Dresbachian

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Key events in the Cambrian
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Orsten Fauna
Archaeocyatha extinction
SSF diversification, first brachiopods & archaeocyatha
Treptichnus pedum trace
Large negative peak δ 13Ccarb excursion
First Cloudina & Namacalathus mineral tubular fossils
Stratigraphic scale of the ICS subdivisions and Precambrian/Cambrian boundary.
Intensity of Dresbachian extinction event

The Dresbachian is a Maentwrogian regional stage of North America, lasting from 501 to 497 Ma.[1] It is part of the Upper Cambrian and is defined by four trilobite zones. It overlaps with the ICS-stages Guzhangian, Paibian and the lowerst Jiangshanian.[citation needed]

The Dresbachian overlies the Middle Cambrian Albertan series, and is the lowest stage of the Upper Cambrian Croixian series, followed by the Franconian stage. The Dresbachian extinction event, circa 502 m.y.a., was followed by the Cambro-Ordovician extinction event about 485.4 ± 1.9 million years ago.

Naming[edit]

The term is derived from the town of Dresbach which is located in southeastern Minnesota on the Mississippi River.

Definition[edit]

The Dresbachian is defined by four trilobite zones: Cedaria-, Crepicephalus-, Aphelaspis- and Dunderbergia trilobite zones.[citation needed]

Events[edit]

The Dresbachian extinction event during the Late Cambrian was the second of two severe extinctions during the first period of the Paleozoic era; the first being the End Botomian extinction event during the Middle Cambrian. According to data on extinction intensity (see below), both extinction events slashed approximately 40 percent of marine genera. However, the two are poorly documented due to a paucity of fossil evidence so early in the evolution of life.

References[edit]

  • Chen Jun-yuan & Teichert C, 1983; Cambrian Cephalopods, Geology Vol 11, pp647–650, Nov 1983
  • Flower R.H.1964, The Nautiloid Order Ellesmerocerida (Cephalopoda) Menoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM
  • Harland,W. B. et all 1990. A Geologic Time Scale 1989. Cambridge University Press, Cambridge . Ref in Paleobiology Database on line.
  • Moore, Lalicker, and Fischer 1952; Invertebrate Fossils; McGraw-Hill; fig 1-17.
  • Geowhen database. [1]