| Unknown |
| Very Young |
| Pliocene |
| Miocene |
| Pliocene-Oligocene |
| Miocene-Oligocene |
| Oligocene |
| Eocene |
| Oligocene-Paleocene |
| Quaternary-Tertiary |
|
| Tertiary |
| Upper Cretaceous-Tertiary |
|
| Upper Cretaceous and Lower Tertiary |
| Cretaceous-Tertiary |
| Upper Cretaceous |
| Cretaceous |
| Lower Cretaceous |
| Upper Jurassic-Lower Cretaceous |
| Jurassic and Cretaceous |
|
| Jurassic to Upper Cretaceous |
| Middle-Upper Jurassic |
|
| Middle Jurassic |
| Jurassic |
| Upper Jurassic |
| Upper Triassic-Lower Jurassic |
| Triassic-Jurassic |
| Triassic |
| Mesozoic |
| Permian |
| Pennsylvanian and Permian |
|
| Pennsylvanian |
| Mississippian |
| Mississippian-Pennsylvanian |
|
| Carboniferous |
| Devonian |
| Paleozoic - no differentiation |
