Biogeography and diversity gradients of Oligocene larger foraminiferal assemblages from the Western Tethys

This study represents a first order analysis of the palaeobiogeographic distribution of Oligocene larger foraminifera of the Western Tethys area. This study is based on an extensive literature survey and is based on species level distributions of larger foraminiferal assemblages from 23 distinct areas of the Western Tethys as well as neighbouring areas in the Indo-Pacific, Northern Atlantic, Paratethys and North Sea Basin. We aim to discern basic palaeogeographic patterns and diversity gradients and relate these to palaeoclimate, trophic regimes and further ecological parameters such as facies restrictions, especially pertaining to carbonate environments where these larger foraminifera thrive. An occurrence matrix of (X taxa Y localities) was used to calculate diversity coefficients and multivariate ordination techniques using Parsimony Analysis of Endemicity were applied to quantify the distributional patterns. Taxon distributions are compared including those of higher taxonomic units such as porcellaneous imperforate versus hyaline perforate larger foraminiferal assemblages. The results are analysed with respect to the evolution of larger foraminifera during the Palaeogene and possible dispersal routes (gateways). The biogeography of these larger foraminifera is compared to that of other key benthic organisms (marine invertebrates) and the palaeobiographic concepts of Tethyan and Mediterranean areas based on these. First results show that the distribution of larger foraminiferal species is related to the ecological tolerances of each taxa; this has previously been hypothesized, but not rigorously tested for larger foraminifera in this region. Decreasing diversity gradients are observed, for example, from the southern Mediterranean–Tethyan margin to the northern Paratethys region.