Tournaisian

The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from 358.9 Ma to 346.7 Ma.^[4] It is preceded by the Famennian (the uppermost stage of the Devonian) and is followed by the Viséan.

Tournaisian
358.9 ± 0.4 – 346.7 ± 0.4 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Paleogeography of the Tournaisian (350 Ma)
Chronology
−360 — – −355 — – −350 — – −345 — – −340 — – −335 — – −330 — – −325 — – −320 — – −315 — – −310 — – −305 — – −300 — – P a l e o z o i c D C a r b o n i f e r o u s P M i s s i s s i p p i a n P e n n s y l v a n i a n L D E a r l y M i d d l e L a t e E a r l y M i d L a t e C S Famennian Tournaisian Viséan Serpuk. Bashkirian Moscovian Kasimovian Gzhelian Asselian     ← Carboniferous Rainforest Collapse ← Mazon Creek Fossils ← End of Romer's Gap ← Start of Romer's Gap Subdivision of the Carboniferous according to the ICS, as of 2021.^[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 conodont Siphonodella sulcata (discovered to have biostratigraphic issues as of 2006).^[2]
Lower boundary GSSP	La Serre, Montagne Noire, France 43°33′20″N 3°21′26″E / 43.5555°N 3.3573°E / 43.5555; 3.3573
Lower GSSP ratified	1990^[3]
Upper boundary definition	FAD of the benthic foraminifer Eoparastaffella simplex
Upper boundary GSSP	Pengchong Section, Guangxi, China 24°26′00″N 109°27′00″E / 24.4333°N 109.4500°E / 24.4333; 109.4500
Upper GSSP ratified	2008

Name and regional alternatives

The Tournaisian was named after the Belgian city of Tournai. It was introduced in scientific literature by Belgian geologist André Hubert Dumont in 1832. Like many Devonian and lower Carboniferous stages, the Tournaisian is a unit from West European regional stratigraphy that is now used in the official international time scale.^[5]

The Tournaisian correlates with the regional North American Kinderhookian and lower Osagean stages and the Chinese Tangbagouan regional stage. In British and global stratigraphy, the Tournaisian contains two substages: the Hastarian (lower Tournaisian) and Ivorian (upper Tournaisian).

Stratigraphy

The base of the Tournaisian (which is also the base of the Carboniferous system) is at the first appearance of the conodont Siphonodella sulcata within the evolutionary lineage from Siphonodella praesulcata to Siphonodella sulcata. The first appearance of ammonite species Gattendorfia subinvoluta is just above this and was used as a base for the Carboniferous in the past.^[6] The GSSP for the Tournaisian is near the summit of La Serre hill, in the Lydiennes Formation of the commune of Cabrières, in the Montagne Noire (southern France).^[7] The GSSP is in a section on the southern side of the hill, in an 80 cm deep trench, about 125 m south of the summit, 2.5 km southwest of the village of Cabrières and 2.5 km north of the hamlet of Fontès.

The top of the Tournaisian (the base of the Viséan) is at the first appearance of the fusulinid species Eoparastaffella simplex (morphotype 1/morphotype 2).

The Tournaisian contains eight conodont biozones:

• the zone of Gnathodus pseudosemiglaber and Scaliognathus anchoralis
• the zone of Gnathodus semiglaber and Polygnathus communis
• the zone of Dollymae bouckaerti
• the zone of Gnathodus typicus and Siphonodella isosticha
• the zone of Siphonodella quadruplicata and Patrognathus andersoni (upper zone of Patrognathus andersoni)
• the lower zone of Patrognathus andersoni
• the zone of Patrognathus variabilis
• the zone of Patrognathus crassus

Paleoenvironments

The Tournaisian coincides with Romer's gap, a period of remarkably few terrestrial fossils, thus constituting a discontinuity between the Devonian and the more modern terrestrial ecosystems of the Carboniferous.

The middle of the Tournaisian is marked by a southern glaciation event, of a slightly lesser extent than the glaciations which swept over Gondwana in the later Carboniverous and the very end of the Devonian.^[8][9] During the Tournaisian, South America was located at south polar latitudes and formed the westernmost part of the supercontinent Gondwana. The southwestern coastline of Gondwana was bustling with distinctive cold-water brachiopod and bivalve faunas.^[10]

Coal is less common in the Tournaisian than in the rest of the Carboniferous, and forests and swamps were at low-density despite some trees reaching heights of up to 40 meters (131 feet). Anabranching channels and anastomosing rivers (with permanent channels splitting around large vegetated islands) would not develop until the Viséan, and river systems of the Tournaisian were more similar to those of the Late Devonian.^[11]

