Hettangium

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system series step ≈ age ( mya )
higher higher higher younger
law Upper Jurassic Tithonium 145
⬍
152.1
Kimmeridgium 152.1
⬍
157.3
Oxfordium 157.3
⬍
163.5
Middle Jurassic Callovium 163.5
⬍
166.1
Bathonium 166.1
⬍
168.3
Bajocium 168.3
⬍
170.3
Aalenium 170.3
⬍
174.1
Lower Jurassic Toarcium 174.1
⬍
182.7
Pliensbachium 182.7
⬍
190.8
Sinemurium 190.8
⬍
199.3
Hettangium 199.3
⬍
201.3
deeper deeper deeper older

The Hettangium (in German often shortened to Hettang , more rarely also modified to Hettangien) is a chronostratigraphic stage of the Jura in geological history , which geochronologically corresponds to the period from 201.3 to 199.3 million years ago and thus lasted about two million years. The hettangium is the first (oldest) stage of the Jurassic (or the Lower Jurassic series) and follows the stage of the rhaetium of the Upper Triassic . The Hettangium is followed by the Sinemurium .

History and naming

The hettangium was named after the place Hettange-Grande ( Département Moselle ) in Lorraine (France). The stage and name were suggested by Eugène Renevier in 1864.

Definition and GSSP

The beginning of the hettangium is defined by the first appearance of the ammonite species Psiloceras spelae * . The GSSP (= "Global Stratotype Section and Point", corresponds roughly to a type profile) is located on the Kuhjoch in the Karwendel in Austria . The first appearance of the ammonite genera Vermiceras and Metophioceras was set as the upper limit or rather as the beginning of the Sinemurian .

* This taxon appears first after the mass extinction at the Triassic-Jura border and follows in the fossil record on the Ceratites Choristoceras marshi and Choristoceras crickmayi , the last ammonites of the Triassic. Psiloceras spelae however, derives not from ceratites but by late Triassic Phylloceratiden from.

Breakdown

Psiloceras planorbis from Watchet, England

The hettangium has so far been divided into three well-defined ammonite zones and nine subzones (from hanging to lying ):

However, the further subdivision of the Lower Hettangium has not been fully clarified. These layers are often summarized as "preplanorbis layers". Some authors distinguish different biostratigraphic horizons within the "preplanorbis layers", including an unnamed zone in Europe with Neophyllites antecedens and Neophyllites imitans, as well as Psiloceras erugatum . Below the erugatum horizon then follows the Psiloceras tilmanni zone with Psiloceras pacificum , Psiloceras tilmanni and Psiloceras spelae at the base.

Sea level

In general, the sea ​​level was rising during the entire Hettangian period (Hettangic transgression). However, three regression / transgression cycles were superimposed on this long-term trend. Immediately at the beginning of the hettangium there was a drastic decrease, the regression He 1 . The second regression He 1.1 then occurred at the beginning of the Caloceras johnstoni subzone . He 2 was at the beginning of the Alsatites liasicus zone . He 3 finally separated the Schlotheimia extranodosa from the Schlotheimia complanata subzone . After this last regression, the sea level rose again further into the Sinemurium. The three cycles showed increasing intensity towards the hanging wall.

Chemical stratigraphy

Carbon isotopes

The δ 13 C values ​​for the hettangium range between 1 and 2 ‰ (PDB), with their maximum in the middle section. They are therefore generally somewhat lower than in the rest of the Jura, i.e. H. the organic carbon production was lower or the prevailing conditions a little more anoxic and restrictive.

Oxygen isotopes

The values ​​for δ 18 O are - 2 ‰ (PDB) with a slightly increasing tendency. With the exception of the Toarcian, they are lower than in the rest of the Jura and suggest a fairly warm climate in the Hettangian, which, however, gradually cooled.

Strontium isotopes

The ratio of 87 Sr / 86 Sr in sea water was very high with an average of 0.7077. It reached a maximum value at the end of the hettangium and then fell steadily until the beginning of the toarcium. The drop in the strontium ratio after the hettangium is correlated with increased submarine volcanism and is likely to reflect the increasing opening of the North Atlantic (breaking up of the Pangea and reducing continental sediment input).

Biostratigraphy

Dinoflagellates

The hettangium forms the lower half of the dinoflagellate zone Dpr , named after the predominant taxon in the boreal region, Dapcodinium priscum . As a zone designation for the Hettangian also is DSJ1 in use.

Calcareous nannoplankton

The calcareous nannoplankton appeared for the first time in the world's oceans shortly before the start of the hettangium with the end-Triassic transgression.

The hettangium belongs entirely to the nannoplankton zone NJ1 , which is characterized by the first appearance ( FAD ) of the taxon Schizosphaerella punctulata . This ends with the first appearance of Parhabdolithus liasicus .

Foraminifera

Based on the foraminifera , three zones can be identified for the hettangium:

Living world

Mass extinction

The turn of the Triassic / Jurassic is one of the five most important mass extinctions in the history of the earth. The conodonts fell victim to this event , but there was also a drastic decline in biodiversity among the ammonites and the bivalvia.

fauna

Ammonite Alsatites proaries , a medium-Hettangian representative from the group of the Arietitidae, collected in the Northern Limestone Alps , private collection Reiter

During the Hettangian, the seas were populated by predatory ichthyosaurs with the taxon Ichthyosaurus , Leptonectes and Temnodontosaurus, and by plesiosaurs with Atychodracon , Macroplata and Rhomaleosaurus . They were the predators of the ammonites , which gradually spread again in the oceans after the extinction event at the Triassic-Jura border. The appearance of the neoammonoids (ammonites in the narrower sense) in the early Hettangian is characteristic of the fauna change at the Triassic-Jura border. These undergo a relatively fast radiation , so that a larger number of genera and species already existed again in the middle Hettangian. In contrast to later epochs, the fossilization conditions were apparently not optimal, so that only a few sites with well-preserved hettangium ammonites are known worldwide.

