Hettangian

The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 199.6 ± 0.6 Ma and 196.5 ± 1 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triassic period) and is followed by the Sinemurian.