Abstract:

The dating methods of relative age and absolute age of lunar stratigraphic units are summarized. There are four ways to establish the relative age: the geological law of superposition, crater sizefrequency distribution, crater morphology as degradation, and soil maturity, whereas the absolute age can be determined only by isotopic geochronology or lunar cratering chronology. To better know about the lunar stratigraphic subdivisions presently used, the formation and evolution of the stratigraphic units are reviewed here. Based on the analysis of the established lunar stratigraphic subdivisions and lunar evolution theory, we suggest that use the term Eolunarisian Eon for representation of the lunar history when endogenic process dominated, that use the term Paleolunarisian Eon for the lunar history when endogenic process and exogenic process were both weighty, and that use the term Neolunarisian Eon for the lunar history when exogenic process dominated. And we propose that the pre-Nectarian Period could be substituted by pre-Aitkenian Period and Aitkenian Period, and the two periods are divided by the impact event forming south poleaitken basin. The pre-Aitkenian Period was included in Eolunarisian Eon, while the Aitken Period represents the early stage of Paleolunarisian Eon, during which the impact event was the most typical geologic process. This kind of modified subdivisions not only corresponds to the lunar dynamic evolvement rule, but also provides convenience for the study of lunar farside.

Key words:  geochronology, stratigraphic unit, south pole-aitken basin, the Aitkenian Period