Evidence for 15 m.y. of continuous deep-sea biogenic siliceous sedimentation in early Paleozoic oceans

Upper Cambrian to Lower Ordovician radiolarites (alternations of ribbon-ban ded radiolarian cherts and siliceous shales) from Kazakhstan are dated accu rately by means of conodonts. They represent the only known continuous sequ ence of abyssal deposits across the Cambrian-Ordovician boundary. The radio larites are associated with remnants of oceanic crust (ophiolites) and form the oldest-known radiolarian ooze accumulations, which presumably formed i n equatorial paleolatitudes. The Cambrian cherts contain clusters of conodo nts (especially paraconodonts) that are very poorly known at present, despi te their potential for improved understanding of conodont community structu re and paleoecology.