In the Lunar geologic timescale, the Lower Imbrian epoch occurred between 3850 million years ago to about 3800 million years ago. The impact which created the Mare Imbrium basin occurred at the start of the epoch, and it represents the period during which the newer large basins were formed. These filled with basalt largely during the following Upper Imbrian epoch. The Lower Imbriam was preceded by the Nectarian.