**Geochronologic and Chronostratigraphic Nomenclature to be used in AAPG Publications**

* Geochronologic modifiers are in regular type while chronostratigraphic modifiers are in italics.

Formal	Informal	Formal	Informal
Cenozoic	early, lower, middle, middle, late, upper	Paleozoic	early, lower, middle, middle, late, upper
Quaternary Holocene (Recent) Pleistocene Tertiary (Neogene + Paleogene) Pliocene Miocene Oligocene Eocene Paleocene	early, lower, late, upper early, lower, late, upper early, lower, late, upper early, lower, late, upper early, lower, late, upper early, lower, middle, middle, late, upper early, lower, late, upper early, lower, middle, middle, late, upper early, lower, late, upper	Permian Late, Upper Early, Lower Carboniferous Pennsylvanian or Late, Upper Carboniferous Mississippian or Early, Lower Carboniferous Devonian Late, Upper Middle, Middle Early, Lower Silurian Late, Upper Early, Lower Ordovician Late, Upper Middle, Middle Early, Lower Cambrian Late, Upper Middle, Middle Early, Lower	middle, middle middle, middle middle, middle **
Mesozoic	early, lower, middle, middle, late, upper	Precambrian	early, lower, middle, middle, late, upper
Cretaceous Late, Upper Early, Lower Jurassic Late, Upper Middle, Middle Early, Lower Triassic Late, Upper Middle, Middle Early, Lower	middle, middle	Proterozoic Late Middle Early Archean Late Middle Early	upper, Precambrian Z and VI middle, Precambrian Y and V lower, Precambrian X and IV upper, Precambrian W and III middle, Precambrian V and II lower, Precambrian U and I ***

* For tables of generally accepted formal Age/Stage names, see one or more of the following: Salvador (1985); Palmer (1983); Harland et al. (1982); Odin (1982a, b; 1984). These references include isotopic ages of Age/Stage boundaries. They do not, however, agree on all Age/Stage names or numerical ages of boundaries.

** The four references cited above formally recognize a two-fold subdivision of the Silurian. The US Geological Survey formally recognizes three (Luttrell et al. 1986).

*** Regular, or Roman numerals are widely used for Precambrian subdivisions in the USSR.

Reproduced from The Journal of Sedimentary Petrology, Vol. 57, No. 2, March 1987, p. 363-372 by permission of The Society of Economic Paleontologists and Mineralogists

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**Geochronologic and Chronostratigraphic Nomenclature to be used in AAPG Publications**