Distribution of Atdabanian (Early Cambrian) Trilobites, Archaeocyaths, and Small Shelly Fossils in the Altai–Sayan Folded Area

Abstract

The distribution of the main faunal groups of the Atdabanian Age of Early Cambrian in the Altai–Sayan folded area (ASFA) are analyzed. It is shown that Late Atdabanian assemblages of small shelly fossils of the Kuznetsk Alatau and Altai Mountains include in general the same taxa. At that time, these territories were probably situated rather close to each other and connected with the Siberian Platform. A similar result was obtained analyzing the distribution of trilobite assemblages. It is shown that the Western and Eastern Sayan Mountains have more similar forms with Mongolian assemblages. It is also shown that, in the Atdabanian, the greatest taxonomic diversity of trilobites was confined to the areas of the paleobasin where there was accumulation of organogenic carbonate sediments. It is shown that archaeocyaths from ASFA are older than the taxa characteristic of the assemblage from the Nochoroicyathus mariiskii Zone. At the boundary of the Kiya and Kameshki horizons, archaeocyaths sharply increase in abundance and many taxa with the ring and complex internal walls appeared. This boundary is traced throughout the territory of ASFA.