Spatio-Temporal Changes of Paleozoic-Mesozoic Radiolarian Faunas in Japan and Paleoenvironmental Changes

Abstract

Abstract. The radiolarian faunal changes across the Permian/Triassic boundary and during Bajocian (early Middle Jurassic) time in Japan are briefly summarized, and the relationships between the radiolarian faunal changes and the paleoenvironmental changes are discussed in this paper. The cause of the radiolarian faunal change from the latest Permian to earliest Triassic time is not well understood, but it is believed due to rapid changes in the marine environment that were disadvantageous to radiolarians. The survival of radiolarians depends on temperature, depth (quantity of light), the amount of dissolved oxygen, nourishment, food and so on. Moreover, it is possible that difference in shell structure may have allowed survivors to adapt more easily to the rapid environmental change across the Permian/Triassic boundary. The Bajocian radiolarian fauna in the Unuma section, central Japan is composed of about 320 species in each horizon and the total reaches about 510 combined in 5 horizons. About 50 origina...