The Dresbachian is a Maentwrogian regional stage of North America, lasting from 501 to 497 million years ago. It is part of the

Upper Cambrian The Furongian is the fourth and final epoch and series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three sta ...

and is defined by four

trilobite zone Trilobites are used as index fossils to subdivide the Cambrian period. Assemblages of trilobites define trilobite zones. The '' Olenellus''-zone has traditionally marked the top of the Lower Cambrian, and is followed by the '' Eokochaspis'' zon ...

s. It overlaps with the

ICS ICS may refer to: Computing * Image Cytometry Standard, a digital multidimensional image file format used in life sciences microscopy * Industrial control system, computer systems and networks used to control industrial plants and infrastructu ...

-stages

Guzhangian The Guzhangian is an uppermost stage of the Miaolingian Series of the Cambrian. It follows the Drumian Stage and precedes the Paibian Stage of the Furongian Series. The base is defined as the first appearance of the trilobite ''Lejopyge lae ...

Paibian The Paibian is the lowest stage of Furongian series of the Cambrian. It follows the Guzhangian ( 3rd series of the Cambrian) and is succeeded by the Jiangshanian Stage. The base is defined as the first appearance of the trilobite ''Glyptagnostus ...

and the lowest

Jiangshanian The Jiangshanian is the middle stage of the Furongian series. It follows the Paibian Stage and is succeeded by the still unnamed Stage 10 of the Cambrian. The base is defined as the first appearance of the trilobite '' Agnostotes orientalis'' whi ...

. 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, about 502 million years ago, was followed by the Cambrian–Ordovician extinction event about million years ago.

Naming

The term is derived from the town of

Dresbach Dresbach Township is a township in Winona County, Minnesota, United States. The population was 456 at the 2010 census. Geography According to the United States Census Bureau, the township has a total area of ; is land and , or 14.02%, is water. ...

which is located in southeastern

Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the List of U.S. states and territories by population, 22nd most populous, with over 5.75 million residents. Minne ...

on the

Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it ...

Definition

The Dresbachian is defined by four trilobite zones: '' Cedaria''-, '' Crepicephalus''-, '' Aphelaspis''- and '' Dunderbergia''

Events

The Dresbachian extinction event during the

Late Cambrian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

was the second of two severe

extinction Extinction is the termination of a kind of organism or of a group of kinds ( taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed ...

s during the first period of the

Paleozoic era The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ''z ...

; the first being the

End-Botomian extinction event The end-Botomian mass extinction event, also known as the late early Cambrian extinctions, refer to two extinction intervals that occurred during Stages 4 and 5 of the Cambrian Period, approximately 513 to 509 million years ago. Estimates for the ...

during the

Middle Cambrian Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ...

. According to data on extinction intensity (see below), both extinction events slashed approximately 40 percent of

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...

. However, the two are poorly documented due to a paucity of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

evidence so early in the evolution of life.

References

* 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 al. 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

{{Geological history, p, p Cambrian geochronology Cambrian United States Cambrian North America Extinction events Cambrian Minnesota Guzhangian Paibian Jiangshanian