Marine carbonate systems in the Sarmatian (Middle Miocene) of the Central Paratethys: the Zsambek Basin of Hungary

The study of eight stratigraphic sections at the margin of the semi-enclosed Zsa´mbe´k Basin (Hungary) allows the sedimentary anatomy of oolitic–bioclastic systems in the Sarmatian of the Central Paratethys to be reconstructed. The mollusc, foraminiferal and ostracod associations indicate that the carbonate systems are Latest Badenian to Late Sarmatian in age. The Lower–Upper Sarmatian deposits are organized in superimposed subaqueous dunes prograding towards the basin on a low-angle ramp. During the Late Sarmatian, the ramp underwent subaerial erosion linked to a moderate relative fall in sea-level. Lagoonal deposits were later formed and microbial–nubeculariid–bryozoan–serpulid buildups were emplaced. The ‘abnormal’ marine conditions of the Sarmatian, conducive to the development of a poorly diversified flora and fauna and dominant non-skeletal grains, are linked to fluctuating salinities, mesotrophic to eutrophic conditions and perhaps high alkalinity.