Abstract
A drastic faunal turnover of radiolarians in the early Toarcian, termed the Toarcian Radiolarian Event (TRE), recognized in bedded chert sequences of southwestern Japan, is marked by the first co-appearance of the genus Praeparvicingula and Mesosaturnalis hexagonus and by high diversity among multicyrtids. The event resulted in the replacement of latest Triassic through earliest Jurassic taxa by Late Jurassic to Early Cretaceous taxa. At TRE levels in bedded cherts in southwestern Japan, the size of radiolarians decreased drastically, reworked conodont fossils appeared, and anoxic sediments (black cherts with FeS2 nodules) were deposited. The lithologic and faunal changes suggest that global marine environmental changes, including the occurrence of anoxia, caused the TRE.
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