Flora

The Tournaisian saw a new diversification of arborescent (tree-sized) lycophytes and giant sphenophytes (horsetails). They coexisted alongside ferns and lignophytes (wood-bearing plants), including early seed plants such as lyginopteridalean pteridosperms ("seed ferns").^[12] The Tournaisian was a transitional stage for lignophyte evolution: Devonian progymnosperm taxa such as Archaeopteris had gone extinct, but new types of woody trees such as Pitus and Protopitys set the stage for even greater morphological diversity. There is still much debate over the proportion of spore-bearing (progymnosperm) to seed-bearing (spermatophyte) woody plants, but both were evidently major parts of Tournaisian ecosystems.^[13]

Tropical and subtropical swamps, in what is now Europe, North America, and China, represent a low-latitude paleobiogeographical realm known as the Amerosinian realm.^[12] Divaricating (widely branching) trunks of Lepidodendropsis lycophytes are by far the most abundant and widespread plant fossils of the Tournaisian, yet there was some minor variation in other flora through time and space. In eastern North America, lyginopterids and probable progymnosperms were also common, as indicated by leaf form genera such as Adiantites, Rhodeopteridium, and Genselia.^[12] The progymnosperm leaf Triphyllopteris may be more common in Europe while the lycophyte Sublepidodendron characterizes Tournaisian China. Late Devonian seed plants like Rhacopteris also persisted into the Tournaisian tropics. Lepidodendron, a massive arborescent lycophyte which would dominate coal forests through the rest of the Carboniferous, first appeared near the Tournaisian-Viséan boundary.^[12]

Northern Asia (Kazakhstan and Siberia) was positioned within subtropical or temperate northern latitudes, and developed its own endemic floras, the Angaran realm. The most common plant fossils in this region were shrub-sized lycophytes such as Ursodendron and Tomiodendron, shorter than their arborescent tropical relatives.^[12]

Gondwanan plant fossils are uncommon: southernmost Gondwana was covered by dwarf lycophytes, even smaller than those of the Angaran realm.^[14] Subtropical and temperate lycophytes such as Lepidodendropsis, Archaeosigillaria, and Frenguellia could be found in some parts of the supercontinent, such as Argentina and Australia.^[12] In the middle Tournaisian glaciation, species-poor frigid tundra developed in western Argentina.^[14] These south polar tundras hosted the oldest known seed plants in Gondwanan territories, which likely spread south across a land bridge once the Rheic Ocean closed between Laurussia and Gondwana.^[15] Tournaisian terrestrial sediments in South America are additionally characterized by the miospore index fossil Waltzispora lanzonii. The floral diversity of Tournaisian southern tundra consists almost entirely of relict Devonian genera; this suggests that Late Devonian land plant extinctions in lower latitudes were mostly driven by competition from new tropical species, rather than global environmental pressures.^[15]

Notable formations

• Albert Formation (New Brunswick, Canada)
• Agua de Lucho Formation (Argentina)
• Ballagan Formation / Cementstone Group (Scotland)
• Herbesskaya Formation (Russia)
• Horton Bluff Formation (Nova Scotia, Canada)
• Mansfield Group (Australia)
• Price Formation (West Virginia / Virginia, United States)
• Tournai Formation (Belgium)

