Quantitative stratigraphy of sedimentary sequences: A case study of the Middle Ordovician event

The irreversibility of evolution is one of the most reliable tools to date geological events, which makes the palaeontological record valuable in reconstruction of the history of sedimentary basins. The resolution of palaeontological time scales can be improved by applying methods of quantitative stratigraphy, due to more rigorous and/or more complete approach by using the distribution of taxa as a reliable tool for correlation, i.e. a time scale (Shaw 1964; Guex 1987; Agterberg 1990). Moreover, the ordinal scales of taxa which are independent of the strati-graphical framework can be used to describe the dynamics in the diversity of taxa and, to some extent, the evolution of the corresponding groups. Such an opportunity was noted by Paul (1985), but mostly ignored in studies on radiation and extinction of taxa, in spite of the actuality of the problem (Sepkoski 1995a; Holland 1989).