Important Phanerozoic Boundaries

Abstract

A geologic time scale is conventionally considered as equivalent to a biological time scale that is based on evolution of life on the Earth. Using radiogenic isotopes is critical for understanding short-term geologic processes responsible for quick reorganizations of ecosystems at geologically important boundaries. In the Phanerozoic, significant events of mass extinctions occurred in the Early Cambrian, Late Ordovician, Frasnian–Famennian, Permo–Triassic, Late Triassic, Cenomanian–Turonian, and Cretaceous–Tertiary (Erwin 1998). Hereafter we focus on specifications and dating problems of three remarkable transitions: (1) Vendian–Cambrian (V–C), (2) Permo–Triassic (P–T), and (3) Cretaceous–Tertiary (K–T). The available data demonstrate that these boundaries have been caused by different geologic processes and, in fact, cannot be strictly compared to each other.