Hettangian

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 Ma and 199.3 ± 0.3 Ma (million years ago).^[4] The Hettangian follows the Rhaetian (part of the Triassic Period) and is followed by the Sinemurian.^[5]

Hettangian
201.4 ± 0.2 – 199.5 ± 0.3 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Chronology
−205 — – −200 — – −195 — – −190 — – −185 — – −180 — – −175 — – −170 — – −165 — – −160 — – −155 — – −150 — – −145 — – −140 — Mesozoic T Jurassic K LT Early Middle Late EK Rhaetian Hettangian Sinemurian Pliensbachian Toarcian Aalenian Bajocian Bathonian Callovian Oxfordian Kimmeridgian Tithonian Berriasian       ← Triassic–Jurassic extinction event Subdivision of the Jurassic according to the ICS, as of 2024.[1] Vertical axis scale: Millions of years ago
Etymology
Name formality	Formal
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Age
Stratigraphic unit	Stage
Time span formality	Formal
Lower boundary definition	FAD of the Ammonite Psiloceras spelae tirolicum.
Lower boundary GSSP	Kuhjoch section, Karwendel mountains, Northern Calcareous Alps, Austria 47.4839°N 11.5306°E / 47.4839; 11.5306
Lower GSSP ratified	2010[2]
Upper boundary definition	FAD of the Ammonites Vermiceras quantoxense and Vermiceras palmeri
Upper boundary GSSP	East Quantoxhead, West Somerset, England, UK 51.1909°N 3.2364°W / 51.1909; -3.2364
Upper GSSP ratified	2000[3]

In European stratigraphy the Hettangian is a part of the time span in which the Lias 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.

Stratigraphic definitions

The Hettangian was introduced in the literature by Swiss palaeontologist, Eugène Renevier, in 1864. The stage takes its name from Hettange-Grande, a town in north-eastern France, just south of the border with Luxembourg on the main road from Luxembourg City to Metz.

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.^[6] The top of the Hettangian Stage (the base of the Sinemurian) is at the first appearances of ammonite genera Vermiceras and Metophioceras.

Biostratigraphy

The Hettangian contains three ammonite biozones in the Tethys domain:

• zone of Schlotheimia angulata
• zone of Alsatites liasicus
• zone of Psiloceras planorbis

See also

• Triassic-Jurassic extinction event