The Wattendorf Plattenkalk (Upper Kimmeridgian) – a new conservation lagerstätte from the northern Franconian Alb, southern Germany

A new occurrence of fossiliferous plattenkalks from the lower Upper Kimmeridgian Eudoxus Zone at Wattendorf, northern Franconian Alb, is briefly described. The laminated micritic limestones consist of two types of microfacies, graded packstones and microbial bindstones. The plattenkalk facies occurs as several decimetre-thick intercalations between graded pack- to rudstones, which accumulated in depressions of a distinct submarine palaeorelief. This relief was formed by microbialite-sponge reefs, which are now preserved as massive dolostone. So far, more than 70 taxa have been recovered from the plattenkalk. The biota are dominated by benthic molluscs and brachiopods, but fossils present include also algae, plants, sponges, crustaceans, polychaetes, ammonites, belemnites, echinoderms, fishes, and fragments of reptiles. The ecological and taphonomic analysis of the benthic faunal elements shows that probably none of them were autochthonous, but that most of them were swept into the plattenkalk environment from neighbouring topographic highs via storm-produced suspension clouds. It cannot be excluded with certainty that the most common bivalve, Aulacomyella, episodically colonised the soupy substrate, but a pseudoplanktonic mode of life is regarded as more likely. It is proposed that the plattenkalk formed in small, restricted depressions of the topographic relief provided by dead microbialite-sponge reefs. In these depressions lack of circulation led to establishment of dysoxic to anoxic conditions favouring preservation of soft parts and of articulated skeletons.