摘要
1 Introduction Stratigraphy,placing the sequence of events in Earth history into order,is a fundamental part of the geosciences.Traditionally the starting point is a regional stratigraphy,based on lithological,mappable units,correlated by fossils with local,regional and global chronostratigraphical schemes.Chronostratigraphic units were traditionally defined on their fossil content,as essentially unit stratotypes.But,commonly there were no clear boundaries.
基金
the Leverhulme Trust for financial support.This is a contribution to IGCP 653 project’The onset of the Great Ordovician Biodiversification Event’.
