| 词条 | Danian |
| 释义 |
The Danian is the oldest age or lowest stage of the Paleocene epoch or series, the Paleogene period or system and the Cenozoic era or erathem. The beginning of the Danian age (and the end of the preceding Maastrichtian age) is at the Cretaceous–Paleogene extinction event {{ma|Danian|Ma}}. The age ended {{ma|Selandian|Ma}}, being followed by the Selandian age.[1] Stratigraphic definitionsThe Danian was introduced in scientific literature by German-Swiss geologist Pierre Jean Édouard Desor in 1847. It is named after the Latin name for Denmark{{why?|date=August 2017}}. The Montian stage from Belgian stratigraphy (named after the city of Mons) is now known to be roughly equivalent to the Upper Danian and is considered a junior synonym and is no longer in use.[2] The base of the Danian is defined at the iridium anomaly which characterized the Cretaceous–Paleogene boundary (K–T boundary) in stratigraphic sections worldwide. A section in El Kef, Tunisia was appointed as a reference profile (GSSP) for this important boundary.[3] The Danian is the oldest age of the Paleocene, defined at its base by the K-Pg boundary. It is very important because the readily recognized iridium anomaly and primitive Danian planktonic foraminifers define the base of the Danian. Danian foraminiferans repopulated the Paleocene seas after the Cretaceous mass extinction (Olsson et al., 1996). The first replacement foraminiferan of the Paleogene is the Globigerina eugubina, which is used to define the base of the Danian Age (Stainforth et al., 1975). This foraminiferan replaced the Cretaceous genus Globotruncana. The top of the Danian stage (the base of the Selandian) is close to the boundary between biozones NP4 and NP5 from marine biostratigraphy. It is slightly after the first appearances of many new species of the calcareous nanoplankton genus Fasciculithus (F. ulii, F. billii, F. janii, F. involutus, F. tympaniformis and F. pileatus) and close to the first appearance of calcareous nanoplankton species Neochiastozygus perfectus. The Danian stage overlaps the Puercan and Torrejonian North American land mammal ages and the Shanghuan and lowest part of the Nongshanian Asian land mammal ages. It includes the oldest Mammal Paleogene zones, all included in the 1 - 5 group.[4] PaleontologyThough the non-avian dinosaurs were gone, the mammals and other land animals remained small, most not even bigger than a sheep; however; a few (like Ankalagon saurognathus) reached the size of a medium-sized bear. Numerous lineages of modern birds also survived, particularly in the area around Australia but also elsewhere, e.g. Scaniornis of the North Sea region. The oceans remained much the same as the Late Cretaceous seas, only that there was less life, few remaining marine reptiles (mostly turtles, choristodera and crocodiles), and other lesser-known animals. There are controversial reports of ammonites still being around at this time, although they didn't survive the stage.[5] References1. ^International Commission on Stratigraphy 2017 2. ^{{cite journal | url=http://popups.ulg.ac.be/1374-8505/index.php?id=1219&file=1 | title=Disused Paleogene regional stages from Belgium: Montian, Heersian, Landenian, Paniselian, Bruxellian, Laekenian, Ledian, Wemmelian and Tongrian |author1=De Geyter G. |author2=De Man E. |author3=Herman J. |author4=Jacobs P. |author5=Moorkens T. |author6=Steurbat E. |author7=Vandenberghe N. | journal=Geologica Belgica | year=2006 | volume=9 | issue=1-2 | pages=203–213}} 3. ^The GSSP for the Danian stage was established by Molina et al. (2006) 4. ^{{cite web|url=http://fossilworks.org/bridge.pl?action=viewTimeScale&scale_no=125|title=Mammal Paleogene zones|last=Alroy|first=John|date=|website=Fossilworks: Gateway to the Paleobiology Database|publisher=|page=|accessdate=2016-10-13}} 5. ^Squid Empire: The Rise and Fall of the Cephalopods by Danna Staaf Literature{{Wikisource portal|Cenozoic#Paleogene}}
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