Abstract:
The deep-water successions in Japan, Sikhote-Alin, and Nevada demonstrate a sharply decreased silica productivity across the Permian-Triassic boundary, accumulation of carbonaceous shales, and virtually absolute absence of fossil radiolarians and sponges. In Japanese sections, this stratigraphic level is enriched in titanium, phosphorus, and yttrium, and also demonstrate a sharp decline in cerium content relative to other rare-earth elements. These phenomena are directly or indirectly related to the biotic crisis at the Permian-Triassic boundary. The geochemical anomalies are interpreted as related to significant environmental changes in response to intense tectonic activity. The changes caused extinction of many marine biotic groups, including siliceous plankton, and increased the primary productivity of lower phytoplankton taxa. The event in question differs from the Mesozoic anoxic episodes in its origin, significance, and duration, being followed by the well-manifested biotic crisis.
