Editing Jurassic (section)

=== Stratigraphy ===
[[File:Folding Gasteretal.jpg|thumb|Folded Lower Jurassic limestone layers of the Doldenhorn [[nappe]] at [[Kander (Switzerland)|Gasteretal]], Switzerland]]
[[File:Fm Lajas Maquina Cura.jpg|thumb|Middle Jurassic strata in [[Neuquén Province]], Argentina]]
[[File:Tidwell Member of the Morrison Formation over Wanakah Formation (Jurassic; roadcut near Artists Point, Colorado National Monument, Colorado, USA) 1 (23644153939).jpg|thumb|Tidwell Member of the Morrison Formation (Upper Jurassic), Colorado]]

Jurassic stratigraphy is primarily based on the use of ammonites as [[Biostratigraphy#Index fossils|index fossils]]. The [[first appearance datum]] of specific ammonite [[Taxon|taxa]] is used to mark the beginnings of stages, as well as smaller timespans within stages, referred to as "ammonite zones"; these, in turn, are also sometimes subdivided further into subzones. Global stratigraphy is based on standard European ammonite zones, with other regions being calibrated to the European successions.<ref name="Ogg-2012" /> [[File:Aalenian_GSSP_-_Golden_spike_ceremony_-_Fuentelsaz,_Guadalajara,_Spain_08.jpg|thumb|Base Aalenian GSSP at [[Fuentelsaz]]]]

==== Early Jurassic ====
The oldest part of the Jurassic Period has historically been referred to as the Lias or Liassic, roughly equivalent in extent to the Early Jurassic, but also including part of the preceding [[Rhaetian]]. The Hettangian Stage was named by Swiss palaeontologist [[Eugène Renevier]] in 1864 after [[Hettange-Grande]] in north-eastern France.<ref name="Ogg-2012" /> The GSSP for the base of the Hettangian is located at the Kuhjoch Pass, [[Karwendel|Karwendel Mountains]], [[Northern Limestone Alps|Northern Calcareous Alps]], Austria; it was ratified in 2010. The beginning of the Hettangian, and thus the Jurassic as a whole, is marked by the [[First appearance datum|first appearance]] of the ammonite ''[[Psiloceras|Psiloceras spelae tirolicum]]'' in the [[Kendlbach Formation]] exposed at Kuhjoch.<ref>{{Cite journal|last1=Hillebrandt|first1=A.v.|last2=Krystyn|first2=L.|last3=Kürschner|first3=W.M.|last4=Bonis|first4=N.R.|last5=Ruhl|first5=M.|last6=Richoz|first6=S.|last7=Schobben|first7=M. A. N.|last8=Urlichs|first8=M.|last9=Bown|first9=P.R.|last10=Kment|first10=K.|last11=McRoberts|first11=C.A.|date=2013-09-01|title=The Global Stratotype Sections and Point (GSSP) for the base of the Jurassic System at Kuhjoch (Karwendel Mountains, Northern Calcareous Alps, Tyrol, Austria)|journal=Episodes|language=en|volume=36|issue=3|pages=162–198|doi=10.18814/epiiugs/2013/v36i3/001|issn=0705-3797|doi-access=free}}</ref> The base of the Jurassic was previously defined as the first appearance of ''Psiloceras planorbis'' by Albert Oppel in 1856–58, but this was changed as the appearance was seen as too localised an event for an international boundary.<ref name="Ogg-2012" />

The Sinemurian Stage was first defined and introduced into scientific literature by Alcide d'Orbigny in 1842. It takes its name from the French town of [[Semur-en-Auxois]], near [[Dijon]]. The original definition of Sinemurian included what is now the Hettangian. The GSSP of the Sinemurian is located at a cliff face north of the hamlet of [[East Quantoxhead]], 6 kilometres east of [[Watchet]], [[Somerset]], [[England]], within the [[Blue Lias]], and was ratified in 2000. The beginning of the Sinemurian is defined by the first appearance of the ammonite ''[[Vermiceras|Vermiceras quantoxense]].''<ref name="Ogg-2012">{{Citation|last1=Ogg|first1=J.G.|title=Jurassic|date=2012|url=https://linkinghub.elsevier.com/retrieve/pii/B9780444594259000263|work=The Geologic Time Scale|pages=731–791|publisher=Elsevier|language=en|doi=10.1016/b978-0-444-59425-9.00026-3|isbn=978-0-444-59425-9|access-date=2020-12-05|last2=Hinnov|first2=L.A.|last3=Huang|first3=C.}}</ref><ref>{{Cite journal|last1=Bloos|first1=Gert|last2=Page|first2=Kevin N.|date=2002-03-01|title=Global Stratotype Section and Point for base of the Sinemurian Stage (Lower Jurassic)|journal=Episodes|volume=25|issue=1|pages=22–28|doi=10.18814/epiiugs/2002/v25i1/003|issn=0705-3797|doi-access=free}}</ref>

