Early Jurassic (Pliensbachian) brachiopod biogeography in the western Tethys: The Euro-Boreal and Mediterranean faunal provinces revised
Abstract The Pliensbachian brachiopod biogeography of the western Tethyan region and the Euro-Boreal vs. Mediterranean faunal provinciality is evaluated. The data base was developed from improved and mostly revised taxonomical data of 25 Pliensbachian brachiopod localities selected from Europe and North Africa. The revised list and presence-absence data of 405 Pliensbachian brachiopod species formed the taxonomic units of the numerical analysis based on similarity coefficients. Cluster analysis (hCA) carried out from the Jaccard and Raup-Crick coefficient data showed clear dichotomy between the Euro-Boreal and Mediterranean brachiopod biochores. Principal coordinates (PCO) technique and non-metric multi-dimensional scaling (NMDS), complemented with the minimal spanning trees, resulted in similar grouping of the Pliensbachian brachiopod faunas. In de-trended correspondence analysis (DCA), besides the clearly separated Euro-Boreal and Intra-Mediterranean units, the Peri-Mediterranean assemblage formed a discrete scatter between the two major biochores. The three Algerian faunas (Ouar, Trar, Ksou) appear in a somewhat marginal position within the Euro-Boreal province. The above Pliensbachian brachiopod biochores reveal very high degree of endemicity, probably related to the limited dispersal potential of brachiopods. From the complete data set distinctive Euro-Boreal and Mediterranean species, ten from both provinces, were selected. Ribbed spiriferinid morphotypes are frequent among the distinctive Euro-Boreal species, whereas, besides smooth spiriferinids, some rhynchonellid and terebratulid morphotypes with expanded anterior margins are common among the distinctive Mediterranean species. In the Early Jurassic Tethyan palaeogeography, the marked dichotomy between the Euro-Boreal and Mediterranean provinces is interpreted in terms of deep-sea/oceanic barriers, which isolated the intra-Tethyan microcontinent from the European and African shelf regions. Geographical position and local environmental factors caused the differentiation of the Peri-Mediterranean subprovince along the north-western margin of the microcontinent. This palaeobiogeographical unit formed an interface between the Intra-Mediterranean and the Euro-Boreal biochores.