Место издания: Lausanne-Geneve , Год издания: 1991

Principal tendencies of the historical development of Triassic boreal nautiloids are under discussion. Basic assemblages of this group are identified. For the first time the chart of Boreal Triassic subdivision by nautiloids is proposed. A nautiloid - based zonation including 19 biostratons suggests a rather detailed subdivision of Triassic deposits. The zones in the main are of wide range and in many cases suggest detailed correlation within the entire Boreal realm. Wider correlations are usually hampered, however, there are some datum levels (Phaedrysmocheilus ornatus and P. evolutus Zones in Upper Olenekian, Paranautilus smithi Subzone in Upper Anisian and Proclydonautilus goniatites Subzone in Lower Carnian), due to recurrent waves of nautiloid immigration to Boreal regions from the Tethys, which allow wide correlation of Boreal and Tethyan charts to be made. The main changes in systematic composition of Triassic boreal ammonoids and nautiloids coincide through time, consequently many boundaries also coincide, however, this coincidence is not complete.