Chapter 10

Abstract Chronostratigraphy and biochronology are the prime conceptual methods for relating biologic events to the geologic time scale. Chronostratigraphy is the dominant method applied in the oceanographic-marine realm, and biochronology is the dominant method for the terrestrial realm. These concepts were conceived in the early half of the 20th century, and major advances in both occurred during the latter half of the 20th century. Historical development of both chronostratigaphy and biochronology is briefly reviewed, and it is concluded that the early definition and application of biochronology is tainted by reference to and inference from biostratigraphy. It is proposed that biochronology be redefined as the organization of geologic time according to the irreversible process of organic evolution, following the characterization and application by Berggren and Van Couvering (1978, G.V. Cohee, M.F. Glaessner, and H.D. Hedberg [editors], Contributions to the geologic time scale: 39–55. Tulsa, OK: American Association of Petroleum Geologists). The new term “chronostratigraphic marker” is proposed and defined as any chronologically significant event (biologic, isotopic, isotopic-ratio, or paleomagnetic), recorded in a stratigraphic sequence, that can be directly related to and/or tied to any other chronostratigraphic marker. According to definitions given herein, a biochronologic event can become a chronostratigraphic marker, but only when tied to a discrete stratigraphic sequence and related to other stratigraphic sequences and/or chronostratigraphic markers. The terms and concepts “datum event”, “land mammal age”, “stage of evolution”, and “appearance event ordination” are discussed and defined. A datum event is defined as any chronostratigraphic marker. Land mammal ages, along with European Neogene and Paleogene mammal units, are considered biochronologic entities; they are defined as relatively short intervals of geologic time that can be recognized and distinguished from earlier and later such units (in a given region or province) by a characterizing assemblage of mammals. Stage of evolution is a very basic biochronologic concept defined as the chronologic ordering of faunal assemblages based on morphological (evolutionary) differences observed in members of a single, well-established phyletic lineage. Appearance event ordination is a new tool of biochronology. It is defined as ordering the appearance of fossil mammal genera by multivariate analysis, using overlapping (conjunctive) and nonoverlapping (disjunctive) range distributions in large sets of data.