Выпуск: 5 , Том: 38 , Год издания: 1997

The authors offer a boreal zonal standard scale in order to achieve an effective panboreal correlation and efficient determination of geological age of Mesozoic boreal sediments. The standard section of boreal Mesozoic represents the most complete succession of mollusk (mainly ammonites) zones that are known on the territory of the boreal realm. It is composed of fragments of zonal successions that are established on more than 30 Triassic, Jurassic, and Cretaceous sections from Northern Eurasia, North America and Greenland. Boreal standard of the Triassic system consists of 36 ammonite zones and 2 bivalve zones; Jurassic - 70 ammonite zones; Cretaceous - 37 zones, subzones and layers on ammonite, 6 bivalve zones, and 11 zones and subzones on belemnites. Siberia and Northeastern Asia provide stratigraphic sections many of which are the best in the boreal realm regarding their stratigraphic completeness and detailed zonal subdivision. In addition, there is a type section of the Olenekian stage and one of the most complete boreal sections of the Indian stage. Infrazonal scales are constructed for both Indian and Olenekian stages as well as for the Middle and Upper Anisian. Successions of ammonite zones from Hettangian, Sinemurian, Toarcian, and Upper Pliensbachian sections, which are located in Northeastern Asia as well as Lower Oxfordian substage from Northern Siberia and Kimmeridgian stage of Subpolar Urals, are selected as boreal standards. There is a more complete ammonite zonal scale of the Upper Volgian substage in Northern Siberia than that of the Gorodishche type section from Volga River region. The most complete and continuous successions of ammonite zones in boreal Berriasian and Valanginian are established in Northern Siberia. They are accepted as a composite boreal standard. Studies of the North-Siberian Upper Cretaceous sections in stratigraphical interval from Upper Cenomanian to Santonian-Campanian boundary revealed equivalents of all the East- and West-European Inoceramid zones. In addition to ammonid zones for all the Mesozoic systems in Siberia and Northeastern Asia, the authors used the same sections to construct independent parallel zonal scales on the parastratigraphical groups of fauna and flora. They also constructed a bivalve-based "through" scale which was incorporated into the boreal standard for some intervals such as Upper Triassic and Upper Cretaceous. For the entire Triassic interval the authors offer zonation based on nautiloids as well as those on conodonts and foraminifera for some other intervals. For Jurassic interval they developed a system of the following biostratigraphic scales: on belemnites, foraminifera, ostracods, dinocysts, spores and pollen. Dinocysts and foraminifera scales are available for the Cretaceous. In combination, the parallel scales may provide a very detailed regional correlation. However, many of them like a zonal bivalve-based scale make it possible to achieve a direct panboreal, and even boreal-peritethyan correlation for the intervals such as Upper Triassic, Lower Liassic, Upper Jurassic, Neocomian, and Upper Cretaceous.