The Hettangian is the earliest

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

and lowest

stage Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

of the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

Period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

of the

geologic timescale The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochron ...

. It spans the time between 201.3 ± 0.2 Ma and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

(part of the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

Period) and is followed by the

Sinemurian In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...

. 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 The Blue Lias is a formation (stratigraphy), geological formation in southern, eastern and western England and parts of South Wales, part of the Lias Group. The Blue Lias consists of a sequence of limestone and shale layers, laid down in latest ...

, which has an upper Rhaetian to Sinemurian age. Another example is the lower Lias from the

Northern Limestone Alps The Northern Limestone Alps (), also called the Northern Calcareous Alps, are the ranges of the Eastern Alps north of the Central Eastern Alps located in Austria and the adjacent Bavarian lands of southeastern Germany. The distinction from the ...

where well-preserved but very rare ammonites, including ''

Alsatites ''Alsatites '' is an extinct genus of cephalopod belonging to the Ammonite subclass. They lived during the Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic Period of the geologic timescale. It spans the time be ...

'', have been found.

Stratigraphic definitions

The Hettangian was introduced in the literature by Swiss palaeontologist,

Eugène Renevier Eugène Renevier (26 March 1831 – 4 May 1906) was a Swiss geologist. Biography Renevier was born in Lausanne, Switzerland on 26 March 1831, as a descendant of a noble family. After about three years of study at the polytechnical school of Stu ...

, in 1864. The stage takes its name from

Hettange-Grande Hettange-Grande (; ; Lorraine Franconian: ''Grouss-Hetténgen'') is a commune in the Moselle department in Grand Est in north-eastern France. The town gives its name to the Hettangian age, the earliest age of the Jurassic period of the geolog ...

, a town in north-eastern

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

, just south of the border with

Luxembourg Luxembourg, officially the Grand Duchy of Luxembourg, is a landlocked country in Western Europe. It is bordered by Belgium to the west and north, Germany to the east, and France on the south. Its capital and most populous city, Luxembour ...

on the main road from

Luxembourg City Luxembourg (; ; ), also known as Luxembourg City ( or ; ; or ), is the capital city of Luxembourg and the Communes of Luxembourg, country's most populous commune. Standing at the confluence of the Alzette and Pétrusse rivers in southern Luxe ...

Metz Metz ( , , , then ) is a city in northeast France located at the confluence of the Moselle (river), Moselle and the Seille (Moselle), Seille rivers. Metz is the Prefectures in France, prefecture of the Moselle (department), Moselle Departments ...

. The base of the Hettangian Stage (which is also the base of the Lower Jurassic

Series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used i ...

and the entire Jurassic

System A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its open system (systems theory), environment, is described by its boundaries, str ...

) is defined as the place in the stratigraphic column where fossils of the

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

Psiloceras ''Psiloceras'' is an extinct genus of ammonite. ''Psiloceras'' is among the earliest known Jurassic ammonites, and the appearance of the earliest ''Psiloceras'' species form the definition for the base of the Jurassic. Unlike most earlier ammonit ...

'' first appear. A global reference profile (a

GSSP A Global Boundary Stratotype Section and Point (GSSP), sometimes referred to as a golden spike, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. ...

) for the base was defined 2010 for an exposure of the Kendlbach Formation at the Kuhjoch section in the

Karwendel Mountains The Karwendel is the largest mountain range of the Northern Limestone Alps. It is located on the Austria–Germany border. The major part belongs to the Austrian federal state of Tyrol, while the adjacent area in the north is part of Bavaria, ...

of western

Austria Austria, formally the Republic of Austria, is a landlocked country in Central Europe, lying in the Eastern Alps. It is a federation of nine Federal states of Austria, states, of which the capital Vienna is the List of largest cities in Aust ...

.GSSP Table
The top of the Hettangian Stage (the base of the Sinemurian) is at the first appearances of ammonite

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

Vermiceras ''Vermiceras'' is an ammonite that belongs to the order Ammonitida. Its shell is evolute and is covered in nonbranching ribs. Its whorls do not increase in size very fast, but there are many revolutions on its shell, which is fairly narrow. It h ...

'' and '' Metophioceras''.

Biostratigraphy

The Hettangian contains three ammonite

biozone In biostratigraphy, biostratigraphic units or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxon, taxa, as opposed to a Lithostratigraphy, lithostratigraphic unit which is defined by the ...

s in the Tethys domain: *zone of '' Schlotheimia angulata'' *zone of '' Alsatites liasicus'' *zone of '' Psiloceras planorbis''

References

Notes

Literature

*; 2004: ''A Geologic Time Scale 2004'',

Cambridge University Press Cambridge University Press was the university press of the University of Cambridge. Granted a letters patent by King Henry VIII in 1534, it was the oldest university press in the world. Cambridge University Press merged with Cambridge Assessme ...

. *: ''Notices géologiques et paléontologiques sur les Alpes Vaudoises, et les régions environnantes. I. Infralias et Zone à Avicula contorta (Étage Rhaetien) des Alpes Vaudoises'' Bulletin de la Société Vaudoise des Sciences Naturelles 8, p. 39–97.

External links

GeoWhen Database - HettangianLower Jurassic timescale
at the website of the subcommission for stratigraphic information of the ICS
Stratigraphic chart of the Lower Jurassic
at the website of Norges Network of offshore records of geology and stratigraphy {{Geological history, p, m *01 Geological ages