The Eisenrichterstein near Hallthurm, Bavaria: An upper eocene carbonate ramp (Northern Calcareous Alps)

Abstract

Ten facies types were recognized in the Upper Eocene reef complex of the Eisenrichterstein in southern Bavaria. The supratidal to subtidal zone is dominated by carbonate conglomerates and carbonate sandstones. The adjacent lagoon is very rich in molluscs. Here, the sediment consists of well-sorted, fine grained carbonate sandstones which show a rapid transition to detrital lime-stones. The latter are composed of coral debris, foraminifera and unidentified biogenic detritus. A striking feature is the distinct bedding of the detrital limestones. Coral framestones are very rare. More common are accumulations of corals which are not true patch reefs because they lack frame building in spite of the abundance of densely packed corals. A reef core as known from fringing or barrier reefs is completely lacking. Intercalated in the typical reef limestones are some limestone varieties which indicate strong environmental fluctuations within the reef. In the eastern part of the Eisenrichterstein, marly layers are intercalated in the detrital limestone indicating the off-reef environment. Based on the observed facies types a facies model is proposed for the Eisenrichterstein describing a low-dipping carbonate ramp with isolated patch-reef areas.