 7).
� At Mühlstein-South the Triassic base is formed by limestones of the Kössin Formation but the
Triassic-Jurassic boundary is not exposed. A little path leading inside the forest along a normal
fault passes a Jurassic sequence that begins with Kendlbach limestones (2-3 m, Hettangian,
Pl. 1E) followed by bulbous layers of the Scheibelberg Formation (~30 m, “Hornstein-
knollenkalke”, in the lower part: ammonite found of Arietites ? sp., Sinemurian-Lower
Pliensbachian, Pl. 2C). To the top they fade smoothly into red limestones and breccias of the
Adnet Formation (~25 m, Pliensbachian), which is overlain by more condensed red limestones
(Toarcian Klaus Fm.?) and several meters of radiolarites (Oxfordian).
� Samples were taken from Kendlbach limestones, from Hornsteinknollenkalk of the
Scheibelberg Fm. and its transition into the Adnet facies.
� The section at Mühlstein-South is briefly described by Böhm (1992).