AMMONOID ZONES OF THE OLENEKIAN STAGE (LOWER TRIASSIC) AND THEIR CORRELATION

Abstract

Regional ammonoid zonations in Olenekian marine deposits of Siberia, Canada, the United States, Primor'e, China, Nepal, the Salt Range, and Mangyshlak Peninsula are considered. The Siberian zonal scheme is the most complete and detailed, consisting of seven zones and twelve subzones, which exemplify a continuous succession of ammonoid assemblages. Beyond a doubt, this scheme can be used as a global chronostratigraphic standard of the Olenekian Stage. Analogues of Siberian ammonoid zones are easily distinguishable everywhere within the lower Olenekian interval. The interregional correlation of upper Olenekian subdivisions is less convincing because of significant geographic differentiation of ammonoids at that time.