Benthic foraminiferal evidence for the formation of the Holocene mud-belt and bathymetrical evolution in the central Adriatic Sea

Detailed analyses of modern and fossil benthic foraminiferal assemblages collected in the central Adriatic Sea are used as tools to reconstruct the environmental changes that occurred between the Last Deglaciation and the Present (last 14 Kyrs); in particular we focus on the timing and formation of the mud-belt. The modern benthic foraminiferal assemblages display a parallel zonation to the Italian coast controlled by the interaction between food/oxygen availability and water depth. Cluster analysis of 4 sediment cores separates the fossil foraminiferal assemblages in 6 groups: Cluster A is dominated by three Ammonia species; Cluster B consists of Ammonia papillosa, Nonionella turgida, Elphidium advenum and Elphidium decipiens; Cluster C is composed of two taxa, Hyalinea balthica and Trifarina angulosa; Cluster D is dominated by 5 species, Cibicides lobatulus, Buccella granulata, Reussella spinulosa, Textularia agglutinans and Elphidium crispum; Cluster E contains Bulimina spp., Gavelinopsis praegeri, Bolivina spp., Cassidulina neocarinata and Asterigerinata mamilla; and Cluster F is dominated by Bulimina marginata, Valvulineria bradyana, Globocassidulina subglobosa and Melonis padanum. The cluster analysis and contemporary distribution patterns of these taxa are used together with ecological preferences of the most frequent species to reconstruct the spatial and temporal distribution of the different biofacies in the past. This reveals information about Holocene palaeoenvironmental changes that are related to water depth fluctuations and the installment of the coast-parallel mud-belt. The benthic assemblage records the transition from a infralitoral environment (Biofacies I) to deeper marine condition (Biofacies III). After that the sea level reached about the modern level (Biofacies IV) the benthic foraminiferal community evidences the development of the mud-belt and the subsequent transformation of the ecological niches linked to the trophic evolution of the environment.