The role of stratotypes in stratigraphy: Part 2. The debate between Kleinpell and Hedberg, and a proposal for the codification of biochronologic units

The different functions of stratotypes are illustrated by the writings of H.G. Schenck, R.M. Kleinpell, and H.D. Hedberg. Schenck and Kleinpell advocated the use of exemplary stratotypes and flexible biochronologic units for both the standard global time scale and provincial time scales, while Hedberg urged the use of strict boundary-defining stratotypes and permanent definitions for all time scales. In order to provide a stable common language for all geologists, Hedbergʹs view has been accepted for the standard global time scale, but remains problematic for provincial biochrons. leinpellʹs stratigraphic philosophy is representative of many stratigraphers who work with provincial biochrons and who generally opposed Hedbergʹs recommendations. In agreement with Kleinpell, because these entities are intended to reflect the most obvious and/or “natural” paleobiological changes in a given province in a given fossil group, their boundaries are often fuzzy, are always subject to modification with new evidence, and cannot be defined by golden spikes. gʹs restriction of biostratigraphic units to purely empirical entities has left traditional biochronologic/biochronostratigraphic units in limbo. The unit terms age/stage should be assignable to provincial biochronologic/biochronostratigraphic units having geographic names, as long as those names are formalized by the designation of a nominal stratotype or nominal type locality. finition of “biochron” in the International Stratigraphic Guide is unacceptable because in defining biochronologic units in terms of biostratigraphic units, said definition confuses the concepts of the biochron and parachron, does not take into account the problem of reworking, and fails to consider the often enormous difference between the total time subtended by a biostratigraphic unit and the span of time defined by its analogous biochronologic unit. In order to call attention to and solve these problems, a proposal is made for the codification of biochronologic units.