Albert Oppel in 1858 named the Pliensbachian Stage after the hamlet of [[Pliensbach]] in the community of [[Zell unter Aichelberg]] in the [[Swabian Alb]], near [[Stuttgart]], Germany. The GSSP for the base of the Pliensbachian is found at the Wine Haven locality in [[Robin Hood's Bay]], [[Yorkshire]], England, in the [[Redcar Mudstone Formation]], and was ratified in 2005. The beginning of the Pliensbachian is defined by the first appearance of the ammonite ''[[Bifericeras|Bifericeras donovani]]''.<ref>{{Cite journal|last1=Meister|first1=Christian|last2=Aberhan|first2=Martin|last3=Blau|first3=Joachim|last4=Dommergues|first4=Jean-Louis|last5=Feist-Burkhardt|first5=Susanne|last6=Hailwood|first6=Ernie A.|last7=Hart|first7=Malcom|last8=Hesselbo|first8=Stephen P.|last9=Hounslow|first9=Mark W.|last10=Hylton|first10=Mark|last11=Morton|first11=Nicol|date=2006-06-01|title=The Global Boundary Stratotype Section and Point (GSSP) for the base of the Pliensbachian Stage (Lower Jurassic), Wine Haven, Yorkshire, UK|journal=Episodes|volume=29|issue=2|pages=93–106|doi=10.18814/epiiugs/2006/v29i2/003|issn=0705-3797|doi-access=free}}</ref>

The village [[Thouars]] (Latin: ''Toarcium''), just south of [[Saumur]] in the [[Loire Valley]] of [[France]], lends its name to the Toarcian Stage. The Toarcian was named by Alcide d'Orbigny in 1842, with the original locality being Vrines quarry around 2&nbsp;km northwest of Thouars. The GSSP for the base of the Toarcian is located at [[Peniche, Portugal]], and was ratified in 2014. The boundary is defined by the first appearance of ammonites belonging to the subgenus ''[[Dactylioceras]]'' [[Dactylioceras|(''Eodactylites'')]]''.''<ref>{{Cite journal|last1=Rocha|first1=Rogério Bordalo da|last2=Mattioli|first2=Emanuela|last3=Duarte|first3=Luís Vítor|last4=Pittet|first4=Bernard|last5=Elmi|first5=Serge|last6=Mouterde|first6=René|last7=Cabral|first7=Maria Cristina|last8=Comas-Rengifo|first8=Maria José|last9=Gómez|first9=Juan José|last10=Goy|first10=António|last11=Hesselbo|first11=Stephen P.|date=2016-09-01|title=Base of the Toarcian Stage of the Lower Jurassic defined by the Global Boundary Stratotype Section and Point (GSSP) at the Peniche section (Portugal)|journal=Episodes|language=en|volume=39|issue=3|pages=460–481|doi=10.18814/epiiugs/2016/v39i3/99741|s2cid=131791652 |issn=0705-3797|doi-access=free|hdl=10261/140775|hdl-access=free}}</ref>

==== Middle Jurassic ====
The Aalenian is named after the city of [[Aalen]] in Germany. The Aalenian was defined by Swiss geologist [[Karl Mayer-Eymar]] in 1864. The lower boundary was originally between the dark clays of the Black Jurassic and the overlying clayey sandstone and [[Iron|ferruginous]] oolite of the Brown Jurassic sequences of southwestern Germany.<ref name="Ogg-2012" /> The GSSP for the base of the Aalenian is located at [[Fuentelsaz]] in the [[Sistema Ibérico|Iberian range]] near [[Guadalajara, Spain]], and was ratified in 2000. The base of the Aalenian is defined by the first appearance of the ammonite ''[[Leioceras|Leioceras opalinum]]''.<ref>{{Cite journal|last1=Barrón|first1=Eduardo|last2=Ureta|first2=Soledad|last3=Goy|first3=Antonio|last4=Lassaletta|first4=Luis|date=August 2010|title=Palynology of the Toarcian–Aalenian Global Boundary Stratotype Section and Point (GSSP) at Fuentelsaz (Lower–Middle Jurassic, Iberian Range, Spain)|url=https://linkinghub.elsevier.com/retrieve/pii/S0034666710000898|journal=Review of Palaeobotany and Palynology|language=en|volume=162|issue=1|pages=11–28|doi=10.1016/j.revpalbo.2010.04.003|bibcode=2010RPaPa.162...11B }}</ref>

