オーストラリア南東部ラクラン褶曲帯からのオルドビス紀中期放散虫

Microfossil biostratigraphy and examination of pelagic sedimentary feature reveal the biotic event and environmental change in the Early Paleozoic. Radiolarians, conodonts and acri-tarchs occurred from black organic bedded cherts of the Mt. Stavely Complex in the Stawell Terrane of the Lachlan Fold Belt, western Victoria. This Fold Belt is regarded to be consist of Cambrian to early Carboniferous rocks, but paleontological investigation of conodonts and radiolarians indicates supposed Middle Ordovician or younger age for the examined siliceous rocks which previously supposed to be Cambrian.
Acritarchs regarded to be a cause of "red tide" occurred from lower horizon of radiolarian bearing bed, which is an important trigger of the Oceanic Anoxic Events in Late Ordovician. Middle Ordovician radiolarians are characterized by simple shell construction with randomly ornamented spicules and small thick shell. They are grouped into seven of basic skeleton forms and some show close relationship to Late Ordovician radiolarians.