Pliensbachium

from Wikipedia, the free encyclopedia
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 Pliensbachian (in German usually shortened to Pliensbach, more rarely Pliensbachien) is in the Earth's history , a chronostratigraphic stage of the Jura , in the geochronological corresponding structure of the Earth's history as the period of 190.8 to about 182.7 million years. The Pliensbachium is followed by the Toarcium , the Pliensbachium is preceded by the Sinemurium .

Naming and history

The Pliensbachium was named after Pliensbach , the smaller suburb of the municipality of Zell unter Aichelberg in the district of Göppingen in the foothills of the central Swabian Alb , about 30 km east of Stuttgart. The stage and name were introduced by Albert Oppel in 1858.

Definition and GSSP

The beginning is determined by the first appearance of Bifericeras donovani and the genera Apoderoceras and Gleviceras . The end is defined by the first appearance of the ammonite genus Eodactylites . The Wine Haven profile in Robin Hood's Bay (Yorkshire, England) was determined for the Global Stratotype Section and Point (GSSP, corresponds roughly to a type profile) .

Subdivision of the Pliensbachium

Pleuroceras spinatum - Museum of Toulouse

The Pliensbachian in the boreal area (which also includes the southern and northern German Jura) is currently subdivided into the following ammonite zones and subzones (from the hanging wall to the horizontal ):

The following ammonite zones correspond to the Pliensbachian in the Tethyalen area :

Internally, there is a further subdivision into a lower Pliensbachium (regionally also known as " Carixium " - after the Latin name of Charmouth in Dorset ) and an upper Pliensbachium (" Domerium " - after Monte Domaro in the Lombard Alps ). The boundary between the two sub-stages is at the base of the Margaritatus zone and is determined by the first appearance (FAD) of Amaltheus stokesi .

The Pliensbachian is about the same time as the Charmouthian in North America .

Sea level

The Pliensbachian knows two significant transgressions and two regressions or eight small cycles. The first transgression occurred immediately at the beginning of the Pliensbachium. A longer decline followed, which finally culminated in the Pl 4 regression in the upper Davoei zone of the upper Carixium. The subsequent rather rapid transgression peaked in the Margaritatus zone in the lower domerium. Then the sea ​​level fell again to the regression Pl 8 shortly before the end of the Pliensbachian. The transgression pulses of the first cycle steadily decreased in size, whereas they gradually gained strength again in the second cycle.

Chemical stratigraphy

Carbon isotopes

The δ 13 C-values indicate the beginning of the Pliensbachiums a steady increase from a minimum at 1.9 ‰ (PDB) to a maximum value of 3.1 ‰ (PDB) at the end of the step. The transition to the toarcium was marked by a negative carbon excursion back to 1 ‰ (PDB), combined with the widespread sedimentation of C org -rich deposits.

Oxygen isotopes

The δ 18 O values were slightly lower than in the hettangium, but with - 1.0 to - 1.5 ‰ (PDB), they were comparable to the ratios in the Sinemurium. At the turn of the Toarcium, there was a sudden increase to 0.0 ‰ (PDB) and thus a significant cooling of the previously quite mild temperatures. This drop in temperature has been linked to the massive outflow of flood basalts of the Ferrar ( Antarctica ) and Karoo LIP ( South Africa ) that occurred 183 million years ago.

Strontium isotopes

The 87 Sr / 86 Sr values continued their steady decline starting from the end Triassic maximum at 0.70795 via 0.70740 at the beginning of the Pliensbachian and reached a minimum of 0.70708 towards the end of the stage. The end-Triassic maximum is likely to be due to the CAMP volcanism , which was accompanied by the first opening of the North Atlantic . The decline in strontium levels indicates decreasing continentality.

Biostratigraphy

Dinoflagellates

In the case of the dinoflagellate cysts, three zones can be distinguished for the Pliensbachium: DSJ 4 , DSJ 5 and DSJ 6 . The beginning of DSJ 4 and thus the Pliensbachium is determined by the last appearance (LAD) of Liasidium variabile . The first appearance (FAD) of Nannoceratopsis senex defines the beginning of zone DSJ 5 . At the beginning of zone DSJ 6 , Luehndea spinosa , Maturodinium inornatum , Nannoceratopsis gracilis and Valvaeodinium armatum appear for the first time . The Pliensbachium ends with the disappearance of Maturodinium inornatum and Valvaeodinium armatum .

Foraminifera

The foraminifera of the Pliensbachian are predominantly smaller benthic forms , as planktonic foraminifera first developed in the Dogger and then fully developed from the Lower Cretaceous . Denticulina varians and Denticulina tenuistrata appear for the first time in the middle of the Ibex zone (FAD). The Davoei zone is characterized by Marginulina interrupta (separate zone), the lower Margaritatus zone at the beginning of the domery of Bolivina liassica (also separate zone). After the disappearance of Bolivina liassica (LAD), almost the entire remaining domerium is dominated by the forms Denticulina arbuscula , Denticulina obscurus , Denticulina terqueni , Lenticulina carinata , Lenticulina speciosa and Marginulina prima . Shortly before the end of the domerium, Lenticulina sublaevis appears .

Calcareous nanoplankton

In the case of calcareous nanoplankton , the outstanding event was the radiation of the plate- bearing coccolithophores (algae) at the turn of the Sinemurium / Pliensbachium. The following five zones are designated for the Pliensbachium: NJ 3 , NJ 4a , NJ 4b , NJ 5a and NJ 5b . The first appearance (FAD) of Similscutum cruciulus towards the end of the Jamesoni zone marks the beginning of NJ 4a , the last appearance (LAD) of Crepidolithus pliensbachensis the beginning of NJ 4b in the middle of the Ibex zone. NJ 5a begins with the first appearance of Lotharingius hauffii within the Margaritatus zone . The first appearance of Axopodorhabdus atavus in the lower spinatum zone finally marks the onset of NJ 5b , which extends into the lowest toarcium and comes to an end with the last appearance of Calcivascularis jansae .

