Mosaic of environments recorded by bryozoan faunas from the Middle Miocene of Hungary

The marine sediments of the Badenian (Middle Miocene) of Hungary (Pannonian Basin, Central Paratethys) are composed of abundant bryozoan skeletal grains. Seventy-one bulk samples collected at 18 localities (outcrops and boreholes) yielded a total number of 238 bryozoan species. er to reconstruct the Badenian palaeoenvironments, the present study investigates the composition of this very diverse fauna using a combination of statistical and palaeoecological methods. The statistical analyses make use of Cluster Analysis and Non-metric Multi-Dimensional Scaling. The palaeoecological approaches are based on the known ecological requirements of the bryozoan colonial growth forms and of the numerous extant species. acies have first been differentiated on the basis of sedimentological and palaeontological features: coral buildups, coralline algal limestones, biocalcarenites, sands, and marls. Each of them is characterized by the abundance, the diversity and the types of growth forms of the bryozoans. laeoecological, statistical and facies analyses further permitted to identify four depositional settings: carbonate platform (distal and proximal), terrigenous platform, slope, and basin. These environments developed at depths between 0 to about 300 m in a mixed carbonate–siliciclastic depositional system. Skeletal production and spatial distribution of carbonate factories were predominantly controlled by terrigenous input. This resulted in a complex mosaic of facies/habitats where rich bryozoan faunas could thrive. arm-water organisms, among them foraminifers, zooxanthellate corals, molluscs, bryozoans, and echinoids, were recorded from the study sites. The coexistence of coralgal and bryomol carbonate skeletal assemblages in this subtropical setting is explained mostly by variations in the productivity of surface waters. Periods of nutrient enrichment and increased benthic eutrophication affected coral diversity and abundance in favour of bryozoans.