| Abstract: | The Kimmeridgian series of the northern Aquitaine margin is representative of the marine sedimentation on the Western European Shelf. It has been used to demonstrate a fundamental relationship between relative sea-level changes and the biogeographic dynamics of the Kimmeridgian ammonites. This synthesis, based on comparative sedimentological and paleobiogeographical studies, shows that the shelf was settled by submediterranean and/or subboreal ammonites during transgressive phases and maximum sea-level rises. Endemic lineages differentiated during the sea-level highstands and the beginning of lowstands. Correlative with the long-term sea-level rise, endemic elements have progressively taken a prominent role within the Kimmeridgian ammonite faunas of the shelf. The patterns of faunal changes have been deduced from studies of ammonite lineages from distinctive biogeographic origins: Rasenioides, Lithacosphinctes, Orthaspidocerasand Gravesia. Compared with subboreal ammonites, it seems that the submediterranean species were more tolerant of changing environments and adapted to new environments more easily. Therefore most of the endemic lineages which settled the Western European area originated in submediterranean faunas. |
