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The Hettangian is the earliest age and lowest stage of the Jurassic Period of the geologic timescale. It spans the time between 201.3 ± 0.2 annum and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triassic Period) and is followed by the Sinemurian.For a detailed geologic timescale, see Gradstein et al. (2004)
In European stratigraphy the Hettangian is a part of the time span in which the Lias Group was deposited. An example is the British Blue Lias, which has an upper Rhaetian to Sinemurian age. Another example is the lower Lias from the Northern Limestone Alps where well-preserved but very rare ammonites, including Alsatites, have been found.
The base of the Hettangian Stage (which is also the base of the Lower Jurassic Series and the entire Jurassic System) is defined as the place in the stratigraphic column where fossils of the ammonite genus Psiloceras first appear. A global reference profile (a GSSP) for the base was defined 2010 for an exposure of the Kendlbach Formation at the Kuhjoch section in the Karwendel Mountains of western Austria. GSSP Table The top of the Hettangian Stage (the base of the Sinemurian) is at the first appearances of ammonite genus Vermiceras and Metophioceras.
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