Piacenzian

The Piacenzian is in the international geologic timescale the upper stage or latest age of the Pliocene. It spans the time between 3.6 ± 0.005 Ma and 2.588 ± 0.005 Ma (million years ago). The Piacenzian is on top of the Zanclean and is followed by the Gelasian (part of the Pleistocene).

The Piacenzian is roughly coeval with the European Land Mammal Mega Zone MN 16, overlaps the late Chapadmalalan and early Uquian South American Land Mammal Ages, and falls inside the more extensive Blancan North American Land Mammal Age. It also correlates with regional stages like the Astian, Redonian, Waltonian (England), Reuverian (Netherlands) or Romanian (Central Europe).

Definition

The Piacenzian was introduced in scientific literature by Swiss stratigrapher Karl Mayer-Eymar in 1858. It is named after the Italian city of Piacenza.

The base of the Piacenzian is at the base of magnetic chronozone C2An (the base of the Gauss chronozone and at the extinction of the planktonic forams Globorotalia margaritae and Pulleniatina primalis. The GSSP for the Piacenzian stage is at Punta Piccola on Sicily, Italy.^[1]

The top of the Piacenzian (the base of the Quaternary system and the Pleistocene series) is defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone (at the Gauss-Matuyama reversal), and isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: Discoaster pentaradiatus and Discoaster surculus.^[2]

Climate

Climate of the Piacenzian would have started as a somewhat wet and warm period in North America occurring just after a brief cooling period of the Zanclean. Deposition of sediments and mollusks of the Piacenzian correspond with the rise in sea level creating the Tamiami Subsea and Jackson Subsea of Florida, Duplin Subsea generally of South Carolina, and Yorktown Subsea of the Outer Banks and inland North Carolina. Dates have been established on the basis of the genera and species of mollusks found.^[3]

Origin of the genus Homo

The late Piacenzian may be when the genus Homo developed out of the ancestral genus Australopithecus.^[4] While the oldest known fossils unambiguously identified as Homo habilis date to just after the end of the Piacenzian (the early Gelasian), a fossilized jawbone that exhibits traits transitional between Australopithecus and Homo habilis was discovered in the Afar Triangle in 2015. The find was made by Ethiopian student Chalachew Seyoum at a site called Ledi-Geraru between the Mille and Awash rivers, in Afar Regional State (near 11°22′N 40°52′E / 11.36°N 40.86°E / 11.36; 40.86).^[5][6] Based on geological evidence from the Afar region, the individual would have lived just after a major climate shift, during which forests and waterways were rapidly replaced by arid savanna, in keeping with hypotheses emphasizing the savanna environment as the ancestral environment that shaped the evolution of early Homo.^[7]

References

Notes

Literature

Wikisource has original works on the topic: Cenozoic#Neogene

• Castradori, D.; Rio, D.; Hilgen, F.J. & Lourens, L.J.; (1998) "The Global Standard Stratotype section and Point (GSSP) of the Piacenzian Stage (Middle Pliocene)" Episodes 21(2): pp 88–93.
• Gradstein, F.M.; Ogg, J.G. & Smith, A.G. (eds.) (2005) A Geologic Time Scale 2004 Cambridge University Press, Cambridge, UK, ISBN 0-521-78142-6.
• Rio, D., R. Sprovieri, D. Castradori, and E. Di Stefano (1998) "The Gelasian Stage (Upper Pliocene): A new unit of the global standard chronostratigraphic scale" Episodes 21(2): 82-87.
• Thompson, R. S. and Fleming, R. F. (1996) "Middle Pliocene vegetation: reconstructions, paleoclimatic inferences, and boundary conditions for climate modeling" Marine Micropaleontology 27(1): pp. 27–49

External links

• GeoWhen Database - Piacenzian
• Neogene timescale, at the website of the subcommission for stratigraphic information of the ICS
• Neogene timescale at the website of the Norwegian network of offshore records of geology and stratigraphy
• Piacenzian Microfossils: images of Piacenzian Foraminifera