A short history of the Ordovician System: from overlapping unit stratotypes to global stratotype sections and points

The Ordovician System was introduced by Charles Lapworth as solution to the overlapping unit stratotypes loosely defined by Adam Sedgwick, for the Cambrian, and Roderick Murchison, for the Silurian. The Ordovician has emerged as one of the longest and most significant of the geological periods. Following an interval of intensive research of all the key regions of the globe, unit stratotypes in the type areas of England and Wales have been replaced by seven global stages and three series based on Global Stratotype Sections and Points, enhancing the definition of these chronostratigraphic units and facilitating global correlation. As a consequence, the biological and geological events during the period can be recognised and the magnitude and significance of originations and extinctions understood with some confidence.