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

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� The section at Hochfelln summit starts with the Hochfelln layers (Rhaetian-Liassic). The
Triassic-Jurassic boundary seems to be hidden in these sediments that are formed by material of
Triassic reef debris. The section continues with Liassic grey limestones (Fleckenkalk), exposed
at the spot where the cross of the Hochfelln summit is erected. Liassic sponge remains were
found in these latter cherty sediments.
� Short descriptions of the locality are given by Nöth (1926) and Doben (1970), whereas the
fossil record was studied first by Böhm (1910).
Facies Analyses:
� “Fleckenkalke” / cherty limestones (samples HF 3+4, Pl. 3G-H): The sediment is almost
completely formed by densely packed isolated sponge spicules. Except of the lack of large-sized
burrows, the facies is quite similar to the facies of “Fleckenkalk” that has already been described
from preceding localities. In contrast to some layers with high abundance of micropeloidal
automicrites (sample HF 4), one sample from the base layers (sample HF 3) shows high
quantities of thick-rayed monaxon and/or hexactin spicules and a very small amount of micrite in
between. It also shows siliceous bulbs that have been formed by silicification of the micritic
matrix, thus the bulb material still displays the cross sections of siliceous sponge spicules that are
now surrounded by the chert that evolved in the former micritic interspace. Additionally the
bulbs are partly surrounded by a small micritic horizon that is dominated by monaxon meso- or
microscleres.
Sponge Analyses:
� There are only isolated sponge spicules (monaxons and hexactines) that belong to the group
of Lyssacinosida. Orientation and distribution of the spicules in the sediment points at a mainly
allochthonous origin. High amount of peloidal automicrites in some of the layers points to
microbially induced carbonate precipitation inside the organic residue of highly collapsed sponge
remains. Dense spicule arrangements around cherty bulbs most likely do not represent original
configurations of collapsed sponge skeletons but were fomed by the effect of matrix
displacement during bulb diagenesis.