Alcide d'Orbigny in 1842 named the Bajocian Stage after the town of [[Bayeux]] (Latin: ''Bajoce'') in Normandy, France. The GSSP for the base of the Bajocian is located in the Murtinheira section at [[Cabo Mondego]], Portugal; it was ratified in 1997. The base of the Bajocian is defined by the first appearance of the ammonite ''[[Hyperlioceras|Hyperlioceras mundum]].''<ref>{{Cite journal|last1=Pavia|first1=G.|last2=Enay|first2=R.|date=1997-03-01|title=Definition of the Aalenian-Bajocian Stage boundary|journal=Episodes|volume=20|issue=1|pages=16–22|doi=10.18814/epiiugs/1997/v20i1/004|issn=0705-3797|doi-access=free}}</ref>

The Bathonian is named after the city of [[Bath, Somerset|Bath]], England, introduced by Belgian geologist [[Jean Baptiste Julien d'Omalius d'Halloy|d'Omalius d'Halloy]] in 1843, after an incomplete section of oolitic limestones in several quarries in the region. The GSSP for the base of the Bathonian is Ravin du Bès, Bas-Auran area, [[Alpes-de-Haute-Provence|Alpes de Haute Provence]], France; it was ratified in 2009. The base of the Bathonian is defined by the first appearance of the ammonite ''[[Gonolkites|Gonolkites convergens]]'', at the base of the [[Zigzagiceras|''Zigzagiceras zigzag'']] ammonite zone''.''<ref>{{cite journal|last1=López|first1=Fernández|last2=Rafael|first2=Sixto|last3=Pavia|first3=Giulio|last4=Erba|first4=Elisabetta|last5=Guiomar|first5=Myette|last6=Paiva Henriques|first6=María Helena|last7=Lanza|first7=Roberto|last8=Mangold|first8=Charles|last9=Morton|first9=Nicol|last10=Olivero|first10=Davide|last11=Tiraboschi|first11=Daniele|date=2009|title=The Global Boundary Stratotype Section and Point (GSSP) for base of the Bathonian Stage (Middle Jurassic), Ravin du Bès Section, SE France|journal=Episodes|volume=32|issue=4|pages=222–248|doi=10.18814/epiiugs/2009/v32i4/001|doi-access=free |s2cid=51754708 |df=dmy}}</ref>

The Callovian is derived from the [[Latinisation of names|Latinized]] name of the village of [[Kellaways]] in [[Wiltshire]], England, and was named by Alcide d'Orbigny in 1852, originally the base at the contact between the [[Forest Marble Formation]] and the [[Cornbrash Formation]]. However, this boundary was later found to be within the upper part of the Bathonian.<ref name="Ogg-2012" /> The base of the Callovian does not yet have a certified GSSP. The working definition for the base of the Callovian is the first appearance of ammonites belonging to the genus ''[[Kepplerites]].<ref name="jurassic.stratigraphy.org">{{Cite web|title=International Commission on Stratigraphy-Subcommission on Jurassic Stratigraphy|url=https://jurassic.stratigraphy.org/our-work|access-date=2021-04-09|website=jurassic.stratigraphy.org}}</ref>''

==== Late Jurassic ====
The Oxfordian is named after the city of [[Oxford]] in England and was named by Alcide d'Orbigny in 1844 in reference to the [[Oxford Clay]]. The base of the Oxfordian lacks a defined GSSP. [[William Joscelyn Arkell|W. J. Arkell]] in studies in 1939 and 1946 placed the lower boundary of the Oxfordian as the first appearance of the ammonite ''[[Quenstedtoceras|Quenstedtoceras mariae]]'' (then placed in the genus ''[[Vertumniceras]]''). Subsequent proposals have suggested the first appearance of ''[[Cardioceras|Cardioceras redcliffense]]'' as the lower boundary.<ref name="Ogg-2012" /><ref name="jurassic.stratigraphy.org" />

The village of [[Kimmeridge]] on the coast of [[Dorset]], England, is the origin of the name of the Kimmeridgian. The stage was named by Alcide d'Orbigny in 1842 in reference to the [[Kimmeridge Clay]]. The GSSP for the base of the Kimmeridgian is the Flodigarry section at [[Staffin|Staffin Bay]] on the [[Isle of Skye]], [[Scotland]],<ref>{{Cite journal|last=BARSKI|first=Marcin|date=2018-09-06|title=Dinoflagellate cyst assemblages across the Oxfordian/Kimmeridgian boundary (Upper Jurassic) at Flodigarry, Staffin Bay, Isle of Skye, Scotland – a proposed GSSP for the base of the Kimmeridgian|url=http://dx.doi.org/10.5604/01.3001.0012.4594|journal=Volumina Jurassica|volume=XV|issue=1|pages=51–62|doi=10.5604/01.3001.0012.4594|doi-broken-date=1 November 2024 |s2cid=133861564|issn=1731-3708}}</ref> which was ratified in 2021. The boundary is defined by the first appearance of ammonites marking the boreal Bauhini Zone and the subboreal Baylei Zone.<ref name="jurassic.stratigraphy.org" />

