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

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All interpretations refer to thin sections because corroded specimens are absent. Thereby
separation of species was highly complicated due to the presence of diverse growth stages that
were additionally cut in different levels both characterized by their own spicule configurations.
Furthermore prostalia basalia (spicules used for substrate attachment) are difficult to detect
because skeletal remains of species are often closely intertwined.
To summarize, the abundance of isolated hexactins and related types points to a dominance of
non-rigid Hexactinellida in all studied sections. Settlement took place only on softgrounds and
gravel, thus most of them were apparently attached by anchor spicules (lophophytose
attachment), most likely by monaxons of intermediate length. Otherwise the preservation of the
entire sponge skeletal structure differs between several localities. At Adnet, for example, a lot of
sponges are entirely preserved, whereas at Steinplatte most are highly compressed. Taking
altogether, from settings of the upper platform slope to those of the deeper basin the frequency of
well preserved individuals decreases whereas the amount of dislocated spicules that derived from
completely collapsed skeletons increases. Further investigations revealed a close relation
between the kind of preservation, the sedimentation rate, and the degree of microbially induced
carbonate precipitation that took place inside formerly decaying organic matter (Fig. 36, 37).
Fig. 36. Correlation between sedimentation rate, microbialite formation and related micro-environmental
milieu during taphonomic processes in different palaeobathymetric Lower Liassic settings (supplymented by
localities from non-Jurassic reef cavities and slope settings).
1: Delecat et al. (2001). 2: Reitner (1993). 3: Brückner (2003). 4: Brückner et al. (2003).