EVIDENCE FOR 15 MILLION YEARS OF CONTINUOUS DEEP-SEA BIOGENIC SEDIMENTATION IN EARLY PALAEOZOIC OCEANS

Abstract

Upper Cambrian to Lower Ordovician radiolarites (alternations of ribbon-banded radiolarian cherts and siliceous shales) from Kazakhstan are dated accurately by means of conodonts. They represent the only known continuous sequence of abyssal deposits across the Cambrian-Ordovician boundary. The radiolarites are associated with remnants of oceanic crust (ophiolites) and form the oldest-known radiolarian ooze accumulations, which presumably formed in equatorial paleolatitudes. The Cambrian cherts contain clusters of conodonts (especially paraconodonts) that are very poorly known at present, despite their potential for improved understanding of conodont community structure and paleoecology.