Live reconstruction of the primitive crocodile Protosuchus

In the continental vertebrate fauna were dinosaurs prevalent, including the bird dinosaurs ( Ornithischia ) with the "primitive" species Abrictosaurus , fabrosaurus , Heterodontosaurus , Lanasaurus , Lycorhinus , Scelidosaurus , scutellosaurus and Stormbergia and lizards dinosaurs ( Saurischia ) with theropods such Lophostropheus and the oldest Jurassic Dracoraptor dinosaur . The body fossil record of the terrestrial vertebrates of the Hettangium is generally sparse. It is different with corresponding trace fossils . The localities in the Mecsek Mountains in Hungary, from which the genus Komlosaurus was described, offer a European example . In North America, extensive trace material is found on the east coast in the sediments of the Newark supergroup .

The airspace was dominated by "primitive" (long-tailed) pterosaurs such as Dimorphodon .

Typical representatives of the archosaur crocodile line are Sphenosuchus and Protosuchus , an early genus of the "crocodiles in the broader sense" ( Crocodyliformes ).

As a representative of early mammals is Haramiya to name.

Occurrence

Grès de Luxembourg (Grès d'Hettange)
General reports
Handpiece of transgression anesthesia of the Aquitaine pelvis at Nontron

The hettangium is (partially) represented in the following countries in the form of the following rock units (selection):

Individual evidence

  1. ↑ A. v. Hillebrandt, L. Krystyn, WM Kürschner, NR Bonis, M. Ruhl, S. Richoz, MAN Schobben, M. Urlichs, PR Bown, K. Kment, CA McRoberts, M. Simms, A. Tomãsových: The Global Stratotype Sections and Point (GSSP) for the base of the Jurassic System at Kuhjoch (Karwendel Mountains, Northern Calcareous Alps, Tyrol, Austria). Episodes. Vol. 36, No. 3, 2013, pp. 162–198 ( PDF 7.9 MB)
  2. ^ Jean Guex: Relations entre le genre Psiloceras et les Phylloceratida au voisinage de la limite Trias-Jurassique. Bulletin de la Société Vaudoise des Sciences Naturelles. Vol. 76, No. 361, 1982, pp. 47-51, doi: 10.5169 / seals-278144
  3. ↑ Bloos, G .: Aspects of the turn Trias / Jura . Ed .: N. Hausche & V. Wilde. Trias - a completely different world. Dr. Friedrich Pfeil, Munich 1999, p. 43-68 .
  4. ↑ Martin D. Ezcurra, Gilles Cuny: The coelophysoid Lophostropheus airelensis , gen. Nov .: a review of the systematics of “Liliensternus” airelensis from the Triassic-Jurassic outcrops of Normandy (France). Journal of Vertebrate Paleontology. Vol. 27, No. 1, 2007, pp. 73–86, [[doi: 10.1671 / 0272-4634 (2007) 27 [73: TCLAGN] 2.0.CO; 2]] (alternative full text access: ResearchGate )
  5. ↑ David M. Martill, Steven U. Vidovic, Cindy Howells, John R. Nudds: The Oldest Jurassic Dinosaur: A Basal Neotheropod from the Hettangian of Great Britain. PLoS One. Vol. 11, No. 4, 2016, Item No. e0154352, doi: 10.1371 / journal.pone.0145713
  6. ↑ Attila Ősi, József Pálfy, Lászlá Makádi, Zoltán Szentesi, Péter Gulyás, Márton Rabi, Gábor Botfalvai, Kinga Hips: Hettangian (Early Jurassic) Dinosaur Tracksites from the Mecsek Mountains, Hungary. Ichnos. Vol. 18, 2011, pp. 79-94, doi: 10.1080 / 10420940.2011.573603
  7. ^ Robert E. Weems, Lawrence H. Tanner, Spencer G. Lucas: Synthesis and revision of the lithostratigraphic groups and formations in the Upper Permian? –Lower Jurassic Newark Supergroup of eastern North America. Stratigraphy. Vol. 13, No. 2, 2016, pp. 111-153

literature

  • Gert Bloos and Kevin N. Page: Global Stratotype Section and Point for base of the Sinemurian Stage (Lower Jurassic) . In: Episodes . tape 25 (1) . Beijing 2001, p. 22-28 . PDF
  • Felix Gradstein, Jim Ogg, Jim & Alan Smith: A Geologic timescale . Cambridge University Press, 2005, ISBN 978-0-521-78673-7 .
  • Hans Murawski & Wilhelm Meyer: Geological dictionary. 10., rework. u. exp. Ed., 278 . Enke Verlag, Stuttgart 1998, ISBN 3-432-84100-0 .
  • Eugène Renevier: Notices géologiques et paleontologiques sur les Alpes Vaudoises, et les régions environnantes. I. Infralias et Zone à Avicula contorta (Ét. Rhaetien) des Alpes Vaudoises. In: Bulletin de la Société Vaudoise des Sciences Naturelles . tape 8 . Lausanne 1864, p. 39-97 .

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