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Table of Contents
Chronostratigraphy - Geological Time Scales
In the 21st century after over 200 years of mulling over the issues. it may come as a surprise to many geologists, that many of the chronostratigraphic (e.g. stage) names in which we place so much emphasis (e.g. Aptian, Visean, Miocene etc.) still lack a formal definition. The reason for this is… historical… in all senses of the word.
Similarly, even some stages which were once thought to be well-known, understood and “stable” in the hierarchy have been redefined and, in many cases, now occupy positions quite different to what they were in the past. For example, relatively recent changes in the position of the Maastrichtian – Campanian boundary (which has jumped 2 ammonite zones and three planktonic foram zones!) have rendered many publications and industry reports misleading due to references to sections of “Early Maastrichtian” age which are now more correctly “Late Campanian”.