Fossils

Cryolophosaurus

The municipal natural history museum in Göppingen shows fossils from this time.

Ammonites

In the Pliensbachium, the Psiloceratoidea , which ruled the Hettangium and Sinemurium, disappeared . In their place, the Eoderoceratoidea spread and dominated the north-western European fauna.

The development of the ammonite populations during the Pliensbachian was impaired by two major species extinctions: in the Gibbosus subzone in the outgoing domerium (species loss up to 81%) and directly at the transition to the Toarcian. The latter event was serious and in the fossil record represents a second-order mass extinction (species loss of up to 90%). A so-called oceanic anoxic event (OAE) in the world's oceans is now considered to be the cause of this , which may have been triggered by the LIP flood basalts of the Karoo / Ferrar volcanism. Even in the Valdani (species loss up to 66%) and in the Stokesi subzone (species loss up to 60%), populations had already declined after an initial bloom.

Vertebrates

Characteristic of the vertebrates of the Pliensbachian are the cartilaginous fish ( Chondrichthyes ) Palaeospinax and the bony fish ( Osteichthyes ) Coccolepis , Pholidophorus , Pholidophoroides and Pteroniscus . Among the amphibians , Siderops and the frogs ( Anura ) Prosalirus and Vieraella - the oldest known frog to date - should be mentioned. Among the reptiles are represented fins lizards ( Sauropterygia ) plesiosaur and Rhomaleosaurus , the crocodiles ( Crocodylia ) Calsoyasuchus , Eopneumatosuchus , Kayentasuchus and Protosuchus , the pterosaurs ( Pterosauria ) Dimorphodon that ichthyosaurs ( Ichthyosauria ) Leptonectes and Temnodontosaurus that ornithischia ( Ornithischia ) bienosaurus , Scelidosaurus and Scutellosaurus and the pelvic lizard dinosaur ( Saurischia ) Anchisaurus , Cryolophosaurus , Dilophosaurus , Fabrosaurus , Megalosaurus , Megapnosaurus , Segisaurus and Vulcanodon .

Within the class of synapsids , the mammal-like Tritylodontidae ( Cynodontia ) Bienotherium , Dinnebitodon , Kayentatherium and Oligokyphus are worth mentioning.

Among the real mammals were Dinnetherium and Haramiya .

Photo gallery

  • Pholidophorus bechei

  • Siderops kehli

  • Vieraella autumni

  • Rhomaleosaurus cramptoni

  • Protosuchus richardsoni

  • Dimorphodon macronyx

  • Leptonectes tenuirostris

  • Scutellosaurus lawleri

  • Vulcanodon karibaensis

  • Oligocyphus triserialis

Occurrence

The Pliensbach in the middle of the Amaltheentons, eponymous locality of the Pliensbachium

Examples of formations of the Pliensbachium with the associated sedimentation spaces are:

  • Ammonitico Rosso of the Lombard Alps

  • Adnet marble

  • Everyday stories of the Tannheim mountains

  • Numismalis marl in the foothills of the Alb

  • Spotted marl at the yoke tip

  • Grisons slate from the Lukmanier Pass

  • Stevens Arch in Navajo Sandstone

literature

  • Felix M. Gradstein, James G. Ogg and Alan G. Smith (Eds.): A Geologic Time Scale 2004 . Cambridge University Press, Cambridge (UK) 2005, ISBN 0-521-78673-8 .
  • Christian Meister, Martin Aberhan, Joachim Blau, Jean-Louis Dommergues, Susanne Feist-Burkhardt, Ernie A. Hailwood, Malcom Hart, Stephen P. Hesselbo, Mark W. Hounslow, Mark Hylton, Nicol Morton, Kevin Page and Greg D. Price : The Global Boundary Stratotype Section and Point (GSSP) for the base of the Pliensbachian Stage (Lower Jurassic), Wine Haven, Yorkshire, UK . In: Episodes . tape 29 (2) , 2006, ISSN  0705-3797 , p. 93-106 ( episodes.org [PDF]).
  • Hans Murawski and Wilhelm Meyer: Geological dictionary . 10., rework. u. exp. Edition Enke Verlag, Stuttgart 1998, ISBN 3-432-84100-0 , p. 278 .
  • Albert Oppel: The Jura formation of England, France and southwestern Germany: divided and compared according to their individual members. Ebner & Seubert, Stuttgart 1856, p. 857 .

Web links

Individual evidence

  1. ↑ a b H. C. Jenkyns et al .: Chemostratigraphy of the Jurassic system: applications, limitations and implications for palaeoceanography . In: Journal of the Geological Society of London . tape 159 , 2002, pp. 351-378 .
  2. ↑ JM McArthur, R. Howarth and TR Bailey: Strontium isotope stratigraphy: LOWESS Version 3. Best-fit line to the marine Sr-isotope curve for 0 to 509 Ma and accompanying look-up table for deriving numerical age. In: Journal of Geology . tape 109 , 2001, p. 155-169 .
  3. ^ Christian Meister, Joachim Blau and Jean-Luc Dommergues: A proposal for a stratotype of the Pliensbachian stage . In: Eclogae Geologicae Helvetiae . tape 96 , 2003, p. 275-298 .
  4. ↑ Guillaume Dera et al: High-resolution dynamics of Early Jurassic marine extinctions: the case of Pliensbachian – Toarcian ammonites (Cephalopoda) . In: Journal of the Geological Society, London . Vol. 167, 2010, pp. 21-33 , doi : 10.1144 / 0016-76492009-068 .