K. Iwata et al., LATTER CAMBRIAN EARLY ORDOVICIAN AGE OF T HE ZASURIA BASALT-SILICEOUS-TERRIGENOUS FORMATION (NORTHWESTERN GORNY ALTAI), Geologia i geofizika, 38(9), 1997, pp. 1427-1444
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.