Sponge communities from the Lower Liassic of Adnet (Northern Calcareous Alps, Austria) |
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Authors: | Stefan Delecat Joachim Reitner |
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Institution: | (1) Geowissenschaftliches Zentrum der Universität Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany |
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Abstract: | The lower slope of the drowned Alpine Adnet Reef was recolonized in Hettangian time by sponge communities of hexactinellid (hexactinosid and lyssacinosid) taxa and a few demosponges. Special taphonomic processes caused an excellent preservation of these sponges. The preservation allows to define several growth forms and to study original spicule configurations of the mainly non-rigid skeletons. Sponge faunas of presumably similar associations are known from adjacent basins, but only by isolated spicules of completely collapsed specimens. In Adnet the sponges are embedded in biodetrital limestones of the Schnöll Formation. Orientation and distribution of the sponges reflect autochthonous faunas that have been mixed with dislocated individuals by local water currents. The predominance of erect sponge types indicates intermediate sedimentation rates and/or occasional high-energy events. Sponge types and community structures are comparable with those ones from Middle Paleozoic mud mounds. Several hiatuses, mostly characterized by ferromanganese crusts have been kept free of sponge settlement. Carbon stable isotopes of the sponge-rich sequence show a small negative δ13Ccarb excursion that covers the period from Lower Hettangian to Lower Sinemurian.This revised version was published online in May 2005 because several displayed passages had been inadvertently deleted in the original published version. |
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Keywords: | Spiculite Sponges Hexactinellida Lyssacinosida Microbialite Stromatactis Adnet Schnö ll Formation Jurassic (Hettangian) |
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