LATTER CAMBRIAN EARLY ORDOVICIAN AGE OF T HE ZASURIA BASALT-SILICEOUS-TERRIGENOUS FORMATION (NORTHWESTERN GORNY ALTAI)

Present paper considers the structural position and reports the first data on the paleontology of the Zasur'ia Formation from the sections o f the Gorny-Altai Series in northwestern part of Gorny Altai. Conodont s and Radiolaria have been found in the siliceous rocks of this format ion after chemical preparation. Associations of conodont taxa are corr elated with complexes of three Upper Cambrian conodont zones (Muellero dus? erectus, Westergaardodina matsushitai, Procoaodontus) have been d etermined from some localities in the Charysh River basin (Krasnoshche kovo village area, river-head of rivers Talitsa and Maralushka). Two l ocalities (river-head of Talitsa river and near village Krasnoshchekov o) contain conodont complexes including Paracordylodus gracilis Lindst rom, Oistodus gracilis Lindstrom, Acontiodus reclinatus Lindstrom, and Oepicodus evae Lindstrom allowed the host siliceous rocks to be dated by Early Ordovician (Upper Tremadocian - Lower Arenigian). Under disc ussion are the problems of correlation of Zasur'ia Formation with stra ta from the western part of Altai-Sayan Folded Area occupying the same stratigraphical position and similar in composition. On the basis of new paleontological data Upper Cambrian - Lower Ordovician stage of th e active margine and the evolution of the Paleoasian Ocean is proved.