The geocratic character of the Permian stage in the development of the earth's crust is shown in the destruction of the marine basins and in the endemism of faunas. Those circumstances, along with the progressively strengthening climatic gradient, make interregional correlations extremely difficult and in some cases even impossible. However, combined studies of the detailed biostratigraphic zonations and geologic analyses of basins and sequence stratigraphy have resulted in resolution of some of the problems of the Permian correlation.

Correlations of Permian deposits in the Tethys have traditionally been based on fusulinids, which were widespread and rapidly evolving in the Permian Tethys, as well as on ammonoids and conodonts. Most of the biostratigraphic zones have been defined on a phylogenetic basis and can be recognized throughout the Tethyan realm (Figures 4.1 and 4.2). Correlations within the Boreal realm have been based on the continuous and well-dated sections of the Taymir-Kolyma region (northeastern Russia) using ammonoid and brachiopod zonations. Those zones can be recognized from Novaya Zemlya to Mongolia (Figures 4.3 and 4.4). Recently the uppermost zone of the Dzhigdali horizon (Kolymaella ogonerensis) was defined in the upper part of the Solikamsk horizon of the Ufimian stratotype. Several bivalve and small-foraminifera zones established in northeastern Russia (Kashik et al., 1990) can also be recognized in the Boreal realm. These data allow reliable correlation of parts of the section and recognition of the significant biotic events.