STAGES IN DEVELOPMENT OF THE SILURIAN FAUNA AND FLORA IN THE TYPE AREAS OF EAST SIBERIA

Abstract

Three hundred twenty one species of graptolites, chitinozoans, acritarchs, cephalopods, trilobites, brachiopods, scolecodonts, conodonts, bryozoans, ostracodes, gastropods, crinoids, tetracorals, tabulates, heliolitids, stromatoporoids, and tentaculitids were recorded in the Silurian type areas of East Siberia. Three type areas, namely, Moiero, Turukhansk, and Noril'sk, are situated within the belt of shallow shelf facies predominantly bearing benthic species intermediate between the deep-water and shoal biotas. Faunal and floral evolutionary stages were analyzed within local biointervals that correspond to the global biointervals (biochrons). The species of wide and limited stratigraphic ranges and peculiarities of their appearance and disappearance were revealed. The major trend of species evolution in the type Silurian areas of East Siberia is their mass appearance and disappearance at the initial and terminal Silurian time. This was associated with the global Silurian transgression at the beginning of the period and with the global regression at the end. Both events affected most sedimentary basins of the platform. Secondary stages were associated with oscillations of the global sea level.