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

Fossil Record of Sponges 79
Fig. 37. Illustration of the fossil record of non-rigid sponge types, depending on the
taphonomic processes of different palaeoenvironments.
Since under ordinary conditions (standard salinity and alkalinity) microbialite formation does not
occur, automicrites are previously described from, e.g., non-alpine reef cavities (Lizard
Island/Australia: Reitner 1993, Langenberg-Oker/Germany: Delecat et al. 2001), where
microbialite formation is mostly restricted to close or semi-close environments with prevailing
anoxic conditions. Thus, the best preserved non-rigid sponges are known from localities where
dead (decaying) sponges quickly got separated from the open marine environment. Such
conditions were detected at Adnet and Steinplatte, where episodic sedimentation led to a fast
bury of dead sponges. Both localities also highlights the sensitivity of the balance between
sedimentation rate and sponge preservation: A slightly higher sedimentation rate at Adnet
already caused a better preservation, even of the aquiferous system of the sponges, because in
that case sponge degradation predominantly happened first when dead specimens were already
enclosed completely by the sediment. In contrast at Steinplatte locality a lot of the sponge