Origin of the upper jurassic limestones of the Swabian Alb

The Upper Jurassic of the Swabian Alb features a unique association of facies types, characterized by a sequence of micritic limestones and marls that interdigitate with bioherms formed by algae and siliceous sponges. The algae produced calcareous crusts or stromatolites, primarily growing on the sponges, which are generally preserved as calcareous material. These bioherms developed in relatively deep and calm waters, as indicated by the presence of siliceous sponges, ammonite fauna, and their relationship to micritic sediments. Toward the end of the Jurassic, a shallowing of the sea is evident through the emergence of corals and coral reefs, along with the deposition of bioclastic and oolitic limestones. The micritic facies sequence exhibits a rhythmic succession of marls and limestones, which is also present in the bioherm areas. In the older Jurassic strata, these rhythmic sequences correlate well over larger distances, but in younger beds, local conditions increasingly influenced sedimentation, further indicating the shallowing sea. The Upper Jurassic sequence also reveals a variety of geological features, including slumping structures, resedimentary intraformational breccias, dolomites, dedolomites, siliceous concretions, and calcirhythmites.