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

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(Hornsteinknollenkalke, Scheibelberg Formation). They both represent slumping masses and
olistholites of grey siliceous limestones (Pl. 1A-D) that merge at their top into the red bulbous
sediments of the Adnet Formation. The lower (older) allochthonous sequence additionally
encloses dislocated Kendlbach limestones (with fish fossils, psiloceratid ammonites and
ichthyosaurs) of Hettangian age.
� Since sponge spicules have been reported only from the base of the Glasenbach profile,
sampling in this study was restricted to the Lower Liassic part of the section.
� Previous work about the section were published by Bernoulli and Jenkyns (1970), Vortisch
(1970), Plöchinger (1983) and Böhm (1992).
Facies Analyses:
� “Fleckenkalke” (samples GK 1 – GK 7, Pl. 1B-C): Biomicrites (wacke- to packstones)
dominated by radiolarians and different, predominantly high amounts of broken sponge spicules
that build up layers in the sediment. Most cross sections of spicules seem to be of monaxons and
fragments of hexactins which original siliceous material is dissolved and replaced by
microsparite. Only in a few cm-sized horizons recrystallization did not happen and spicules
served as nucleus for silicification of the surrounding matrix that resulted in cherty bulbs.
Stromatactis cavities are absent. Bioturbation frequently occurs in kind of roundish burrows
which appear as dark blotches or strias in the lighter sediment (German name of the sediment:
“Flecken” = blotches). The infill of the burrows shows densely packed fragments of spicules and
a minor amount of partly pyritisized micritic matrix.
� “Hornsteinknollenkalke” (samples GK 8 - GK 11, Pl. 1D): Biomicrites (wacke- to
packstones) with radiolarian, bivalves, foraminifers, small gastropods, brachiopods,
echinoderms, ostracods, and sponge spicules. Layers differ strongly in the amount of the
biogenous fraction: Spiculitic layers that are dominated by sponge spicules and radiolarians often
alternate with layers showing either small amounts of fossil debris or high amounts of mainly
ostracods and broken shells of bivalves. Isolated sponge spicules are unequally scattered in the
sediment. Most of them are fragments of thin hexactins, monaxons and probably triaens and
tetraxons. A few spicules still show arrangements of skeletal structures, others are preserved in
small irregular clusters, bound by microbial carbonates. Rarely dictyonal skeletons of probably
lithistid demosponges occur, but they are very badly preserved due to recrystallization processes.
In contrast to the “Fleckenkalk” horizons, cherty bulbs more frequently occur and represent a
characteristic feature of the “Hornsteinknollenkalk” (German name of the sediment:
“Hornsteinknollen” = cherty bulbs). Edges of some of the bulbs show remnants of sponge
spicules and micropeloidal micrites. In some cases, the interior of the bulbs, too, show the
outlines of isolated hexactinellid spicules or less frequently the skeletal remains of lithistid