2.4.6 Description
A formal unit should be defined and described sufficiently clearly to enable any subsequent investigator to find it geographically and identify it geologically. Features which characterize a unit may be composition, texture, structures, fossils and organic remains, distinctive minerals, geochemistry, geophysical properties, structural occurrence and properties, three-dimensional form and geomorphological expression. Geological time units should be defined and described on the basis of physical referents (specific rock sequences or bodies), or defined geochronologically with reference to standardized methods for numerical age determination.