The thorough study of the Upper Triassic reference section located at the Tikhaya River in the central part of Kotel'nyi Island and characterized by uniform clayey lithology and containing diverse cephalopod, molluscan, and radiolarian assemblages made it possible to specify its structure and paleontological characteristic and establish for the first time the upper Anisian Sirenites yakutensis Zone. It is shown that different Late Triassic faunal groups are represented by mixed dominant Boreal and subordinate Tethyan elements. Such proportions are observable through the entire section beginning from the lower Carnian to upper Norian layers. The peculiar taxonomic composition of Late Triassic radiolarian and cephalopod assemblages provides grounds for attributing the region to an autonomous paleobiochore (New Siberian subprovince). The occurrence of both Siberian and Canadian elements in the Late Triassic faunas emphasizes the specific position of this paleobiochore determined by wide connections between basins at that time.