The Tithonian was introduced in scientific literature by Albert Oppel in 1865. The name Tithonian is unusual in geological stage names because it is derived from [[Greek mythology]] rather than a place name. [[Tithonus]] was the son of [[Laomedon]] of [[Troy]] and fell in love with [[Eos]], the Greek goddess of [[dawn]]. His name was chosen by Albert Oppel for this [[Stratigraphy|stratigraphical]] stage because the Tithonian finds itself hand in hand with the dawn of the Cretaceous. The base of the Tithonian currently lacks a GSSP.<ref name="Ogg-2012" /> The working definition for the base of the Tithonian is the first appearance of the ammonite genus ''[[Gravesia (ammonite)|Gravesia]]''.<ref name="jurassic.stratigraphy.org" />

The upper boundary of the Jurassic is currently undefined, and the Jurassic–Cretaceous boundary is currently the only system boundary to lack a defined GSSP. Placing a GSSP for this boundary has been difficult because of the strong regionality of most biostratigraphic markers, and lack of any [[Chemostratigraphy|chemostratigraphic]] events, such as [[isotope]] excursions (large sudden changes in [[Stable isotope ratio|ratios of isotopes]]), that could be used to define or correlate a boundary. [[Calpionellid]]s, an enigmatic group of [[plankton]]ic [[protist]]s with urn-shaped calcitic [[Test (biology)|tests]] briefly abundant during the latest Jurassic to earliest Cretaceous, have been suggested to represent the most promising candidates for fixing the Jurassic–Cretaceous boundary<ref>{{Cite journal|last=WIMBLEDON|first=William A.P.|date=2017-12-27|title=Developments with fixing a Tithonian/Berriasian (J/K) boundary|url=https://www.researchgate.net/publication/321670503|journal=Volumina Jurassica|volume=15 |issue=1 |pages=107–112|doi=10.5604/01.3001.0010.7467|doi-broken-date=2024-11-14 |issn=1731-3708}}</ref> In particular, the first appearance ''[[Calpionella|Calpionella alpina]],'' co-inciding with the base of the eponymous Alpina subzone, has been proposed as the definition of the base of the Cretaceous.<ref>{{Cite journal|last1=Wimbledon|first1=William A.P.|last2=Rehakova|first2=Daniela|last3=Svobodová|first3=Andrea|last4=Schnabl|first4=Petr|last5=Pruner|first5=Petr|last6=Elbra|first6=Tiiu|last7=Šifnerová|first7=Kristýna|last8=Kdýr|first8=Šimon|last9=Frau|first9=Camille|last10=Schnyder|first10=Johann|last11=Galbrun|first11=Bruno|date=2020-02-11|title=Fixing a J/K boundary: A comparative account of key Tithonian–Berriasian profiles in the departments of Drôme and Hautes-Alpes, France|url=https://www.sav.sk/index.php?lang=sk&doc=journal-list&part=article_response_page&journal_article_no=18100|journal=Geologica Carpathica|volume=71|issue=1|doi=10.31577/GeolCarp.71.1.3|s2cid=213694912|doi-access=free|bibcode=2020GCarp..71..1.3W }}</ref> The working definition for the boundary has often been placed as the first appearance of the ammonite ''[[Strambergella jacobi]],'' formerly placed in the genus ''[[Berriasella]]'', but its use as a stratigraphic indicator has been questioned, as its first appearance does not correlate with that of ''C. alpina''.<ref>{{Cite journal|last1=Frau|first1=Camille|last2=Bulot|first2=Luc G.|last3=Reháková|first3=Daniela|last4=Wimbledon|first4=William A.P.|last5=Ifrim|first5=Christina|date=November 2016|title=Revision of the ammonite index species Berriasella jacobi Mazenot, 1939 and its consequences for the biostratigraphy of the Berriasian Stage|url=http://linkinghub.elsevier.com/retrieve/pii/S0195667116301057|journal=Cretaceous Research|language=en|volume=66|pages=94–114|doi=10.1016/j.cretres.2016.05.007|bibcode=2016CrRes..66...94F }}</ref>