Geological history of the southern franconian Alb - The area of the Solnhofen lithographic limestone

An overview on the geological development of the Upper Jurassic in Southern Germany is presented. The geological and tectonic framework for the formation of bedded limestones and massive limestones as well as of so-called sponge-reefs is discussed. Historical interpretations (e.g. sponge-reefs, sponge-biostroms) and new interpretations (carbonate sand facies) are documented without final conclusions about their validity. Many observations allow the interpretation of varying models of the depositional environment of the Solnhofen Plattenkalks and especially of the Solnhofen Lithographic Limestone. Examples of characteristic embeddings of fossils in micrite can help to understand the deposition in extremely calm probably anoxic environments in different Plattenkalk basins sometimes altered by local events (e.g. turbidites). Furthermore, weak bottom currents and varying input of fine detrital sediment must to be taken into account. The Plattenkalk may have developed under conditions with salinity stratification. The carbonate mud of the lithographic limestones was probably washed into the stagnant water of the bottom zone from suspension load brought into the environment by storm events. The organisms embedded in this micrite originate from various environments in the surroundings of the basins. They stem from uppermost surface waters, extensive soft sediment areas on top of the surrounding sponge microbial mounds, from carbonate sand areas, from hardgrounds and reefal habitats, and from surrounding emerged island areas. The parameters discussed herein represent a basis for further discussions to understand the unique sedimentary conditions, the taphonomy of fossils, and finally the local varying preservation conditions.