Problems in chronostratigraphy: stages, series, unit and boundary stratotypes, global stratotype section and point and tarnished golden spikes

"Stratigraphy is a magnificent subject-magnificent in its breadth and scope , magnificent in its importance to so many lines of human endeavor. It is e ssentially that branch of geology which deals with the arrangement, the dis tribution, and the chronological succession of rock strata land other assoc iated rock bodies), with respect to any or all of the various characters, p roperties, and attributes which rocks may possess (Hedberg, 1958, p. 1881). " Chronostratigraphy-the temporal ordering of geologic strata-is at the heart of earth history. In reviewing chronostratigraphic theory, from d'Orbigny to Hedberg, we see that concepts and practices have evolved under pressure of constant improvements in time control and data quality. Such stimuli are naturally felt more strongly in the youngest part of the stratigraphic rec ord, where dating is most precise and the biostratigraphic data are most ab undant and well-preserved. It is not surprising, therefore, to find that ch ronostratigraphy is conceptually more advanced in the Cenozoic Erathem than in the Mesozoic and Paleozoic Erathems, where biostratigraphy and chronost ratigraphy are widely confused, evidently out of necessity. Taking the five inter-series boundaries in the Cenozoic Erathem as case histories, we revi ew their current status in relation to the lower boundary of the lowest 'st andard' stage above the boundary, in light of the hierarchical principle re commended in the International Stratigraphic Guide (Hedberg, 1976; Salvador , 1994). In each instance, what should be a simple nested relationship turn s out to be complex and difficult, and in the cases of the proposed global stratotype section and point (GSSPs) for the Eocene/Oligocene Series bounda ry and the Paleocene/Eocene Series boundary there are discrepancies so larg e with regard to the base of the Rupelian and Ypresian standard stages, res pectively, that some essential relaxation of the hierarchic rule seems to b e required if the historic value of these long-known stages is not to be vi olated. Since stage boundaries should not be defined a posteriori to fit se ries boundaries, we propose here to reconsider the role of the Standard Sta ge as the obligate elemental subdivision in a rigidly hierarchical chronost ratigraphic scale and suggest that series and subseries should be formalize d and their boundaries defined by GSSPs. We do not suggest that stages be a bandoned. On the contrary, we propose to integrate them in a two-step hiera rchical chronostratigraphic framework, so as to use them in complementary f ashion with series and subseries. However, the boundary concept is more app ropriate for stage than the GSSP. We recognize the need for precise and glo bally valid chronostratigraphic correlations based on GSSPs in attempts to understand the earth system, while at the same time, we emphasize the need for conceptual continuity with regard to the central place that the stage h as played in chronostratigraphy over several decades. (C) 1999 Elsevier Sci ence B.V. All rights reserved.