VOLUME 5 (2)/June 1975

A Plate Tectonics model for the geodynamic development of the Western Mediterranean area since the Cretaceous is proposed. Two main series of contraction are distinguished: (1) the Cretaceous-Eocene phase, and (2) the Miocene and post-Miocene one. During the Cretaceous-Eocene phases the arc-trench systems, located along the palaeo-African continental margin, migrated northward ("Alpine" polarity) up to their collision with the European continent (arc-continent collision type). At the end of this event the Mesozoic oceanic crust, originally interposed between the European and African continents, was almost completely destroyed by the subduction processes, while new litosphere had been created in the Cretaceous-Eocene back-arc marginal basins. During the Miocene and post-Miocene phases new arc-trench systems with reversed southsoutheast polarity formed and migrated, consuming the previous marginal basin crust. The shifting of these reversed arcs was accompanied by the development of new back-arc marginal basins (present Western Mediterranean basins) and by the formation of remnant arcs (Sardinia and Corsica). The subduction is still active along the Calabrian arc.

S. Breskovski. Ammonite Zones and Subzones of the Barremian in Northeastern Bulgaria. The succession of ammonite fauna in 96 sections of the Barremian in Northeast Bulgaria suggests the subdivision of two ammonite zones and four subzones:
       Upper Barremian:
          2. Pseudosaynella strettostoma zone
               b. Matheronites soulieri subzone
               a. Barremites cassidoides subzone
       Lower Barremian
          1. Crioceratites emerici zone
               b. Holcodiscus perezianus subzone
               a. Pseudothurmannia pseudomalbosi subzone
For each established (sub)zonal subdivision, data for the index type and nomenclature are given. Argumentation of the boundaries is made. The genera and species established in each (sub)zone are subdivided into three groups: (I) Typical for the subdivision; (2) Present in the given subdivision but occurring also below its lower boundary; (3) Present in the given subdivision but occurring also above its upper boundary. The success ions studied are shown on the applied figures in which all established taxons of the generic and species group of the Barremian in Northeastern Bulgaria are included.