References

1. "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
2. Kaiser 2009. sfn error: no target: CITEREFKaiser2009 (help)
3. Paproth, Feist & Flajs 1991. sfn error: no target: CITEREFPaprothFeistFlajs1991 (help)
4. Gradstein et al. (2004)
5. Heckel & Clayton (2006)
6. Menning et al. (2006); for the old definition, see Paeckelmann & Schindewolf (1937)
7. The GSSP was published by Paproth et al. (1991)
8. Ezpeleta, Miguel; Rustán, Juan José; Balseiro, Diego; Dávila, Federico Miguel; Dahlquist, Juan Andrés; Vaccari, Norberto Emilio; Sterren, Andrea Fabiana; Prestianni, Cyrille; Cisterna, Gabriela Adriana; Basei, Miguel (2020). "Glaciomarine sequence stratigraphy in the Mississippian Río Blanco Basin, Argentina, southwestern Gondwana. Basin analysis and palaeoclimatic implications for the Late Paleozoic Ice Age during the Tournaisian". Journal of the Geological Society. 177 (6): 1107–1128. doi:10.1144/jgs2019-214. ISSN 0016-7649. S2CID 226194983.
9. López-Gamundí, Oscar; Limarino, Carlos O.; Isbell, John L.; Pauls, Kathryn; Césari, Silvia N.; Alonso-Muruaga, Pablo J. (2021). "The late Paleozoic Ice Age along the southwestern margin of Gondwana: Facies models, age constraints, correlation and sequence stratigraphic framework". Journal of South American Earth Sciences. 107: 103056. doi:10.1016/j.jsames.2020.103056. S2CID 230528910.
10. Sterren, A.F.; Cisterna, G.A.; Rustán, J.J.; Vaccari, N.E.; Balseiro, D.; Ezpeleta, M.; Prestianni, C. (2021). "New invertebrate peri-glacial faunal assemblages in the Agua de Lucho Formation, Río Blanco Basin, Argentina. The most complete marine fossil record of the early Mississippian in South America". Journal of South American Earth Sciences. 106: 103078. doi:10.1016/j.jsames.2020.103078. S2CID 230594251.
11. Davies, Neil S.; Gibling, Martin R. (2013-05-01). "The sedimentary record of Carboniferous rivers: Continuing influence of land plant evolution on alluvial processes and Palaeozoic ecosystems". Earth-Science Reviews. 120: 40–79. doi:10.1016/j.earscirev.2013.02.004. ISSN 0012-8252.
12. Opluštil, Stanislav; Cleal, Christopher J.; Wang, Jun; Wan, Mingli (2022). "Carboniferous macrofloral biostratigraphy: an overview". Geological Society, London, Special Publications. 512 (1): 813–863. doi:10.1144/SP512-2020-97. ISSN 0305-8719. S2CID 229457094.
13. Decombeix, Anne-Laure; Meyer-Berthaud, Brigitte; Galtier, Jean (2011). "Transitional changes in arborescent lignophytes at the Devonian–Carboniferous boundary". Journal of the Geological Society. 168 (2): 547–557. doi:10.1144/0016-76492010-074. ISSN 0016-7649. S2CID 129970719.
14. Prestianni, Cyrille; Rustán, Juan José; Balseiro, Diego; Vaccari, N. Emilio (2022-10-02). "Porongodendron minitensis gen. nov. sp. nov. a new lycopsid from the Mississippian of Argentina with adaptations to tundra-like conditions". Botany Letters. 169 (4): 527–539. doi:10.1080/23818107.2022.2101515. ISSN 2381-8107. S2CID 251117143.
15. Prestianni, C.; Rustán, J. J.; Balseiro, D.; Vaccari, E.; Sterren, A. F.; Steemans, P.; Rubinstein, C.; Astini, R. A. (2015-01-01). "Early seed plants from Western Gondwana: Paleobiogeographical and ecological implications based on Tournaisian (Lower Carboniferous) records from Argentina". Palaeogeography, Palaeoclimatology, Palaeoecology. 417: 210–219. doi:10.1016/j.palaeo.2014.10.039. ISSN 0031-0182.

Bibliography

• Dumont, A.H.; 1832: Mémoire sur la constitution géologique de la province de Liège, Mémoires couronnés par l'Académie Royale des Sciences et Belles-Lettres de Bruxelles 8 (3), VII. (in French)
• Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press
• Heckel, P.H. & Clayton, G.; 2006: The Carboniferous system, use of the new official names for the subsystems, series and stages, Geologica Acta 4(3), pp 403–407
• Menning, M.; Alekseev, A.S.; Chuvashov, B.I.; Davydov, V.I.; Devuyst, F.-X.; Forke, H.C.; Grunt, T.A.; Hance, L.; Heckel, P.H.; Izokh, N.G.; Jin, Y.-G.; Jones, P.J.; Kotlyar, G.V.; Kozur, H.W.; Nemyrovska, T.I.; Schneider, J.W.; Wang, X.-D.; Weddige, K.; Weyer, D. & Work, D.M.; 2006: Global time scale and regional stratigraphic reference scales of Central and West Europe, East Europe, Tethys, South China, and North America as used in the Devonian–Carboniferous–Permian Correlation Chart 2003 (DCP 2003), Palaeogeography, Palaeoclimatology, Palaeoecology 240 (1-2): pp 318–372
• Paeckelmann, W. & Schindewolf, O.H.; 1937: Die Devon-Karbon-Grenze, Comptes Rendus (2) du Cinquième Congrès International de Stratigraphie et Géologie du Carbonifère, Heerlen 1935 (2), pp 703–714 (in German)
• Paproth, E.; Feist, R. & Flajs, G.; 1991: Decision on the Devonian–Carboniferous Boundary Stratotype, Episodes 14 (4), pp 331–336

External links

• at the website of the Norwegian network of offshore records of geology and stratigraphy
• Tournaisian, Geowhen Database
• , www.palaeos.com

Coordinates: 43°33′20″N 3°21′26″E / 43.5556°N 3.3572°E / 43.5556; 3.3572